Both MTHFR C677T TT homozygous and CT heterozygous genotypes were significantly associated with increased AD risk for all samples pooled from 44 study groups (TT genotype: RR = 1.13, 95% CI [1.04, 1.23], p = 0.0047; CT genotype: RR = 1.12, 95% CI [1.06, 1.19], p < 0.0001). The gene discussed is MTHFR; the disease is Alzheimer disease.