To retrospectively review the diagnostic odyssey for 247 families ascertained over 2012-2022 with inherited neuromuscular conditions and triaged into research-led genomic testing.  To quantify diagnostic yield from parallel DNA sequencing modalities (targeted-capture gene panel, exome, genome), additional diagnoses secured through auxiliary RNA and protein investigations, to define an optimised diagnostic algorithm to maximise diagnostic yield in NMD.

Adoption of massively parallel sequencing (MPS) has transformed the diagnostic landscape for inherited neuromuscular disorders (NMDs). As genomic and transcriptomic technologies accelerate, there is a widening gap in clinical guidelines mapping their optimal integration into the diagnostic pathway.

Integration of MPS and a suite of functional genomics investigations has diagnosed 62% (152/247) involving 67 known NMD genes, 6 novel disease genes and one novel class of pathogenic splicing variant.

45% (69/152) of total diagnoses required post-exome investigations.  Arrestingly, novel disease genes account for only 4% (6/152) of diagnoses whereas 39% of diagnoses (59/152) involve at least one splice-altering or structural variant. Protein studies quantifying a measurable decrement in the gene product supported 18% (27/152) diagnoses.

The key lesson is simple: “go back to where you think the problem (gene) is and have a really good look.”  Expert clinical phenotyping remains of profound importance to target scrutiny of all rare, coding and non-coding variation in phenotypically consistent genes.  We emphasise diagnoses due to splice-altering or structural variants in known NMD genes outnumber diagnoses involving novel genes or phenotypes by 7-fold. With contemporary NMD gene lists, modern-day exomic sequencing (+/- 50 intronic bases) would identify 85% of causal variants.   We provide a diagnostic algorithm recommending optimised deployment of different investigations to most effectively and expeditiously reach the same diagnoses.