一个罕见HLA—C等位基因间重组家系的遗传背景研究

The genetic study on a rare inter-allelic recombination of HLA-C locus in a Chinese Han family

目的 研究HLA-C等位基因座位上的交换重组,探讨HLA新等位基因产生的分子遗传背景.方法 采集拟进行造血干细胞移植的1例慢性粒细胞白血病患者、患者父母以及2名哥哥的静脉血,采用AlleleSEQR HLA 测序分型试剂进行HLA-A、C、B、DRB1和DQB1共5个位点的高分辨基因分型;再采用Protrans S4 HLA单倍体测序技术分离2个HLA-C等位基因,以确定序列异常的1个C等位基因;进一步采用分子克隆和测序方法进行患者及父母HLA-C等位基因的全长单倍体序列分析.按遗传规律分析该家系的HLA 5个位点的连锁单倍型,同时将HLA-C等位基因全长序列经IMGT/HLA Database中的＂BLAST＂程序进行序列的对比,以确定C等位基因重组发生的精确位置.结果 经HLA测序及遗传家系分析,该家系中父亲的2条HLA连锁单倍型分别为a：A＊0207-C＊010201-B＊550201-DRB1＊090102-DQB1＊030302与b：A＊240201-C＊120202-B＊5201-DRB1＊1502-DQB1＊0601;母亲的分别为：c：A＊300101-C＊060201-B＊130201-DRB1＊0405-DQB1＊0401与d：A＊110101-C＊070201-B＊4001-DRB1＊080302-DQB1＊0601.患者的2名哥哥均分别正常遗传了父母的2条单倍体a、d及b、c.患者的2条单倍体分别为母源单倍体c及父源重组单倍体a/b,其中A＊240201来自父亲的1条染色单体b,而B＊550201-DRB1＊090102-DQB1＊030302则来自父亲的另1条染色单体a.对比患者携带的C未知新等位基因与父亲的1对C＊010201 、C＊120202等位基因的全长单倍体序列,推断父亲的2条染色单体在减数分裂时,由于HLA-C等位基因的第273位至330位碱基区域之间发生了交换,重组后形成新的C等位基因及单倍型并遗传给了患者.该C新等位基因的全长序列已递交GenBank,并被世界卫生组织HLA因子命名委员会正式命名为C＊0121.结论 本研究发现了1个罕见的中国汉族人群HLA-C基因座位上的基因重组家系,阐明了HLA-C＊0121新等位基因及单倍型的产生来源,为更深入研究基因重组及HLA多态性形成机制提供了理论依据.

Objective To study the inter-allelic recombination event occurring in the HLA-C locus in a family of Chinese Han nationality, and to evaluate the molecular genetic background of the new HLA allele.Methods Peripheral blood samples were collected from a Chinese leukemia woman patient, as well as her healthy parents and two brothers.HLA-A, C, B, DRB1 and DQB1 alleles were typed by high-resolution PCR-sequence-based typing （SBT） method using Atria Genetic AlleleSEQR HLA SBT kits.The Protrans S4 HLA-C single allele-specific sequencing strategy was used to separate the two HLA-C alleles and to determine novelty of the allele.The full length sequences of HLA-C alleles of the patient and her parents were further analyzed using cloning and haplotype sequencing method. The HLA five loci linked haplotypes and the recombination site were analyzed by family study, meanwhile the full length sequences of the five HLA-C alleles were compared with the IMGT/HLA database by the program ＂BLAST＂.Results The two haplotypes of the father and mother were a：A＊0207-C＊010201-B＊550201-DRB1＊090102-DRQ1＊030302 and b：A＊240201-C＊120202-B＊5201-DRB1＊1502-DRQ1＊0601, c：A＊300101-C＊060201-B＊130201-DRB1＊0405-DRQ1＊0401 and d：A＊110101-C＊070201-B＊4001-DRB1＊080302-DRQ1＊0601,respectively.The two brothers inherited their parent′s haplotypes a, d and b, c respectively.The two haplotypes of the patient were the maternal c and paternal recombinant a/b haplotype.The recombinant a/b haplotype A＊240201-C＊new-B＊550201-DRB1＊090102-DRQ1＊030302, A＊240201 came from the paternal haplotype b,while B＊550201-DRB1＊090102-DRQ1＊030302 came from the other paternal haplotype a.When comparing the full length sequences of the HLA-C new allele with the father′s allele C＊010201 and C＊120202, it could deduce that the recombinant a/b haplotype derived from a recombination event occurring between the paternal chromosome 6 during meiosis.The crossover site was between genomic nt273 and nt330 of HLA-C alleles, which created a HLA-C new allele and the fifth haplotype of the family, and inherited it to the patient.The full length sequences of the new allele had been submitted to Genbank, and officially named C＊0121 by WHO nomenclature committee.Conclusion This study demonstrates a rare inter-allelic recombination event occurring in the HLA-C locus within a Chinese Han family and illustrates the process of novel allele and haplotype, and provides direct theory for further studying the mechanisms of gene recombination and HLA polymorphism.