MTHFR and hearing loss disorder: The MTHFR 677T allele was significantly associated with a reduced risk for hearing impairment only when the participants were wild-type homozygotes for MTR A2756G (per-T allele OR of MTHFR for development hearing impairment in the MTR AA genotype: 0.7609 [95% CI: 0.6178–0.9372]).