CYP27A1 and cerebrotendinous xanthomatosis: This established mutation has been demonstrated to lead to alternative pre-mRNA splicing and decreased sterol 27-hydroxylase activity, thereby causing cerebrotendinous xanthomatosis.20 To confirm the pathogenicity of this variant, we confirmed the characteristic reduction of 27-OH-cholesterol (below the detection threshold), a sterol 27-hydroxylase product, and compensatory increases of 7-alpha-OH-cholesterol (1372 ng/ml) and cholestanol (3410 ng/dl) in our patient.