DMD基因c.2622+2T>C导致假肥大型肌营养不良的时空表达特异性分析

Spatiotemporal expression specificity analysis of Duchenne/Becker muscular dystrophy caused by DMD gene c.2622+2T>C variant

目的:对一例假肥大型肌营养不良(DMD)患儿进行基因变异分析,探究基因型和临床表型的相关性。方法:采集家系成员的临床数据和家族史,采用多重连接探针扩增技术(MLPA)检测目标基因拷贝数变异是否异常、全外显子组测序(WES)分析先证者致病基因、Sanger测序验证可疑位点。针对发现的剪切位点突变构建mini-gene表达载体,采用mRNA体外剪接mini-gene实验验证变异对mRNA剪切的影响。结果:该家系先证者男,双下肢无明显受累,外周血肌酸激酶(CK)水平升高(700-1600U/L),肌电图示肌源性损害。MLPA检测未发现受检者DMD基因存在外显子拷贝数变异。测序结果显示先证者携带DMD基因(NM_004006.2)c.2622+2T>C母源剪切变异。体外mini-gene实验发现该变异影响剪切且产生多种新转录本。结合患儿临床表现及基因检测结果,推测受检者为DMD基因剪切变异导致的假肥大型肌营养不良。结论:本研究明确了DMD基因剪切变异为一例DMD患儿致病原因,进一步丰富了中国DMD突变谱,证实了DMD基因c.2622+2T>C变异可产生多种转录本导致不同的功能受损,对患者临床表现与基于时空表达相关联,有一定的基因型-表型对应关系的参考意义。

Objective:To analyze the gene variants of a patient affected with Duchenne/Becker muscular dystrophy in a pedigree and further explore the genotype-phenotype correlation for providing basis for family genetic counseling.Methods:The clinical features and family history of family members were collected.Multiplex ligation-dependent probe amplification(MLPA)was utilized to detect copy number variation of target genes.The pathogenic variations were analyzed by whole exome sequencing(WES).The suspected gene variations were verified by Sanger sequencing.For the splice site mutations,mini-gene was constructed and expressed in vitro to detect the number of transcript and cDNA sequence.Results:The proband of this family is a male,with no obvious involvement of the lower limbs.Laboratory tests showed an elevated level of creatine kinase(CK)in peripheral blood(700-1600U/L),and electromyography showed myogenic damage.MLPA did not detect pathogenic exon copy number variation in dystrophin(DMD)gene.Genetic testing showed the proband carried a maternal hemizygotic splicing variation of DMD gene(NM_004006.2):c.2622+2T>C.An in vitro mini-gene splicing assay confirmed that this splicing mutation could affect RNA splicing.According to clinical features and genetic testing results,the proband was speculated first proof of Duchenne/Becker muscular dystrophy(DMD/BMD)caused by DMD gene mutation.Conclusion:This study identified the pathogenic variation of a proband with DMD/BMD of DMD gene,which enriched the variation spectrum of DMD/BMD in China.It was confirmed that the splicing variation of the DMD gene c.2622+2T>C can produce multiple transcripts leading to different functional impairments,and based on the specificity of temporal and spatial expression,it corresponded to the mild clinical manifestations of the patient,providing some reference value for the correlation between genotype and phenotype.