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MCCC1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

MCCC1 gene

The MCCC1 gene provides instructions for creating a critical component of an enzyme responsible for breaking down proteins from food.

Normal Function

The MCCC1 gene provides instructions for making one part (the alpha subunit) of an enzyme called 3-methylcrotonoyl-CoA carboxylase or MCC. These alpha subunits join with smaller beta subunits made from the MCCC2 gene; six of these pairings together form a functioning enzyme. The alpha subunit also includes a region for binding to the B vitamin biotin, which is required for the enzyme to function.

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 MCCC1 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, but a few lead to the production of an abnormally short version of the enzyme. Variants in the MCCC1 gene severely reduce or eliminate the activity of MCC. 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 1
  • 3-methylcrotonyl-CoA carboxylase alpha
  • 3-methylcrotonyl-CoA carboxylase biotin-containing subunit
  • MCCA
  • MCCase subunit alpha
  • MCCCalpha
  • MCCCα
  • methylcrotonoyl-CoA carboxylase 1
  • methylcrotonoyl-CoA carboxylase 1 alpha

Frequently Asked Questions

Diagnosis relies on a combination of metabolic testing and genetic analysis. Elevated levels of 3‑hydroxy‑isovaleric acid and 3‑methylcrotonylglycine in urine organic acid panels are classic clues. Blood acylcarnitine profiles may show increased C5‑OH. Definitive confirmation is achieved by sequencing the MCCC1 (or MCCC2) gene to identify pathogenic variants.
Typical early signs include poor feeding, vomiting, lethargy, developmental delay, and episodes of low blood sugar. Some children develop a characteristic “sweaty feet” odor, seizures, or liver enlargement. Symptoms often worsen after a high‑protein meal or during illness when metabolic stress is increased.
Carriers (heterozygotes) are usually asymptomatic because one normal copy of the gene provides enough enzyme activity. No specific dietary restrictions are needed, but it can be helpful to know your carrier status for family planning. Genetic counseling is recommended if you are considering having children, as two carriers have a 25 % chance of having an affected child.
low‑leucine diet is the cornerstone of management. This means limiting high‑protein foods such as meat, dairy, beans, and certain grains, while ensuring adequate calories from carbohydrates and fats. Many families work with a metabolic dietitian to calculate precise leucine allowances and to use specialized medical formulas that provide essential nutrients without excess leucine.
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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