Tuberous sclerosis (TSC) is a rare genetic disease that causes benign tumors to grow in the brain and on other vital organs such as the kidneys, heart, eyes, lungs, and skin. It commonly affects the central nervous system. In addition to the benign tumors that frequently occur in TSC, other common symptoms include seizures, mental retardation, behavior problems, and skin abnormalities. TSC may be present at birth, but signs of the disorder can be subtle and full symptoms may take some time to develop. Three types of brain tumors are associated with TSC: cortical tubers, which generally form on the surface of the brain; subependymal nodules, which form in the walls of the ventricles (the fluid-filled cavities of the brain); and giant-cell astrocytomas, a type of tumor that can block the flow of fluids within the brain.