evidence: As one of the key enzymes in metabolic regulation, MTHFR is also one of the important candidate genes for common neurodevelopmental disorders. More than 10 mutations have been found contributing to effects of the MTHFR enzyme, of which C677T is one of the most common mutations found up to the present (24, 25). Decreased enzyme activity and heat tolerance caused by mutations can lead to folic acid metabolic abnormalities, methylation abnormalities, and neurodevelopmental disorders (17). This study suggested that carriers of MTHFR 677T allele were more likely to show an increased risk of autism than carriers of CC homozygotes (P = 0.004, OR = 1.18, 95% CI = 1.02–1.29), to some extent, which verifies that MTHFR may be one of the predisposing genes for autism. Paşca et al. (39) first reported the association between MTHFR C677T and risk of autism; however, it was a small sample study that just was carried out in 15 cases of autism and 25 cases of autism spectrum disorders. However, dos Santos (40) did not find any association between MTHFR C677T and risk of autism in Brazilian population.