Severe methylenetetrahydrofolate reductase (MTHFR) deficiency: a case report of nonclassical homocystinuria.

Severe methylenetetrahydrofolate reductase deficiency is an autosomal recessive metabolic disorder of folate metabolism causing elevated plasma homocysteine levels and homocystinuria (MIM 236250). A developmentally delayed 10-year-old girl presented with symptoms of progressive ataxia, dysarthria, tremor, mental status changes, and white-matter changes on magnetic resonance imaging. These changes occurred during a 3- to 4-month time period, with an acceleration of symptoms during 2 to 3 weeks. The patient was found to have extremely high serum homocysteine and low-normal serum methionine. She received treatment with vitamin B12, folate, betaine, multivitamins, and aspirin, with subsequent improvement of her symptoms and reduction in her serum homocysteine level. This case emphasizes the need to include homocystinuria in the differential diagnosis of children with acute/subacute neurological changes, particularly in the context of developmental delay.