CYP27A1 and Cognitive impairment: It caused by mutations in the mitochondrial enzyme, sterol 27-hydroxylase (CYP27A1) gene,[1]and classically characterized by bilateral Achilles tendon xanthoma; bilateral cataract formation; and progressive neurological dysfunction with mainly pyramidal tract signs, cerebellar ataxia, and cognitive impairment.[2] Diagnosis can be confirmed by high plasma cholestanol levels and elevated bile alcohols in urine.[3]