More than 1,100 mutations in the TSC2 gene have been identified in individuals with tuberous sclerosis complex, a condition characterized by developmental problems and the growth of noncancerous tumors in many parts of the body. Most of these mutations insert or delete a small number of DNA building blocks (base pairs) in the TSC2 gene. Other mutations change a single base pair in the TSC2 gene or create a premature stop signal in the instructions for making tuberin.

People with TSC2-related tuberous sclerosis complex are born with one mutated copy of the TSC2 gene in each cell. This mutation prevents the cell from making functional tuberin from that copy of the gene. However, enough tuberin is usually produced from the other, normal copy of the TSC2 gene to regulate cell growth effectively. For some types of tumors to develop, a second mutation involving the other copy of the gene must occur in certain cells during a person's lifetime.

When both copies of the TSC2 gene are mutated in a particular cell, that cell cannot produce any functional tuberin. The loss of this protein allows the cell to grow and divide in an uncontrolled way to form a tumor. A shortage of tuberin also interferes with the normal development of certain cells. In people with TSC2-related tuberous sclerosis complex, a second TSC2 gene mutation typically occurs in multiple cells over an affected person's lifetime. The loss of tuberin in different types of cells disrupts normal development and leads to the growth of tumors in many different organs and tissues.

Link:
TSC2 gene - Genetics Home Reference - NIH