A Homozygous Deep Intronic Mutation Alters the Splicing of Nebulin Gene in a Patient With Nemaline Myopathy.

Nathalie Laflamme,Serge Rivest,Nicolas Chrestian,Baiba Lace,Samarth Thonta Setty,Arnaud Droit,Yvan Labrie,Nadie Rioux

doi:10.3389/fneur.2021.660113

Abstract

Nemaline myopathy is a rare disorder affecting the muscle sarcomere. Mutations in nebulin gene (NEB) are known to be responsible for about 50% of nemaline myopathy cases. Nebulin is a giant protein which is formed integrally with the sarcomeric thin filament. This complex gene is under extensive alternative splicing giving rise to multiple isoforms. In this study, we report a 6-year-old boy presenting with general muscular weaknesses. Identification of rod-shaped structures in the patient' biopsy raised doubt about the presence of a nemaline myopathy. Next-generation sequencing was used to identify a causative mutation for the patient syndrome. A homozygous deep intronic substitution was found in the intron 144 of the NEB. The variant was predicted by in silico tools to create a new donor splice site. Molecular analysis has shown that the mutation could alter splicing events of the nebulin gene leading to a significant decrease of isoforms level. This change in the expression level of nebulin could give rise to functional consequences in the sarcomere. These results are consistent with the phenotypes observed in the patient. Such a discovery of variants in this gene will allow a better understanding of the involvement of nebulin in neuromuscular diseases and help find new treatments for the nemaline myopathy.

Highlights

Nemaline myopathies (NM) are a rare form of early-onset myopathy presenting at birth or early childhood with generalized muscle weaknesses and hypotonia
We present a novel variant in the NEB gene of a young boy with nemaline myopathy
Variants were analyzed through PRISMES’s pipeline. Both PRISMES and clinical genetic analysis have identified a novel homozygous mutation NM_001271208.1: c.21522+119C>G in the intron 144 of NEB gene, which positively segregates in a family

Summary

Introduction

Nemaline myopathies (NM) are a rare form of early-onset myopathy presenting at birth or early childhood with generalized muscle weaknesses and hypotonia. The spectrum of clinical phenotypes is wide, ranging from severe, intermediate, and typical congenital form to mild childhood or juvenile onset form. Presence of nemaline bodies observed in muscle histopathological biopsy of affected individuals are characteristics that are sometimes found in NM [3,4,5]. These rod-like structures derive mainly from sarcomeric Z disc aggregates and thin filament proteins which are made visible by Gömöri trichrome staining [6].

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