Prenatal diagnosis of low-level mosaicism for a small supernumerary marker chromosome derived from chromosome 9q (9q13-q21.33) in a pregnancy with a favorable outcome, and cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes

摘要

ObjectiveWe present prenatal diagnosis of low-level mosaicism for a small supernumerary marker chromosome (sSMC) derived from chromosome 9q (9q13-q21.33) in a pregnancy with a favorable outcome, and cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes.Case reportA 36-year-old, primigravid woman underwent amniocentesis at 17 weeks of gestation because of advanced maternal age. Cytogenetic analysis on cultured amniocytes revealed a karyotype of 46,XY in 20/20 colonies. Simultaneous array comparative genomic hybridization (aCGH) on the DNA extracted from uncultured amniocytes revealed 30% mosaicism for ade novo20.3-Mb gene dosage increase at 9q13-q21.33. Repeat amniocentesis and cordocentesis were performed at 21 weeks of gestation. Cytogenetic analysis on cord blood revealed a karyotype of 47,XY,+mar [3]/46,XY [37]. aCGH analysis of cord blood revealed 7.5% mosaicism for a 17.15-Mb gene dosage increase at 9q21.11-q21.33. aCGH analysis of uncultured amniocytes revealed 11.7% mosaicism for a 17.15-Mb gene dosage increase at 9q21.11-q21.33. Polymorphic DNA marker analysis excluded uniparental disomy 9. The parental karyotypes were normal. The pregnancy was carried to 37 weeks of gestation, and a 2955-g phenotypically normal male baby was delivered. At birth, the cord blood had a karyotype of 47,XY,+mar [3]/46,XY [37], the placenta had a karyotype of 47,XY,+mar [10]/46,XY [30], and the umbilical cord had a karyotype of 47,XY,+mar [14]/46,XY [36]. aCGH analysis on the DNA extracted from cord blood at birth revealed no genomic imbalance. Interphase fluorescencein situhybridization analysis on buccal mucosal cells at age two months detected 3.8% (4/106?cells) mosaicism for the sSMC, compared with 2% (2/100?cells) in the normal control. The neonate had normal physical development at age two months.ConclusionCytogenetic discrepancy between cultured amniocytes and uncultured amniocytes may exist in the pregnancy with fetal mosaic sSMC. Low-level mosaicism for an sSMC derived from chromosome 9q13-q21.33?at prenatal diagnosis can be associated with a favorable outcome in the fetus.