Non-invasive prenatal testing (NIPT) has been established as a routine prenatal screening to assess the risk of common foetal aneuploidy disorder (trisomy 21, 18, and 13). NIPT has high sensitivity and high specificity, but false positive and false negative results still exist. False negative NIPT results involving Down syndrome are rare, but have a high clinical impact on families and society. We described a case of a foetus that tested “negative” for trisomy 21 (Z-score was 0.664) by NIPT based on the semiconductor sequencing platform (SSP). The foetal fraction of cell-free DNA was 16.9%; this percentage was much larger than the threshold of 4% for obtaining accurate NIPT results. However, postnatally, the newborn was diagnosed with Down syndrome with the 46,XY,der(21;21)(q10;q10),+ 21 karyotype. We presented a case of false negative NIPT results, which may occur through biological mechanisms rather than poor quality, technical errors or negligence. It is imperative for clinical geneticists and their patients to understand that NIPT is still a screening test.

中文翻译：

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罕见的唐氏综合征胎儿，从头进行21q; 21q重排，在无创产前检查中导致假阴性结果：一例病例报告。

非侵入性产前检查（NIPT）已被确定为常规的产前检查，以评估常见胎儿非整倍性疾病（21、18和13号三体症）的风险。NIPT具有高灵敏度和高特异性，但假阳性和假阴性结果仍然存在。涉及唐氏综合症的假阴性NIPT结果很少见，但对家庭和社会有很高的临床影响。我们描述了一个胎儿的案例，该胎儿通过基于半导体测序平台（SSP）的NIPT测试为21三体阴性（Z得分为0.664）。无细胞DNA的胎儿比例为16.9％；这个百分比远大于获得准确NIPT结果的4％阈值。然而，在出生后，该新生儿被诊断为唐氏综合症，具有46，XY，der（21; 21）（q10; q10）+ 21核型。我们提出了一个假阴性NIPT结果的案例，它可能是由于生物学机制而不是质量差，技术错误或过失造成的。临床遗传学家及其患者必须了解NIPT仍是一项筛查测试。