title: Prenatal diagnosis using genetic sequencing and identification of a novel mutation in MMACHC.
abstract: BACKGROUND
  Combined methylmalonic aciduria and homocystinuria, cobalamin(cbl)C deficiency, is a rare disorder of intracellular vitamin B12(cbl) metabolism caused by mutations in the MMACHC gene. Both genetic and biochemical approach have been established to diagnose children and fetuses with cblC deficiency, while in China there is no report of prenatal genetic diagnosis of cblC deficiency. The aim of the present study was to characterize the mutational spectrum of cblC deficiency and investigate the feasibility of genetic-sequencing-based prenatal diagnosis for cblC deficiency.
  
  
  METHODS
  10 pedigrees were recruited in this study with the probands clinically and biochemically confirmed combined methymalonic aciduria and homocystinuria. Peripheral blood samples were collected for MMACHC genetic test from the probands and their parents (4 probands had already dead) and 50 control subjects. The entire coding region and adjacent splice sites of MMACHC were sequenced. After the genotypes of the pedigrees were identified, chorionic villi sampling were performed for 3 high-risk pregnant women for prenatal genetic diagnosis.
  
  
  RESULTS
  A total of 7 mutations were identified: c.217C > T (R73X), c.394C > T (R132X), c.463G > C (G155R), c.609G > A (W203X), c.616C > T (R206W), c.658-660delAAG (220delK), and c.567dupT (I190YfsX13), as well as 2 polymophsims: c.321G > A(V107V), c.-302G > T. And G155R is a novel mutation that haven't been reported in the literatures. All the 6 probands identified with compound heterozygous mutations or homozygous mutations of MMACHC gene, and all the parents of the probands were found to have one MMACHC mutation at a heterozygous level. Prenatal diagnosis of fetuses from 3 families with a child affected cblC deficiency showed that one fetus had the same compound heterozygous mutations as the proband, one did not have MMACHC mutation, and the third fetus had a mutation at a heterozygous level of MMACHC gene. Results from the follow-ups were consistent with the prenatal diagnosis.
  
  
  CONCLUSIONS
  A novel mutation p.G155R of the MMACHC gene is identified. Genetic diagonsis is an accurate and convenient method for prenatal diagnosis and early intervention of combined methylmalonic aciduria and homocystinuria.
authors.affiliation: Center of Prenatal Diagnosis, the First Affiliated Hospital of Zhengzhou University, Zhengzhou, 450052, People's Republic of China. zongyn0021@163.com.
authors.forename: Yanan
authors.initials: Y
authors.lastname: Zong
authors.affiliation: Center of Prenatal Diagnosis, the First Affiliated Hospital of Zhengzhou University, Zhengzhou, 450052, People's Republic of China. liuning903@163.com.
authors.forename: Ning
authors.initials: N
authors.lastname: Liu
authors.affiliation: Center of Prenatal Diagnosis, the First Affiliated Hospital of Zhengzhou University, Zhengzhou, 450052, People's Republic of China. princesszzh@163.com.
authors.forename: Zhenhua
authors.initials: Z
authors.lastname: Zhao
authors.affiliation: Center of Prenatal Diagnosis, the First Affiliated Hospital of Zhengzhou University, Zhengzhou, 450052, People's Republic of China. kongxd@263.net.
authors.forename: Xiangdong
authors.initials: X
authors.lastname: Kong
mesh_terms: D000592:Amino Acid Metabolism, Inborn Errors / Q000235:genetics* / Q000473:pathology*; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics*; D002681:China; D019295:Computational Biology; D005260:Female; D016231:Fluorescence Polarization Immunoassay; D006710:Homocysteine / Q000097:blood; D006712:Homocystinuria / Q000235:genetics* / Q000473:pathology*; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008969:Molecular Sequence Data; D020125:Mutation, Missense / Q000235:genetics*; D010088:Oxidoreductases; D010375:Pedigree; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods*; D017422:Sequence Analysis, DNA; D016482:Urinalysis; D014806:Vitamin B 12 Deficiency / Q000151:congenital
chemical_list: D002352:Carrier Proteins; D006710:Homocysteine; C508359:MMACHC protein, human; D010088:Oxidoreductases