Multimodal Sequencing and Reanalysis Approaches to End the Diagnostic Odyssey of Individuals with Suspected Rare Monogenic Diseases

Background/Objectives: Genomic testing has transformed rare-disease diagnostics, yet a substantial proportion of individuals remain without a molecular diagnosis even after short-read exome sequencing (SR-ES) or short-read genome sequencing (SR-GS) and repeated conventional analysis. Methods: To address this persistent gap, we evaluated a coordinated multimodal reanalysis framework for deeply investigated families with suspected monogenic disease. Six families (20 individuals; 8 affected individuals) that had remained unsolved after prior comprehensive testing were reviewed prospectively in weekly interdisciplinary case conferences over one year. Available data included SR-ES, SR-GS, long-read genome sequencing (LR-GS), RNA-seq, optical genome mapping, mobile-element analysis, and mitochondrial genome analysis. The goal was not to test a single modality in isolation, but to assess whether systematic escalation across complementary assays plus continued reinterpretation could improve case resolution. Results: Three families (50%) achieved a reportable molecular diagnosis, two (33%) yielded strong candidate findings requiring additional evidence, and one (17%) remained without a definitive new molecular diagnosis, although reinterpretation of a previously identified NOTCH3 variant provided a possible partial explanation. Resolved cases included compound-heterozygous variants in KLHL40, a 119 kb multi-exon deletion in TTN, and a recurrent insertion in RNU4-2. Candidate findings included biallelic NARS2 variants and a 1.3 kb intragenic deletion involving ZEB2. Functional transcriptomic analyses supported the KLHL40 and TTN diagnoses but did not demonstrate a splicing consequence for the candidate NARS2 intronic variant in cardiac tissue. Conclusions: This small pilot cohort is not intended to estimate general diagnostic yield, but it demonstrates that a coordinated multimodal framework can reveal different sources of added value, including structural variant discovery, orthogonal functional support, and reinterpretation of existing short-read data as knowledge evolves. These findings underscore that archived short-read exome and genome data can retain substantial diagnostic value years after initial testing, particularly when reanalyzed with updated pipelines, expanded disease gene knowledge, and orthogonal multimodal evidence. Adoption of iterative, team-based multimodal strategies may help resolve the most complex unsolved rare-disease cases.