CYP27A1 and cerebrotendinous xanthomatosis: CTX is characterized by CYP27A1 deficiency, and as CYP27A1 is essential in CDCA synthesis, CTX patients have severely decreased levels of endogenous CDCA, stimulating increased production of bile acids and the generation and accumulation of atypical sterol molecules including bile alcohols (and their corresponding glucoronides) and cholestanol [3].