Abstract
A girl aged 7.5 years with deficiency of 5,10-methylenetetrahydrofolate reductase was treated from early infancy with betaine, 3-6 g daily. She has slight microcephaly, moderate developmental delay, and impaired vision but there have been no obvious signs of folate deficiency. From 4 years of age, she developed an unexplained extreme increase in appetite and weight. Recent magnetic resonance imaging of her brain was normal. The plasma methionine levels have been normal but in the lower range, and the total plasma homocysteine concentrations have been moderately increased (54 to 85 mumol/l) without obvious correlation with the different betaine doses given. Folic acid has sometimes been added.