A rare cause of high anion gap metabolic acidosis.

Methylmalonic aciduria is an inborn error in the organic acids metabolism. Deficiency of methylmalonyl CoA mutase or its coenzyme, adenosylcobalamine, leads to accumulation of methymalonic acid in body fluids. The disease manifests with recurrent episodes of dehydration, metabolic acidosis, coma and death. We report a case of methylmalonic aciduria diagnosed in a female infant who presented with recurrent episodes of high anion gap metabolic acidosis. The particularity of this case is the presence of a rare pathogenic mutationhomozygous c.556C>T (p.Arg186Trp). This is a form of vitamin B12-responsive methylmalonic aciduria. The frequency of this mutation is reported to be 0.0002 in european and american population, and it was not detected in afro-american population. Our patient receives treatment with vitamin B 12, levocarnitine and low protein diet and the outcome was good.