Discordance between traditional cytogenetic and molecular cytogenetic tests is rare but not uncommon. The explanation of discordance between two genetic methods is difficult but especially important for genetic counseling, particularly for prenatal genetic diagnosis. Two unrelated fetuses were diagnosed with cardiac defects by prenatal ultrasound examination, and invasive cordocentesis was performed to obtain cord blood samples for prenatal genetic diagnosis. For both fetuses, chromosomal microarray analysis (CMA) detected a novel approximately 27-Mb mosaic duplication with a high copy number of approximately six to seven copies on chromosome 8q24.1q24.3 that was not identified by karyotyping. To exclude artificial errors and validate laboratory detection results, multiple procedures including copy number variation sequencing, fluorescence in situ hybridization, and short tandem repeat and single-nucleotide polymorphism genotype comparison were performed, confirming the discordant results between CMA and karyotyping. The potential causes of discordance between CMA and karyotyping using fetal blood lymphocytes are discussed; we suggest that extrachromosomal DNA or cell-free DNA fragmentation originating from certain tumor tissues with 8q24.1q24.3 duplication might deserve further investigation. This study may be helpful for prenatal evaluation and genetic counseling for subsequent patients with similar mosaic 8q24.1q24.3 duplications. Additionally, more cases and further research are needed to understand whether mosaic 8q24.1q24.3 duplication is associated with certain genetic disorders and to investigate the causes of discordance between molecular and morphological methods.

中文翻译：

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在两个患有心脏缺陷的不相关胎儿中，通过染色体微阵列检测到 8q24.1q24.3 的马赛克重复，但未通过核型分析检测到

传统细胞遗传学和分子细胞遗传学测试之间的不一致很少见，但并不罕见。解释两种遗传方法之间的不一致很困难，但对于遗传咨询尤其是产前遗传诊断尤其重要。两名无关胎儿经产前超声检查确诊为心脏缺陷，并进行有创脐带穿刺术获取脐带血样本进行产前基因诊断。对于这两个胎儿，染色体微阵列分析 (CMA) 检测到染色体 8q24.1q24.3 上存在约 27 Mb 的新型嵌合重复，其高拷贝数约为 6 至 7 个拷贝，但核型分析未发现该重复。为了排除人为错误并验证实验室检测结果，进行了拷贝数变异测序、荧光原位杂交、短串联重复和单核苷酸多态性基因型比较等多种程序，证实了CMA与核型分析之间不一致的结果。讨论了 CMA 与使用胎儿血液淋巴细胞进行核型分析之间不一致的潜在原因；我们认为源自某些具有 8q24.1q24.3 重复的肿瘤组织的染色体外 DNA 或无细胞 DNA 片段可能值得进一步研究。这项研究可能有助于后续具有类似嵌合体8q24.1q24.3重复的患者的产前评估和遗传咨询。此外，还需要更多的病例和进一步的研究来了解嵌合8q24.1q24.3重复是否与某些遗传性疾病相关，并调查分子和形态学方法之间不一致的原因。