Smith-Lemli-Opitz syndrome: Biosynthetic pathways

The effect of Smith-Lemli-Opitz syndrome on the biosynthesis of estriol by the fetalplacental unit A mutation of the enzyme C7-reductase in the fetus prevents the conversion of 7-dehydrocholesterol (DHC) to cholesterol. This blockade leads to impaired biosynthesis of estriol. Conversion of 7-DHC to cholesterol by the mother, who is a carrier of the mutation and is not affected, is not impaired.