CYP26B1 and migraine disorder: Both 1) the downregulated CYP26B1-levels, which are reliant on the substrate, all-trans retinoic acid (atRA) in the heart and vasculature [49–51] and 2) the lack of CYP26B1 SNPs associated with migraine even on a nominal level, indicated a marker role for CYP26B1 for reduced atRA levels in MO.