7-dehydrocholesterol reductase of the cholesterol biosynthetic pathway reducing the C7-C8 double bond of cholesta-5,7-dien-3beta-ol (7-dehydrocholesterol/7-DHC) and cholesta-5,7,24-trien-3beta-ol, two intermediates in that pathway. cholesterol + NADP(+) = 7-dehydrocholesterol + H(+) + NADPH 7-dehydrodesmosterol + H(+) + NADPH = desmosterol + NADP(+) Steroid biosynthesis; cholesterol biosynthesis. Interacts with DHCR24; this interaction regulates DHCR7 activity. Deficient mice die within one day of birth due to respiratory and suckling problems. They exhibit abnormal cholesterol homeostasis with reduced tissue cholesterol levels and total sterol levels, enlarged bladders and sometimes cleft palate. Belongs to the ERG4/ERG24 family.