Tuberous sclerosis is a dominantly inherited syndrome of high penetrance characterised pathologically by the presence of hamartomas in multiple organ systems. The clinical features of epilepsy, learning difficulties, and skin signs are well known, but recent epidemiological and genetic research has begun to reveal the complexity of the condition.

Compared with many other genetic diseases tuberous sclerosis is common. The two most recent and highest estimates of its prevalence in the United Kingdom have been 3.7 per 100 000 population in the west of Scotland and 3.8 per 100 000 population in Wessex. 1 2 A recent capture-recapture analysis of the Wessex data suggests that this survey failed to identify about half the prevalent cases. The total population prevalence may therefore be as high as 8-9 per 100 000, which means that many people with tuberous sclerosis are receiving neither specialist medical supervision nor genetic counselling.3

We know now that over half the affected individuals have normal intelligence and a quarter do not …