The gene mutated in bare patches and striated mice encodes a novel 3 beta-hydroxysteroid dehydrogenase

X-linked dominant disorders that are exclusively lethal prenatally in hemiz ygous males have been described in human and (1). None of the genes respons ible has been isolated in mouse either species; The bare patches (Bpa):and striated (Str) mouse mutations were originally identified in female offspri ng of X-irradiated males(2) (3). Subsequently, additional independent allel es were described. We have previously mapped these X-linked dominant, male- lethal mutations to an overlapping region:of 600 kb that is homologous to h uman Xq28 (ref. 4) and identified several candidate genes in this: interval (5). Here we report mutations in one of these genes, Nsdhl, encoding an NAD (P)H steroid dehydrogenase-like protein, in two independent Bpa and three i ndependent Str alleles. Quantitative analysis of sterols from tissues of af fected Bpa mice support a role for Nsdhl in cholesterol biosynthesis. Our r esults demonstrate that Bpa and Sfr are allelic mutations and identify the first mammalian locus associated with an X-linked dominant, male-lethal phe notype. They also expand the spectrum of phenotypes associated with abnorma lities of cholesterol metabolism.