|Abstract: ||Objective: To present prenatal diagnosis of true trisomy 7 mosaicism.
Materials, Methods and Results: A 36-year-old woman underwent amniocentesis at 18 weeks of gestation. Amniocentesis revealed a karyotype
of 47,XY,þ7/46,XY. The parental karyotypes were normal. Repeated amniocentesis was performed at 20 weeks of gestation. Array
comparative genomic hybridization (aCGH) analysis on uncultured amniocytes manifested a genomic gain in chromosome 7. Quantitative
fluorescent polymerase chain reaction (QF-PCR) analysis on uncultured amniocytes showed a biparental diallelic pattern with a dosage increase
in the maternal allele. Interphase fluorescence in situ hybridization (FISH) on uncultured amniocytes revealed three 7q-specific signals in 13 of
50 (26%) of the cells. The cultured amniocytes had a karyotype of 47,XY,þ7/46,XY. The ultrasound findings were unremarkable. The
pregnancy was subsequently terminated, and a fetus was delivered with facial dysmorphisms. Postnatal tissue samplings revealed the mosaic
trisomy 7 level of 37.5% (15/40), 30% (12/40), 42.5% (17/40), 82.5% (33/40), 52.5% (21/40), and 27.5% (11/40) in skin, liver, lungs, placenta,
membrane, and cord, respectively. The cord blood had a karyotype of 46,XY. PEG1/MEST methylation-sensitive high-resolution melting PCR
assay of cord blood showed no uniparental disomy for chromosome 7.
Conclusion: Interphase FISH, QF-PCR, and aCGH analyses on uncultured amniocytes are useful for rapid distinguishing of true mosaicism from
pseudomosaicism for trisomy 7 at amniocentesis. Cord blood sampling for confirmation of fetal trisomy 7 mosaicism is not practical.
Copyright 2012, Taiwan Association of Obstetrics & Gynecology. Published by Elsevier Taiwan LLC. All rights reserved.