The Smith-Lemli-Opitz syndrome is themost common autosomal recessive disease of this type (affects 1 in 20,000newborns) resulting from mutations in the dhcr7 gene encoding7-dehydrocholesterolreductase (Dhcr7) [70].Severe forms are deleterious for fetal development andnewborn infant. The gene discussed is DHCR7; the disease is autosomal recessive disease.