5,10-Methylenetetrahydrofolate reductase deficiency. Clinical and biochemical features of a further case.

We report the case of a boy with 5,10-methylenetetrahydrofolate reductase deficiency. The clinical features consisted of severe mental retardation, spasticity and seizures remaining static to 7 years of age followed by a phase of rapid deterioration and death at 7 1/2 years of age. The main biochemical findings were homocystinaemia, homocystinuria, a normal methionine level in plasma and cerebrospinal fluid, an increased excretion of methionine in urine and a very low level of folate in the cerebrospinal fluid. The activity of 5,10-methylenetetrahydrofolate reductase was greatly reduced in the patient's lymphocytes and liver.