CYP27A1 and cerebrotendinous xanthomatosis: Patients suffering from cerebrotendinous xanthomatosis (CTX), where CYP27A1 is deficient, like patients with SPG5, can present with motor dysfunction, and patients with both disorders are found to be deficient in the cholestenoic acid, 3β,7α-dihydroxycholest-5-en-(25R)26-oic acid (3β,7α-diHCA) [21].