Tuberous sclerosis: A genetic disorder that is characterized by abnormalities of the skin, brain, kidney, and heart. Skin abnormalities are present in all cases of tuberous sclerosis. They include tiny benign tumors (angiofibromas) on the face and depigmented areas anywhere on the body. The brain abnormalities of tuberous sclerosis are mainly benign cortical tumors (tubers) that cause seizures, developmental delay, and mental retardation. The kidneys in a person with tuberous sclerosis often contain multiple cysts and benign tumors (angiomyolipomas). The heart problems of tuberous sclerosis include arrhythmias and benign heart muscle tumors (rhabdomyomas). Diagnosis is made via clinical observation, for example, in a child with a seizure disorder who has white spots on the skin that are most easily seen under ultraviolet light. Tuberous sclerosis is inherited in an autosomal dominant manner and results from mutation of either one of two genes: the TSC1 gene on chromosome 9 or the TSC2 gene on chromosome 16. TSC1 and TSC2 encode products called hamartin and tuberin, respectively, which act as tumor suppressors. Two-thirds of cases of tuberous sclerosis are due to new mutations, and the other one-third are inherited from parents.