Next generation sequencing panel as an effective approach to genetic testing in patients with a highly variable phenotype of neuromuscular disorders.

Neuromuscular disorders (NMDs) include a wide range of diseases affecting the peripheral nervous system. The genetic diagnoses are increasingly obtained with using the next generation sequencing (NGS). We applied the custom-design targeted NGS panel including 89 genes, together with genotyping and multiplex ligation-dependent probe amplification (MLPA) to identify a genetic spectrum of NMDs in 52 Polish patients. As a result, the genetic diagnosis was determined by NGS panel in 29 patients so its diagnostic utility is estimated at 55.8%. The most pathogenic variants were found in CLCN1, followed by CAPN3, SCN4A, and SGCA genes. Genotyping of myotonic dystrophy type 1 and 2 (DM1 and DM2) as a secondary approach has been performed. The co-occurrence of CAPN3 and CNBP mutations in one patient as well as DYSF and CNBP mutations in another suggests possibly more complex inheritance as well as expression of a phenotype. In 7 individuals with single nucleotide variant found in NGS testing, the MLPA of the CAPN3 gene was performed detecting the deletion encompassing exons 2-8 in the CAPN3 gene in one patient, confirming recessive limb-girdle muscular dystrophy type 1 (LGMDR1). Thirty patients obtained a genetic diagnosis (57.7%) after using NGS testing, genotyping and MLPA analysis. The study allowed for the identification of 27 known and 4 novel pathogenic/likely pathogenic variants and variants of uncertain significance (VUS) associated with NMDs.In conclusion, the diagnostic approach with diverse molecular techniques enables to broaden the mutational spectrum and maximizes the diagnostic yield. Furthermore, the co-occurrence of DM2 and LGMD has been detected in 2 individuals.