Molecular Cytogenetic Characterization Of Small Supernumerary Marker Chromosomes

Objective: Combined with the traditional cytogenetic banding techniques,this study identified the small supernumerary marker chromosomes(sSMCs)carried by humans using molecular genetic techniques such as chromosomal microarray analysis(CMA)and fluorescence in situ hybridization(FISH).The relationship between genotypes of sSMC in different populations and clinical phenotypes of carriers was analyzed to provide more information and to provide more scientific prenatal diagnosis and genetic counseling for clinic.Methods: The subjects were patients diagnosed with sSMC who went to the Center for Reproduction Medicine and Prenatal Genetics of the First Hospital of Jilin University between July 2010 and November 2020 for prenatal diagnosis.Inclusion criteria were as follows:(1)The parents of the carrier and the fetus carrier have no infection,no genital trauma,no previous history of major diseases;(2)No previous history of long-term radiation exposure or radiotherapy or chemotherapy.A total of 51 patients were enrolled as main subjects.All adult male subjects underwent routine semen analysis and serum reproductive hormone analysis.Ultrasound examination,serological screening and non-invasive prenatal genetic testing were performed on the prenatal carriers.Chromosome karyotype analysis was performed on all carriers.Chromosome microarray analysis,fluorescence in situ hybridization and other detection techniques were performed after informed consent to identify sSMC more accurately.The subjects were grouped according to different indications and the relationship between the genotypes and phenotypes of sSMC was analyzed.Results:1.A total of 51 samples of sSMC carriers were collected in this study,including 19 adult males with sSMC of 24783 patients accounting for 0.0767%;15 adult females with sSMC of 23067 patients,accounting for 0.065%;14 prenatal fetuses with sSMCof 14341 patients,accounting for 0.097%;3 juvenile patients with sSMC of 1252 patients,accounting for 0.240%.2.The karyotype of 47,XN,+marwas found in 30 of 51 sSMC carriers(59%,30/51)in this study.The karyotype of47,XN,+mar/46,XN was found in 11 of 51 sSMC carriers(22%,11/51),the mosaic proportion ranged from 38% to 92%;nine cases showed more complex karyotype results.3.CMA was performed on 20 patients,3 of them showed no abnormality,and 17 of them detected different chromosome deletions and duplications.4.FISH was performed on 10 patients,and the chromosomal origin of sSMC was successfully identified.Three sSMCs were identified from Y chromosome,threesSMCs were identified from 14/22,two sSMCs were identified from 13/21,and two sSMCs were identified from 15.5.Among the 14 cases of prenatal sSMC,7 cases had pregnancy termination and 7 cases had successful pregnancy.All the newborns had normal phenotype,but long-term follow-up is still needed to determine whether abnormal phenotype occurs during the growth and development of the newborns.Conclusions:1.CMA and FISH combined with karyotype analysis can identify the source,mosaic proportion and structural composition of sSMC.2.Male carriers with sSMC(Y)often present with severe spermatogenesis disorders.The sSMC(13/21),sSMC(14/22)and sSMC(15)in infertile carriers are mainly composed of heterochromatin.3.Prenatal carriers with sSMC may show high risk of Down’s screening,high risk of Non-invasive Prenatal Testing and high risk of abnormal ultrasound.The identification of sSMC is beneficial to genetic counseling.Healthy newborns with sSMC should be followed up.