MMACHC and Cognitive impairment: In subjects with intellectual impairment, the multivariate logistic regression analysis showed that onset of symptoms (OR 12.31, 95% CI 5.11–29.66; p = 0.000), the mutation of c.609G>A (p.W203X) (OR 2.53, 95% CI 1.48–4.31; p = 0.001) and c.567dupT in the MMACHC gene (OR 2.57, 95% CI 1.17–5.66; p = 0.019) independently predicted the outcome of intellectual impairment (Table 4).