Methylmalonic Acid

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Subject: Methylmalonic Acid

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Definition

  • Methylmalonic acid (MMA) is an intermediate in the propionate degradation pathway. Deficient activity of the enzyme responsible for the conversion of methylmalonyl CoA to succinyl CoA (methylmalonyl CoA mutase) results in the organic aciduria known as methylmalonic aciduria, with a classical presentation of neonatal onset metabolic acidosis, hyperammonemia, and poor outcome if untreated. The concentrations of the metabolic markers MMA and homocysteine (Hcy) are considered to be more sensitive indicators of vitamin B12 status. Both MMA and Hcy increase in vitamin B12 deficiency. However, Hcy has been shown to have low specificity, being influenced by lifestyle factors such as smoking and alcohol intake and increasing in patients with folate deficiency and renal impairment.

  • Normal range: 0.00–0.40 μmol/L.

Use

  • Evaluation of methylmalonic academia in children.

  • Evaluation of megaloblastic anemia (cobalamin deficiency). Serum MMA may be a more reliable marker of cobalamin deficiency than direct cobalamin determination.

Interpretation

Increased In

  • Vitamin B12 deficiency

  • Pregnancy

  • Cobalamin genetic defects

  • Methylmalonic acidemia

Limitations

  • Serum and urine levels are more reliable markers of cobalamine deficiency than direct cobalamine determination.

  • Diet, nutritional status, and age should be considered in the evaluation of serum MMA level.

 
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