Homozygous mutations in DHCR7 cause the Smith-Lemli-Opitz syndrome, which is associated with elevated serum 7-DHC levels, low serum cholesterol levels, and multiple congenital abnormalities, but heterozygous carriers have been proposed to be protected against rickets and osteomalacia from hypovitaminosis D [11]. The gene discussed is DHCR7; the disease is rickets.