Phenotypic variability and origins of mutations in the gene encoding 3β-hydroxysteroid dehydrogenase type II

Abstract

Mutations in HSD3B2, the gene for 3β-hydroxysteroid dehydrogenase type II (3β-HSD II) have been detected and activities analysed through the in vitro expression of mutant cDNAs. Two full sibs with male pseudohermaphroditism were found to be double heterozygotes: N100S/266ΔA. This genotype leads to the most profound loss of 3β-HSD II enzyme activity (1·3% of normal) described to date in cases without severe salt-loss. One sib (N100S/266ΔA) is the first reported male case of type II deficiency affected with premature adrenarche. Three apparently independent kindreds had propositi affected with the HSD3B2 mutation A82T/A82T, which is associated with a non salt-losing phenotype with variable expressivity in females. These three families had the same extended HSD3B haplotype and are likely to have inherited the same ancestral mutation. The significance of this finding is discussed in the light of the presence of A82T mutation at a homologous position in pseudogene φ5 that is present in the HSD3B cluster.