描述
3-Methylcrotonyl-Coenzyme A Carboxylase Deficiency Type I (3-MCC Deficiency; MCCD Type I; Methylcrotonylglycinuria Type I; 3-Methylcrotonylglycinuria I) is caused by a defect in the MCCC1 and MCCC2 genes. 3-methylcrotonyl-coenzyme A carboxylase plays an essential role in breaking down proteins from the diet. Specifically, the enzyme is responsible for the fourth step in processing leucine. If a mutation in the MCCC1 or MCCC2 gene reduces or eliminates the activity of 3-methylcrotonyl-CoA carboxylase, the body is unable to process leucine properly. As a result, toxic byproducts of leucine processing build up to harmful levels, damaging the brain and nervous system. Symptoms include recurring episodes of vomiting and diarrhea, lethargy, hypotonia, seizures, and coma.