Smith-Lemli-Opitz syndrome (SLOS) is a genetic syndrome caused by mutations in the
3beta-hydroxysterol Delta(7)-reductase gene (DHCR7). SLOS patients have decreased
cholesterol and increased
7-dehydrocholesterol (7-DHC) levels.
Dietary cholesterol supplementation improves systemic biochemical abnormalities; however, because of the blood-brain barrier, the central nervous system (CNS) is not treated.
Simvastatin therapy has been proposed as a means to treat the CNS. Mice homozygous for a null disruption of Dhcr7, Dhcr7(Delta3-5/Delta3-5), die soon after birth, thus they cannot be used to study postnatal development or
therapy. To circumvent this problem, we produced a hypomorphic SLOS mouse model by introducing a mutation corresponding to DHCR7(T93M). Both Dhcr7(T93M/T93M) and Dhcr7(Delta3-5/T93M) mice are viable. Phenotypic findings in Dhcr7(T93M/Delta3-5) mice include CNS ventricular dilatation and two to three
syndactyly. Biochemically, both Dhcr7(T93M/T93M) and Dhcr7(T93M/Delta3-5) mice have elevated tissue
7-DHC levels; however, the biochemical defect improved with age. This has not been observed in human patients, and is due to elevated Dhcr7 expression in mouse tissues.
Dietary cholesterol therapy improved
sterol profiles in peripheral, but not CNS tissues. However, treatment of Dhcr7(T93M/Delta3-5) mice with
simvastatin decreased
7-DHC levels in both peripheral and brain tissues. Expression of Dhcr7 increased in Dhcr7(T93M/Delta3-5) tissues after
simvastatin therapy, consistent with the hypothesis that
simvastatin therapy improves the biochemical phenotype by increasing the expression of a Dhcr7 allele with residual enzymatic activity. We conclude that
simvastatin treatment is efficacious in improving the SLOS-associated
sterol abnormality found in the brain, and thus has the potential to be an effective therapeutic intervention for behavioral and learning problems associated with SLOS.