 Smith-Lemli- Opitz syndrome SLOS is an autosomal recessive genetic condition caused by a deficiency of the enzyme 3beta-hydroxysterol delta7- reductase DHCR7. DHCR7 is the final enzyme in the sterol synthetic pathway and converts 7- dehydrocholesterol 7DHC to cholesterol. This results in low cholesterol and elevated 7DHC levels. SLOS has a wide phenotypic spectrum. Mildly affected individuals may have subtle dysmorphic features along with learning and behavioral disabilities. Typical clinical manifestations include microcephaly, ptosis, anteversion of the nostrils, micrognathia, high arched or cleft palate, congenital heart defects, clinodactyly, post- axial polydactyly, and 2-3 toe syndactyly. More severely affected individuals have multiple congenital anomalies, may be miscarried, stillborn, or die within the first few weeks of life. 