| Abstract: | A 34-year-old, primigravid woman underwent amniocentesis at 18 weeks of gestation because of advanced maternal age. Cytogenetic analysis of the cultured amniocytes revealed mosaicism for a small supernumerary marker chromosome (sSMC) and a karyotype of 47,XY,+mar[15]/46,XY[5]. Among 20 colonies of cultured amniocytes, 15 colonies had a karyotype of 47,XY,+mar, while the other five colonies had a karyotype of 46,XY. The parental karyotypes were normal. Level II ultrasound findings were unremarkable. She underwent repeat amniocentesis at 29 weeks of gestation. Array comparative genomic hybridization (aCGH) on DNA extracted from the uncultured amniocytes obtained from 10 mL of amniotic fluid was performed using NimbleGen ISCA Plus Cytogenetic Array (Roche NimbleGen, Madison, WI, USA). aCGH revealed no genomic imbalance in the pericentromeric euchromatic regions of all 24 chromosomes. Cytogenetic analysis of cultured amniocytes revealed a karyotype of 47,XY,+mar[12]/46,XY[10]. In 12/22 separated colonies of cultured amniocytes, a karyotype of 47,XY,+mar (Fig. 1) was noted, while the other 10 colonies had a karyotype of 46,XY. Fluorescence in situ hybridization (FISH) was performed on cultured amniocytes using the probes of Aquarius Satellite Enumeration (Cytocell Inc., Adderbury, Oxfordshire, UK) and Vysis Prader-Willi/Angelman Region (Abbott Inc., Abbott Park, IL, USA). The probes used included CEP15 (D15Z4, 15p11.1-q11.1; D15Z1, 15p11.2), CEP1/5/19, CEP6, CEP7, CEP10, CEP18, CEP13/21, and CEP14/22 (Cytocell), and LSI SNRPN (15q11.2) and LSI PML (15q15) (Abbott). FISH analysis revealed that the sSMC was positive for D15Z4 ( Fig. 2) and negative for D15Z1, SNRPN, and PML ( Fig. 3). FISH analysis also revealed a negative result for CEP1/5/19, CEP6, CEP7, CEP10, CEP18, CEP13/21, and CEP14/22. The sSMC was derived from chromosome 15 without involvement of the Prader-Willi/Angelman region. The karyotype at repeat amniocentesis was 47,XY,+mar.ish der(15)(D15Z4+, D15Z1-, SNRPN-, PML-)[12]/46,XY[10]. Methylation analysis of the Prader-Willi/Angelman critical region (PWACR) by the methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) kit of SALSA MS-MLPA ME028-B1 Prader-Willi syndrome/Angelman syndrome (PWS/AS) probemix (MRC-Holland bv. Amsterdam, The Netherlands) using the DNA extracted from uncultured amniocytes excluded uniparental disomy (UPD) 15 ( Fig. 4). The parents decided to continue the pregnancy. At 40 weeks of gestation, a healthy male baby was delivered with a body weight of 3004 g and a karyotype of 47,XY,+mar[21]/46,XY[19] in cord blood. |
