Discrepancy in the trisomy mosaicism level between cultured amniocytes and uncultured amniocytes in prenatally detected mosaic trisomy 20

A gravida 2, para 1 woman 35 years of age underwent amniocentesis at 16 weeks of gestation because of advanced maternal age.Cytogenetic analysis of cultured amniocytes revealed a karyotype of 47,XY,þ20[26]/46,XY [9].Among 35 colonies of cultured amniocytes investigated by in situ cultured method, 26 colonies had a karyotype of 47,XY,þ20, while nine colonies had a karyotype of 46,XY.The level of trisomy in the cultured amniocytes was 74.3% (26/35).She was referred to the hospital for rapid positive confirmation of mosaic trisomy 20 at 23 weeks of gestation, and repeated amniocentesis was performed.Interphase fluorescence in situ hybridization (FISH) analysis using the bacterial artificial chromosome (BAC) clone probe RP11-2E8 (20p12.2) showed three 20p-specific signals in 10% (5/50) of the uncultured amniocytes and two 20p-specific signals in 90% (45/50) of the uncultured amniocytes, indicating 10% mosaicism for trisomy 20 in the uncultured amniocytes (Fig. 1).Quantitative fluorescent polymerase chain reaction (QF-PCR) analysis on the uncultured amniocytes showed equal fluorescent activity from two different parental alleles.Array comparative genomic hybridization (aCGH) analysis on the uncultured amniocytes revealed no gene dosage change on chromosome 20.