Tuberous sclerosis overview

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Tuberous sclerosis complex (TSC), is a rare autosomal dominant congenital disorder that affects multiple organ systems and is characterized by an abnormal growth of ectodermal and mesodermal cells that causes non-cancerous tumours to grow in the brain and on other vital organs such as the kidneys, heart, liver, eyes, lungs, and skin.

A combination of symptoms may include seizures, intellectual disability, developmental delay, behavioral problems, skin abnormalities, and lung and kidney disease. TSC is caused by a mutation of either of two genes, TSC1 and TSC2, which code for the proteins hamartin and tuberin, respectively. These proteins act as tumor growth suppressors, agents that regulate cell proliferation and differentiation.

The disease presents with a myriad of symptoms, having been described by multiple doctors throughtout the 19th century and called by many different names, but it is now called tuberous sclerosis complex, and the relationship between benign brain tumors and the symptoms of the disease was first described by Désiré-Magloire Bourneville in 1880.

Historical Perspective

Tuberous Sclerosis was described as a specific disease in the 19th century, being initially referred to adenoma sebaceum, epiloia, Pringle's disease or Bourneville's disease. Rayer, a French dermatologist, was the one to first describe the disease and the fibrovascular papules that characterize it, making illustrations of it. He described two cases of tuberous sclerosis in patients who had the nasolabial papular eruption with telangiectasias at the base. In 1850 the first written report of tuberous sclerosis appeared in "Vitiligoidea", published by Addison and Gull. It was not recognized as a distinct disease but was classified as "vitiligoidea tuberosa". In 1862, von Recklinghausen reported a tumor of the heart found in a newborn during autopsy, and by that he is credited to be the first that described the microscopic appearance of tuberous sclerosis. Bourneville in 1880, a French neurologist, described the case of a girl who presented at the age of 3 with facial eruption and died at 15 years of age due to epilepsy, which complicated with pneumonia and inanition. He found brain and kidney tumors on the autopsy which were correctly believed to be the cause of her seizures and mental retardation. In 1911, E. B. Sherlock, superintendent of Belmont Asylum of Idiots, London, coined the word "epiloia" that indicated a clinical triad of epilepsy, low intelligence and adenoma sebaceum.

In 2002, treatment with rapamycin was found to be effective at shrinking tumours in animals. This has led to human trials of rapamycin as a drug to treat several of the tumors associated with TSC.

Classification

There is no established system for the classification of tuberous sclerosis.

Pathophysiology

Patients with tuberous sclerosis have loss-of-function germline mutations in both alleles of the following tumor suppressor genes: TSC1 or TSC2. One third of the mutations is inherited, two thirds are de novo mutations. The mutations causes the loss of one allele, but as long as the second one remains intact, the cell won't present any metabolic change. When there is a second TSC1 or TSC2 mutation, which typically occurs in multiple cells over a person's lifetime, then the disease starts to manifest (fitting the "two-hit" tumor-suppressor gene model, with the germline mutation inactivating one gene and then a somatic event inactivating the remaining other one). TSC1 codes for a protein called hamartin, and TSC2 codes for a protein called tuberin. They belong to a protein complex that inhibits the mammalian target of rapamycin (mTOR) complex 1 via RAS homologue enriched in brain (RHEB) which regulates cell growth. In a normal patient, RHEB activates mTORC1 when bound to GTP, but in TSC there is a hyperactivarion of RHEB and consequently of mTORC1. mTOR regulates cellular proliferation, autophagy, growth and protein and lipid synthesis and it enhances protein translation when activated, reprograming the cell metabolism, which increases cell proliferation but also may make it vulnerable to death in nutrient-restricted media. Besides the TSC-RHEB-mTORC1 pathway, there is evidence of alternate pathways also having a role in the disease that are mTORC1 independent, but they are currently under investigation.

Causes

Loss of function mutation of the genes TSC1 and TSC2 which are responsible for the production of hamartin and tuberin. These proteins regulate the cell cycle. Damage to this pathway leads to a very variable presentation of benign tumors in multiple systems. TSC1 and TSC2 are both tumor suppressor genes that function according to Knudson's "two hit" hypothesis. That is, a second random mutation must occur before a tumor can develop. This explains why, despite its high penetrance, TSC has wide expressivity.

Hamartin
Identifiers
Symbol	TSC1
Entrez	7248
HUGO	12362
OMIM	605284
RefSeq	NM_000368
UniProt	Q92574
Other data
Locus	Chr. 9 q34

Tuberin
Identifiers
Symbol	TSC2
Entrez	7249
HUGO	12363
OMIM	191092
RefSeq	NM_000548
UniProt	P49815
Other data
Locus	Chr. 16 p13.3

Differentiating Tuberous Sclerosis from other Diseases

Tuberous sclerosis must be differentiated from other diseases that cause myxoma or other benign tumors and/or seizures, such as Sturge Weber, hypomelanosis of Ito, Birt-Hogg-Dube syndrome, multiple endocrine neoplasia and various seizures disorders.

Epidemiology and Demographics

Tuberous sclerosis complex affects about 1 in 6,000 people, occurring in all races and ethnic groups, and in both genders. Prior to the invention of CT scanning to identify the nodules and tubers in the brain, the prevalence was thought to be much lower and the disease associated with those people diagnosed clinically with learning disability, seizures, and facial angiofibroma. Whilst still regarded as a rare disease, TSC is common when compared to many other genetic diseases, with at least 1 million individuals worldwide.

Risk Factors

There are no established environmental risk factors for tuberous sclerosis. One third of the cases are familial, so family history can be a risk factor for the disease.

Screening

As it is a rare disease, screening is not recommended.

Natural History, Complications, and Prognosis

Skin

Symptoms develop in almost all patients with TSC and include ungual fibromas, facial angiofibromas (may demand treatment and may worsen with UV exposure), shagreen patches (oval-shaped lesions, generally skin-colored but can be sometimes pigmented, may be crinkled or smooth), focal hypopigmented macules (ash-leaf spots), dental enamel pits (present in 100% of the patients), oral fibromas, retinal astrocytic hamartomas (tumors of the retinal nerve), retinal achromic patches (light or dark spots on the eye).

Renal

TSC leads to the formation of renal angiomyolipomas (present in 60-80% of the TSC patients), benign tumors composed of abnormal vessels, smooth-muscle cells and fat cells which may cause hematuria. These tumors can be detectable in early childhood by MRI, CT or ultrasound. Although benign, in TSC they are commonly multiple and bilateral. Angiomyolipomas larger than 4 cm are at risk for potentially catastrophic hemorrhage either spontaneously or with minimal trauma. Patients may also develop epithelial cysts, polycystic kidney disease (as 2-3% of the patients carries a deletion that affects both TSC2 gene and one of the genes that lead to autosomal dominant polycystic kidney disease) and renal-cell carcinomas that may be diagnosed at a younger age (mean 28 years). Patients ≥18 years may have higher rates of chronic kidney disease, hematuria, kidney failure, embolization (EMB), and partial and complete nephrectomy compared to patients <18 years.

Pulmonary

Lymphangiomyomatosis affects mostly women and is a proliferation of smooth-muscle cells that may result in cystic changes in the lungs. Recent genetic analysis has shown that the proliferative bronchiolar smooth muscle in TSC-related lymphangioleiomyomatosis is monoclonal metastasis from a coexisting renal angiomyolipoma. Cases of TSC-related lymphangioleiomyomatosis recurring following lung transplant have been reported. Diagnosed mostly during early adulthood, may cause pneumothorax. Multifocal micronodular pneumocyte hyperplasia can occur in both men and women and are mostly asymptomatic.

In 2020 a paper showed that epilepsy remission by appropriate treatment in early life can possibly prevent autism and intellectual disability.

Neurologic

These manifestations are one of the major causes of morbidity in patients with TSC. TSC may cause epilepsy, which is the most common neurological presentation occurring in 70-80% of patients and may complicate with infantile spasms, a severe form of epileptic syndrome. If epilepsy presents with an early onset t is associated with cognitive disabilities, which are also very prevalent in such patients. Neuropsychiatric disorders are present in two-thirds of the patients and anxiety is one of the most common presentations. Autism is one possible manifestation and is especially associated with cerebral cortical tubers. It consists of neurologic tissue that grows in a different pattern, losing the normal six-layered cortical structure, with dysmorphic neurons, large astrocytes and giant cells. Some patients may also present with subependymal giant cell astrocytomas, which may cause obstructive hydrocephalus. Risk of such benign tumors decreases after age of 20.

Cardiovascular

Rhabdomyomas may be present, being intramural or intracavitary in its distribution along the myocardium. May be detected in utero on fetuses and is associated with cardiac failure. Often disappear spontaneously in later life. 80% of children under two-years-old with TSC have at least one rhabdomyoma, and about 90% of those will have several.

Diagnosis

Tuberous sclerosis complex is diagnosed if a set of diagnostic criteria are met. These criteria include major and minor features. If a case meets the clinical diagnostic criteria, then it is performed a genetic molecular testing which is seem mostly as corroborative. Most of the patients seek medical assistance due to their dermatologic lesions or seizures but for making this diagnosis an evaluation that assesses all the clinical features of the tuberous sclerosis complex is necessary, as these manifestations have variable penetrance. The latest diagnostic criteria was developed by the 2012 International Tuberous Sclerosis Complex Consensus Conference, and it is showed at the table below:

Diagnostic Criteria for Tuberous Sclerosis Complex

Major Features
	Location	Sign	Onset	Note
1	Skin	Hypomelanotic macules	Infant – child	At least three, at least 5 mm in diameter.
2	Head	Facial angiofibromas or fibrous cephalic plaque	Infant – adult	At least three angiofibromas
3	Fingers and toes	Ungual fibroma	Adolescent – adult	At least two
4	Skin	Shagreen patch (connective tissue nevus)	Child
5	Eyes	Multiple retinal nodular hamartomas	Infant
6	Brain	Cortical dysplasias (includes tubers and cerebral white matter radial migration lines)	Fetus
7	Brain	Subependymal nodule	Child – adolescent
8	Brain	Subependymal giant cell astrocytoma	Child – adolescent
9	Heart	Cardiac rhabdomyoma	Fetus
10	Lungs	Lymphangioleiomyomatosis	Adolescent – adult
11	Kidneys	Renal angiomyolipoma	Child – adult	At least two. Together, 10 and 11 count as one major feature.
Minor Features
	Location	Sign	Note
1	Skin	"Confetti" skin lesions
2	Teeth	Dental enamel pits	At least three
3	Gums	Intraoral fibromas	At least two
4	Eyes	Retinal achromic patch
5	Kidneys	Multiple renal cysts
6	Liver, spleen and other organs	Nonrenal hamartoma

TSC can be first diagnosed at any stage of life. Prenatal diagnosis is possible by chance if heart tumours are discovered during routine ultrasound. In infancy, white patches on the skin may be noticed, or the child may present with epilepsy, particularly infantile spasms, or developmental delay may lead to neurological tests. In childhood, behavioural problems and autism spectrum disorder may also lead to a clinical investigation and a diagnosis. During adolescence it is usually that skin problems appear while in adulthood, kidney and lung problems may become evident. An individual may also be diagnosed at any time as a result of genetic testing of family members of another affected person.

History and Symptoms

The most common symptoms of tuberous sclerosis are due to the growth of the already disclosed benign tumors. Tumors in the CSN may cause epilepsy, autism and children may also present with cognitive disabilities. Tumors in the kidneys may compromise renal function and metastasize to the lungs, which in most cases is asymptomatic. Tumors in the heart may compromise heart function, but they tend to spontaneously disappear later in life.

The frequency of signs in children with TSC, grouped by age

Physical Examination

Physical examination of patients with tuberous sclerosis is a very rich one due to the different skin lesions that the disease can cause and it is usually remarkable for dental enamel pits (present in 100% of the patients),hypomelanotic macules, shagreen patches, and forehead plaques.

Laboratory Findings

There are no typical diagnostic laboratory findings associated with tuberous sclerosis. Patients may present with elevated BUN or creatinine if their renal angiomyolipomas compromise renal function or if they also present with autosomal dominant polycystic kidney disease.

Electrocardiogram

There are no ECG findings associated with tuberous sclerosis.

X-ray

There are no typical x-ray findings associated with tuberous sclerosis, but patients may present with pneumothorax and/or chylous pleural effusions due if they develop lymphangioleiomyomatosis.

Echocardiography or Ultrasound

Echocardiography/ultrasound may be helpful raising the suspicion of tuberous sclerosis. Echocardiographs can detect cardiac rhabdomyomas, present in more than 80% of the children with TSC. Ultrasound can detect hepatic angiomyolipomas, renal angiomyolipomas (present in 55-75% of patients) and renal cysts (present in 18-55% of the patients).

CT scan

CT scan may be helpful in the diagnosis of tuberous sclerosis. It can diagnose cortical or subependymal tubers and white matter abnormalities, subependymal hamartomas, subependymal giant cell astrocytomas, renal angiomyolipomas, renal cysts, renal cell carcinoma (associated with tuberous sclerosis), retroperitoneal lymphangiomyomatosis, gastrointestinal polyps, pancreatic neuroendocrine tumors, lymphangioleiomyomatosis, multifocal micronodular pneumocyte hyperplasia and cardiac rhabdomyomas.

MRI

MRI may be helpful in the diagnosis of tuberous sclerosis as it can find the same abnormalities found on CT scan which are described above, some of them with much more detail, but it is especially useful for evaluating white matter changes seen in the disease.

Other Imaging Findings

There are no other imaging findings associated with tuberous sclerosis.

Other Diagnostic Studies

Genetic testing may be helpful in the diagnosis of tuberous sclerosis but some patients may not have detectable genetic mutations on the test and still have the disease. It is considered to be a corroborative test.

Treatment

Tuberous sclerosis complex affects multiple organ systems so a multidisciplinary team of medical professionals is required.

Screening of complications:

In suspected or newly diagnosed TSC, the following tests and procedures are recommended by 2012 International Tuberous Sclerosis Complex Consensus Conference.

• Take a personal and family history covering three generations. Genetic counselling and tests determine if other individuals are at risk.
• A magnetic resonance imaging (MRI) of the brain to identify tubers, subependymal nodules (SEN) and sub-ependymal giant cell astrocytomas (SEGA).
• Children undergo a baseline electroencephalograph (EEG) and family educated to identify seizures if/when they occur.
• Assess children for behavioural issues, autism spectrum disorder, psychiatric disorders, developmental delay, and neuropsychological problems.
• Scan the abdomen for tumours in various organs, but most importantly angiomyolipomata in the kidneys. MRI is superior to CT or ultrasound. Take blood pressure and test renal function.
• In adult women, test pulmonary function and perform a high-resolution computed tomography (HRCT) of the chest.
• Examine the skin under a Wood's lamp (hypomelanotic macules), the fingers and toes (ungual fibroma), the face (angiofibromas), and the mouth (dental pits and gingival fibromas).
• In infants under three, perform an echocardiogram to spot rhabdomyomas, and electrocardiogram (ECG) for any arrhythmia.
• Use a fundoscope to spot retinal hamartomas or achromic patches.

Treatment:

The various symptoms and complications from TSC may appear throughout life, requiring continued surveillance and adjustment to treatments. The following ongoing tests and procedures are recommended by 2012 International Tuberous Sclerosis Complex Consensus Conference:

• In children and adults younger than 25 years, a magnetic resonance imaging (MRI) of the brain is performed every one to three years to monitor for subependymal giant cell astrocytoma (SEGA). If a SEGA is large, growing or interfering with ventricles, the MRI is performed more frequently. After 25 years, if there are no SEGAs then periodic scans may no longer be required. A SEGA causing acute symptoms are removed with surgery, otherwise either surgery or drug treatment with an mTOR inhibitor may be indicated.
• Repeat screening for TSC-associated neuropsychiatric disorders (TAND) at least annually. Sudden behavioural changes may indicate a new physical problem (for example with the kidneys, epilepsy or a SEGA).
• Routine EEG determined by clinical need.
• Infantile spasms are best treated with vigabatrin and adrenocorticotropic hormone used as a second-line therapy. Other seizure types have no TSC-specific recommendation, though epilepsy in TSC is typically difficult to treat (medically refractory).
• Repeat MRI of abdomen every one to three years throughout life. Check renal (kidney) function annually. Should angiomyolipoma bleed, this is best treated with embolisation and then corticosteroids. Removal of the kidney (nephrectomy) is strongly to be avoided. An asymptomatic angiomyolipoma that is growing larger than 3cm is best treated with an mTOR inhibitor drug. Other renal complications spotted by imaging include polycystic kidney disease and renal cell carcinoma.
• Repeat chest HRCT in adult women every five to 10 years. Evidence of lymphangioleiomyomatosis (LAM) indicates more frequent testing. An mTOR inhibitor drug can help, though a lung transplant may be required.
• A 12-lead ECG should be performed every three to five years.

The mTOR inhibitor everolimus was approved in the US for treatment of TSC-related tumors in the brain (subependymal giant cell astrocytoma) in 2010 and in the kidneys (renal angiomyolipoma) in 2012.  Everolimus also showed evidence of effectiveness at treating epilepsy in some people with TSC. In 2017, the European Commission approved everolimus for treatment of refractory partial-onset seizures associated with TSC.

Neurosurgical intervention may reduce the severity and frequency of seizures in TSC patients. Embolization and other surgical interventions can be used to treat renal angiomyolipoma with acute hemorrhage. Surgical treatments for symptoms of lymphangioleiomyomatosis (LAM) in adult TSC patients include pleurodesis to prevent pneumothorax and lung transplantation in the case of irreversible lung failure.

Other treatments that have been used to treat TSC manifestations and symptoms include a ketogenic diet for intractable epilepsy and pulmonary rehabilitation for LAM. Facial angiofibromas can be reduced with laser treatment and the effectiveness of mTOR inhibitor topical treatment is being investigated. Laser therapy is painful, requires anaesthesia, and has risks of scarring and dyspigmentation.

Tuberous sclerosis or tuberous sclerosis complex (TSC) is a rare, multi-system genetic disease that causes benign tumours to grow in the brain and on other vital organs such as the kidneys, heart, eyes, lungs, and skin.