MTHFR and schizophrenia: Furthermore, there are studies showing that the C677T polymorphism in the MTHFR gene is associated with an earlier age of schizophrenia onset (El-Hadidy et al. 2013; Vares et al. 2010); however, some authors have not confirmed this finding (Saetre et al. 2011, 2012; Peerbooms et al. 2010).