Neurologically normal development of a patient with severe methionine adenosyltransferase I/III deficiency after continuing dietary methionine restriction

• We report a case with severe MAT I/III deficiency, who had homocystinuria.
• We identified novel compound heterozygous mutations of the MAT1A gene.
• Plasma methionine levels were kept within 750 μmol/L up to 5 years old.
• Patient's physical growth and psychomotor development have been normal.
• Strict methionine restriction may prevent neurological deteriorations.

BackgroundThere is not much information on established standard therapy for patients with severe methionine adenosyltransferase (MAT) I/III deficiency.Case presentationWe report a boy with MAT I/III deficiency, in whom plasma methionine and total homocysteine, and urinary homocystine were elevated. Molecular genetic studies showed him to have novel compound heterozygous mutations of the MAT1A gene: c.191T>A (p.M64K) and c.589delC (p.P197LfsX26). A low methionine milk diet was started at 31 days of age, and during continuing dietary methionine restriction plasma methionine levels have been maintained at less than 750 μmol/L. He is now 5 years old, and has had entirely normal physical growth and psychomotor development.ConclusionsAlthough some severely MAT I/III deficient patients have developed neurologic abnormalities, we report here the case of a boy who has remained neurologically and otherwise normal for 5 years during methionine restriction, suggesting that perhaps such management, started in early infancy, may help prevent neurological complications.