Editor—Van Slegtenhorst et al 1 reported a mutational analysis of 225 patients with tuberous sclerosis (TSC) and concluded that there was no evidence for genotype-phenotype correlation. At virtually the same time, Joneset al 2 from Cardiff published supportive evidence for genotype-phenotypic correlation in their comprehensive mutational analysis of TSC1and TSC2 in 150 families. How can such conflicting conclusions be reconciled?

It is now well established that tuberous sclerosis (TSC) is a multisystem disorder characterised by an autosomal dominant pattern of inheritance, locus heterogeneity (TSC1 on 9q34 and TSC2 on 16p13.3), and widely variable expression. It is associated with neurodevelopmental abnormalities, manifestations of which include epilepsy, mental retardation, and behavioural syndromes such as autism. Both genes have been positionally cloned and act as tumour suppressors. Linkage analysis suggested that about half of large families were linked toTSC1 and half toTSC2. It was assumed that the same would apply to sporadic cases (representing about 70% of all TSC …