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MMAA gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

MMAA gene

The MMAA gene provides instructions for making a protein essential for the formation of adenosylcobalamin, a compound derived from vitamin B12 that is necessary for normal metabolic function.

Normal Function

The MMAA gene provides instructions for making a protein involved in the formation of a compound called adenosylcobalamin (AdoCbl). AdoCbl, which is derived from vitamin B12 (also called cobalamin), is necessary for the normal function of an enzyme known as methylmalonyl CoA mutase. This enzyme helps break down certain proteins, fats (lipids), and cholesterol.

Research indicates that the MMAA protein may play a role in the transport of vitamin B12 into mitochondria, where it is converted into AdoCbl. Additional studies suggest the MMAA protein may help stabilize methylmalonyl CoA mutase and protect the enzyme from being inactivated.

Health Conditions Related to Genetic Changes

Methylmalonic acidemia

More than 25 mutations in the MMAA gene have been found to cause methylmalonic acidemia, a condition characterized by feeding difficulties, developmental delay, and long-term health problems. These mutations can lead to the production of an unstable or nonfunctional MMAA protein.

Without the activity of this protein, AdoCbl may not be made properly. A lack of AdoCbl impairs the function of methylmalonyl CoA mutase, resulting in the incomplete breakdown of certain proteins and lipids. This defect allows toxic compounds to build up in the body's organs and tissues, causing the signs and symptoms of the disorder.

Other Names for This Gene

  • cblA
  • methylmalonic aciduria (cobalamin deficiency) cblA type
  • methylmalonic aciduria (cobalamin deficiency) type A
  • methylmalonic aciduria type A
  • MMAA_HUMAN

Frequently Asked Questions

During a crisis, immediate hospitalization is required. Treatment includes intravenous glucose to suppress catabolism, high‑dose hydroxocobalamin (vitamin B12) to maximize any residual enzyme activity, and, if needed, sodium bicarbonate for acidosis. Hemodialysis may be used to rapidly lower toxic metabolites. Long‑term, a protein‑restricted diet with supplemental B12 is maintained to prevent future decompensations.
Yes, most patients benefit from lifelong hydroxocobalamin injections (typically 1 mg intramuscularly weekly or every other week) because oral B12 is poorly utilized in this disorder. Dosing is adjusted based on plasma methylmalonic acid levels and clinical response; regular monitoring every 3–6 months is standard.
Carrier couples have a 25 % chance of having an affected child with each pregnancy. Options include natural conception with prenatal diagnostic testing (chorionic villus sampling or amniocentesis) to determine fetal genotype, pre‑implantation genetic testing for monogenic disorders (PGT‑M) with IVF, or use of donor gametes. Genetic counseling should be sought to review risks and benefits of each approach.===
Most state newborn screens flag an elevated propionyl‑carnitine (C3) level. A reflex confirmatory test measuring plasma methylmalonic acid will be markedly increased, prompting urgent referral for metabolic evaluation and genetic testing of the MMAA gene.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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