DHCR7 and Smith-Lemli-Opitz syndrome: Located on chromosome 7, loss-of-function homozygous or compound heterozygous mutations in DHCR7 result in the Smith-Lemli-Opitz-Syndrome (SLOS, OMIM #270400) (3, 4, 5), which is the most common cause of inborn errors of cholesterol synthesis (6, 7).