Detection of cryptic balanced chromosomal rearrangements using high-resolution optical genome mapping

Chromosomal rearrangements have profound consequences in diverse human genetic diseases. Currently, the detection of balanced chromosomal rearrangements (BCRs) mainly relies on routine cytogenetic G-banded karyotyping. However, cryptic BCRs are hard to detect by karyotyping, and the risk of miscarriage or delivering abnormal offspring with congenital malformations in carrier couples is significantly increased. In the present study, we aimed to investigate the potential of single-molecule optical genome mapping (OGM) in unravelling cryptic chromosomal rearrangements.

Eleven couples with normal karyotypes that had abortions/affected offspring with unbalanced rearrangements were enrolled. Ultra-high-molecular-weight DNA was isolated from peripheral blood cells and processed via OGM. The genome assembly was performed followed by variant calling and annotation. Meanwhile, multiple detection strategies, including FISH, long-range-PCR amplicon-based next-generation sequencing and Sanger sequencing were implemented to confirm the results obtained from OGM.

High-resolution OGM successfully detected cryptic reciprocal translocation in all recruited couples, which was consistent with the results of FISH and sequencing. All high-confidence cryptic chromosomal translocations detected by OGM were confirmed by sequencing analysis of rearrangement breakpoints. Moreover, OGM revealed additional complex rearrangement events such as inverted aberrations, further refining potential genetic interpretation.

To the best of our knowledge, this is the first study wherein OGM facilitate the rapid and robust detection of cryptic chromosomal reciprocal translocations in clinical practice. With the excellent performance, our findings suggest that OGM is well qualified as an accurate, comprehensive and first-line method for detecting cryptic BCRs in routine clinical testing.