7-Dehydrocholesterol

7-Dehydrocholesterol is a biosynthetic precursor to previtamin D 3 in human skin and to cholesterol in tissues. Although the level of 7-dehydrocholesterol is normally low in human tissues and fluids, it is significantly elevated in a number of human disorders, including Smith Lemli-Opitz syndrome (SLOS) and cerebrotendinous xanthomatosis.

The Smith-Lemli-Opitz syndrome (SLOS) is a common birth defect syndrome characterized biochemically by low plasma cholesterol levels and high concentrations of the cholesterol precursor 7dehydrocholesterol. It is a metabolic and developmental disorder caused by mutations in the gene encoding the enzyme 7-dehydrocholesterol reductase (Dhcr7).

In SLOS, the tissue cholesterol and total sterol levels are markedly reduced while the concentrations of 7-dehydrocholesterol are greatly elevated. This elevation in 7-dehydrocholesterol inhibits the activity of Hmgcr, thus further exacerbating the cholesterol deficit.

Cholesterol in mammals is synthesized from acetate with the final two steps being the conversion of lathosterol to 7-dehydrocholesterol and 7-dehydrocholesterol to cholesterol.
7-Dehydrocholesterol