断裂点精确定位在平衡易位胚胎染色体分析中的应用

Application of precise location of breakpoint in haplotype analysis of balanced translocation families

目的尝试一种新的精确平衡易位断裂点的分析方法,以便区分染色体正常型和平衡易位携带型胚胎。方法基于两例染色体平衡易位携带同胞兄弟,利用基因芯片测序结合荧光强度比(LRR)、B等位频率(BAF)、单体型连锁分析(PGH)和基因型识别两对夫妇(夫妇A、B)、男方母亲及胚胎的染色体结构,尽可能精确定位以缩小平衡易位断裂点的识别范围;参考胚胎各染色体拷贝数变异(CNV)检测与PGH结果,区分不平衡易位型、正常型与平衡易位携带型胚胎;筛选染色体完全正常的单囊胚植入,妊娠后行产前诊断。结果将平衡易位断裂点的识别范围由±3 Mb大小缩小至412 Kb(chr14:69340569~69752603)。最终为夫妇A确定了2枚可优先移植的胚胎(1-3和1-6号胚胎),为夫妇B确定了4枚可优先移植的胚胎(2、3、5和7号胚胎)。辅助生殖技术(ART)助孕后,两对夫妇分别选择染色体结构正常的1-3号和5号单囊胚植入后成功妊娠,并最终足月顺利分娩健康宝宝。结论LRR、BAF、PGH和基因型的结合分析可显著提高平衡易位断裂点定位的准确性,可在植入前区分染色体正常型和易位携带型胚胎。

Objective:To use a new analytical method to accurately locate the breakpoint of balanced translocation to distinguish between normal chromosomal and balanced translocation carrying embryos.Methods:Chip sequencing was carried out on the family samples of two siblings with the same chromosomal balanced translocation,and then gene chip sequencing combined with fluorescence intensity ratio(LRR),B allele frequency(BAF),haplotype linkage analysis(PGH)and genotype to identify two couples(couple A,B),the man’s mother and the chromosomal structure of embryo,to minimize the identification range of the translocation breakpoint.Then,refer to the results of copy number variation(CNV)of each chromosome of embryos and PGH to distinguish between unbalanced translocation,normal embryo and translocation carrying embryo.Single blastocyst with completely normal chromosomes was selected for implantation,and prenatal diagnosis was performed after pregnancy.Results:The range of translocation breakpoint was reduced from±3 Mb to 412 Kb(chr14:69340569-69752603).Two embryos(1-3,1-6)for couple A and 4 embryos(2,3,5,and 7)for couple B were finally selected.With assisted reproductive technology(ART),the two couples were successfully pregnant after implantation of single blastocyst(1-3)and(5)with normal chromosome structure and finally delivered a healthy baby at full term.Conclusions:Combined analysis of LRR,BAF,PGH and genotype can significantly improve the accuracy of the location of translocation breakpoint,which can be used for distinguishing chromosomal normal embryos and translocation carrying embryos before implantation.