The complex cholesterol biosynthesis pathway involves various enzymes and complex cellular mechanisms of intracellular sorting and transport. The deficiency of these enzymes causes the accumulation of specific intermediates and inhibits the formation of important biomolecules.

The Smith–Lemli–Opitz Syndrome (SLOS) is an autosomal recessive multiple malformation syndrome, due to an inborn error of cholesterol synthesis. The SLOS is caused by deficiency of sterol delta-7- reductase (DHCR7) that catalyzes the last step of cholesterol biosynthesis, resulting in low cholesterol and increased 7- and 8-dehydrocholesterol (7-DHC, 8-DHC) plasma levels.

Cerebrotendinous xanthomatosis (CTX) is a rare autosomal-recessive inborn disorder of bile acid metabolism caused by mutations CYP27A1 gene. The mutations result in production of a defective sterol 27-hydroxylase enzyme. The clinical manifestations are progressive cerebellar ataxia, chronic diarrhea, bilateral cataracts, dementia, cataract, and tendon xanthomas. CTX is associated with abnormally high levels of cholestanol in the plasma and accumulation of cholestanol and cholesterol in tissues.