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

Kim, Jin Kyung

Abstract

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).