Although BA levels have not been described in brain and circulation system of HD, the expression of CYP46A1 and level of the metabolite 24 S-OHC have been found to be reduced in the plasma of HD patients [113, 114] as well as in the brain of several yeast artificial chromosome (YAC) mice (carrying progressively increased CAG repeats) and knock-in mouse models [113–115]. Here, CYP46A1 is linked to Huntington disease.