TET1 and neural tube defect: To address the possibility that the cycling of folate derivatives may be uncoupled with that of methionine (the direct substrate for the generation of SAM), we also tested injections of methionine at 70 mg/kg (Leung et al, 2017) in CD1-Tet1 HET dams (Fig. 1F), but this treatment showed no effect on NTD rates in KO offspring (Fig. 1G).