DHCR7 and Smith-Lemli-Opitz syndrome: 7-Dehydrocholesterol reductase enzyme deficiency in patients with SLOS leads to reduced levels of plasma cholesterol as well as an increase in plasma concentrations of the cholesterol precursor 7-dehydrocholesterol (7-DHC; cholesta-5,7-dien-3β-ol) and its isomer 8-dehydrocholesterol (8-DHC; cholesta-5,8-dien-3β-ol) [1, 4–6].