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Reviewed July 2011

What is the official name of the MMAB gene?

The official name of this gene is “methylmalonic aciduria (cobalamin deficiency) cblB type.”

MMAB is the gene's official symbol. The MMAB gene is also known by other names, listed below.

Read more about gene names and symbols on the About page.

What is the normal function of the MMAB gene?

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

The MMAB enzyme is active in mitochondria, which are specialized structures inside cells that serve as energy-producing centers. Once vitamin B12 has been transported into mitochondria, the MMAB enzyme converts a form of the vitamin called cob(I)alamin to AdoCbl. Studies suggest that this enzyme may also deliver AdoCbl to methylmalonyl CoA mutase.

How are changes in the MMAB gene related to health conditions?

methylmalonic acidemia - caused by mutations in the MMAB gene

At least 25 mutations in the MMAB gene have been found to cause methylmalonic acidemia, a condition characterized by feeding difficulties, developmental delay, and long-term health problems. Some of these genetic changes delete or duplicate a small amount of genetic material in the MMAB gene. Other mutations change a single protein building block (amino acid) used to make the MMAB enzyme. Researchers believe that nearly all of these mutations lead to the production of a nonfunctional version of the enzyme. As a result, AdoCbl cannot be made properly. A lack of AdoCbl impairs the function of methylmalonyl CoA mutase, which results 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 methylmalonic acidemia.

Where is the MMAB gene located?

Cytogenetic Location: 12q24

Molecular Location on chromosome 12: base pairs 109,553,715 to 109,573,553

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBIThis link leads to a site outside Genetics Home Reference.)

The MMAB gene is located on the long (q) arm of chromosome 12 at position 24.

The MMAB gene is located on the long (q) arm of chromosome 12 at position 24.

More precisely, the MMAB gene is located from base pair 109,553,715 to base pair 109,573,553 on chromosome 12.

See How do geneticists indicate the location of a gene? in the Handbook.

Where can I find additional information about MMAB?

You and your healthcare professional may find the following resources about MMAB helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the MMAB gene or gene products?

  • ATP:Cob(I)alamin Adenosyltransferase
  • ATR
  • cblB
  • CFAP23
  • cob(I)alamin adenosyltransferase
  • methylmalonic aciduria (cobalamin deficiency) type B

Where can I find general information about genes?

The Handbook provides basic information about genetics in clear language.

These links provide additional genetics resources that may be useful.

What glossary definitions help with understanding MMAB?

aciduria ; amino acid ; ATP ; breakdown ; cholesterol ; CoA ; cobalamin ; cofactor ; compound ; deficiency ; developmental delay ; enzyme ; gene ; mitochondria ; protein ; toxic ; vitamin B12

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.

See also Understanding Medical Terminology.

References (9 links)


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.

Reviewed: July 2011
Published: February 8, 2016