Methylmalonic acidemia due to methylmalonyl-CoA epimerase deficiency is a rare inborn error of metabolism disease characterized by mild to moderate, persistent elevation of methylmalonic acid in plasma, urine and cerebrospinal fluid. Clinical presentation may include acute metabolic decompensation with metabolic acidosis (presenting with vomiting, dehydration, confusion, hallucinations), nonspecific neurological symptoms, or may also be asymptomatic. The disease is methylmalonic acidemia due to methylmalonyl-CoA epimerase deficiency (MONDO_0009615). Also known as: MCEE deficiency, methylmalonic acidemia due to methylmalonyl-CoA racemase deficiency, methylmalonic aciduria due to methylmalonyl-CoA epimerase deficiency, methylmalonic aciduria due to methylmalonyl-CoA racemase deficiency.