In contrast to the Cyp27−/− mice, CYP3A upregulation is not induced in patients with cerebrotendinous xanthomatosis (CTX), which results from an inherited mutation of the CYP27 gene with an excessive accumulation of intermediates in BA synthesis in various tissues and manifested by tendon xanthomatosis, premature atherosclerosis, cholesterol gallstones, osteoporosis, and progressive neurologic dysfunction52. Here, CYP27A1 is linked to osteoporosis.