Abstract：
BACKGROUND: A fetus with increased copy number of chromosome 20 was identified by NIPT. Here we utilize several genetic tests and analyses to illuminate the etiology of such aneuploidy.
METHODS: Amniotic fluid cells were extracted from pregnant woman and sent for karyotype and chromosomal microarray analysis (CMA). Trio pedigree analysis was conducted with Chromosome Analysis Suite and uniparental disomy (UPD)-tool software.
RESULTS: CMA identified consistent results, which were 2 regions of homozygosity: arr[GRCh37]20p12.2q11.1 (11265096_26266313)hmz and arr[GRCh37]20q11.21q13.2(29510306_54430467)hmz. The trio pedigree analysis discovered that the fetal chromosome 20 was the entire maternal UPD mosaic with isodisomy and heterodisomy.
CONCLUSIONS: When a large segment of chromosome is homozygous, appropriate genetic tests are required to find the potential mechanisms for UPD formation.
METHODS: Amniotic fluid cells were extracted from pregnant woman and sent for karyotype and chromosomal microarray analysis (CMA). Trio pedigree analysis was conducted with Chromosome Analysis Suite and uniparental disomy (UPD)-tool software.
RESULTS: CMA identified consistent results, which were 2 regions of homozygosity: arr[GRCh37]20p12.2q11.1 (11265096_26266313)hmz and arr[GRCh37]20q11.21q13.2(29510306_54430467)hmz. The trio pedigree analysis discovered that the fetal chromosome 20 was the entire maternal UPD mosaic with isodisomy and heterodisomy.
CONCLUSIONS: When a large segment of chromosome is homozygous, appropriate genetic tests are required to find the potential mechanisms for UPD formation.
摘要：
背景：通过NIPT鉴定了20号染色体拷贝数增加的胎儿。在这里，我们利用几种遗传测试和分析来阐明这种非整倍体的病因。
方法：从孕妇中提取羊水细胞，并送去进行核型和染色体微阵列分析（CMA）。使用染色体分析套件和单亲二体（UPD）工具软件进行三人系谱分析。
结果：CMA确定了一致的结果，它们是2个纯合性区域:ARR[GRCh37]20p12.2q11.1(11265096_26266313)hmz和ARR[GRCh37]20q11.21q13.2(29510306_54430467)hmz。三人系谱分析发现，胎儿20号染色体是具有等体性和异体性的整个母体UPD马赛克。
结论：当染色体的大部分是纯合的，需要进行适当的基因测试以发现UPD形成的潜在机制。
方法：从孕妇中提取羊水细胞，并送去进行核型和染色体微阵列分析（CMA）。使用染色体分析套件和单亲二体（UPD）工具软件进行三人系谱分析。
结果：CMA确定了一致的结果，它们是2个纯合性区域:ARR[GRCh37]20p12.2q11.1(11265096_26266313)hmz和ARR[GRCh37]20q11.21q13.2(29510306_54430467)hmz。三人系谱分析发现，胎儿20号染色体是具有等体性和异体性的整个母体UPD马赛克。
结论：当染色体的大部分是纯合的，需要进行适当的基因测试以发现UPD形成的潜在机制。
