Targeted Next-Generation Sequencing in a Large Cohort of Genetically Undiagnosed Patients with Neuromuscular Disorders in Spain.

L González-Quereda ,Eduard Gallardo,Pau Riera,Daniel Natera-De Benito,Miren Zulaica,Isabel Llano,C Ortez ,Marí­a José Rodrí­guez ,Jorge Alonso‐Pérez ,Ivonne Jericó ,Jordi Díaz‐Manera ,José C Milisenda ,A Nascimento ,Laura González-Mera ,Juan José Poza ,Montse Olivé ,Laura Torné ,Aurora Sánchez ,Glòria Garrabou ,Marcos Madruga‐Garrido ,Adolfo López De Munaín ,P Gallano

doi:10.3390/genes11050539

Abstract

The term neuromuscular disorder (NMD) includes many genetic and acquired diseases and differential diagnosis can be challenging. Next-generation sequencing (NGS) is especially useful in this setting given the large number of possible candidate genes, the clinical, pathological, and genetic heterogeneity, the absence of an established genotype-phenotype correlation, and the exceptionally large size of some causative genes such as TTN, NEB and RYR1. We evaluated the diagnostic value of a custom targeted next-generation sequencing gene panel to study the mutational spectrum of a subset of NMD patients in Spain. In an NMD cohort of 207 patients with congenital myopathies, distal myopathies, congenital and adult-onset muscular dystrophies, and congenital myasthenic syndromes, we detected causative mutations in 102 patients (49.3%), involving 42 NMD-related genes. The most common causative genes, TTN and RYR1, accounted for almost 30% of cases. Thirty-two of the 207 patients (15.4%) carried variants of uncertain significance or had an unidentified second mutation to explain the genetic cause of the disease. In the remaining 73 patients (35.3%), no candidate variant was identified. In combination with patients’ clinical and myopathological data, the custom gene panel designed in our lab proved to be a powerful tool to diagnose patients with myopathies, muscular dystrophies and congenital myasthenic syndromes. Targeted NGS approaches enable a rapid and cost-effective analysis of NMD- related genes, offering reliable results in a short time and relegating invasive techniques to a second tier.

Highlights

Neuromuscular disorders (NMD) is an umbrella term for genetic and acquired diseases that have traditionally been classified as primary disorders of the muscle, neuromuscular transmission disorders, or primary disorders of the peripheral motor neuron
Causative mutations were detected in 102 of the 207 patients (49.3%), involving 42 different
We implemented a diagnostic strategy within a routine genetic diagnostic procedure by using a custom next-generation sequencing-based panel directed to several neuromuscular diseases

Summary

Introduction

Neuromuscular disorders (NMD) is an umbrella term for genetic and acquired diseases that have traditionally been classified as primary disorders of the muscle (myopathies and muscular dystrophies), neuromuscular transmission disorders (myasthenia and myasthenic syndromes), or primary disorders of the peripheral motor neuron (spinal muscular atrophies and neuropathies). Myopathy and muscular dystrophy are broad terms that encompass many diseases in which the muscle fibers do not function properly. These diseases are usually characterized by degeneration of the skeletal muscles or structural abnormalities of the muscle fiber causing generalized muscle weakness and motor disability [2]. Congenital myopathies (CM) present specific structural changes in the muscle fiber, such as cores, nemaline bodies and central nuclei [5], distinguished by histochemistry and electron microscopy

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