MTHFR and Alzheimer disease: The MTHFR C677T CT heterozygous genotype was associated with increased AD risk in South Asian (RR = 1.56, 95% CI [1.25, 1.95], p < 0.0001), Middle Eastern (RR = 1.35, 95% CI [1.09, 1.66], p = 0.0052), and African samples (RR = 1.50, 95% CI [1.10, 2.04], p = 0.0107).