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目的:对3例微小额外标记染色体(small supernumerary marker chromosomes，sSMC)的来源与结构进行鉴定，探讨其发生机理，为临床遗传咨询提供参考。方法:应用染色体显带技术(G带、C带、N带)进行染色体核型分析，基因芯片技术明确sSMC片段的来源和区域，并用荧光原位杂交(fluorescence n in situ hybridization，FISH)技术进行验证。n 结果:例1 外周血染色体核型为47，XY，＋mar，为新发变异，sSMC为双着丝粒双随体结构，芯片结果示未包含已知人类疾病相关致病基因，推测不增加子代表型异常的风险。例2胎儿染色体核型结果为47，XY，＋mar[17]/46，XY[33]，为新发变异，常规显带技术提示mar上有常染色质，芯片检测结果为arr[hg19]5p12q11.1(45 694 574-49 475 697)×3，经FISH验证，明确胎儿sSMC片段含有n HCN1基因部分区段的5p12片段。例3胎儿染色体核型为45，XY，-13[25]/46，XY，r(13)[18]/46，XY，-13，＋mar[7]，夫妻双方拒绝进一步检查。n 结论:传统的显带技术联合分子检测技术能对sSMC的结构及来源进行分析，可明确sSMC的致病性，为临床遗传咨询提供参考。“,”Objective:To delineate the origin and structure of 3 cases of small supernumerary marker chromosomes (sSMCs) through cytogenetic and molecular genetic analysis.Methods:Conventional G, C and N banding were carried out to analyze the chromosomal karyotypes. Chromosomal microarray analysis (CMA) and fluorescence n in situ hybridization (FISH) were used to delineate the origin and structure of the sSMCs.n Results:In case 1, chromosomal karyotype of peripheral blood sample was 47, XY, + mar. This n de novo sSMC was a dual-satellited dicentric inverted duplicated marker chromosome, for which CMA yielded a normal result. It was predicted to not increase the risk of offspring. In case 2, the fetal chromosome karyotype was 47, XY, + mar[17]/46, XY[33]. Chromosomal banding suggested that thisn de novo segment contained euchromatin, and the result of CMA was arr[hg19] 5p12q11.1(45 694 574-49 475 697)×3. FISH showed the sSMC to be a fragment from 5p12 containing the n HCN1 gene. Case 3 was found to have a fetal karyotype of 45, XY, -13[25]/46, XY, r(13)[18]/46, XY, -13, + mar[7]. Both parents refused any further examination.n Conclusion:Conventional chromosomal banding combined with molecular methods can delineate the origin and structure of the sSMCs, which can help with prediction of their pathogenicity and facilitate genetic counseling.