Fig. 1.

Overview of bile acid synthesis pathways. Important intermediates of the classical pathway of bile acid synthesis as the main route of cholesterol catabolism in the liver are displayed on the left. Next to it, intermediates of alternate pathways including the acidic pathway initiated by CYP27A1 (expressed in many tissues including the lung and brain), the cerebral pathway (CYP46A1; only expressed in brain), and the 25-hydroxylation pathway (CH25H) are shown. Reactions catalyzed by CYP27A1, the enzyme lacking in CTX, are highlighted by red lettering of CYP27A1. Reactions catalyzed by CYP7A1 and CYP8B1, the main enzymes upregulated in CTX, are highlighted by green lettering. Red arrowheads (significantly increased/decreased) and bars (unchanged) indicate differences measured in patients with CTX in relation to controls in serum. Blue arrowheads exhibit differences between the groups in CSF. Only metabolites with symbols were analyzed. CSF, cerebrospinal fluid; CTX, cerebrotendinous xanthomatosis.