Deficiency of 3-methylcrotonyl-CoA carboxylase (MCC) results in elevated excretion of 3-methylcrotonylglycine (3-MCG) and 3-hydroxyisovaleric acid (3-HIVA).

3-methylcrotonyl-CoA carboxylase (MCC) is a heteromeric mitochondrial enzyme comprising biotin-containing alpha subunits and smaller beta subunits, encoded by MCCA and MCCB, respectively.

Mutations in genes MCCA and MCCB cause isolated MCC deficiency, an autosomal recessive disorder with a variable phenotype that ranges from severe neonatal to asymptomatic adult forms.

Synopsis

 seizures
 progressive psychomotor retardation
 elevated excretion of 3-MCG and 3-HIVA
 deficiency of MCC activity in fibroblasts