Objective:To explore the genetic background in monochorionic diamniotic (MCDA) twins discordant for karyotypes.Methods:This study retrospectively analyzed four pregnant women who were diagnosed as having MCDA twins with prenatal diagnostic indications by ultrasound at Maternity and Child Health Care of Guangxi Zhuang Autonomous Region from January 2016 to December 2019. Dual amniocentesis was performed for all cases guided by ultrasound and the twin amniotic fluids were taken for karyotyping and single nucleotide polymorphism (SNP) array testing. Zygosity was determined by SNP genotype analysis.Results:The karyotypes of four MCDA twins were 47,XX,+18 and 46,XX, 45,X and 46,XX, 47,XXY[17]/46,XY[33] and 47,XXY, and 47,XX,+21 and 46,XX, respectively. The results of SNP were arr(18)×3 and arr(1-22,X)×2, arr(X)×1 and arr(1-22,X)×2, arr(X)×1~2,(Y)×1 and arr(X)×2,(Y)×1, arr(21)×3 and arr(21)×2~3. All of them were monozygotic twins according to the SNP genotypes. Three out of the four cases chose to terminate the pregnancy due to fetal chromosomal abnormalities and one was lost to follow-up. One gave birth to a healthy child in the next pregnancy.Conclusions:Clinicians should be alert to the discordant karyotypes in MCDA twins, of which the mechanism is yet to be explored.

Objective To investigate the genetic basis of patients with intellectual disability,and to assess the application of single nucleotide polymorphisms (SNP)-array in the molecular diagnosis of intellectual disability.Methods Sixty-four patients with intellectual disability who were identified in Maternal and Child Health Hospital of Guangxi Zhuang Autonomous Region from January 2013 to June of 2015 were enrolled.Genomic DNA was extracted from peripheral blood and was analyzed with Illumina Humancyto SNP-12 300K gene array chip.All identified copy number variants (CNVs) were analyzed with references from databases such as ClinVar,DECIPHER,OMIM and DGV(Database of Genomic Variants),as well as comprehensive literature review from PubMed database to determine the pathogenicity of CNVs.Results Sixteen cases of the above 64 patients were found to have CNVs with genomic alterations,including 6 cases microdeletions/microduplications associated with known syndromes,3 cases microdeletions and microduplications with clear clinical relevance (non-syndrome),1 case numerical chromosome aberration,1 case unbalanced translocation and 5 cases CNVs of unknown clinical significance.The detection rate was 25% (16/64 cases).Among these 16 abnormalities,6 cases of them could not be detected by using karyotyping analysis because their sizes were less than 5 Mb,and the smallest detected missing fragment was 0.53 Mb.Conclusion SNP-array gene chip technique with the advantages of higher efficiency,high-resolution and good accuracy,which can be applied to the genetic diagnosis of intellectual disability.

OBJECTIVE: To assess the value of chromosomal karyotyping analysis and single nucleotide polymorphism-based microarray (SNP-array) for the detection of chromosomal mosaicisms in amniotic fluid samples. METHODS: Seventy four pregnant women with fetal mosaicisms detected by both methods were retrospectively analyzed. RESULTS: Among the 74 mosaicisms, 12 were pseudo and 62 were true mosaicisms, which included 1 Robertsonian translocation, 3 deletions, 4 supernumerary markers, 19 autosomal aneuploidy mosaicisms, 30 sex chromosome aneuploidy mosaicisms and 5 isometric chromosome mosaicisms. CONCLUSION Chromosome karyotyping analysis and SNP-array have their own advantages and limitations for the diagnosis of mosaicisms. When the two methods have yielded inconsistent results, fluorescence in situ hybridization may be used for further verification.
Aneuploidy ; Chromosome Aberrations ; Female ; Humans ; In Situ Hybridization, Fluorescence ; Mosaicism ; Pregnancy ; Prenatal Diagnosis/methods* ; Retrospective Studies ; Sex Chromosome Aberrations