Molecular cytogenetic characterization of a de novo small supernumerary marker chromosome derived from chromosome 15 in a pregnancy with incidental detection of a maternal Robertsonian translocation of 45,XX,der(13;14) (q10;q10).

OBJECTIVE

We present molecular cytogenetic characterization of a small supernumerary marker chromosome (sSMC) derived from chromosome 15 in a pregnancy with incidental detection of a maternal Robertsonian translocation of 45,XX,der(13; 14) (q10; q10).

CASE REPORT: A 37-year-old, primigravid woman underwent amniocentesis at 16 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype of 47,XY,+mar. Simultaneous array comparative genomic hybridization (aCGH) analysis on the DNA extracted from uncultured amniocytes showed the result of no genomic imbalance or arr (1-22) × 2, (X,Y) × 1. Cytogenetic analysis of the parents showed a karyotype of 45,XX,der(13; 14) (q10; q10) in the mother and a karyotype of 46,XY in the father. Prenatal ultrasound was unremarkable. At 38 weeks of gestation, a 2790-g phenotypically normal male baby was delivered. The cord blood had a karyotype of 47,XY,+mar. Metaphase fluorescence in situ hybridization (FISH) analysis showed the result of +mar.ish dic(15) (D15Z1++, SNRPN-, PML-) (18/20). The extra chromosome was derived from chromosome 15.

CONCLUSION

Metaphase FISH analysis is useful for the identification of the origin of an sSMC in the presence of no genomic imbalance at aCGH analysis. Prenatal diagnosis of a de novo sSMC may be associated with a Robertsonian translocation in the parents, and parental cytogenetic analysis is necessary under such a circumstance.