In the case of SLOS, where the cause of the disorder is deficiency in the enzyme 7-dehydrocholesterol reductase (DHCR7) and main biochemical feature is elevated levels of the cholesterol precursor 7-DHC, the origin of 7-OC is likely to be the enzymatic oxidation of 7-DHC to 7-OC by CYP7A1 [39]. This evidence concerns the gene DHCR7 and Smith-Lemli-Opitz syndrome.