DHCR7 and Smith-Lemli-Opitz syndrome: Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder caused by biallelic pathogenic variants in DHCR7 (HGNC:2860), which encodes 7-dehydrocholesterol reductase (DHCR7), the enzyme responsible for the last step in cholesterol biosynthesis [1–3].