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.

A Case of Asymptomatic 3-methylcrotonylglycinuria Detected by Tandem Mass Spectrometry in Newborn Screening / 소아과

3-Methylcrotonylglycinuria is an autosomal recessive inborn error of leucine catabolism that results from the deficiency of 3-methylcrotonyl-CoA carboxylase(3-MCC). In 3-MCC deficiency 3-methylcrotonyl-CoA, may form glycine and carnitine conjugates. The primary metabolites are 3-hydroxyisovaleric acid(3-HIVA), 3-hydroxyisovaleryl carnitine(3-HIVC) and 3-methylcrotonylglycine(3-MCG). 3-hydroxyisovaleric acid(3-HIVA) and 3-methylcrotonylglycine(3-MCG) are increased in urine, and 3-hydroxyisovaleryl carnitine(3-HIVC) is found in blood and urine. 3-MCC is one of the four biotin- dependent carboxylases known in humans and is a heteromeric mitochondrial enzyme comprised of biotin-containing alpha-subunits and smaller beta-subunits. The gene for alpha-subunits(MCCC1) is located on chromosome 3q25-q27, beta-subunits(MCCC2) is located in 5q12-q13. Mutation in either of these genes may result in the deficiency of the enzyme activity. The introduction of tandem mass spectrometry in newborn screening has revealed an unexpectedly high incidence of this disorder and has also revealed that the range of clinical symptoms has become even wider ranging from neonatal onset with severe neurological involvement to asymptomatic newborns and adults. We report a case of a 43-day-old Korean asymptomatic girl with 3-Methylcrotonylglycinuria, detected by tandem mass spectrometry in newborn screening. This is resulted from the deficiency of 3-MCC by urine organic acid analysis. We found 2 mutations in the MCC2 gene of this patient. They are misssence mutation (D280Y) and splicing mutation(T357T). This patient on leucine restriction in conjunction with oral carnitine and glycine shows normal growth and development until now(10 months).