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MCCC2 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

MCCC2 gene

The MCCC2 gene provides instructions for creating the beta subunit of the MCC enzyme, which is essential for processing specific proteins.

Normal Function

The MCCC2 gene provides instructions for making one part (the beta subunit) of an enzyme called 3-methylcrotonoyl-CoA carboxylase or MCC. These beta subunits join with larger alpha subunits made from the MCCC1 gene; six of these pairings together form a functioning enzyme.

The MCC enzyme is found in mitochondria, which are the energy-producing centers inside cells. This enzyme plays a critical role in breaking down proteins obtained from food. Specifically, it is responsible for the fourth step in the breakdown of leucine, an amino acid that is a building block of many proteins. This step converts a molecule called 3-methylcrotonyl-CoA to a molecule called 3-methylglutaconyl-CoA. Additional chemical reactions convert 3-methylglutaconyl-CoA into molecules that are later used for energy.

Health Conditions Related to Genetic Changes

3-methylcrotonyl-CoA carboxylase deficiency

Many variants (also called mutations) in the MCCC2 gene have been identified in people with 3-methylcrotonyl-CoA carboxylase deficiency (also called MCC deficiency). MCC deficiency is an inherited disorder in which the body is unable to process certain proteins properly.

Most of these variants change single amino acids in MCC, which severely reduces the activity of the enzyme. Other variants prevent the production of any functional enzyme. As a result, leucine cannot be broken down properly, and byproducts of leucine processing can build up in the body. Some people with these genetic changes will show signs and symptoms of MCC deficiency.

Other Names for This Gene

  • 3-methylcrotonyl-CoA carboxylase 2
  • 3-methylcrotonyl-CoA carboxylase non-biotin-containing subunit
  • 3-methylcrotonyl-CoA carboxylase, beta
  • MCCase subunit beta
  • MCCB
  • MCCCbeta
  • MCCCβ
  • methylcrotonoyl-CoA carboxylase 2
  • methylcrotonoyl-CoA carboxylase beta
  • methylcrotonoyl-Coenzyme A carboxylase 2 (beta)

Frequently Asked Questions

Collect a fresh blood sample (usually via a standard venipuncture) or a saliva kit if the lab permits. No special fasting is needed, but it’s helpful to have a clear medication list, as some drugs can affect metabolic labs. Discuss the purpose of testing with a genetic counselor so you understand possible results, including variants of uncertain significance.
dults with mild or atypical forms can remain asymptomatic for years, especially if they have a partially functional enzyme. If there is a known pathogenic MCCC2 variant in the family, targeted testing is advisable. Even if the sibling tests positive, management usually involves modest dietary adjustments and periodic metabolic monitoring rather than aggressive treatment.
Yes, many newborn screening programs include an acylcarnitine profile that detects elevated C5‑OH, which flags possible MCC deficiency. The test is highly sensitive but not 100 % specific; abnormal results are followed up with confirmatory urine organic acid analysis and genetic testing of the MCCC2 gene.
Management combines dietary restriction of leucine, supplementation with L‑carnitine to enhance excretion of toxic metabolites, and, in some cases, biotin (a co‑factor for the MCC enzyme) at high doses. During acute metabolic crises, hospitalization for intravenous glucose and monitoring of ammonia and acid‑base status may be required.
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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