Novel heterozygous MCCC1 mutations identified in a patient with 3-methylcrotonyl-coenzyme A carboxylase deficiency

Isolated 3-methylcrotonyl-CoA carboxylase deficiency is an autosomal recessive disorder affecting leucine metabolism; it is one of the most common inborn metabolic diseases detected in newborn screening. Mutations in the genes MCCC1 or MCCC2 cause a defect in the enzyme 3-methylcrotonyl-CoA carboxylase, with MCCC2 mutations being the form predominantly reported in Korea. The majority of infants identified by neonatal screening usually appear to be asymptomatic and remain healthy; however, some patients have been reported to exhibit mild to severe metabolic decompensation and neurologic manifestations. Here we report the clinical features of a patient with asymptomatic 3-methylcrotonyl-CoA carboxylase deficiency and novel heterozygous MCCC1 mutations.