TUBEROUS SCLEROSIS

Background and Design: Tuberous sclerosis (TS) is a genetic disease with prominent cutaneous and brain involvement whose clinical and molecular genetics are reviewed. Observations: Tuberous sclerosis is a systemic disorder (incidence one in 10 000) characterized by benign growths (hamartias and hamartomas) in multiple organ systems. Involvement of the brain can result in persistent seizures and mental retardation; skin involvement includes facial angiofibromas, subungual fibromas, hypomelanotic macules, forehead fibrous plaques, and Shagreen's patches. Approximately 60% of TS occurs as apparent sporadic cases. In families, it has autosomal dominant inheritance with high penetrance (approximately 95%), with careful clinical and radiologic evaluation. Genetic linkage analysis indicates that about half of all TS families show linkage to chromosome 9q34, and about half to chromosome 16p13. There are no distinguishing features in the two groups of families showing linkage to the two genomic regions, nor strong evidence for a third causative gene. Positional cloning efforts for both chromosomal regions have limited the region containing the gene to about 1 to 2 million bases. Conclusions: Identification of the two TS genes should illuminate the pathogenesis of TS and provide opportunities for genetic counseling, prenatal diagnosis, and therapeutic intervention.