3-Methylcrotonyl-CoA Carboxylase Deficiency (MCCC2-Related) (MCCC2)

3-Methylcrotonyl-CoA carboxylase deficiency (MCCC2-related) is a pan-ethnic, autosomal recessive disease caused by pathogenic variants in the MCCC2 gene. These variants impair the ability of the enzyme 3-methylcrotonyl-CoA carboxylase to break down proteins that contain the amino acid leucine. Presentation in childhood or early infancy is characterized by feeding difficulties, vomiting and diarrhea, excessive fatigue, and hypotonia. If detected early, the condition can be managed with a low-protein diet. If untreated, this disorder can eventually cause developmental delay, seizures, and coma. However, most individuals with this condition remain asymptomatic into adulthood. Life expectancy depends on the severity of presentation. No clear genotype-phenotype correlation has been noted.

For information about carrier frequency and residual risk, please see the residual risk table.