Mutations in a Δ8-Δ7 sterol isomerase in the tattered mouse and X-linked dominant chondrodysplasia punctata

Tattered (Td) is an X-linked, semi-dominant mouse mutation associated with prenatal male lethality(1). Heterozygous females are small and at 4-5 days of age develop patches of hyperkeratotic skin where no hair grows, resulting in a striping of the coat in adults(2). Craniofacial anomalies and twisted toes have also been observed in some affected females(3,4). A potential second allele of Td has also been described(5). The phenotype of Td is similar to that seen in heterozygous females with human X-linked dominant chondrodysplasia punctata (CDPX2, alternatively known as X-linked dominant Conradi-Hunermann-Happle syndrome) as well as another X-linked, semi-dominant mouse mutation, bare patches (Bpa). The Bpa gene has recently been identified(6) and encodes a protein with homology to 3 beta-hydroxysteroid dehydrogenases that functions in one of the later steps of cholesterol biosynthesis. CDPX2 patients display skin defects including linear or whorled atrophic and pigmentary lesions, striated hyperkeratosis, coarse lusterless hair and alopecia, cataracts and skeletal abnormalities including short stature, rhizomelic shortening of the limbs, epiphyseal stippling and craniofacial defects (MIM 302960). We have now identified the defect in Td mice as a single amino acid substitution in the Delta(8)-Delta(7) sterol isomerase emopamil binding protein (Ebp; encoded by Ebp in mouse) and identified alterations in human EBP in seven unrelated CDPX2 patients.