Karyosequencing: Integrating Genome-Wide and Targeted Sequencing for Comprehensive Diagnosis of Lymphoproliferative Disorders

Introduction: Molecular diagnostic testing for lymphoproliferative disorders (LPDs) includes detection of clonal immunoglobulin (IG) and/or T cell receptor (TCR) rearrangements, translocations, copy number alterations (CNA) and somatic mutations. To date, laboratories still rely on subjective and labour-intensive technologies, e.g. karyotyping/FISH to detect complex genomic alterations. Whole Genome Sequencing (WGS) can detect all genomic alterations, but factors such as cost, computation/storage, DNA requirements and poor detection of clinically relevant subclonal mutations limits the routine implementation of WGS in clinical diagnostics. We have developed “KaryoSequencing” (KS), a novel approach that combines targeted deep-sequencing, using a targeted hybridisation capture NGS panel, for rare mutation and translocation detection with shallow WGS (sWGS) for genome wide copy number analysis, in a single test. Methods: KS was validated using 138 clinical samples from patients with acute lymphoblastic leukaemia (ALL) (n=46), chronic lymphocytic leukaemia (CLL) (n=46) and plasma cell myeloma (PCM) (n=46) samples from 3 UK laboratories. Samples underwent library preparation and hybridisation using the EuroClonality-NDC assay. A KS library for each sample was prepared by combining the pre-capture and post-capture libraries at an optimised ratio to enable high coverage (>500 x) at regions covered by the targeted panel while providing 0.5-1x coverage genome-wide. Forty-six KS libraries were pooled and sequenced per NovaSeq 6000 run, using a 200-cycle SP flow cell and a 100bp paired-end strategy. For analysis of targeted regions, somatic mutation calling was performed using VarDict and structural variants (rearrangements and translocations) were detected using ARResT/Interrogate. For analysis of large chromosomal copy number variation using sWGS, a modified version of QDNASeq/ACE with a window size of 50kb was performed. For sWGS analysis, bioinformatic exclusion of all target capture regions and panel-specific off-target regions was performed using a panel of 48 DNA samples from healthy individuals ran on the same KS protocol. Results: Analysis of genome-wide copy number by sWGS was concordant in 477 of 503 (95%) evaluable FISH tests, including precise detection of hyper and hypo-diploidy and other complex karyotypes. The performance of the targeted deep-sequencing component of the KS approach was assessed to ensure comparable performance to previously validated