MTRR and schizophrenia: We report a patient with refractory schizophrenia and comorbidities of treatment-resistant hypertension, old infraction, and seizure who had hyperhomocysteinemia and folic acid deficiency due to two rare mutations in the MTRR gene, which encodes methionine synthase reductase (MSR), another key regulating enzyme involved in the folate cycle that contributes to the metabolism of homocysteine.