Molecular delineation of de novo Small Supernumerary Marker Chromosomes in prenatal diagnosis, a retrospective study

Objective To define the genotype-phenotype correlation of small supernumerary marker chromosomes (sSMC) and conduct precise genetic counseling.Methods We retrospectively searched and reviewed the de novo sSMC cases detected during prenatal diagnosis in The First Affiliated Hospital of Zhengzhou University. Chromosome karyotypes of 20314 cases of amniotic fluid from pregnant women were performed. For 17 samples with de novo sSMC, 11 of them were subjected to single nucleotide polymorphism (SNP) array or low-coverage massively parallel copy number variation sequencing (CNV-seq) analysis. Results Among the 11 sSMC cases, two sSMC were derived from chromosome 9, four sSMC were derived from chromosome 12, 18, 22 and X , separately. For the remaining 5 cases, they were not identified by SNP array or CNV-seq because they lacked euchromatin or had low proportion mosaicism. Four of them with the karyotype of 47,XN,+mar presented normal molecular cytogenetic results (seq[hg19] 46,XN ) , the left one with the karyotype of 46,XN,+mar was Turner syndrome (seq[hg19] 45,XO). Five sSMC samples were mosaics of all these 17 cases. Conclusion Considering the variable origins of sSMC, further genetics testing of sSMC should be performed by SNP array or CNV-seq. The detailed molecular characterization would allow precise genetic counseling for prenatal diagnosis.