CYP7B1 and Parkinson disease: Considering the effect of each P450 gene on the association with IPD, it also has to be taken into account which of the two pathways (CYP46A1/CYP39A1 or CY27A1/CYP7B1) is contributing most to the degradation of cholesterol from brain (forming precursors of bile acids) and to PD.