• Smith-Lemli-Opitz syndrome (SLOS) is caused by biallelic pathogenic, loss of function variants in the DHCR7 gene, resulting in a deficiency of the enzyme 7-dehydrocholesterol reductase. • Biochemical phenotype includes elevated serum 7-dehydrocholesterol (7DHC) and, in most cases, low serum cholesterol. • Features include cleft palate, postaxial polydactyly, congenital heart defects, renal anomalies, cataracts, strabismus, photosensitivity, behavioral disturbances, and hypospadias in males. The gene discussed is DHCR7; the disease is cataract.