Analytical and clinical performance of chromosomal microarrays compared with FISH panel and conventional karyotyping in patients with chronic lymphocytic leukemia

Analysis of complex chromosomal rearrangement involving chromosome 6 via the integration of optical genomic mapping and molecular cytogenetic methodologies

Complex chromosomal rearrangements (CCRs) can result in spontaneous abortions, infertility, and malformations in newborns. In this study, we explored a familial CCR involving chromosome 6 by combining optical genomic mapping (OGM) and molecular cytogenetic methodologies. Within this family, the father and the paternal grandfather were both asymptomatic carriers of an identical balanced CCR, while the two offspring with an unbalanced paternal-origin CCR and two microdeletions presented with clinical manifestation. The first affected child, a 5-year-old boy, exhibited neurodevelopmental delay, while the second, a fetus, presented with hydrops fetalis. SNP-genotype analysis revealed a recombination event during gamete formation in the father that may have contributed to the deletion in his offspring. Meanwhile, the couple's haplotypes will facilitate the selection of normal gametes in the setting of assisted reproduction. Our study demonstrated the potential of OGM in identifying CCRs and its ability to work with current methodologies to refine precise breakpoints and construct accurate haplotypes for couples with a CCR.

High-resolution structural variant profiling of myelodysplastic syndromes by optical genome mapping uncovers cryptic aberrations of prognostic and therapeutic significance

Chromosome banding analysis (CBA) remains the standard-of-care for structural variant (SV) assessment in MDS. Optical genome mapping (OGM) is a novel, non-sequencing-based technique for high-resolution genome-wide SV profiling (SVP). We explored the clinical value of SVP by OGM in 101 consecutive, newly diagnosed MDS patients from a single-center, who underwent standard-of-care cytogenetic and targeted NGS studies. OGM detected 383 clinically significant, recurrent and novel SVs. Of these, 224 (51%) SVs, seen across 34% of patients, were cryptic by CBA (included rearrangements involving MECOM, NUP98::PRRX2, KMT2A partial tandem duplications among others). SVP decreased the proportion of normal karyotype by 16%, identified complex genomes (17%), chromothripsis (6%) and generated informative results in both patients with insufficient metaphases. Precise gene/exon-level mapping allowed assessment of clinically relevant biomarkers (TP53 allele status, KMT2A-PTD) without additional testing. SV data was complementary to NGS. When applied in retrospect, OGM results changed the comprehensive cytogenetic scoring system (CCSS) and R-IPSS risk-groups in 21% and 17% patients respectively with an improved prediction of prognosis. By multivariate analysis, CCSS by OGM only (not CBA), TP53 mutation and BM blasts independently predicted survival. This is the first and largest study reporting the value of combined SVP and NGS for MDS prognostication.