It was reported that plasma HCY was higher after N2O anesthesia in patients with MTHFR gene mutation than in those with the wild‐type gene (Nagele et al., 2008); and neonates with MTHFR deficiency developed severe neurologic symptoms and died after inhaling a small amount of N2O (Erbe & Salis, 2003). This evidence concerns the gene MTHFR and hyperinsulinemic hypoglycemia, familial, 4.