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Henske 2016 Tuberous sclerosis

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PRIMER
Tuberous sclerosis complex
Elizabeth P. Henske1, Sergiusz Jóźwiak2,3, J. Christopher Kingswood4, Julian R. Sampson5
and Elizabeth A. Thiele6
Abstract | Tuberous sclerosis complex (TSC) is an autosomal dominant disorder that affects multiple
organ systems and is caused by loss‑of‑function mutations in one of two genes: TSC1 or TSC2.
The disorder can affect both adults and children. First described in depth by Bourneville in 1880, it is
now estimated that nearly 2 million people are affected by the disease worldwide. The clinical features
of TSC are distinctive and can vary widely between individuals, even within one family. Major
features of the disease include tumours of the brain, skin, heart, lungs and kidneys, seizures and
TSC-associated neuropsychiatric disorders, which can include autism spectrum disorder and
cognitive disability. TSC1 (also known as hamartin) and TSC2 (also known as tuberin) form the TSC
protein complex that acts as an inhibitor of the mechanistic target of rapamycin (mTOR) signalling
pathway, which in turn plays a pivotal part in regulating cell growth, proliferation, autophagy and
protein and lipid synthesis. Remarkable progress in basic and translational research, in addition to
several randomized controlled trials worldwide, has led to regulatory approval of the use of mTOR
inhibitors for the treatment of renal angiomyolipomas, brain subependymal giant cell astrocytomas
and pulmonary lymphangioleiomyomatosis, but further research is needed to establish full indications
of therapeutic treatment. In this Primer, we review the state‑of‑the-art knowledge in the TSC field,
including the molecular and cellular basis of the disease, medical management, major knowledge
gaps and ongoing research towards a cure.
Correspondence to E.P.H.
Pulmonary and Critical Care
Medicine Division, Brigham
and Women’s Hospital,
Harvard Medical School,
15 Francis Street, Boston,
Massachusetts 02115, USA.
[email protected]
Article number: 16035
doi:10.1038/nrdp.2016.35
Published online 26 May 2016
Tuberous sclerosis complex (TSC) is a disorder that
affects multiple organ systems1–3. The clinical manifest­
ations of TSC include tumours of the brain, skin, heart,
lungs and kidneys, and neurological disease, which can
include seizures, autism spectrum disorder and cogni­
tive disability (FIG. 1). The name of the disorder, com­
posed of the Latin word tuber (root-shaped growths) and
the Greek word skleros (hard), refers to thick, firm and
pale gyri called ‘tubers’ that can be found post-mortem
in the brains of patients with TSC. These tubers were
first described by Desire-Magloire Bourneville in 1880.
TSC is inherited in an autosomal dominant manner,
with clinical features varying widely between individ­
uals, even within the same family. All patients with
TSC carry loss‑of‑function germline mutations in
either of the tumour-suppressor genes TSC1 or TSC2.
Approximately two-thirds of individuals with TSC carry
de novo germline mutations (some of which are mosaic),
whereas one-third of TSC1 and TSC2 ­mutations
are inherited4.
The clinical features of TSC are distinctive and
include malformations of the cerebral cortex (tubers),
cardiac rhabdomyomas that can arise during fetal
life and usually regress during early childhood, renal
angiomyolipomas (AMLs) that contain aneurysmal
tumour-derived vascular structures, facial angiofibro­
mas (benign blood vessel-filled tumours on the face),
hypomelanotic macules (white patches on the skin)
and pulmonary lymphangioleiomyomatosis (LAM),
which is a destructive lung disease that almost exclu­
sively affects women (FIG. 2). Infantile spasms and autism
spectrum disorder also occur frequently in patients with
TSC. Some other clinical manifestations associated
with TSC may rarely occur and are listed in BOX 1.
The TSC protein complex, which includes TSC1
(also known as hamartin) and TCS2 (also known as
tuberin), inhibits mechanistic target of rapamycin
(mTOR) complex 1 (mTORC1). mTORC1 controls
and mediates major processes including cell growth,
proliferation, autophagy and protein and lipid synthe­
sis5. Extraordinary progress in basic and translational
research led to randomized controlled trials of mTOR
inhibitors in TSC. As a result, in the past 5 years, the US
FDA and the European Medicines Agency (EMA) have
approved mTOR-inhibiting agents for the treatment of
renal AMLs, brain subependymal giant cell astrocyto­
mas (SEGAs) and pulmonary LAM (TABLE 1). In this
Primer, we discuss the genetic, molecular and cellular
basis of TSC, clinical diagnosis and management of the
disease, and key areas that require further research.
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PRIMER
Author addresses
Pulmonary and Critical Care Medicine Division, Brigham
and Women’s Hospital, Harvard Medical School, 15 Francis
Street, Boston, Massachusetts 02115, USA.
2
Department of Pediatric Neurology, Medical University
of Warsaw, Warsaw, Poland.
3
Children’s Memorial Health Institute, Warsaw, Poland.
4
Sussex Kidney Unit, Royal Sussex County Hospital,
Brighton, UK.
5
Institute of Medical Genetics, Division of Cancer and
Genetics, Cardiff University School of Medicine, Cardiff, UK.
6
Department of Neurology, Massachusetts General Hospital,
Harvard Medical School, Boston, Massachusetts, USA.
1
Epidemiology
TSC can occur in all races and ethnic groups and rates
of TSC do not vary according to sex 6. Almost 2 ­million
people worldwide are estimated to have TSC, with
approximately 50,000 individuals affected in the United
States alone. Many cases may remain undiagnosed for
several years owing to the mild symptoms experienced
by some patients and the relative obscurity of the dis­
ease. The incidence of TSC is approximately 1 case
per 6,000–10,000 live births2,7. The diagnostic criteria
for TSC were revised in 2012 (REF. 3) to include muta­
tion analysis and the improved identification of the
associated clinical features. Despite the advantages of
these approaches, there have been few new data on the
preva­lence of the disease and no epidemiological stud­
ies using the revised diagnostic criteria have been done
since 1999 (REF. 3).
The prognosis for individuals with TSC depends on
the severity of their symptoms. Individuals with mild
forms of TSC generally do well and have a n
­ ormal life
expectancy. Overall, the most common cause of death
in patients with TSC in a Mayo Clinic series pub­
lished in 1991 (REF. 8) was status epilepticus (that is, one
prolonged or several epileptic fits in quick ­succession)
or bronchopneumonia. Other leading causes of death
docu­mented in this series included brain tumour,
kidney complications, LAM and cardiac failure in
neonates due to rhabdomyomas. However, because
this case series predated specific therapy for infantile
spasms and targeted therapy for tumours and LAM in
TSC, the prognosis of patients with TSC in 2016 might
differ considerably from what was found in 1991.
Sudden unexplained death due to epilepsy has also been
described in patients with TSC9. The causes of death in
the current era of mTOR inhibition therapy have not
yet been reviewed.
Genetics
TSC2 mutations have been identified in ~70% and TSC1
mutations in 20% of patients with a clinical diagnosis
of TSC10–12. Recently, using techniques such as next-­
generation sequencing and RNA-based approaches,
some of the remaining 10% in whom no mutation was
initially identified have been shown to have low level
somatic mosaicism or intronic splicing variants affect­
ing TSC1 or TSC2 (REFS 13,14). As such, the existence of
other germline TSC-causative genes now seems unlikely.
Over 1,800 different small TSC-causing mutations
have been defined and these are distributed throughout
the coding regions of both genes, except for the final
exon (23) of TSC1 and the alternatively spliced exons
(25 and 31) of TSC2. Mutations are catalogued at http://
chromium.lovd.nl/LOVD2/TSC. The great majority
of TSC1 mutations are small truncating nonsense and
insertion or deletion (indel) mutations with only a small
number of functionally confirmed missense mutations
identified, all of which occur in the 5ʹ region of the
gene15,16. By contrast, TSC2 mutations include frequent
missense mutations (30% of cases) and large deletions
and other rearrangements (5% of cases).
All TSC manifestations are less frequent and less
severe overall in TSC1‑associated than TSC2‑associated
disease10–12,17,18, and TSC1‑associated disease is more
likely to be familial. However, there is great variability
in disease expression, even among different patients or
family members carrying the same mutation. Several
studies have suggested correlations between the nature
and/or the location of TSC1 and TSC2 mutations and a
reduction in IQ or seizure severity 19–21. A small n
­ umber
of TSC2 missense mutations — such as p.R905Q22,
R1200W23 and p.Q1503P — are also consistently associ­
ated with mild disease and some seem to result in the
incomplete inactivation of the affected protein in in vitro
functional studies22–24. Deletions involving TSC2 and
the adjacent polycystin 1, transient receptor potential
channel interacting (PKD1) gene are associated with a
distinct phenotype of TSC with severe polycystic kid­
ney disease (PKD)25. Penetrance is almost complete,
but some individuals carrying ‘mild mutations’ may not
­fulfil clinical criteria for definite TSC.
Brain
Epilepsy. Neurological manifestations including seizures
are among the major causes of morbidity in patients with
TSC. Epilepsy is the most common symptom, affecting
80–90% of patients with TSC, and often begins during
the first year of life26. Some patients develop epilepsy in
the neonatal period, which is usually associated with
existing large cortical malformations27. The early onset
of seizures (in the first 6 months of life) is often associ­
ated with delays in psychomotor development and
abnormal speech as well as autistic behaviours in up to
50% of patients with TSC28,29. In most infants, epilepsy
starts with subtle partial seizures that generalize with
time, leading, in some patients, to infantile spasms30.
Medically intractable or refractory epilepsy develops in
two-thirds of individuals with TSC — which is twice as
often as in the general epilepsy population. One-third of
infants with TSC develop infantile spasms31.
Subependymal giant cell astrocytomas. SEGAs (also
called subependymal giant cell tumours) occur in
10–15% of individuals with TSC, and are often an
important source of TSC-related morbidity and occa­
sionally mortality. Presentation typically occurs during
the first two decades of life; fetal and infantile cases have
been reported31,32. For uncertain reasons, the propensity
for SEGAs to develop drastically decreases after 20 years
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Other
• 50% oral fibromas
• 50% retinal astrocytic
hamartomas
Brain
• 90% epilepsy
• 80–90% SEN
• 10–15% SEGA
• 90% TAND
• 50% intellectual
disability
• 40% autism spectrum
disorder
Lung
Women
• 80% asymptomatic
LAM
• 5–10% symptomatic
LAM, can lead to
respiratory failure
Men and women
• 10% MMPH
Heart
Infants
• 90% cardiac
rhabdomyoma
Adults
• 20% cardiac
rhabdomyoma
Skin
• 75% angiofibroma
• 20–80% ungual
fibroma
• 25% fibrous cephalic
plaques
• >50% shagreen
patches
• 90% focal
hypopigmentation
Kidney
• 70% angiomyolipoma
• 35% simple multiple
cysts
• 5% polycystic kidney
disease
• 2–3% renal cell
carcinoma
Figure 1 | Clinical manifestations of TSC are diverse and affect multiple organs.
Nature
Reviews
| Disease
Primers
The most commonly affected systems and their associated
lesions
are shown.
Percentages
represent the approximate incidence in patients with tuberous sclerosis complex (TSC).
LAM, lymphangioleiomyomatosis; MMPH, multifocal micronodular pneumocyte
hyperplasia; SEGA, subependymal giant cell astrocytoma; SEN, subependymal nodule;
TAND, tuberous sclerosis complex-associated neuropsychiatric disorder.
of age, at which point SEGAs also invariably become cal­
cified. The growth of SEGAs can occur after 20 years
of age, but this is an uncommon observation. Although
there is not a consensus definition of a SEGA, most
researchers agree that a subependymal nodule (SEN)
showing growth of >1 cm between assessments, particu­
larly in the region of the foramen of Monro, should be
considered to be a SEGA33.
TSC-associated neuropsychiatric disorders. Cognitive
and neurobehavioural issues are common in TSC.
Approximately 50% of individuals with TSC have some
degree of intellectual disability 34, which may be severe
and is usually seen in the setting of early age of onset and
refractory epilepsy. Even among those with a normal IQ,
specific cognitive impairments are common. Up to 40%
of individuals with TSC have an autism spectrum dis­
order 35. Mental health issues are very common in TSC,
affecting approximately two-thirds of individuals with
the disorder. To help emphasize the prevalence of mental
health issues, the term TSC-associated neuro­psychiatric
disorders (TANDs) has recently been proposed 36.
Anxiety is particularly common (30–60% of patients
with TSC)36. Individuals with TSC frequently develop
obsessive behaviours about things, and these behaviours
commonly relate to interpersonal relationships.
Lung
LAM is the primary pulmonary manifestation of TSC37–40.
LAM can cause cystic lung destruction, pneumothorax
(lung collapse) and chylous pleural effusion. Symptoms
of LAM can include shortness of breath, fatigue and chest
pain. Asymptomatic LAM (as defined by the presence of
multiple lung cysts) occurs in up to 80% of women with
TSC (FIG. 1). There have been only a few case reports of
men with TSC who have biopsy-documented LAM40,41.
However, recent studies have shown that between 10%
and 13% of men with TSC42–44 have lung cysts, although
virtually none of these men are symptomatic or have
had biopsies, making it impossible to know if these
asympto­matic cysts have the same histopathology and
pathogenesis as LAM in TSC. Symptomatic LAM occurs
in ~5–10% of women with TSC and can lead to respir­
atory failure. LAM tends to progress more rapidly in pre­
menopausal women than in postmenopausal women45.
There have been many reports of worsening of shortness
of breath or the development of pneumothoraces during
pregnancy, but a clear causal relationship has not been
proven. Multifocal micronodular pneumocyte hyper­
plasia (MMPH) can occur in both men and women
with TSC and is usually asymptomatic46–48. The overall
­incidence of MMPH in TSC is not well defined.
Kidney
AMLs and cysts, the two most common renal lesions in
TSC, can be detected in early childhood (FIG. 3). In one
cohort, AMLs were found in 17% of children by the time
they reached 2 years of age and 65% by the time they
reached 9–14 years of age49,50. By adulthood, up to 67% of
patients with TSC have AMLs (identified at autopsy)51.
It is believed that AMLs continue to grow throughout
childhood and early adulthood52 (FIG. 3). Up to 35%
of patients with TSC will have multiple ­simple renal
cysts53,54, which need to be distinguished from the PKD
that occurs in 5% of patients25. More rare manifest­ations
include renal cell carcinoma, the epithelioid variant of
AML and oncocytoma53. Renal cell cancer occurs in
2–3% of the TSC population, can affect children, can
be multicentric and may be of several histological
types44,55,56. Focal and segmental glomerulosclerosis have
also been recognized but are poorly documented.
Skin and other manifestations
Skin manifestations develop in almost all individuals
with TSC57. These include facial angiofibromas (small
swellings on the nose and cheeks that are present in 75%
of patients), ungual fibromas (fibrous growths around
the nails that are present in 20–80% of patients), fibrous
cephalic plaques (large areas of raised skin usually found
on the forehead that are present in 25% of patients),
shagreen patches (areas of thickened raised skin ­usually
found on the lower back that are present in >50% of
patients) and focal hypopigmentation changes (present
in 90% of patients). These signs emerge at different time
points and are often instrumental in making a clinical
diagnosis of TSC57 (FIG. 3). Facial angiofibromas are a
considerable concern for patients and frequently require
treatment. Oral fibromas (present in 50% of patients),
­retinal astrocytic hamartomas (glial tumours of the retinal
nerve that are present in 50% of patients), retinal achromic
patches (light or darks spots on the eye that are present in
40% of patients), dental enamel pits (present in 100% of
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a
b
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Figure 2 | Images of clinical manifestations of TSC. a | Chest CT scan from a patient
Nature Reviews | Disease Primers
with lymphangioleiomyomatosis showing characteristic diffuse cystic lung disease.
b | Abdominal CT scan (left panel) and renal angiogram (right panel) in a patient with
angiomyolipoma. c | Head CT scan showing subependymal nodules. d | Classic skin
and ocular findings in patients with tuberous sclerosis complex (TSC): hypomelanotic
macule, facial angiofibroma, retinal hamartoma and subungual fibroma of the nail
(going counter clockwise).
patients) and visceral hamartomas (such as hepatic AMLs
and haemangiomas) are frequent and are usually asymp­
tomatic manifestations. By contrast, sclerotic or cystic
bone changes and neuroendocrine and other tumours of
the endocrine glands are rarely associated with TSC3,58,59.
Mechanisms/pathophysiology
Signalling
Tumours in TSC — including SEGAs, AMLs, LAM and
angiofibromas — develop because of inactivation of
both alleles of either TSC1 or TSC2 (REFS 60–66). Thus,
TSC fits the Knudson ‘two-hit’ tumour-suppressor gene
model, with the germline mutation inactivating one
allele of TSC1 or TSC2 and a somatic event (often loss
of hetero­zygosity) inactivating the remaining wild-type
allele (FIG. 4). By contrast, molecular genetic studies in
cortical or subcortical tubers that represent prenatal
develop­mental abnormalities of the brain have gener­
ated less clear cut evidence of somatic events that may
involve just a subpopulation of cells67 and/or may include
TSC protein phosphorylation changes rather than genetic
changes68. The possible effects of TSC1 or TSC2 hetero­
zygosity on more-subtle aspects of brain structure and
function are a focus of current research.
TSC1 and TSC2 exist in a heterotrimeric complex with
TBC1 domain family member 7 (TBC1D7) — referred to
as the TSC protein complex 69,70. The TSC protein com­
plex controls the activity of mTORC1 via RAS homo­
logue enriched in brain (RHEB), which is the target of
the GTPase-activating domain of TSC2. RHEB bound
to GTP activates mTORC1; tumour cells in TSC have
hyperactivation of RHEB and consequently of mTORC1
(REFS 5,70,71). Activation of mTORC1 can be observed
using antibodies that recognize the downstream targets
of mTORC1, including phospho‑p70 ribosomal S6 kinase,
phospho-ribosomal protein S6 and phospho‑4EBP1
(eukaryotic translation initiation factor 4E‑binding pro­
tein 1). It has been recognized for many years that acti­
vation of mTORC1 enhances protein translation. More
recently, hyperactivation of mTORC1 has been discov­
ered to lead to extensive metabolic reprogramming,
including effects on glycolysis, autophagy, nucleotide
biosynthesis and lipid biosynthesis5,69–71. In many cases,
this reprogramming leads to vulnerabilities that induce
cell death under particular conditions, such as growth
in nutrient-restricted media. These discoveries have led
to the hypothesis that the altered metabolism of cells
with mTORC1 hyperactivation will provide therapeutic
opportunities. By contrast, inhibition of mTORC1 with
allosteric inhibitors, including sirolimus and everolimus,
restores TSC2‑deficient cells to metabolic homeostasis
and may thereby ‘protect’ them from cell death72 (FIG. 5a).
In addition to the well-established or ‘canonical’ TSC–
RHEB–mTORC1 pathway, there is evidence of non-­
canonical pathways73. These include targets of TSC1 that
are TSC2 independent, targets of TSC1 and TSC2
that are RHEB independent and targets of RHEB that are
mTORC1 independent (FIG. 5b). This is an emerging and
important area of research, as the precise mechanisms
and disease relevance of these non-canonical pathways
are incompletely understood.
The primary focus to date in the TSC field has been
the cell-autonomous effect of mTORC1 hyperactiva­
tion on TSC1‑deficient or TSC2‑deficient cells. Less is
known about the non-cell-autonomous effect of TSC
deficiency on the tumour microenvironment, including
stromal cells and inflammatory cells. This is an emerg­
ing and potentially important area, as evidenced by work
demonstrating the effects of TSC2‑deficient cells on
neighbouring wild-type cells74,75, lymphatic endothelial
cells76,77 and inflammatory cells and pathways in the brain
and in tumours76,78.
Brain
Epilepsy. The origin of epilepsy in TSC is not well under­
stood. Although cortical tubers (malformed areas in the
cortex after which the disease was named) have been
thought to be the neuropathological substrate of epilepsy
in TSC, increasing evidence supports the importance of
the perituberal cortex 79.
There are many factors that might contribute to epi­
leptogenesis and the associated neurocognitive difficul­
ties in individuals with TSC. Experimental studies have
shown that mutations in TSC1 and TSC2 and consequent
overactivation of mTORC1 result in altered cellular mor­
phology with cytomegalic (oversized) neurons, altered
synaptogenesis and an imbalance between excitation
and inhibition. In the brains of patients with TSC many
­γ-­aminobutyric acid type A receptor (GABAAR) subunits
are downregulated, including GABAARα1, GABAARα4
and GABAARα5 (REF. 80). This downregulation probably
provides a neuroanatomical substrate for the early appear­
ance of seizures and for the encephalopathic process81,82.
In addition, mTORC1 overactivation is thought to be
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responsible for alterations in the migration and orienta­
tion of neural cells, leading to abnormal cortical lamina­
tion and dendritic arborization (branching)83. Repetitive
seizures and delayed treatment probably influence longterm potentiation, short-term plasticity and connec­
tivity, which might contribute to neurodevelopmental
delay and the drug resistance of seizures. Interestingly,
prenatal rapamycin treatment in animal studies seems to
prevent mTORC1 cascade hyperactivation and reduce the
­neurological deficits in animal models of TSC84.
Subependymal giant cell astrocytomas. It is hypoth­
esized that SEGAs arise from SENs, which are present
in 80–90% of individuals with TSC and are thought to
develop from neural progenitor cells. SEGAs are usually
located under the ependymal lining of the ventricular
wall, typically in the region of the foramen of Monro.
Although the mechanisms that lead to SEGA develop­
ment from a SEN are not completely understood, it has
been suggested that ERK activation might play a part 85.
Some evidence has suggested that SEGAs develop via
a classic Knudsen model two-hit genetic mechanism,
although a relatively small number of tumours have been
studied60,86. Pathologically, SEGAs usually contain cells
with both astrocytic and neuronal characteristics, but
they do not contain prominent giant cells. SEGA cells
typically contain abundant cytoplasm and have an eccen­
tric nucleus, often with a prominent nucleolus. Mitotic
figures and cellular structural abnormalities in these cells
are rare, whereas calcification is common87.
Box 1 | Rare clinical manifestations of TSC
The organs most affected by tuberous sclerosis complex (TSC) are the brain, heart, skin,
kidney, lung and eye (FIG. 1). These organs show the most medically and diagnostically
important symptoms of the disease. However, the uncontrolled cell growth and
proliferation associated with TSC can also result in abnormal tumours and cysts in other
areas of the body (see below).
Bones
Sclerotic and hypertrophic lesions are considered a minor feature in the diagnostic
criteria and rarely cause difficulty and discomfort192.
Gastrointestinal system
Hamartomas and polyposis of the stomach, intestine and/or colon are commonly
observed in patients with TSC193, but they tend to be small and rarely cause
considerable symptoms. Rectal polyps have also been reported194.
Liver
Approximately 24% of patients with TSC develop benign tumours in the liver, with a
higher prevalence in women than in men (sex ratio of 5/1). These are generally
asymptomatic and non-progressive and, in rare cases, require surgical removal195.
Gums and teeth
Approximately 70% of adults with TSC develop nodular growths on their gums known
as gingival fibroma196, which may cause irritation and affect tooth alignment. Almost
100% of patients with TSC will develop pits in their dental enamel. Oral hygiene is of
the utmost importance in these patients197.
Pancreas
There have been rare case reports of pancreatic neuroendocrine tumours in patients
with TSC198.
Spleen
Rare cases of large, progressive splenic hamartomas have been reported in patients
with TSC199.
TSC-associated neuropsychiatric disorders. A history of
infantile spasms, a history of medically intractable epi­
lepsy and a disease-causing mutation in TSC2 are all key
risk factors for the development of cognitive impairment
and autism spectrum disorder in TSC, both of which are
important components of TAND19,35. The relationship
between cognitive impairment and the neuroanatomical
features of TSC, including cortical tubers and SENs, is not
well understood. Tuber location has been suggested as a
possible variable to explain the presence of autism spec­
trum disorder in TSC88,89. However, patients with TSC
who have a history of infantile spasms and/or normal
intelligence and who have temporal tubers in the absence
of autistic behaviour have also been identified, suggest­
ing that cortical tubers do not necessarily cause autism
spectrum disorder in TSC90. The pathophysiology of the
other mental health issues in TSC is even less understood.
Considerable work is required to better characterize these
mental health issues, as they often have appreciable
effects on the quality of life of patients with TSC.
Lung
LAM is caused by the proliferation of abnormal ‘LAM
cells’ that proliferate diffusely and bilaterally in the lungs.
LAM cells can also be found in lymph nodes, chylous
fluid, the uterus91 and other sites. LAM cells carry biallelic
inactivating TSC1 or TSC2 mutations62,92,93. In patients
with TSC, a germline event inactivates one allele and a
somatic event (often loss of heterozygosity) inactivates
the remaining wild-type allele (FIG. 4a).
In the sporadic form of LAM, which occurs in women
who do not have TSC, inactivation of both alleles of TSC2
— or, much less frequently, inactivation of both alleles of
TSC1 — occurs somatically 92,94 (FIG. 4b). Approximately
60% of women with the sporadic form of LAM have a
renal AML, most often a single tumour. The occurrence
of identical somatic mutations in LAM cells and in renal
AMLs from women with the sporadic form of LAM92 has
led to the hypothesis that LAM cells metastasize to the
lungs from an unknown primary site. Consistent with
this hypothesis, in mouse models, oestrogen enhances
the number of circulating TSC2‑deficient cells95,96.
In humans, circulating LAM cells are found in the blood
of the majority of women with LAM97–99 and LAM can
recur after lung transplantation100.
The cell of origin of LAM is unknown. The expres­
sion of neural crest lineage markers, including multiple
melano­cyte markers, has led to speculation that LAM cells
arise from the neural crest. The occurrence of LAM
cells in the uterus and the development of a mouse model
in which inactivation of Tsc2 under the control of the pro­
gesterone receptor promoter leads to lesions that resemble
LAM101 have led to the suggestion that LAM cells arise
from the uterus. However, this would not explain the rare
cases of LAM in men that have been pathologically docu­
mented or the cystic lung disease detected by CT scanning
that can develop in men with TSC. The fact that LAM cells
are pathologically nearly identical to AML cells implies
that LAM cells might arise within AMLs, although this
cannot explain the 30–40% of women with the s­ poradic
form of LAM who do not have a detectable AML.
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Table 1 | Completed and ongoing clinical trials on TSC in the past 15 years
Drug or
intervention
Clinical trial
accession
number
(trial name)
Study
period
Population
Phase Number of
participants
(age)
Status
Study primary end point
NCT00411619 2007–2014 Patients with SEGA
and TSC
I/II
28 (>3 years)
Completed Safety and efficacy study to assess
the effect on SEGA tumour volume
NCT00789828 2009–2014 Patients with SEGA
(EXIST‑1)
and TSC
III
118 (all ages)
Completed SEGA response, measured as a
change in SEGA volume
NCT01289912 2011–2014 Patients with TSC
II
50
(6–21 years)
Completed Safety and efficacy study to assess
the effect on neurocognition
NCT01730209 2011–2016 Patients with autism
(RAPIT)
spectrum disorder
and TSC
II/III
60
(4–15 years)
Recruiting
Cognitive ability measured by IQ
NCT01954693 2012–2016 Patients with TSC
(TRON)
II
48 (>16 years)
Recruiting
Effect on neurocognition as
assessed by learning tests
NCT01713946 2013–2016 Patients with seizures
(EXIST‑3)
and TSC
III
326 (all ages)
Active
Effect on the frequency of
partial-onset seizures
NCT01266291 2010–2013 Patients with seizures
and TSC
IV
12 (>18 years)
Completed Safety and efficacy study
Octreotide§
NCT00005906 2000–2008 Patients with LAM
II
4 (18 years)
Completed Reduction in tumour volume, pain
and other symptoms
Sirolimus||
NCT00414648 2006–2011 Patients with LAM
(MILES)
III
120 (>18 years) Completed Effect on FEV1 response and
severity of adverse events
Fasting
NCT00552955 2007–2018 Patients with LAM
N/A
35 (>18 years)
Completed Effect on the size of the LAM
Doxycycline¶
NCT00989742 2009–2013 Patients with LAM
IV
24 (>18 years)
Completed Effect on FEV1 response
Everolimus*
NCT01059318 2009–2012 Patients with LAM
II
22 (>18 years)
Completed Safety, pharmacokinetics and
VEGFD levels
Letrozole#
NCT01353209 2011–2015 Patients with LAM
(TRAIL)
II
17 (>18 years)
Completed Effect on FEV1 response
Sirolimus||
NCT01687179 2012–2016 Women with LAM
and hydroxy­ (SAIL)
chloroquine**
I
18 (>18 years)
Active
Safety of dose-escalation study
of drug combination
Simvastatin‡‡
NCT02061397 2014–2017 Patients with LAM
and TSC
I/II
10 (>18 years)
Recruiting
Safety study and effect on
pulmonary measures
Saracatinib§§
NCT02116712 2014–2015 Patients with LAM
(SLAM‑1)
I
9 (>18 years)
Completed Safety and efficacy study
Celecoxib||||
NCT02484664 2015–2018 Patients with LAM
(COLA)
and TSC
II
12 (>18 years)
Yet to
recruit
Sirolimus||
NCT00457808 2002–2006 Patients with
sporadic LAM and TSC
II
25 (>18 years)
Completed Effect on AML volume
Sirolimus||
NCT00490789 2005–2009 Patients with LAM
(TESSTAL)
and TSC
II
14 (>18 years)
Completed Safety study, effect on AML
diameter and effect on FEV1
Sirolimus||
NCT00126672 2005–2010 Patients with AML
II
36 (>18 years)
Completed Safety and efficacy study, effect
on AML and other lesions
Everolimus*
NCT00457964 2005–2013 Patients with AML,
sporadic LAM and TSC
I/II
36 (>18 years)
Completed Effect on AML volume
Sirolimus||
NCT01217125 2008–2011 Patients with AML
IV
18 (>10 years)
Completed Effect on AML volume
Everolimus*
NCT00792766 2008–2013 Patients with AML
I/II
20 (>18 years)
Completed Long-term tolerance and effect
on AML volume
Everolimus *
NCT00790400 2009–2015 Patients with AML(EXIST‑2)
associated TSC or LAM
III
118 (>18 years) Active
Effect on AML volume
Propranolol¶¶
NCT02104011 2014–2017 Patients with AML
(STBETA)
II
15 (>18 years)
Effect on AML volume and renal
function
Brain
Everolimus*
Vigabatrin‡
Lung
Safety and efficacy study by assessing
FEV1 and the size of the AML
Kidney
Recruiting
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Table 1 (cont.) | Completed and ongoing clinical trials on TSC in the past 15 years
Drug or
intervention
Phase Number of
participants
(age)
Status
NCT01031901 2009–2011 Patients with NF1
and TSC
I
52
(>13 years)
Completed Safety study and effect on lesion size
and appearance
NCT01526356 2012–2014 Patients with
angiofibromas and TSC
II
177
(>18 years)
Completed Safety study and effect on lesion size
and appearance
NCT01853423 2014–2017 Patients with
angiofibromas and TSC
I
15
(3–45 years)
Recruiting
Clinical trial
accession
number
(trial name)
Study
period
Population
Study primary end point
Skin
Topical
rapamycin
Safety study and effect on lesion size
and appearance
AML, angiomyolipoma; COX2, cyclooxygenase 2; FEV1, forced expiratory volume in 1 second; GABA, γ-aminobutyric acid; HMG-CoA, 3‑hydroxy‑3‑methylglutarylcoenzyme A; LAM, lymphangioleiomyomatosis; mTOR, mechanistic mammalian target of rapamycin; N/A, not applicable; NF1, neurofibromatosis type 1; SEGA,
subependymal giant cell astrocytoma; TSC, tuberous sclerosis complex; VEGFD, vascular endothelial growth factor D. *mTOR inhibitor, earlier code name RAD001.
‡
GABA transaminase inhibitor. §Glucagon and insulin inhibitor. ||mTOR inhibitor, also known as rapamycin. ¶Angiogenesis inhibitor. #Aromatase inhibitor.
**Autophagy and lysosomal inhibitor. ‡‡HMG-CoA reductase inhibitor. §§SRC kinase inhibitor. ||||COX2 inhibitor. ¶¶β-blocker.
LAM cells exist in the lung within a network of lym­
phatic endothelial cells, and serum levels of vascular
endothelial growth factor D (VEGFD) are increased in
many women with LAM. The presence of this lymphatic
network in the lung is hypothesized to contribute to the
metastasis and survival of LAM cells in the lung; further
research is needed to address this hypothesis. A VEGFD
level >800 pg per ml in conjunction with a characteristic
CT scan appearance is considered diagnostic of LAM102.
The mechanisms through which LAM cells destroy lung
parenchyma are not well understood. Secretion of pro­
teases including matrix metalloproteinase 2 (MMP2)
and MMP9 has been reported103, which might mediate
this destruction.
The reasons that LAM predominantly affects women
are also not completely understood. LAM cells express
oestrogen receptor-α and progesterone receptor 104,
and LAM progresses more rapidly in premenopausal
women than in postmenopausal women, suggesting
that the development and/or progression of LAM might
be dependent on female sex hormones45. In support of
this hypothesis, in mouse models, oestrogen enhances
the metastasis and survival of TSC2‑deficient cells95.
As noted above, one theory is that LAM cells arise in a
female-specific organ, such as the uterus.
Kidney
Angiomyolipomas. AMLs have been described as
perivascular epithelioid cell tumours (PEComas) because
of their immunoreactivity to histological markers — as
detected by HMB‑45 and Melan‑A antibodies — that
are characteristic of the PEComa family of tumours105,106.
The cell of origin of AMLs is unknown. Consequently, it
has been hypothesized that AMLs arise from neural crest
tissue107. However, because the characteristic molecular
pathology of TSC-deficient cells results in arrested (and
possibly altered) differentiation66,108, whether AMLs
arise from embryonic mesenchyme109 or another cellular
­lineage remains undetermined.
AML cells in general show loss of heterozygosity for
either TSC1 or TSC2 (REFS 63,109,110), which is consist­
ent with clonality and the formation of these tumours
following the model proposed by Knudson’s two-hit
hypothesis111. This in turn leads to overactivation of
the mTORC1 pathway, AML cell growth and increased
production of VEGFD110,112. VEGFD is a cytokine that
­promotes vascular growth, enabling the AML to m
­ aintain
its nutrition as it enlarges and thus remain viable.
AMLs that behave in a malignant manner have been
described and are also often referred to as PEComas.
Interestingly, malignant forms of AML have been reported
in patients with TSC113, but the vast majority of malignant
PEComas occur in patients who do not have TSC114.
Renal cell carcinoma. Renal cell carcinoma is now
recognized as a manifestation of TSC, with distinctive
pathological features compared with other forms of
renal cellZcarcinoma44,55,115–117. In some patients with
TSC, renal cell carcinomas seem to arise from renal
cysts44,118. In a patient with multiple renal cell carcinomas,
genetic analy­sis has shown that these arise i­ ndependently
through distinct second-hit genetic events119.
Contiguous gene deletions. A small subset of patients
with TSC have a contiguous gene syndrome caused
by a deletion of part or all of TSC2 and PKD1 at 16p,
which inactivates both genes25,120. The renal phenotype
associ­ated with this syndrome is usually severe, with
early onset of cysts and renal failure often in late child­
hood or early adult life. Some patients with contiguous
deletions have less-severe cystic phenotypes that are
associ­ated with mosaicism25 or possibly by later timing
of second hits108.
Skin
Factors that might promote second-hit mutations in
the skin of those with TSC include exposure to UV
light. Indeed, an analysis of somatic TSC1 and TSC2
mutations in dermal fibroblast-like cells cultured from
facial angiofibromas revealed a signature characterized
by CC>TT transitions, implicating UV light d
­ amage
through the formation of cyclobutane pyrimidine
dimers in the aetiology of 50% of these growths61. This
class of mutation has never been observed as a germline
change in patients with TSC and was not detected in
other TSC-associated tumours.
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100
Prevalence of disease (%)
90
80
70
60
50
40
30
20
10
0
0
(Birth)
5
10
Cardiac
rhabdomyoma
15
20
25
30
35
40
45
50
55
60
Age (years)
Facial
angiofibroma
Renal
angiomyolipoma
Ungual
fibroma
Pulmonary
LAM*
Nature Reviews
| Diseaseof
Primers
Figure 3 | Approximate kinetics of age-dependent clinical
manifestations
TSC.
A model of the age-dependent manifestations of tuberous sclerosis complex (TSC) based
on data from REF. 3 and the research and clinical experience of the authors. Although
rare, ungual fibromas can be observed in children <10 years of age. In addition, although
the general natural history of cardiac rhabdomyomas is steady regression after birth,
these tumours can occasionally become transiently more prominent (increase in size)
during puberty. *Presence in women with TSC, rather than the entire patient population,
as lymphangioleiomyomatosis (LAM) occurs predominantly in women. 80% of LAM cases
are asymptomatic.
mTORC1 activation is an important factor in the
aetiology of angiofibromas, hypopigmented macules,
cephalic plaques and shagreen patches. For instance, case
reports, case series and trials have demonstrated consist­
ent partial responses of these lesions to both ­systemic and
topical mTORC1 inhibitor therapy 121–123.
Diagnosis, screening and prevention
The 2012 consensus statement on diagnosis
Diagnosis of TSC may be made through the documen­
tation of clinical signs and radiographic findings or by
genetic testing. Diagnostic evaluation can be initiated
because of a positive family history or because of clin­
ical signs or symptoms. Revised diagnostic criteria
were agreed at an international consensus conference
in 2012 and published in 2013 (REF. 3) (BOX 2). As none
of the many manifestations of TSC is independently
pathognomonic, definitive clinical diagnosis rests on
the demonstration of combinations of clinical and/or
radiographic findings. A diagnostic evaluation is often
tailored to the individual situation but may include
imaging of the brain, heart, lungs and kidneys, cognitive
and developmental evaluation, seizure monitoring and
an examin­ation by a dermatologist including a Wood’s
lamp evaluation to detect hypomelanotic skin lesions.
The identification of a pathogenetic TSC mutation in
normal tissue is now considered sufficient to make a
definitive diagnosis, although mutations are not detected
in all individuals with clinical TSC. Mutation detection
may be useful to confirm the diagnosis in individuals
who do not fulfil definitive clinical criteria, to enable
prenatal or pre-implantation genetic diagnosis or to
identify individuals at particular risks, for example, of
severe and early renal disease in cases with contiguous
TSC2 and PKD1 deletions.
Early diagnosis of TSC remains challenging in many
parts of the world for several reasons. For example, diag­
nostic guidelines developed through consensus confer­
ences may be impractical in some regions where there
is limited access to specialized care providers, limited
availability of imaging, such as CT and MRI, and lim­
ited access to genetic testing. In addition, classic clinical
presentation includes epilepsy, skin lesion and intellectual
impairment, yet only 29% of patients with TSC exhibit
all of these symptoms124, further potentiating the under­
diagnosis in the absence of other diagnostic tools. Despite
these challenges, local effort to increase disease awareness
and the development of specialized centres will help to
improve diagnosis and care. TSC International (TSCi)
is a worldwide association of TSC organizations with
members in South Africa, China, Japan, Taiwan, Israel,
Australia, New Zealand, Russia and 19 other countries in
Western and Eastern Europe. It also includes organiza­
tions in North and South America. Initiated in the
mid‑1980s, TSCi aims to establish internationally recog­
nized diagnostic criteria, surveillance and treatment
guidelines, in addition to stimulate, c­ oordinate and fund
research on TSC around the world.
Monitoring and prevention of manifestations
Epilepsy. Close monitoring using electroencephalography
(EEG) during the first months of life is currently used
in many centres as it is thought to be the best-available
detection tool for epileptogenesis125, and video EEG (the
simultaneous recording of brainwaves and patient behav­
iour) may be a particularly good technique to monitor
epilepsy in infants with TSC. However, in the majority of
patients, epilepsy is diagnosed following the onset of clin­
ical s­ eizures. Careful electroencephalographic follow‑up
was recommended recently by the International TSC
Consensus Meeting for Epilepsy 126. According to these
recommendations, frequent EEG studies should be con­
sidered during the first year of life. By contrast, according
to the 2012 TSC Consensus Conference guidelines127,
EEG should be performed at the time of diagnosis and
whenever clinical seizure activity is suspected. Particularly
given the high incidence of infantile spasms in TSC, an
electroencephalogram should be obtained whenever an
infant develops behaviours suggestive of infantile spasms.
It is important to remember that infants with TSC who
develop infantile spasms may not exhibit hypsarrhythmia
(an abnormal pattern of activity between convulsions that
is characteristic of infantile spasms) on an electroencepha­
logram. If the electroencephalogram is not diagnostic,
video EEG monitoring should be performed if possible to
determine if the repetitive behaviours are associated with
a relative flattening of the electroencephalogram, which is
consistent with infantile spasms30.
Subependymal giant cell astrocytomas. A major advance
in the care of individuals with TSC over the past few decades
has been surveillance monitoring for possible develop­
ment of a SEGA. In the past, SEGAs were diagnosed
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after an individual presented with clinical symptoms
that were suggestive of increased intracranial pressure or
more-subtle clinical features, such as changes in behav­
iour or increased seizure activity. However, recent recom­
mendations have been to perform routine neuroimaging
to monitor for the development of a SEGA. The 2012
TSC Consensus Conference guidelines127 recommend
imaging every 1–3 years until 25 years of age. If growth
occurs between imaging time points, shorter intervals
between neuroimaging is usually performed to assess
for continued growth.
a
Angiofibroma
LAM
AML and RCC
Germline mutation
TSC2
Somatic second-hit mutation
16p13
b
Sporadic
LAM only
Somatic first-hit
mutation
Sporadic LAM
and/or
sporadic AML
Somatic second-hit
mutation
16p13
Figure 4 | The two-hit tumour-suppressor gene modelNature
in TSC.Reviews
Genetic| mechanisms
Disease Primers
of tumorigenesis in tuberous sclerosis complex (TSC) fit the Knudson two-hit tumoursuppressor gene model. a | Germline inactivating mutations in TSC1 or TSC2 are followed
by somatic second-hit mutations that inactivate the remaining wild-type allele. This leads
to angiofibroma, lymphangioleiomyomatosis (LAM), angiomyolipoma (AML) and renal cell
carcinoma (RCC) in patients with TSC. b | Somatic first-hit and second-hit mutations that
inactivate each wild-type allele of TSC2 lead to sporadic LAM and/or sporadic AML.
TSC-associated neuropsychiatric disorders. Intellectual
disability, autism spectrum disorder and mental health
disorders are often underdiagnosed and undertreated
in individuals with TSC. According to the 2012 TSC
Consensus Conference guidelines127, children with
TSC should undergo a thorough neurocognitive evalu­
ation at the time of their TSC diagnosis. Individuals with
TSC should then be followed throughout childhood and
adolescence to characterize their neurocognitive pro­
files and optimize educational and treatment strategies.
A TAND checklist has been developed and once vali­
dated may be a useful tool for such evaluation36. As dif­
ferent types of epilepsy, particularly infantile spasms and
refractory epilepsy, are variables in the development of
cognitive impairment and autism spectrum disorder in
TSC, treatment of epilepsy should aggressively attempt
to control seizure activity.
Lung. Women who have TSC have a high risk of develop­
ing LAM. All women with TSC should have a baseline
CT scan in early adulthood (around 18 years of age) and
regular pulmonary function testing should be performed
for women who are cognitively able to perform these
studies. Monitoring of pulmonary function in women
who are unable to perform pulmonary function testing
remains an area of unmet need. Evidence of shortness of
breath or other respiratory symptoms should be sought
as part of regular medical care for women with TSC.
Airflow limitation can be quantified using the forced
expiratory volume in 1 second (FEV1) and is often used
to assess the lung function of patients with LAM.
There are currently no proven strategies for the
prevention of LAM and the benefits of early treatment
are unknown. As a considerable number of girls with
TSC have been and continue to be treated with mTOR
inhibitors, information about whether mTOR inhib­
ition in childhood prevents the development of LAM
in adulthood should become available in the future.
Acquiring this information will require a mechanism
to ensure that the lung function of this cohort is sys­
tematically followed during their adult years. This will
be a ­challenging endeavour, for both practical and
financial reasons.
Kidney. The new international guidelines127 recommend
assessing renal function and blood pressure at least
annually and renal imaging every 1–3 years. MRI is the
modality of choice because it is superior to ultrasound
and does not carry the risk of radiation that is associ­
ated with CT127,128. As new AMLs are found and enlarge,
nephrologists routinely increase the frequency of imag­
ing up to every 6–12 months to track and pre-emptively
treat those lesions still growing that enlarge >30 mm
in diameter.
Similar to LAM, there are no proven prevention strat­
egies for AMLs, but a great deal of information should
become available retrospectively from children who
began early treatment with mTOR inhibitors for SEGAs.
It will be very important to learn whether the incidence,
age at onset and/or size of AMLs is decreased with early
mTOR inhibitor therapy.
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Angiofibromas. Given the recent evidence of UV‑induced
second-hit mutations in angiofibromas discussed above61,
it is hypothesized that sun-protective measures might
decrease the incidence of angiofibromas, but this is yet
to be demonstrated.
recommendations, vigabatrin should be used as a firstline treatment in infants for both partial seizures and
infantile spasms126,127. Dietary therapy, both the classic
ketogenic diet and the low glycaemic index treatment,
can be very effective in treating epilepsy in TSC129,130.
Vagal nerve stimulation can also be very helpful at
improving seizure control131. The role of mTOR inhib­
itors in the treatment of refractory epilepsy in TSC is
currently under investigation, but a few reports have sug­
gested that they may be effective in some individuals132,133.
Surgical resection of the region of the brain responsible
Management
Central nervous system manifestations
Epilepsy. First-line treatment of epilepsy in TSC, as in
other aetiologies of epilepsy, is with anticonvulsant med­
ication. According to the European and international
a
RSK1
ERK
AKT
TSC2
PDK1
AMPK
TSC1
CDK1
TBC1D7
RHEB
Farnesyltransferase
inhibitors and statins
GTP
mTOR allosteric inhibitors
(except rapamycin)
RAPTOR
mTOR kinase inhibitors
TFEB
ULK1
↓ Autophagy ↓ Autophagy
VEGF
mTORC1
FKBP38
4EBP1
S6K
SREBP1
↓ Apoptosis
↑ Protein
translation
↑ Nucleotide
synthesis
and protein
translation
↑ Lipid
synthesis
Chloroquine
b
MLST8
mTOR
Metabolic inhibitors
RAL-GTP
TSC2
β-Catenin
↑ Invasiveness ↑ Angiogenesis and
lymphangiogenesis
↑ Cell growth
SIN1
TSC1
RICTOR
TBC1D7
MLST8
mTOR
mTORC1
Rheb
GTP
FKBP8
Dynein
↓ Apoptosis
Aggresome
mTORC2
MLST8
mTOR
MMP2
RAPTOR
HIF1A
BRAF
Notch
Altered cell fate
and differentiation
AKT
CAD
↑ Pyrimidine
nucleotide
synthesis
RhoA
Apoptosis and
altered cytoskeletal
dynamics
COX2
Aspirin
and COX2
inhibitors
↑ Prostaglandin
production
Figure 5 | Canonical and non-canonical TSC signalling pathways. a | The tuberous sclerosis
complex| (TSC)
protein
Nature Reviews
Disease
Primers
complex, selected upstream regulators and downstream effectors. Cells with inactivating mutations of TSC1 or TSC2
activate RAS homologue enriched in brain (RHEB). RHEB activates the ‘canonical’ mechanistic target of rapamycin (mTOR)
complex 1 (mTORC1) signalling network, leading to increased protein translation and cell growth on the one hand and
decreased autophagy and apoptosis on the other hand, among many other effects. b | Putative non-canonical signalling
pathways, including pathways regulated by the TSC protein complex in an mTORC2‑mediated manner and pathways
regulated by RHEB that seem to be independent of mTORC1. Potential therapeutic agents are indicated in yellow boxes.
Green boxes represent proteins that promote mTOR activity or are promoted by mTOR. Blue boxes represent proteins
that inhibit mTOR activity or are inhibited by mTOR. 4EBP1, eukaryotic translation initiation factor 4E‑binding protein 1;
AMPK, AMP-activated protein kinase; CAD, carbamoyl-phosphate synthetase 2, aspartate transcarbamylase and
dihydroorotase; CDK1, cyclin-dependent kinase 1; COX2, cyclooxygenase 2; HIF1A, hypoxia-inducible factor 1α;
MLST8, target of rapamycin complex subunit LST8; MMP2, matrix metalloproteinase 2; PDK1, pyruvate dehydrogenase
kinase isoform 1; RAL, RAS-related protein, RAPTOR, regulatory-associated protein of TOR; RICTOR, rapamycininsensitive companion of mTOR; RSK1, ribosomal S6 kinase 1; S6K, S6 kinase; SIN1, stress-activated map-kinaseinteracting protein 1; SREBP1, sterol regulatory element-binding protein 1; TBC1D7, TBC1 domain family member 7;
TFEB, transcription factor EB; ULK1, unc‑51‑like kinase 1; VEGF, vascular endothelial growth factor.
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Box 2 | 2012 updated criteria for TSC diagnosis
Based on the 2012 TSC Consensus Conference, Northrup et al.3 recommended the
incorporation of genetic testing to TSC diagnosis, and also revised and updated
the clinical diagnostic criteria as stated below.
Genetic diagnostic criteria
“The identification of either a TSC1 or TSC2 pathogenic mutation in DNA from normal
tissue is sufficient to make a definitive diagnosis of TSC. A pathogenic mutation is
defined as a mutation that clearly inactivates the function of the TSC1 or TSC2 proteins
(for example, out‑of‑frame indel or nonsense mutation), prevents protein synthesis (for
example, a large genomic deletion) or is a missense mutation in which the effect on
protein function has been established by functional assessment (see the Leviden Open
Variation Database (http://chromium.lovd.nl/LOVD2/TSC))15. Other TSC1 or TSC2
variants that have a less-certain effect on protein function do not meet these criteria
and are not sufficient to make a definitive diagnosis of TSC. Approximately 10% of
patients with TSC do not have a mutation that can be identified by conventional
genetic testing, and a normal gene test result does not exclude TSC or have any effect
on the use of clinical diagnostic criteria to diagnose TSC.”
Clinical diagnostic criteria
A definitive diagnosis is made if a patient has two major features or one major feature
with at least two minor features. A possible diagnosis is made if the patient has either
one major feature or at least two minor features. Major features include:
• Hypomelanotic macules (≥3 of ≥5 mm in diameter)
• Angiofibromas (≥3) or fibrous cephalic plaque
• Ungual fibromas (≥2)
• Shagreen patch
• Multiple retinal hamartomas
• Cortical dysplasias*
• Subependymal nodules
• Subependymal giant cell astrocytomas
• Cardiac rhabdomyomas
• Lymphangioleiomyomatosis (LAM)‡
• Angiomyolipomas (≥2)‡
Minor features:
• ‘Confetti’ skin lesions
• Dental enamel pits (>3)
• Intraoral fibromas (≥2)
• Retinal achromic patch
• Multiple renal cysts
• Non-renal hamartomas
TSC, tuberous sclerosis complex. *Includes tubers and cerebral white matter radial migration
lines. ‡A combination of the two major clinical features (LAM and angiomyolipomas) without
other features does not meet criteria for a definitive diagnosis. Reproduced with permission
from REF. 3, Elsevier.
for refractory epilepsy can also be successful134. Infants
with TSC who show signs of epilepsy by EEG should
receive treatment with vigabatrin, an irreversible inhib­
itor of GABA transaminase135. This treatment should be
considered if epileptiform features are observed, even in
the absence of clinical seizures.
Subependymal giant cell astrocytomas. Traditionally,
the only option for the management of symptomatic
or growing SEGAs involved neurosurgical resection,
either through a transcallosal or transfrontal approach.
Although often performed without any apparent perma­
nent sequelae, the immediate risks associated with sur­
gical resection of SEGA are well understood, especially
when surgery is performed urgently in the setting of
increased intracranial pressure. Possible complications
of surgical resection include incomplete resection,
haemor­rhage, infection and cerebrospinal fluid obstruc­
tion, which often requires ventriculoperitoneal shunting
to remove excess cerebrospinal fluid from the brain.
Over the past 10 years, experience with the use of
mTOR inhibitors in the treatment of SEGAs has increased.
Following initial reports of mTOR inhibitor treatment
resulting in reduction in the size of SEGAs, clinical trials
have led to the FDA and EMA approval of everolimus in
the treatment of SEGA121. Long-term treatment with these
medications is recommended, as termination of treatment
typically leads to regrowth of the SEGA136. The number of
reports on long-term use of mTOR inhibitor therapy in
SEGAs is increasing. These drugs are fairly well tolerated
during acute therapy, even in children <3 years of age, and
recent data also indicate that the number of adverse effects
decreases over time137,138.
TSC-associated neuropsychiatric disorders. If individ­
uals with TSC are identified as having any aspects of
TAND, then clinical guidelines and practice parameters
as set out for the individual disorders should be imple­
mented30. Management should include multidisciplinary
and multi-agency work including health, educational,
social and other relevant agencies working alongside the
family and care providers. If mental health issues pres­
ent, referral should be made to experienced psychiatrists
and psychologists to help minimize the effect on the
individual’s ability to function. Currently, there are no
TSC-specific interventions, and clinical teams should use
the evidence-based interventions available to the general
population to treat anxiety disorders, attention-deficit/
hyperactivity disorder and attention-deficit disorder in
patients with TSC. Although the studies done by Tillema
et al.139 demonstrated a beneficial effect of everolimus on
brain white matter, which might correspond with an
improvement in TANDs, longer studies are required to
validate this finding. Several Phase II trials exploring the
effect of mTOR inhibition on various levels of TAND are
­ongoing (TABLE 1).
The cognitive impairment in TSC can be severe, and
many individuals will need support throughout their life­
time, including for performing activities of daily living.
Treatment of mental health issues may need to be long
term and should be monitored to optimize efficacy and
minimize any treatment-associated morbidity.
Pulmonary manifestations
Results from the MILES trial45 support the use of siroli­
mus in women with either TSC-associated LAM or spor­
adic LAM whose FEV1 is <70% of the predicted normal
value. The efficacy of everolimus in LAM has been stud­
ied in a Phase II trial140, in which everolimus treatment
was found to improve some measures of lung function
and exercise capacity and reduce serum VEGFD levels.
The threshold for treatment of LAM in women with
TSC is evolving. Earlier therapy should be considered
in women with clear evidence of lung function decline
who have not yet reached this 70% threshold of FEV1.
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Women should be counselled about the risk of pneumo­
thorax, which may be increased during pregnancy, and
on the avoidance of oestrogen, including oestrogen-­
containing oral contraceptives. Progression of LAM dur­
ing pregnancy has been reported anecdotally and should
also be discussed.
Renal complications
The key to effective management of renal complications
in TSC is surveillance as recommended in the new inter­
national guidelines127. Although the prevalence of AMLs
is the same in men and women141, the EXIST‑2 trial122
recruited twice as many women as men needing treat­
ment for their renal AMLs. This and the much higher
prevalence of LAM in women with TSC have reinforced
the clinical impression that high levels of oestrogen may
promote AML growth142. This would have important
implications for advice on oral contraception, pregnancy
and hormone-replacement therapy. However, defini­
tive evidence for this sex hormone effect is lacking and
general advice to avoid exposure to increased levels of
­oestrogen if possible is all that can be given.
Angiomyolipomas. An important consequence of AMLs
is renal bleeding. Two accumulative prevalence surveys
have shown that the risk of bleeding from renal AML
in TSC is between 9% and 21%58,143. The lifetime risk of
haemorrhage from an AML will be higher, but we await
the publication of data from larger studies144. Lesions that
are growing and are >30 mm in diameter are most at risk
of causing bleeding 145.
Treatment of AMLs is ideally pre-emptive to try and
prevent bleeding, reduce tumour size or slow its growth.
If this fails, treatment is initiated once bleeding has been
detected. Percutaneous embolization is the first line of
treatment for acute bleeding in AMLs127. Embolization
involves the use of selective arterial catheterization and
injection of an occluding agent (for example, plastic coils)
or a sclerosant directly into the AML feeding vessel to
block blood supply to the tumour. Adverse effects of
this approach include postembolization syndrome —
a combination of pain, fever, nausea and vomiting that
occurs within 72 hours of the procedure — which can
be markedly ameliorated through the use of prophylactic
steroids146. Systemic mTOR inhibitor therapy rather than
embolization is the preferred pre-emptive treatment for
AMLs because there is a high risk of recurrence post­
embolization147–149 and because collateral damage to
normal renal tissue caused by embolization may exacer­
bate the risk of later impaired renal function127,143,149. For
example, sirolimus was piloted as a treatment for AMLs
with the aim of preventing bleeding and preserving renal
function150–152 and has demonstrated promising shrink­
age of AMLs. In addition, Phase III studies have shown
that everolimus is successful in 95% of adults and 100%
of children in preventing AML growth and reducing
their size122,153 and 100% successful in preventing bleed­
ing while on therapy 154,155. The response to everolimus
is durable, the adverse effects are mainly minor and
the incidence of new AMLs diminishes over time with
­tailoring of individual dosing 154,155.
Nephropathy. Adults with TSC have a high prevalence
of prematurely diminished glomerular filtration rate
(GFR)143,149. Although this reduction can be due to acute
kidney injury from acute haemorrhage caused by AMLs
and collateral damage from surgery and embolization
used to treat bleeding, observations suggest that it is also
common in those who have never had recognized bleed­
ing 156. It has also been proposed that premature apop­
tosis of differentiated renal cells might occur owing to
TSC1 or TSC2 haploinsufficiency associated with modest
mTORC1 overactivation in non-AML renal tissues. Focal
segmental glomerular sclerosis is occasionally reported
in patients with TSC and might also be associated with
increased mTORC1 activity. In the EXIST‑1 (in children)
and the EXIST‑2 (in adults) trials of everolimus154,155, GFR
was maintained in those in whom it was not already
severely diminished (<30 ml per min) prior to the trial.
TSC-associated PKD. The treatment of TSC-associated
PKD, which occurs in patients with contiguous TSC2–
PKD1 deletions, is supportive and involves management
of hypertension, cardiovascular risk factors and the
consequences of renal failure. Formal trials of mTOR
inhibitor therapy for TSC-associated PKD have not
been undertaken.
Two studies in adults with established autosomal
dominant PKD without TSC failed to demonstrate bene­
fit from sirolimus or everolimus therapy in slowing the
decline in renal function157,158. It has been suggested that
the tissue levels of sirolimus were subtherapeutic in these
studies, and the question of whether mTOR inhibitors
are useful in this setting might warrant further investi­
gation159. Because there is an accelerated phenotype in
TSC-associated PKD, a study of the utility of an mTOR
inhibitor in preventing this would be worthwhile. For
neurological complications, early treatment with siroli­
mus has been shown to completely rescue the phenotype
in a mouse model of TSC (a Tsc1 knockout)160. Similarly,
phenotype rescue may be possible for any TSC renal
disease, including TSC-associated PKD, and trials are
being planned.
Dermatological manifestations
Prior to mTOR inhibitor therapy for TSC, management
of skin lesions was by ablation — mostly using carbon
dioxide and pulse dye laser or surgery-based approaches
— or by use of ‘camouflage’ make-up161. Recurrence after
ablative treatments is common and their application is
problematic in children and in adults with learning and
behavioural difficulties, which might necessitate the use
of general anaesthesia. Initial observation of improve­
ment in facial angiofibromas during systemic mTOR
inhibitor treatment162 led to speculative topical treat­
ment of angiofibromas in individual patients, and several
small studies have used topical application of 0.1–1%
rapamycin preparations, all with positive outcomes163–165.
At least one larger formal clinical trial is due to report
soon123. The dermatology expert group at the 2012
TSC Consensus Conference included the use of topical
rapamycin for angiofibromas in their treatment recom­
mendations127. The EXIST‑1 and EXIST‑2 trials121,122
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Table 2 | Monitoring and management of clinical manifestations of TSC
Clinical
manifestation
Diagnosis and monitoring
Management options
Infantile
spasms and
seizures
• EEG
• vEEG
• Steroids
• Anticonvulsants
• Clobazam
• Vigabatrin
• Ketogenic diet
• Vagal nerve stimulation
• Surgical resection
SEGAs
• MRI
• Everolimus
• Surgical resection
TANDs
• Periodic screening
• Special educational programmes
• Neuropsychiatric evaluation and
treatment
LAM
• High-resolution CT scan
• Pulmonary function testing
• Diffusion capacity
• Oxygen monitoring during
exercise
• Sirolimus
AMLs
• MRI (preferred)
• Renal function tests
• CT scan
• Percutaneous embolization
• Everolimus
• Nephron-sparing surgical
resection (avoid if possible)
Skin lesions
• Periodic examination
• Ablation by carbon dioxide
• Pulse laser dye
• Sun protection
• Topical rapamycin
AML, angiomyolipoma; EEG, electroencephalography; LAM, lymphangioleiomyomatosis;
SEGA, subependymal giant cell astrocytoma; TAND, tuberous sclerosis complex-associated
neuropsychiatric disorder; TSC, tuberous sclerosis complex; vEEG, video EEG.
of systemic everolimus therapy for SEGA and AML
also monitored skin manifestations as exploratory out­
comes and both reported significant partial responses of
lesions to everolimus compared with placebo. In addi­
tion, oral sirolimus has been shown to significantly
improve TSC skin tumours, particularly angiofibromas,
during long-term treatment166 (TABLE 2).
Quality of life
TSC as a lifelong, chronic disease
Although a near-normal lifespan is achievable for many
patients with TSC, the disease imparts a high morbidity
and considerable mortality 167. The phenotype is so varied
that there are hundreds of possible unique presentations
and courses of the illness. As a result, this rare genetic dis­
ease becomes ultra-rare in each of its many combinations
of manifestations. Patients are scattered among various
specialists, meaning that each individual physician or ser­
vice provider has little experience or chance to develop
expertise, except for in TSC specialist clinics. The exist­
ence of these clinics and evidence-based guidelines have
had substantial positive outcomes for affected families —
even before specific problems are addressed. For a patient
with TSC, the lifetime risk of a serious ­complication is
high and unpredictable (BOX 3).
In addition to the overt risks, there are less-apparent
ones, such as the increased cardiovascular morbidity
and mortality due to a GFR of <60 ml per min168. The
fear of unpredictable risk adds to the stress for patients
and families who are already overburdened coping with
a serious chronic illness that combines major physical
dangers with psychological traumas due to autism spec­
trum disorder, anxiety, depression, intellectual disability,
severe intractable insomnia, refractory epilepsy and a dis­
figuring facial rash. Often, a family’s earning potential is
adversely affected by their care duties. They have to cope
with a lifelong grief for loss of what might have been.
As children with TSC grow to adulthood, parent carers
become exhausted then become worried about who will
care for their loved one when they are no longer capable
of doing so themselves.
In addition to substantial short-term morbidity and
mortality, the real burden of this chronic, progressive
disorder occurs over the long term for patients, care­
givers, providers and society. With little published lit­
erature regarding the cost of illness and treatment, the
only available economic evidence in TSC comes from
estimates of the cost of genetic testing 169 and two sur­
vey studies evaluating caregiver burden170,171. Thus, the
economic and humanistic burden of this disease remains
poorly studied. Until patient quality of life, caregiver
burden, lost productivity and medical and non-medical
costs are better assessed, the collective burden of TSC will
remain unknown.
Effects of chronic treatment
The long-term effects of chronic mTOR inhibition ther­
apy for TSC are not completely understood since the
use of rapamycin in TSC clinical trials began in 2003.
However, there is a long history of the use of mTOR
inhibitors as immunosuppressants in transplant patients
and in patients with cancer since its FDA approval in
1999. Some of the potential adverse effects of continuing
concern include stomatitis and other cutaneous issues172,
wound-healing complications173, metabolic adverse
effects such as diabetes and hyperlipidaemia174, delayed
sexual maturation175 and infertility. For example, in the
EXIST‑2 trial155, temporary amenorrhoea occurred in
22.5% of at‑risk women (those 18–55 years of age),
hypophosphataemia in 7% of patients and proteinuria in
15.2% of patients, although none of the patients had to
be withdrawn from the trial owing to these problems.
It is important to note that most adverse effects associ­
ated with mTOR inhibitors are moderate or mild and
related to dosage, and many are reversible upon cessation
of treatment176.
Outlook
Following considerable progress in establishing the
­success of mTOR inhibitors for the treatment of several
serious complications of TSC, including SEGAs, renal
AMLs and pulmonary LAM, attention is now focused
on the potential for these agents to prevent the manifest­
ations of TSC before complications arise. TSC is fre­
quently diagnosed prenatally or in early infancy, often
prior to the onset of epilepsy, which allows the possibility
of monitoring and intervening in affected children before
the appearance of seizures and/or neurodevelopmental
delay 126,177. Indeed, the concept of preventative treatment
has been considered for other forms of epilepsy includ­
ing in preterm infants and those with Sturge–Weber
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Box 3 | Lifetime risk of TSC serious complications
• Subependymal giant cell astrocytoma: 10–15%200
• Renal (bleeding or chronic kidney disease): 21–40%58,143
• Symptomatic lymphangioleiomyomatosis: 5–48%
(in women)40
• Resistant epilepsy: up to 33%126
• Disfiguring facial rash: 75%3
• Tuberous sclerosis complex (TSC)-associated
neuropsychiatric disorders: 90%36
disease28,177–179. Improvements in neurological outcomes
have been reported in pilot studies of immediate control
of infantile spasms with vigabatrin177,180; however, there
are no studies on the effect of pre-emptive treatment.
Prevention of seizures in TSC is now being tested in an
international clinical trial — the EPISTOP trial. The pro­
ject began in 2013 and involves scientists from 16 hospi­
tals and laboratories from 10 countries, and aims to better
understand the pathophysiology of epilepsy, to develop a
preventative strategy, to identify new biomarkers and to
develop new therapeutic targets that can block or modify
epileptogenesis in patients with TSC.
Recently, anti-epileptogenic properties of mTOR
inhibitors have been reported in mouse models of TSCassociated epilepsy 181–184. Unlike ‘classic’ anti-epileptic
drugs, which treat epilepsy by decreasing neuronal excit­
ability via modulation of ion channels or neurotrans­
mitters, mTOR inhibitors, such as rapamycin, seem to have
inconsistent effects on acute seizures, but might modulate
underlying molecular and pathological abnormalities
associated with epileptogenesis, such as astrocyte prolifer­
ation, pyramidal cell dispersion and glutamate transporter
expression182. However, these effects in TSC mouse
models, which include mice with targeted inactivation of
the Tsc genes in neurons or glial cells184, are maintained
only with continued rapamycin treatment, as the under­
lying genetic defect driving mTORC1 h
­ yperactivation
persists after the treatment is discontinued185.
Studies of prenatal and early postnatal treatment
with mTOR inhibitors have been undertaken in mouse
­models. Interestingly, wild-type animals prenatally treated
with mTOR inhibitors demonstrated memory deficits
and developmental delay, which were not seen in mice
treated only postnatally 186. This finding may suggest that
inhibiting mTORC1 in a period in which it participates in
processes that are critical for neurodevelopment, such as
neuronal growth, axon guidance and synapse formation,
will permanently alter structures underlying memory
and cognitive functions. If so, determination of a proper
‘time window’ for early treatment is of crucial value.
To date, there is not sufficient evidence to support
the use of mTOR inhibitors as an anti-epileptogenic
therapy in TSC. However, some studies have shown a
reduction in SEGA volume and seizure frequency after
mTOR inhibitor treatment in patients with TSC187, and
the results of ongoing clinical trials might reveal a sub­
set of patients who benefit in terms of seizure control
and/or a key developmental window in which mTOR
inhibition therapy can prevent seizures while minimizing
any therapy-­related adverse effects on brain development
and function. The potential for adverse effects, including
hyperlipidaemia, haematological abnormalities, liver tox­
icity and chronic immunosuppression132, also need to be
considered (TABLE 1).
The implementation of surveillance imaging for
SEGAs with MRI or CT scanning has profoundly
reduced the morbidity and mortality of this TSC-related
symptom. Hopefully, advances in the identification of
better biomarkers of SEGA development and/or in
treatments for SEGAs will help to further minimize the
effect of SEGAs on the lives and health of individuals
with TSC.
The EXIST‑1 trial has shown that everolimus is effec­
tive in stabilizing and partially reversing early renal dis­
ease in children and provides a durable response153,154.
The challenge now is to find ways of targeting current
available therapies (or new ones) for those at highest risk
and to design treatment regimes that minimize adverse
effects while optimizing benefit. We need to explore the
early use of mTOR inhibitors in the prevention of PKD
in children with the TSC2–PKD1 contiguous gene syn­
drome and whether mTOR inhibition therapy can pre­
vent or delay end-stage renal disease in this small group
of patients. Importantly, the relatively small number of
children affected by this syndrome will be a barrier to
clinical trial implementation. By contrast, adequately
powered studies to determine whether mTOR inhib­
ition will prevent the premature loss of GFR observed in a
large proportion of patients with TSC should be feasible.
For LAM, it is clear that mTOR inhibition can stabil­
ize lung function in the majority of affected women,
but the therapy must be continued indefinitely. It is not
yet known whether mTOR inhibition can prevent the
develop­ment of LAM in women with TSC. A n
­ atural
history study of girls who receive mTOR inhibitors for
brain or kidney disease in childhood could be instrumen­
tal in at least partially addressing this crucial question.
Barriers to this type of analysis will include the chal­
lenge of follow­ing these patients as they transition from
paediatric to adult providers, the need to systematic­ally
evaluate lung function and lung cyst formation in early
adulthood, variations in the age at which therapy was
initiated and establishing a control group who did not
receive a rapalogue (that is, a first-generation mTOR
inhibitor) during childhood. Biomarkers of LAM includ­
ing VEGFD could be crucial to this study. Nevertheless,
a great deal can be learnt from this cohort as they reach
adulthood, not only related to the prevention of LAM but
also about the longer-term efficacy and toxicity of mTOR
inhibitors, especially in terms of sexual maturation and
function and bone and renal health. For instance, loss
of menstrual cycles or the failure to begin menstruation
has been observed in girls receiving mTOR inhibitors.
The long-term adverse effects of mTOR inhibitors in TSC
are still being evaluated, and information is expected to
continue to accrue over the next decade. To date, some
studies are showing relatively few clinically important
long-term effects154, whereas other studies are reveal­
ing a higher incidence of toxicities in patients treated
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with mTOR inhibitors than with placebo188. Long-term
­follow‑­up might also reveal benefits of mTOR inhib­
itory therapy. For example, in studies in wild-type yeast
and mice, treatment with mTOR inhibitors can improve
lifespan and or length of health.
Once therapy with an mTOR inhibitor is initiated, it
is generally continued indefinitely because tumours tend
to regrow upon discontinuation. It is not known whether
there are situations in which mTOR inhibitors can be
safely discontinued in individuals with TSC. The natural
history of SEGAs involves growth that occurs primar­
ily during childhood, but whether and when rapalogues
can be stopped in children or adults with SEGAs are
unknown. Similarly, the natural history of LAM involves
progression primarily during the premenopausal years189,
but there is currently no evidence to support withdrawal
of therapy at menopause.
To ‘cure’ tumours in TSC, it will be necessary to
elimin­ate AML, LAM and SEGA cells. Rapalogues
induce a cytostatic response, with tumour regrowth
when the agents are discontinued. In mouse models,
targeting the metabolic vulnerabilities of Tsc1‑deficient
and Tsc2‑deficient cells to induce cell death is an emerg­
ing concept that might enable a selective cytocidal effect
without the use of an mTOR inhibitor 190. Although sev­
eral novel therapies that selectively induce cell death
and/or block cell proliferation in TSC1‑deficient and
TSC2‑deficient cells have been tested in vitro and pre­
clinically 78, there is a long road ahead towards demon­
strating the efficacy of this approach in clinical trials191.
Ongoing support for basic and translational research is
absolutely essential to future clinical progress in TSC.
Throughout the TSC field, the crucial unmet need for
biomarkers of risk of disease progression and therapeutic
response cannot be overemphasized (especially risk of
TANDs, infantile spasms, AML growth and progression
of LAM). For example, studies have shown a significant
correlation between the vascular growth-promoting
1.
2.
3.
4.
5.
6.
7.
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sclerosis complex diagnostic criteria update:
recommendations of the 2012 International Tuberous
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Pediatr. Neurol. 49, 243–254 (2013).
This paper provides the most current diagnostic
criteria for TSC. The previous criteria were from
the consensus conference in 1998.
Jones, A. C. et al. Molecular genetic and
phenotypic analysis reveals differences between
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tuberous sclerosis. Hum. Mol. Genet. 6, 2155–2161
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many effects. Cell. Metab. 19, 373–379 (2014).
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8.
9.
10.
11.
12.
13.
14.
cytokine VEGFD and AML biomass122,152, and VEGFD
levels are correlated with the likelihood of lung function
decline in women with LAM102.
For the skin, inclusion of dermatological end points
will be important in future prevention trials of systemic
mTOR inhibitor therapy for TSC (TABLE 1). In particular,
the typically slow development of facial angiofibromas
from childhood and their characterization by early angio­
matous changes suggest that effective prevention might
be possible.
Our improving understanding of TANDs and neuro­
anatomical features of TSC will probably further improve
our abilities to minimize the effect of these on the lives of
individuals with TSC. Current research is focused on the
pathophysiology of these symptoms in TSC; further work
will obviously be needed to define whether the results
of this work are generalizable to these disorders in the
general population. Recognition, diagnosis and further
characterization of TAND symptoms in TSC will also
probably lead to specific treatment trials that will help to
better determine effective therapies.
In summary, the care of individuals with TSC has
been transformed over the past decade owing to the
incontrovertible evidence generated to support the use
of mTOR inhibitors for the treatment of many manifest­
ations of TSC. Over the next decade, we anticipate addi­
tional breakthroughs as we move towards preventative
therapy and the elimination of the clinical manifesta­
tions of TSC — a cure. Towards this goal, an initiative
called TSCure has begun, with joint sponsorship of the
Tuberous Sclerosis Alliance (USA) and the Tuberous
Sclerosis Association (UK). TSCure is an international
collaboration of TSC researchers and physicians that
includes all five authors of this Primer and aims to tackle
issues that are necessary to plan clinical trials of very early
treatments to either cure TSC or prevent manifestations
of TSC from occurring rather than treating them when
they appear.
Shepherd, C. W., Gomez, M. R., Lie, J. T. &
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Acknowledgements
The work of S.J. in this study has been partially supported by
the 7th Framework Programme of European Commission
within the large-scale integrating project EPISTOP (Proposal
No. 602391–2). The work of E.P.H. was partially supported
by the Lucy J. Engles Program in TSC/LAM Research. E.A.T.
acknowledges the Carol and James Herscot Center for
Children and Adults with TSC at Massachusetts General
Hospital. The authors are grateful to J. Nijmeh for assistance
with preparation of the manuscript.
Author contributions
Introduction (E.P.H.); Epidemiology (E.A.T., E.P.H., J.C.K.,
J.R.S. and S.J.); Mechanisms/pathophysiology (E.A.T.,
E.P.H., J.C.K., J.R.S. and S.J.); Diagnosis, screening and
prevention (E.A.T., J.R.S. and S.J.); Management (E.A.T.,
E.P.H., J.C.K., J.R.S. and S.J.); Quality of life (E.A.T. and
J.C.K.); Outlook (E.A.T., E.P.H., J.C.K., J.R.S. and S.J.);
Overview of Primer (E.P.H.). E.A.T. and E.P.H. contributed
equally to this work.
Competing interests
S.J. has been a consultant for UCB Pharma and Eisai, has
received speaker’s honoraria from Novartis and is a site
principal investigator for Novartis clinical trials. J.R.S. has
received grant funding and honoraria from Novartis. J.C.K.
has received honoraria for lectures and consultancy from
Novartis. E.A.T. is a consultant for GW Pharmaceuticals and
Zogenix, has received grants from GW Pharmaceuticals,
Lundbeck and Cyberonics, is a site principal investigator for
GW Pharmaceuticals and Zogenix clinical trials and has been
a site principal investigator for Novartis clinical trials. E.P.H.
has been a consultant to LAM Therapeutics and was an
investigator on a Novartis-sponsored trial of everolimus in
lymphangioleiomyomatosis, for which no compensation or
salary support was provided.
www.nature.com/nrdp
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