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What is tuberous sclerosis complex (TSC)?

Tuberous sclerosis complex (TSC) is a genetic condition characterized by benign tumors in multiple organs including the skin, heart, lungs, kidneys, eyes, and brain.  The disease affects some people severely, while others are so mildly affected that they often remain undiagnosed.  Some people with TSC experience seizure disorders (epilepsy), developmental delay, intellectual disability and/or autism spectrum disorder.  However, there are also many people with TSC who are living independent, healthy lives and enjoying challenging professions.

How many people have TSC?

At least two children born each day in the United States will have TSC. The current estimate of newborns affected with TSC is 1 in 6,000.  Nearly one million people worldwide have TSC, with approximately 50,000 in the United States. There are many undiagnosed cases of TSC due to the mild symptoms that occur in some people. TSC is as common as ALS (Lou Gehrig’s Disease) or Duchenne Muscular Dystrophy, but it is not well known by the general population.

How does a person develop TSC?

TSC is transmitted either through genetic inheritance from one parent or as a spontaneous genetic mutation (the first case of the disease in a family).  If one parent has this condition, a child has a 50% chance of inheriting TSC.  It appears that most cases of TSC (two-thirds) result from a spontaneous mutation, and the remainder (one-third) are inherited from a parent with TSC.

If a parent has a mild form of TSC, will their child with TSC also be mildly affected?

While this is certainly possible, people with mild cases of TSC can have a child who is much more severely affected.  In fact, some people have such mild cases that they may only find out they also have TSC after their more severely affected child is diagnosed.

How is TSC diagnosed?

A clinical diagnosis of TSC is made after the following tests are performed: a brain MRI and/or CT scan, kidney imaging (preferably MRI, ultrasound or CT), echocardiogram of the heart, EKG, eye exam, and a Wood’s Lamp evaluation of the skin. These tests are able to detect almost all cases of TSC.  In addition, genetic testing for TSC is now widely available.  However, while potentially providing a very clear diagnosis, genetic testing does not detect all cases of TSC and should be used together with clinical-based testing for diagnosis.  Genetic counseling is also very important to help families understand test results and the potential impact on other members of the family.

What genes are responsible for TSC?

Two genes have been identified that cause TSC. Only one of the genes needs to be affected for TSC to be present. The TSC1 gene is located on chromosome 9 and makes a protein called hamartin. The other gene, TSC2, is located on chromosome 16 and makes a protein called tuberin.  Research on the TSC1 and TSC2 genes shows that they play an important role in the regulation of cell function by regulating the mTOR (mammalian target of rapamycin) signaling pathway.  These findings have been rapidly translated into clinical trials to test the safety and efficacy of mTOR inhibitors to treat various manifestations of TSC.  In 2010, Afinitor®, an mTOR inhibitor, was approved by the FDA to treat subependymal giant cell astrocytoma (SEGA) in individuals with TSC.

How can so many different organs be affected by TSC? 

The TSC1 and TSC2 genes help regulate cell growth in the body. When either of these genes is defective, growth is not inhibited and the manifestations of TSC result.  The genes also clearly play a role in the fetal development of the brain which may explain why seizures, behavioral and psychiatric issues, and intellectual disability are seen in many individuals with TSC.

Are the tumors cancerous in TSC?

In general the tumors resulting from TSC are not cancer, but may still cause significant problems. Tumors that grow in the brain (SEGAs) can block the flow of cerebrospinal fluid in the spaces (ventricles) in the brain.  This blockage can lead to behavioral changes, seizures, nausea, lethargy, headaches, or a number of other symptoms. 

In the heart, tumors are usually at their largest at birth and then decrease in size as the individual gets older.  These heart tumors, called cardiac rhabdomyomas, can cause problems at birth if they are blocking the flow of blood or causing severe arrhythmias. Tumors in the eyes are not as common, but they can become problematic if they grow and block too much of the retina.  

Kidney tumors (renal angiomyolipoma) can become so large that they eventually impair normal function, leading to kidney failure.  Abnormal blood vessels in angiomyolipomas may also leak, causing internal bleeding.  Very rarely (less than 2%), individuals with TSC can develop malignant (cancerous) kidney tumors, or renal cell carcinoma.  In addition, adult women with TSC can experience lymphangioleiomyomatosis (LAM) in the lungs.  There is also a sporadic form of LAM in which women without TSC have similar manifestations in the lungs and kidneys.

What is the normal life expectancy of an individual with TSC?

Most people with TSC will live a normal life span.  There can be complications in some organs such as the kidneys and brain that can lead to severe difficulties and even death if left untreated.  To reduce these dangers, people with TSC should be monitored throughout their lives by physicians knowledgeable about TSC.  Thanks to research advancements and improved medical therapies, people with TSC can expect improved health care and quality of life.

Since there is no cure, what can be done?

Early intervention is key. Surgery to remove tumors or stop tumor growth is helping to preserve the function of affected organs.  For example, new technology and medical research have produced advances to help doctors pinpoint the location in the brain responsible for seizures in many individuals and have created new therapies to help control epilepsy.  In addition, advancements in basic science research are continually bringing forward ideas for new and improved therapeutic options.  We must continue to invest in research and the rapid translation of new knowledge to innovative therapies. Every day we are one step closer to realizing better treatments and eventual cures for TSC.

Reviewed and updated by Kevin C. Ess, M.D., Ph.D., Vanderbilt University, TS Alliance Professional Advisory Board, February 2011.

**Tuberous Sclerosis Alliance Information Sheets are intended to provide basic information about TS. They are not intended to, nor do they, constitute medical or other advice. Readers are warned not to take any action with regard to medical treatment without first consulting a physician. The TS Alliance does not promote or recommend any treatment, therapy, institution or health care plan.

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