cblC型甲基丙二酸血症家系的基因变异分析及产前诊断

Genetic variant analysis and prenatal diagnosis for Chinese pedigrees affected with cblC methylmalonic acidemia

目的对110例汉族钴胺素C(cobalamin C,cblC)代谢缺陷型甲基丙二酸血症(methylmalonic acidemia,MMA)患者的MMACHC基因变异进行测序分析,明确其遗传学病因,为产前诊断和遗传咨询提供依据。方法采集先证者及其父母的外周血样,提取基因组DNA,用PCR-Sanger测序和(或)荧光定量PCR法对MMACHC基因进行变异检测,筛查致病性变异位点,并采集其中48例再次妊娠孕妇的绒毛样本进行产前诊断。结果共检出35种变异,包括错义变异、无义变异、移码变异、剪接区变异和大片断缺失等5种类型。最常见的变异为c.609G>A(p.Trp203Ter)(33.64%)、c.658_660delAAG(p.Lys220del)(12.27%)、c.567dupT(p.Ile190Tyrfs*13)(9.09%)以及c.80A>G(p.Gln27Arg)(6.82%),变异集中于第4外显子(73.18%)。此外,c.57_58insT(p.Gly20Trpfs*14)、c.505_506delAT(p.Ile169Argfs*12)为未见报道的新变异。在产前诊断的48例胎儿中,14例正常,24例为携带者,10例为患者。结论新变异的检出扩展了汉族人群中MMACHC基因的变异谱;检测结果为cblC型MMA患者家系再次生育时的产前诊断及遗传咨询提供了依据。

Objective To detect variants of the MMACHC gene among 110 ethnic Han Chinese pedigrees affected with metabolic deficiency methylmalonic acidemia(MMA)of cobalamin C(cblC).Methods Peripheral blood samples were collected from the probands and their parents.Following DNA extraction,the coding regions of the MMACHC gene were subjected to PCR amplification,Sanger sequencing and quantitative PCR assaying.For 48 pedigrees,chorionic villus samples were taken for prenatal genetic diagnosis.Results Thirty five types of variants were detected among the 110 pedigrees,which included missense,nonsense,frameshifting,splicing variants and exonic deletions.Most variants have occurred in exons 4(73.18%).The detection rate for c.609G>A(p.Trp203Ter)variant was the highest(33.64%),followed by c.658_660delAAG(12.27%),c.567dupT(9.09%)and c.80A>G(6.82%).Two variants,namely c.57_58insT(p.Gly20Trpfs*14)and c.505_506delAT(p.Ile169Argfs*12),were unreported previously and both were of frameshifting types.For the 48 pedigrees undergoing prenatal diagnosis,14 fetuses were found to be normal,24 have carried heterozygous variants,the remaining 10 have carried compound heterozygous or homozygous variants.Conclusion The discovery of the two novel variants has expanded the spectrum of the MMACHC gene variants among ethnic Han population.Above finding has provide a basis for the prenatal diagnosis and genetic counseling for the affected pedigrees.