Tuberous Sclerosis Complex Health Article

Definition

Tuberous sclerosis complex (TSC) is a genetic condition that affects many organ systems including the brain, skin, heart, kidneys, eyes, and lungs. Benign (noncancerous) growths or tumors called hamartomas form in various parts of the body, disrupting their normal functions.

Description

The term tuberous sclerosis refers to the small, knoblike growths in the brain of patients with TSC that were found in patients upon autopsy and, today, can be viewed using computed tomography (also called a CT scan). The condition is also referred to as tuberose sclerosis or simply tuberous sclerosis. The designation tuberous sclerosis complex is used to distinguish this condition from another genetic condition called Tourette syndrome that is abbreviated TS.

Persons with TSC have a variety of symptoms ranging from very mild to severe. Affected individuals may experience no serious health problems and, in the absence of a thorough clinical examination, may go through life without knowing that they are affected. Conversely, patients with TSC may have problems with behavioral, mental, and emotional functions as well as with their kidneys, heart, and eyes. In addition, specific skin abnormalities, often medically insignificant, are among the most common symptoms of TSC.

Genetic profile

TSC is an autosomal dominant genetic disorder caused by a single change or alteration in a gene called a mutation in either the TSC1 gene, located on chromosome 9, or the TSC2 gene, located on chromosome 16. Approximately two-thirds (66%) of patients with TSC have it as the result of a new change in one of the TSC genes; that is, it was not inherited from one of their parents. When a new change occurs, it most commonly occurs in the TSC2 gene. An individual must have a mutation in one of these two copies of a TSC-causing gene in order to develop the condition. In addition, a person who has been diagnosed with TSC and who, therefore, has a genetic mutation in one of the TSC genes, has a 50% chance of passing on the genetic mutation to his or her offspring. Laboratory testing for changes in the TSC genes is not currently available.

TSC is a condition that can be caused by a change in either one of two separate genes. In addition, people who have the same change in the same gene may have very different medical problems and symptoms.

TSC1 is responsible for producing the protein hamartin and TSC2, tuberin. Both genes are known as tumor suppressor genes meaning that their normal function is to prevent the growth of tumors. Conversely, when gene function is altered, tumor growth results. Research on how the disruption of either protein results in the clinical condition of TSC is ongoing.

It is currently believed that every person who inherits or develops a mutation in either the TSC1 or TSC2 gene will develop some form of TSC. However, the severity of the disease, with its wide range of symptoms and complications, cannot accurately be predicted by identifying the specific gene mutation.

Germline mosaicism can explain the rare occurrence of unaffected parents having more than one child with TSC. Germline refers to the gonadal cells (sperm in males and eggs in females) and mosaicism refers to the presence of different cell lines in any given individual. A person with germline mosaicism for either the TSC1 or TSC2 gene is not affected with TSC but may have an affected child. Unaffected parents of a child with TSC are quoted a 2-3% chance of having additional affected children. Typical genetic testing methods are performed on somatic (non-germline) tissues such as blood or skin and, therefore, will not detect germline mosaicism.

Demographics

Although tuberous sclerosis complex is considered to be a rare condition, estimates of the prevalence of the disorder have increased as clinical testing methods have improved. In the United States, as many as one child in 6,000 born is affected with TSC and about 50,000 people are currently living in the U.S. with the disease. TSC is seen in all ethnic groups and populations and, worldwide, there are between one and two million cases.