MTHFR and homocystinuria: Liu et al. previously demonstrated that severe homocystinuria due to MTHFR deficiency patients with tardive dyskinesia carried two MTHFR deficiency-associated SNPs (rs748289202 p.Arg335His and rs545086633 p.Leu439Pro) on the MTHFR [9], and their further investigation confirmed that rs545086633 was responsible for the missense mutation of p.Leu439Pro in the C-terminal regulatory domain of MTHFR protein, and the proteasome degradation caused by the mutation led to suppress the expression of MTHFR protein.