The best-characterized disorder of cholesterol biosynthesis is Smith-Lemli-Opitz syndrome [25], [26], caused by mutations in DHCR7, which encodes the 7-dehydrocholesterol reductase that converts 7-dehydrocholesterol to cholesterol [15], [27], [28]. The gene discussed is DHCR7; the disease is Smith-Lemli-Opitz syndrome.