Mutation update: the spectra of nebulin variants and associated myopathies

Abstract

A mutation update on the nebulin gene (NEB) is necessary because of recent developments in analysis methodology, the identification of increasing numbers and novel types of variants, and a widening in the spectrum of clinical and histological phenotypes associated with this gigantic, 183 exons containing gene. Recessive pathogenic variants in NEB are the major cause of nemaline myopathy (NM), one of the most common congenital myopathies. Moreover, pathogenic NEB variants have been identified in core-rod myopathy and in distal myopathies. In this update, we present the disease-causing variants in NEB in 159 families, 143 families with NM, and 16 families with NM-related myopathies. Eighty-eight families are presented here for the first time. We summarize 86 previously published and 126 unpublished variants identified in NEB. Furthermore, we have analyzed the NEB variants deposited in the Exome Variant Server (http://evs.gs.washington.edu/EVS/), identifying that pathogenic variants are a minor fraction of all coding variants (∼7%). This indicates that nebulin tolerates substantial changes in its amino acid sequence, providing an explanation as to why variants in such a large gene result in relatively rare disorders. Lastly, we discuss the difficulties of drawing reliable genotype-phenotype correlations in NEB-associated disease.

Keywords: NEB; actin-myosin; nebulin; nemaline (rod) myopathy; sarcomere.

Figure 1

Different types of variants in NEB. The distribution of 212 different NEB variants identified in this study cohort of 159 families.

Figure 2

Clinical entities caused by variants in NEB. The different forms of NM and their incidence in this study cohort of 159 families. Unspecified NM, clinical data were not available. NM related, families with distal myopathy without nemaline rods, distal forms of NM, core myopathy, distal form of core-rod myopathy, and fetal akinesia/lethal multiple pterygium syndrome.