Prenatal diagnosis and genetic counseling of a case with trisomy 20 mosaicism and mixed-type maternal UPD20.

BACKGROUND: To genetically analyze a prenatal specimen exhibiting mosaic 20q11.2 microdeletion syndrome with uniparental disomy of chromosome 20 (UPD20). The aim is to summarize the symptoms and prognosis of fetuses with this condition and provide guidance for genetic counseling and prenatal diagnosis in similar cases. METHODS: Chromosomal karyotyping and Chromosomal Microarray Analysis (CMA) were performed on prenatal amniotic fluid specimens and peripheral blood samples from the parents. RESULTS: The karyotype analysis of the fetal amniotic fluid cells revealed a mosaic pattern of 46,XN,+20[80]/46,XN[20], indicating an 80 % mosaicism ratio. The CMA results showed arr20p13q13.33(61,662-62,913,645)x2-3 mos with an 11 % mosaicism ratio and arr20p12.2q13.2(9,484,368-50,586,616)x2 hmz, inherited from the mother. CONCLUSION: Through interdisciplinary team discussion and analysis of a 42-year-old pregnant woman's fetus exhibiting mosaic 20q11.2 microdeletion syndrome with mixed-type maternal UPD20, relevant genetic counseling was provided to the pregnant woman, assisting in informed decision-making. The reporting of this case is significant for summarizing the symptoms and prognosis of fetuses with this condition and guiding prenatal diagnosis and genetic counseling in similar cases.