SMITH-LEMLI-OPITZ-SYNDROME IS CAUSED BY MUTATIONS IN THE 7-DEHYDROCHOLESTEROL REDUCTASE GENE

Smith-Lemli-Opitz syndrome is a frequently occurring autosomal recessi ve developmental disorder characterized by facial dysmorphisms, mental retardation, and multiple congenital anomalies. Biochemically, the di sorder is caused by deficient activity of 7-dehydrocholesterol reducta se, which catalyzes the final step in the cholesterol-biosynthesis pat hway-that is, the reduction of the Delta 7 double bond of 7-dehydrocho lestero to produce cholesterol. We identified a partial transcript cod ing for human 7-dehydrocholesterol reductase by searching the database of expressed sequence tags with the amino acid sequence for the Arabi dopsis thaliana sterol Delta 7-reductase and isolated the remaining 5' sequence by the ''rapid amplification of cDNA ends'' method, or 5'-RA CE. The cDNA has an open reading frame of 1,425 bp coding for a polype ptide of 475 amino acids with a calculated molecular weight of 54.5 kD . Heterologous expression of the cDNA in the yeast Saccharomyces cerev isiae confirmed that it codes for 7-dehydrocholesterol reductase. Chro mosomal mapping experiments localized the gene to chromosome 11q13. Se quence analysis of fibroblast 7-dehydrocholesterol reductase cDNA from three patients with Smith-Lemli-Opitz syndrome revealed distinct muta tions, including a 134-bp insertion and three different point mutation s, each of which was heterozygous in cDNA from the respective parents. Our data demonstrate that Smith-Lemli-Opitz syndrome is caused by mut ations in the gene coding for 7-dehydrocholesterol reductase.