Analysis of a twin pregnancy with false negative result for 22q11.2 deletion syndrome by expanded non-invasive prenatal testing
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目的 探讨1例扩展性无创产前检测(NIPT-plus)双胎之一22q11.2缺失综合征(22q11.2 DS)假阴性的原因。 方法 对1例NIPT-plus结果为阴性，后期因超声异常行羊水穿刺的辅助生殖双胎样本，获取胎儿细胞后行核型分析和拷贝数变异测序(CNV-seq)检测。收集并分析孕妇的临床信息及检测数据，探讨假阴性的原因。 结果 NIPT-plus的uniMap reads为11.77 Mb，胎儿游离DNA浓度为3.05%。羊水核型结果显示一胎为46，XY，另一胎儿为46，XX，均正常。CNV-Seq结果显示一胎正常，另一胎为缺失大小为2.58 Mb的22q11.2 DS。 结论 上述假阴性应是由较低的胎儿游离DNA浓度、孕妇较高的BMI、辅助生殖、双胎以及较小的缺失片断等综合因素共同引起。对于NIPT-plus低风险者的后续超声检查不可忽视。 Objective To explore the cause for a twin pregnancy with false negative result for 22q11.2 deletion syndrome by expanded non-invasive prenatal testing (NIPT-plus). Methods A pregnant woman with twin pregnancy through in-vitro fertilization and negative result of NIPT-plus was selected as the study subject. Amniocentesis was conducted after ultrasonic finding of fetal abnormalities. In addition to conventional G-banded karyotyping, copy number variation sequencing (CNV-Seq) was used to detect chromosomal microdeletion and microduplication. Clinical data of the woman were analyzed to explore the reasons underlying the false negative result. Results NIPT-plus has yielded a negative result with 11.77 Mb unique reads and 3.05% fetal fraction. Both fetuses had a normal karyotype (46, XY and 46, XX). CNV-seq indicated that one of the fetuses was normal, whilst the other was diagnosed with a 2.58 Mb deletion in the 22q11.2 region. Conclusion The false negative result may be attributed to the combined influence of low fetal fraction, high BMI, twin pregnancy through IVF and a relatively small deletion fragment. Ultrasonography exam following a low-risk result of NIPT-plus should not be neglected.
Objective To explore the cause for a twin pregnancy with false negative result for 22q11.2 deletion syndrome by expanded non-invasive prenatal testing (NIPT-plus). Methods A pregnant woman with twin pregnancy through in-vitro fertilization and negative result of NIPT-plus was selected as the study subject. Amniocentesis was conducted after ultrasonic finding of fetal abnormalities. In addition to conventional G-banded karyotyping, copy number variation sequencing (CNV-Seq) was used to detect chromosomal microdeletion and microduplication. Clinical data of the woman were analyzed to explore the reasons underlying the false negative result. Results NIPT-plus has yielded a negative result with 11.77 Mb unique reads and 3.05% fetal fraction. Both fetuses had a normal karyotype (46, XY and 46, XX). CNV-seq indicated that one of the fetuses was normal, whilst the other was diagnosed with a 2.58 Mb deletion in the 22q11.2 region. Conclusion The false negative result may be attributed to the combined influence of low fetal fraction, high BMI, twin pregnancy through IVF and a relatively small deletion fragment. Ultrasonography exam following a low-risk result of NIPT-plus should not be neglected.
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