A Next Generation Sequencing (NGS)-based approach to diagnosing Algerian patients with suspected Inborn Errors of Immunity (IEIs)

Abstract

The advent of next-generation sequencing (NGS) technologies has greatly expanded our understanding of both the clinical spectra and genetic landscape of inborn errors of immunity (IEIs). As history has shown and recent large-scale studies of monogenic risk for severe COVID have confirmed, endogamous populations may be enriched for unique, ancestry-specific disease-causing variants as a consequence of geography and/or culture. From a diagnostic perspective, this consideration may significantly impact molecular testing and analysis strategies. Herein, we report on the diagnostic yield of a 2-step NGS-based testing approach beginning with targeted gene panels (TGPs) and reflexing to whole exome sequencing (WES) if negative for Northwest Algerian patients with suspected IEIs. A total of fourteen families were screened using TGPs tailored to their IEI subtypes of common variable immunodeficiency (CVID), inflammatory bowel disease (IBD) or chronic mucocutaneous candidiasis (CMC)-hyperIgE syndrome (HIES), resulting in a total of four definitive or highly likely molecular diagnoses (29% yield). Subsequent application of WES to eight of the ten remaining unsolved cases yielded an additional four diagnoses, giving a 57% overall yield. At least two additional individuals were found to harbor suggestive candidate variants on exome warranting further investigation, while others carried candidate variants or known risk alleles likely contributing to their clinical findings. Only in one patient’s case did we fail to identify any viable potential candidates. By achieving diagnostic yields comparable to those currently quoted for application of short-read NGS to IEI detection, our study demonstrates the viability of a 2-step NGS-based testing strategy in a selected endogamous population. Data from our localized cohort also showed some similarities and differences from NGS studies performed on larger regional IEI cohorts. Finally, our results also highlight many short-comings currently inherent to the application of genomics for clinical IEI diagnostics. Not only does the global community need to address ongoing inequities in representation, access, and infrastructure, but the ability to obtain precise and detailed clinical data remains paramount for achieving diagnostic certainty in the face of complex genotype-phenotype relationships.