Chromosomal abnormalities in recurrent spontaneous abortions: A retrospective study

Purpose: Evaluation of recurrent spontaneous abortions (RSA) can be challenging for a Obstetrician. In case of early first trimester abortions, chromosomal abnormalities can be identified as an important cause. We analysed the RSA cases followed up and diagnosed in the Genetic Clinic or Genetic Lab of 2 hospitals in the region. Methods: Those couples with 3 or more spontaneous abortions were included in the analysis. Karyotyping was one using standard protocol with G-banding and reporting as per ISCN guidelines. Results: Of 97 RSA couples, 20 showed chromosomal abnormalities, and 15 of these had balanced chromosomal rearrangements. The age ranged from 22 years to 37 years, and the median number of abortions was 4. Complex chromosomal rearrangement was seen in 2 couples, in one partner. The spectrum of chromosomal anomalies in couples with RSA is discussed here. Conclusions: Frequency of chromosomal abnormalities in RSA was higher in present study compared to previous studies. Reciprocal translocations were commonest abnormality.

The enrichment of breakpoints in late-replicating chromatin provides novel insights into chromoanagenesis mechanisms

The rise of pangenomic molecular assays allowed uncovering complex rearrangements named chromoanagenesis that were hypothesized to result from catastrophic shattering events. Constitutional cases have typically been reported individually preventing identification of common features and uncovering the mechanisms at play. We characterized 20 new chromoanagenesis and discovered yet undescribed features. While literature differentiates chromothripsis and its shattering event repaired through non-homologous end joining from chromoanasynthesis born to aberrant replicative processes, we identified shattered chromosomes repaired through a combination of mechanisms. In particular, three samples present with “rearrangement hubs” comprising a fragmented kilobase-long sequence threaded throughout the rearrangement.To assess the mechanisms at play, we merged our data with those of 20 published constitutional complex chromosomal rearrangement cases. We evaluated if the distribution of their 1032 combined breakpoints was distinctive using bootstrap simulations and found that breakpoints tend to keep away from haplosensitive genes suggesting selective pressure. We then compared their distribution with that of 13,310 and 468 breakpoints of cancer complex chromosomal rearrangements and constitutional simple rearrangement samples, respectively. Both complex rearrangement groups showed breakpoint enrichment in late replicating regions suggesting similar origins for constitutional and cancer cases. Simple rearrangement breakpoints but not complex ones were depleted from lamina-associated domains (LADs), possibly as a consequence of reduced mobility of DNA ends bound to lamina.The enrichment of breakpoints in late-replicating chromatin for both constitutional and cancer chromoanagenesis provides an orthogonal support to the premature chromosome condensation hypothesis that was put forward to explain chromoanagenesis.