A Retrospective Analysis of Robertsonian Translocations from a Single Center in China.

Robertsonian translocations (ROBs) are the most common structural chromosomal abnormalities in the general population, with an estimated incidence rate of 1/1000 births. In this study, we retrospectively analyzed the cases of ROBs from September 2015 to August 2022 and totally identified ROB carriers from 84,569 specimens karyotyped in a single accredited laboratory in China, including 189 cases of balanced ROBs and 3 of mosaic ROBs. Microsoft Excel and descriptive statistics were used to record and analyze the collected data. The male/female ratio of ROBs is 1/1.29, with der(13;14) and der(14;21) being the main karyotypes. Among the 192 patients, 7 were lost to follow-up, 82 had given birth, and 103 were childless (such as miscarriage, fetal chromosomal abnormalities, in vitro fertilization (IVF) failure, or divorce). A total of 44 amniocenteses were performed in 42 couples; ROB cases with natural pregnancies showed that the normal karyotype and balanced ROBs of fetal accounted for 66.67% (16/24), while the results of assisted pregnancies showed 90.00% (18/20). This study represents the largest collections of ROBs in Jiangxi population and reminder that the ROB carriers can achieve the ideal outcome for pregnancy with the appropriate genetic guidance and assisted reproductive technologies (ART).

Analysis of chromosomal structural variations in patients with recurrent spontaneous abortion using optical genome mapping.

Background and aims: Certain chromosomal structural variations (SVs) in biological parents can lead to recurrent spontaneous abortions (RSAs). Unequal crossing over during meiosis can result in the unbalanced rearrangement of gamete chromosomes such as duplication or deletion. Unfortunately, routine techniques such as karyotyping, fluorescence in situ hybridization (FISH), chromosomal microarray analysis (CMA), and copy number variation sequencing (CNV-seq) cannot detect all types of SVs. In this study, we show that optical genome mapping (OGM) quickly and accurately detects SVs for RSA patients with a high resolution and provides more information about the breakpoint regions at gene level. Methods: Seven couples who had suffered RSA with unbalanced chromosomal rearrangements of aborted embryos were recruited, and ultra-high molecular weight (UHMW) DNA was isolated from their peripheral blood. The consensus genome map was created by de novo assembly on the Bionano Solve data analysis software. SVs and breakpoints were identified via alignments of the reference genome GRCh38/hg38. The exact breakpoint sequences were verified using either Oxford Nanopore sequencing or Sanger sequencing. Results: Various SVs in the recruited couples were successfully detected by OGM. Also, additional complex chromosomal rearrangement (CCRs) and four cryptic balanced reciprocal translocations (BRTs) were revealed, further refining the underlying genetic causes of RSA. Two of the disrupted genes identified in this study, FOXK2 [46,XY,t(7; 17)(q31.3; q25)] and PLXDC2 [46,XX,t(10; 16)(p12.31; q23.1)], had been previously shown to be associated with male fertility and embryo transit. Conclusion: OGM accurately detects chromosomal SVs, especially cryptic BRTs and CCRs. It is a useful complement to routine human genetic diagnostics, such as karyotyping, and detects cryptic BRTs and CCRs more accurately than routine genetic diagnostics.

[Prenatal diagnosis of a fetus with 8q13.3 microdeletion through chromosomal microarray analysis].

OBJECTIVE: To assess the value of chromosomal microarray analysis (CMA) for the prenatal diagnosis of a fetus with structural anomaly detected by ultrasonography. METHODS: The fetus and its parents were subjected to chromosomal karyotyping and CMA analysis. RESULTS: The fetus was found to carry a 46,XN,t(8;11)(q21.2;q13) translocation which was inherited from its mother. CMA has found no copy number variations (CNVs) in both parents but a de novo 2.00 Mb microdeletion in the fetus at 8q13.3. CONCLUSION: CMA is capable of detecting microdeletions and microduplications in fetuses with translocations detected by karyotyping analysis.

[The value of combined use of chromosomal karyotyping and chromosome microarray analysis for prenatal diagnosis].

OBJECTIVE: To assess the value of combined chromosomal karyotyping and chromosomal microarray analysis (CMA) for prenatal diagnosis. METHODS: G-banding karyotyping and CMA were simultaneously performed on 546 women who were subjected to amniocentesis during middle pregnancy. RESULTS: In total 82 cases were detected with chromosomal abnormalities. The two methods were consistent in 43 cases, which included 14 trisomy 21, 6 trisomy 18, 1 trisomy 13, 14 sex chromosomal aneuploidies, 4 chromosomal deletions, 3 chromosomal duplications and 1 sex chromosomal mosaicism. Fifteen fetuses with chromosomal abnormalities detected by CMA were missed by karyotyping analysis, which included 9 microdeletions and 6 microduplications. Sixteen fetuses with chromosomal abnormalities detected by karyotyping analysis were missed by CMA, which included 15 chromosomal translocations and 1 sex chromosomal mosaicism. In 7 cases, the results of karyotyping analysis and CMA were inconsistent. One supernumerary marker chromosome detected by karyotyping analysis was verified by CMA as 9p13.1p21.1 duplication. CONCLUSION: Combined chromosomal karyotyping and CMA can significantly improve the detection rate for chromosomal abnormalities, which has a great value for prenatal diagnosis.