MCCC2

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

The 3-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 the diet. 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.

3-methylcrotonyl-CoA carboxylase deficiency - caused by mutations in the MCCC2 gene

More than 40 mutations in the MCCC2 gene have been identified in people with 3-methylcrotonyl-CoA carboxylase deficiency (also known as 3-MCC deficiency). Most of these mutations change single amino acids in 3-MCC, which severely reduces the activity of the enzyme. Other mutations prevent the production of any functional enzyme. As a result, leucine cannot be broken down properly, and byproducts of leucine processing build up to toxic levels in the body. These toxic substances can damage the brain, causing the characteristic signs and symptoms of 3-MCC deficiency.