Introduction

Tuberous sclerosis (TS) is an autosomal dominant disorder with variable expression, which causes epilepsy, mental retardation and hamartomas in many organ systems. TS is caused by mutations in two genes, TSC1 on 9q34 and TSC2 on 16p13.3. Mutations can be detected in approximately 85% of patients who meet the published consensus clinical diagnostic criteria.1–3 The remainder probably have mutations in intronic or promoter regions, which are not routinely screened, or are mosaic for the condition. Genotype–phenotype correlations have been slow to emerge in this disorder but TSC2 mutations tend to be associated with more severe disease than TSC1 mutations.2 3

Most TSC1 mutations are single base substitutions or small insertions/deletions, and cause protein truncation. A small number are putative splice site mutations but the effects on the proteins produced have not been studied in detail. Splicing is the process in which introns are excised from the RNA and exons joined together to form messenger RNA transcript, which is translated into the protein.

We present a family with an unusually mild phenotype caused by a novel TSC1 splice site (SS) mutation.