CYP26A1 and oculopharyngeal muscular dystrophy: Specific SNP (CYP26B1 rs887844 (A/G), CYP26A1 rs4411227 (C/G), CYP26C1 rs12256889 (A/C), and CYP26B1 rs707718 (G/T)) and environmental factor (> 50 years old) combinations significantly increased the risks (5.75-, 3.92-, 4.07-, and 3.34-fold, respectively) for patients with OPMD compared to health controls with high prevalence of BQ chewing.