SMN基因复合杂合变异所致脊髓性肌肉萎缩症1例患儿的家系分析

Analysis of a Chinese pedigree affected with Spinal muscular atrophy due to compound heterozygous variants of SMN gene

目的分析1个脊髓性肌肉萎缩症(SMA)家系SMN1基因的变异情况,为遗传咨询和产前诊断提供依据。方法以2020年1月在南昌市第一医院就诊的1个SMA家系作为研究对象。采集其外周血样,提取DNA,用多重连接探针杂交(MLPA)法对患儿及其亲属的SMN基因进行检测,再用二代测序(NGS)对患儿进行变异分析,用Sanger测序法对结果进行验证。同时采集外周血样,提取cDNA,以先证者cDNA为模板甄别点变异在SMN1和SMN2基因中的分布情况。结果先证者的SMN1基因存在Exon7+Exon8杂合缺失及c.81G>A复合杂合变异,其中c.81G>A变异遗传自其母亲及外祖,SMN1 Exon7+Exon8杂合缺失遗传自父亲及祖母。其姨妈携带SMN1 c.81G>A杂合缺失,姑姑、姑父及表妹未检测到外显子缺失。通过cDNA扩增和Sanger测序,明确c.81G>A变异位于SMN1基因。结论MLPA联合Sanger测序、NGS技术能够明确SMA患者携带的SMN基因的复合杂合变异。

Objective To analyze variants of SMN gene in a Chinese pedigree affected with Spinal muscular atrophy(SMA).Methods A Chinese pedigree diagnosed at the Nanchang First Hospital in January 2020 was selected as the study subject.Peripheral blood samples were collected for the extraction of DNA.All exons of the SMN gene were detected by multiple ligation-dependent probe amplification(MLPA).Potential variants of the SMN gene were also detected by Whole exome sequencing(WES),and the result was verified by Sanger sequencing.cDNA extracted from fresh blood sample was used as a template to verify the location of variant on the SMN genes.Results The proband was found to harbor a heterozygous deletion of the SMN1 Exon7+Exon8,and a heterozygous c.81G>A variant.The SMN1 Exon7+Exon8 deletion was inherited from her father and grandmother,whilst the c.81G>A variant was inherited from her mother and maternal grandfather.Her aunt was also a carrier of the heterozygous deletion,while her paternal aunt,her husband,and their daughter were not.cDNA amplification and Sanger sequencing confirmed that the c.81G>A variant was located in the SMN1 gene.Conclusion MLPA combined with NGS and Sanger sequencing can identify compound heterozygous variants of the SMN gene in the SMA patients.