Paternal Transmission of Small Supernumerary Marker Chromosome 15 Identified in Prenatal Diagnosis Due to Advanced Maternal Age

The detection of supernumerary marker chromosomes (SMCs) in prenatal diagnosis is always a challenge. In this study, we report a paternally inherited case of a small SMC(15) that was identified in prenatal diagnosis due to advanced maternal age. A 39-year-old woman underwent amniocentesis at 16 weeks of gestation. A fetal abnormal karyotype - 47,XX,+mar - with one sSMC was detected in all metaphases. Since this sSMC was critical in the parental decision to continue or interrupt this pregnancy, we proceeded to study the fetus and their parents. Cytogenetic and molecular analyses revealed a fetal karyotype 47,XX,+mar pat.ish idic(15)(ql2)(D15Zl++,SNRPN-), in which the sSMC(15) was a paternally inherited inverted duplicated chromosome and did not contain the critical region of Prader-Willi/Angelman syndromes. Moreover, fetal uniparental disomy was excluded. Based on this information and normal obstetric ultrasounds, the parents decided to proceed with the pregnancy and a phenotypically normal girl was born at 39 weeks of gestation. In conclusion, the clinical effects of sSMCs need to be investigated, especially when sSMCs are encountered at prenatal diagnosis. Here, although the paternal sSMC(15) was not associated with an abnormal phenotype, its characterization allows more accurate genetic counseling for the family progeny.