An example of this is desmosterolosis, a severe, typically lethal, rare human genetic disorder caused by mutations in the gene encoding DHCR24 (OMIM #602398; EC 1.3.1.72) (277, 278), the enzyme that catalyzes the penultimate step in the mevalonate pathway whereby desmosterol (cholesta-5,24,-dien-3β–ol) is converted to cholesterol. The gene discussed is DHCR24; the disease is desmosterolosis.