Tuberous sclerosis is a relatively common inherited disease that causes multiple 
benign tumours in different organs, frequently leading to skin rashes, seizures 
and mental handicap. The disease can be caused by mutations in either of two 
genes, TSC2, identified in 1993, and TSC1, only recently identified. Here we 
review the current state of knowledge of the molecular genetics of tuberous 
sclerosis and the spectrum of mutations seen in and the implications of recent 
findings for patients. Although both genes appear to function as tumour 
suppressors, the function of their protein products is not understood. A 
speculative model of how these proteins might function is briefly described.