Catalyzes the reduction of the C14-unsaturated bond of lanosterol, as part of the metabolic pathway leading to cholesterol biosynthesis. 4,4-dimethyl-5alpha-cholesta-8,24-dien-3beta-ol + NADP(+) = 4,4-dimethyl-5alpha-cholesta-8,14,24-trien-3beta-ol + H(+) + NADPH 5alpha-cholest-8,14-dien-3beta-ol + H(+) + NADPH = 5alpha-cholest-8-en-3beta-ol + NADP(+) 4,4-dimethyl-8,14-cholestadien-3beta-ol + H(+) + NADPH = 4,4-dimethyl-5alpha-cholest-8-en-3beta-ol + NADP(+) Steroid biosynthesis; cholesterol biosynthesis. Expressed in adult heart, brain, pancreas, lung, liver, skeletal muscle, kidney, ovary, prostate, testis and adrenal gland, but not detected in placenta, spleen, thymus, small intestine, colon (mucosal lining), or peripheral blood leukocytes. By sterol starvation. Belongs to the ERG4/ERG24 family. Sequencing errors. Sequencing errors.