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.