Targeted disruption of the murine 3β-hydroxysterol-Δ7-reductase gene (Dhcr7), an animal model of Smith-Lemli-Opitz syndrome, leads to loss of cholesterol synthesis and neonatal death that can be partially rescued by transgenic replacement of DHCR7 expression in brain during embryogenesis. The gene discussed is DHCR7; the disease is Smith-Lemli-Opitz syndrome.