Fetoplacental discrepancies occur in approximately 1–2% of analyzed prenatal cases. They are typically due to confined placental mosaicism, where an aberration is observed in the placental cells but not found in the fetal cells. Confined placental mosaicism usually involves aneuploidies and more sparsely structural chromosomal aberrations. To the best of our knowledge, this is the first reported case of a discrepancy in the analyses of chorionic villus sampling and amniocentesis involving two different structural chromosomal aberrations of chromosome 21. We report a 33-year-old woman who was referred for a non-invasive prenatal testing due to an increased risk of trisomy 21 gleaned from a combined ultrasound and blood test. The non-invasive prenatal testing showed an increased risk of trisomy 21 with a normalized coverage signal that did not match the fetal cell-free DNA fraction. Rapid aneuploidy detection performed on uncultured chorionic villi indicated mosaicism for trisomy 21. The follow-up analyses revealed discordant chromosomal aberrations: 46,XY,der(21)t(10;21)(p11.21;q10) in the analysis of the chorionic villus sampling and 46,XY, + 21,der(21;21)(q10;q10) in the analysis of the amniocentesis. Thus, the analyses indicated mosaicism for a cell line containing trisomy 21 and a cell line containing a partially duplicated short arm of chromosome 10 in the chorionic villi and complete trisomy 21 resulting from an isochromosome 21 in the amniotic fluid. The analyses of the lymphocytes and the fibroblasts of the woman were normal. We propose a multiple-step mechanism as a possible theoretical explanation for the formation of these discordant structural chromosomal aberrations in the chorionic villi and amniotic fluid. With this case report, we want to highlight the importance of understanding the possible underlying embryological mechanisms when interpreting results from different prenatal analyses.

中文翻译：

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绒毛膜绒毛和羊水中不一致的染色体结构畸变导致等染色体 21 的形成：病例报告

大约 1-2% 的分析产前病例中发生胎盘差异。它们通常是由于局限的胎盘嵌合，在胎盘细胞中观察到畸变，但在胎儿细胞中没有发现。局限性胎盘嵌合通常涉及非整倍体和更稀疏的结构染色体畸变。据我们所知，这是第一个报告的关于 21 号染色体的两种不同结构染色体畸变的绒毛膜取样和羊膜穿刺术分析存在差异的案例。我们报告了一名 33 岁女性，她被转诊为非- 侵入性产前检测，因为从联合超声和血液检测中收集到的 21 三体风险增加。非侵入性产前检测显示 21 三体的风险增加，标准化覆盖信号与胎儿无细胞 DNA 部分不匹配。在未培养的绒毛膜绒毛上进行的快速非整倍体检测表明 21 三体的嵌合现象。后续分析显示不一致的染色体畸变：46,XY,der(21)t(10;21)(p11.21;q10)绒毛膜取样和羊膜穿刺术分析中的 46,XY, + 21,der(21;21)(q10;q10)。因此，分析表明包含 21 三体性的细胞系和包含绒毛膜绒毛中 10 号染色体的部分重复短臂的细胞系和完全的 21 三体性的细胞系存在嵌合现象，这是由羊水中的 21 等染色体引起的。该妇女的淋巴细胞和成纤维细胞的分析是正常的。我们提出了一个多步骤机制，作为可能的理论解释来解释绒毛膜绒毛和羊水中这些不一致的染色体结构畸变的形成。通过本病例报告，我们想强调在解释不同产前分析的结果时了解可能的潜在胚胎学机制的重要性。