Prenatal diagnosis of mosaicism for trisomy 7 in a single colony at amniocentesis in a pregnancy with a favorable outcome.

We present prenatal diagnosis of mosaicism for trisomy 7 in a single colony at amniocentesis with a favorable outcome. A 40-year-old woman underwent amniocentesis at 17 weeks of gestation because of advanced maternal age. Amniocentesis revealed a result of 47,XY,+7[1]/46,XY[26]. In 27 colonies of cultured amniocytes, all five cells in one colony had trisomy 7, while the rest 26 colonies had a normal karyotype. The parental karyotypes were normal. Repeat amniocentesis was performed at 19 weeks of gestation. Interphase fluorescence in situ hybridization (FISH) was applied on the uncultured amniocytes, and the result showed trisomy 7 signals in 4% (3/75 cells) of the uncultured amniocytes compared with 1.4% (1/70 cells) in the normal control. Uniparental disomy (UPD) 7 was excluded by polymorphic DNA marker analysis. The cultured amniocytes at repeat amniocentesis had a karyotype of 46,XY. Prenatal ultrasound findings were unremarkable. A healthy 3332-g male baby was delivered at 38 weeks of gestation. The karyotype of cord blood lymphocytes was 46,XY. The boy was phenotypically normal at age 8 months at follow-up. No trisomy 7 signal could be detected in the postnatal FISH analysis of the urinary cells. Mosaicism for trisomy 7 in a single colony at amniocentesis without UPD 7 can be associated with a favorable outcome.

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