Genetics
SLOS occurs in 1:20,000 to 1:40,000 births from populations of northern or central European ancestry. It is less frequent among Asian and African populations. It is the most common disorder of cholesterol biosynthesis.
This disorder is inherited in an autosomal recessive pattern, which means two copies of the gene must be inherited to have the disorder. It has been estimated that the carrier frequency for SLOS carriers is 1:30. The incidence of the disease is as high as would be suggested by this carrier frequency, possibly indicating an increased incidence of fetal demise or misidentification of mildly affected individuals. Females lack the characteristic genital malformations that affected males have, and thus are less likely to be correctly diagnosed.
Mutations in the DHCR7 gene cause SLOS. The DHCR7 gene makes an enzyme called 7-dehydrocholesterol reductase. This enzyme is responsible for the final step in the production of cholesterol. Cholesterol is an essential nutrient that is necessary for normal embryonic development.
Read more about this topic: Smith-Lemli-Opitz Syndrome