Clinical and genetic features of children with 3-methylcrotonyl-coenzyme A carboxylase deficiency: an analysis of six cases

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To investigate the clinical and genetic features of children with 3-methylcrotonyl-coenzyme A carboxylase deficiency (MCCD). A retrospective analysis was conducted on the clinical manifestations and genetic testing results of six children with MCCD who attended Children's Hospital Affiliated to Zhengzhou University from January 2018 to October 2023. Among the six children with MCCD, there were 4 boys and 2 girls, with a mean age of 7 days at the time of attending the hospital and 45 days at the time of confirmed diagnosis. Of all children, one had abnormal urine odor and five had no clinical symptoms. All six children had increases in blood 3-hydroxyisovaleryl carnitine and urinary 3-hydroxyisovaleric acid and 3-methylcrotonoylglycine, and five of them had a reduction in free carnitine. A total of six mutations were identified in the MCCC1 gene, i.e., c.1630del(p.R544Dfs*2), c.269A>G(p.D90G), c.1609T>A(p.F537I), c.639+2T>A, c.761+1G>T, and c.1331G>A(p.R444H), and three mutations were identified in the MCCC2 gene, i.e., c.838G>T(p.D280Y), c.592C>T(p.Q198*,366), and c.1342G>A(p.G448A). Among these mutations, c.269A>G(p.D90G) and c.1609T>A(p.F537I) had not been previously reported in the literature. There was one case of maternal MCCD, and the child carried a heterozygous mutation from her mother. Five children with a reduction in free carnitine were given supplementation of L-carnitine, and free carnitine was restored to the normal level at the last follow-up visit. This study identifies two new mutations, c.269A>G(p.D90G) and c.1609T>A(p.F537I), thereby expanding the mutation spectrum of the MCCC1 gene. A combination of blood amino acid and acylcarnitine profiles, urine organic acid analysis, and genetic testing can facilitate early diagnosis and treatment of MCCD, and provide essential data for genetic counseling.