一例X-连锁无丙种球蛋白血症患者BTK基因新变异体的鉴定

Identification of a novel BTK variant in a Chinese family with X-linked agammaglobulinemia

目的对一例X-连锁无丙种球蛋白血症(XLA)患者进行致病基因变异鉴定。方法收集患者及家庭成员临床资料并采集外周血,从患者外周血中提取基因组DNA并进行全外显子组测序,筛查可疑致病变异,并对其父母基因组DNA进行Sanger测序验证及基因型-表型共分离分析,从患者外周血中提取RNA,反转录为cDNA后进行Sanger测序,同时进行实时定量PCR实验检测该基因表达水平,进而对该变异的致病性和致病机制进行分析。结果患者携带BTK基因c.240+3A>C新变异,该变异遗传自母亲,在家系中呈基因型-表型共分离,该变异体在dbSNP153、ExAC、gnomAD和HGMD等公共数据库未见报道。该变异属于剪接变异,cDNA测序显示该变异造成BTK基因3号内含子5′端106 bp碱基插入到第3号和第4号外显子之间,引起阅读框改变,最终导致终止密码子提前出现。患者BTK基因mRNA表达水平明显降低。结论BTK基因c.240+3A>C处剪接变异可能导致该患者患X-连锁无丙种球蛋白血症。

Objective To identify the pathogenic variant in a Chinese family with X-linked agammaglobulinemia(XLA).Methods A trio family with suspected X-linked agammaglobulinemia was recruited.The pathogenic variant was detected by the whole exome sequencing,and then confirmed by Sanger sequencing.cDNA sequencing was performed to find the abnormal splicing of the BTK variant.Quantitative real-time PCR was conducted to evaluate the mRNA expression of BTK in the patient.Results A novel hemizygous splicing variant(c.240+3A>C)wasidentified in the BTK gene from this patient.The variant co-segregated with the phenotype of the family members was not listed in the public databases,such as dbSNP153,ExAC,gnomAD or the Human Gene Mutation Database.Further Sanger sequencing demonstrated that the BTK c.240+3A>C variant led to a 106 bp from intron 3 of BTK insertion between exon 3 and exon 4 of the BTK transcript.The mRNA expression of BTK in the patient was significantly reduced as compared to a control individual.Conclusions The novel c.240+3A>C splicing variant in BTK likely results in X-linked agammaglobulinemia in this family.