Polycystic disease has an early onset clinically and is the result of large contiguous deletions on chromosome 16 affecting both the TSC2 gene and the gene for adult onset polycystic kidney disease. 2 Tuberous sclerosis complex exhibits genetic heterogeneity. 3 Mutations in two recently identified genes, TSC1 at 9q34 andTSC2 at 16p13, each result in an apparently similar phenotype, although recent work has suggested that mutations inTSC2 may be associated with more severe disease. 4 Both genes are tumour suppressor genes, the strongest evidence for this being the loss of heterozygosity around the normal gene at 9q34 or 16p13 in hamartomata from tuberous sclerosis patients. 5 6 There is evidence that the severity of learning difficulties in tuberous sclerosis complex is related to the number of hamartomata in the brain. 7 Until now, no one has reported on a correlation between the severity of the phenotype in two or more organs.