Rapid diagnosis of pseudomosaicism in a case of Level II mosaicism for trisomy 5 in a single colony from an in situ culture of amniocytes and a review of mosaic trisomy 5 at amniocentesis

Abstract

ObjectiveWe present prenatal diagnosis of pseudomosaicism for trisomy 5 and a review of the literature of mosaic trisomy 5 at amniocentesis. Case ReportA 39-year-old woman underwent amniocentesis at 17 weeks of gestation, which revealed a karyotype of 47,XY,+5[1]/46,XY[20]. The single colony with trisomy 5 had five metaphase cells, and all five cells had the karyotype of 47,XY,+5. Repeat amniocentesis performed at 20 weeks of gestation revealed a karyotype of 46,XY in 27/27 colonies. Simultaneously, interphase fluorescence in situ hybridization (FISH), array comparative genomic hybridization (aCGH), and quantitative fluorescent polymerase chain reaction (QF-PCR) were performed on uncultured amniocytes. Interphase FISH revealed no trisomy 5 in 100 uncultured amniocytes. aCGH revealed no genomic imbalance. QF-PCR excluded uniparental disomy 5. A healthy 3662-g male baby was delivered with a normal karyotype in cord blood and 3.75% (3/80 cells) of trisomy 5 cells in uncultured urinary cells compared with 0.95% (1/105 cells) of trisomy 5 cells in normal control examined by FISH at 1.5 months of age. A review of seven cases with mosaic trisomy 5 at amniocentesis shows that 4/7 had clinically normal outcome, 3/7 had structural defects, mainly the heart, 6/6 had normal karyotype in blood, and 2/3 had mosaic trisomy 5 in the fetal tissues. ConclusionPrenatal diagnosis of mosaic trisomy 5 should alert the possibility of fetal structural abnormalities, especially the heart, and culture artifacts. We suggest that the application of molecular cytogenetic techniques such as aCGH, interphase FISH, and QF-PCR on uncultured amniocytes is useful in our understanding of the mosaic status at repeat amniocentesis.