Production of cholesterol by reduction of C7-C8 double bond of 7-dehydrocholesterol (7-DHC). Lesions in the gene coding for the enzyme cause dwarfism. cholesterol + NADP(+) = 7-dehydrocholesterol + H(+) + NADPH Lipid metabolism; steroid biosynthesis. A number of isoforms are produced. According to EST sequences. Belongs to the ERG4/ERG24 family.