Prenatal diagnosis and molecular cytogenetic characterization of a small supernumerary marker chromosome (sSMC) inherited from her mosaic sSMC(15) mother and a literature review

We characterized a maternally inherited small supernumerary marker chromosome (sSMC) derived from chromosome 15 according to prenatal detection and made a review on the prenatal sSMC(15) cases with mosaic maternal inheritance. A 29-year-old woman underwent amniocentesis at 19 weeks of gestation due to the high risk of Down syndrome in maternal serum screening. No abnormalities were observed in prenatal ultrasound findings. G-banding analysis revealed a karyotype of 47,XX,+mar. Subsequently, we recalled the couple back for chromosomal analysis. The father's karyotype was normal while the mother's karyotype was 47,XX,+mar[15]/46,XX[35]. Molecular genetic analysis was utilized to identify the marker chromosome. The chromosomal microarray analysis (CMA) results of the mother showed there existed microduplications in the locus of 14q32.33, 15q21.1, 19p12 and Xq26.2, respectively. Then Fluorescence in situ hybridization (FISH) using specific probes for chromosomes 13/21, 14/22, and 15 was applied on the mother and the fetus. And the marker chromosomes for the mother and the fetus were all finally identified as inv dup(15) (D15Z1++, SNRPN-, PML-), which illustrated that the fetus inherited the sSMC(15) from her mother. Finally, a healthy female infant was delivered with no phenotypic abnormalities at 39 weeks. The combined utilization of the molecular genetic technologies, such as FISH and CMA, plays a critical role in the identification of the origins and genetic constitutions of sSMC, which would make a significant contribution to genetic counseling and prenatal diagnosis.