CYP27A1 and neurodegenerative disease: Because ALS is a neurodegenerative disease, we speculated that, when cholesterol is released by neurons as they die, it would be metabolized by CYP46A1 to 24S-hydroxycholesterol (24S-HC) and by CYP27A1 to members of the acidic pathway of bile acid biosynthesis (Figs. 2 and , respectively) (25).