Whole Exome Sequencing Identified a Stop-Gained Mutation in DYSF Gene Associated With Dysferlinopathy in an Iranian Family

Abstract

Introduction: Muscular dystrophy (MD) refers to a group of hereditary disorders characterized by progressive muscle degeneration, often caused by a deficiency or insufficient levels of glycoproteins in muscle cell membranes. Mutations in various genes lead to different types of MD, each with distinct clinical manifestations and inheritance patterns. The genetic heterogeneity of MD complicates the identification of the causative genes. Materials and Methods: This research was conducted to identify the genetic basis of MD in an Iranian family with three affected members. Whole exome sequencing (WES) was performed on a proband who had initially been misdiagnosed with polymyositis. Following the identification of the disease-causing variant via WES, cosegregation analysis was carried out among two affected siblings, the asymptomatic parents, and one unaffected sibling. Results: WES identified a homozygous nonsense variant (c.6001C>T, p.Gln2001Ter) in Exon 53 of the DYSF gene, which encodes dysferlin, a transmembrane protein essential for membrane protection and repair following damage. This stop-gain mutation results in a nonfunctional truncated protein lacking the transmembrane helix, preventing its anchorage to the membrane. Dysfunction of dysferlin is associated with limb-girdle muscular dystrophy 2B (LGMD2B) and Miyoshi myopathy. Discussion: Bioinformatics analyses and clinical findings confirmed the pathogenicity of this variant in a homozygous state, consistent with autosomal recessive inheritance. Furthermore, structural modeling suggested that the mutation significantly disrupts the tertiary structure of dysferlin. Since the disorder onset in the proband and his two affected sisters began in the proximal limb muscles, the condition was classified as LGMD. The study highlights the diagnostic value of WES in accurately identifying disease-causing variants, offering substantial improvements in time and cost efficiency over conventional diagnostic procedures.

Keywords: DYSF; LGMD; WES; dysferlin; muscular dystrophy.

Figure 1

The pedigree of a family with three members diagnosed with myopathy. The filled black symbols represent affected individuals. The white symbols indicate members without any myopathy-related symptoms. The arrow indicates the proband of the family. Doubled lines show the occurrence of consanguineous marriage.

Figure 2

The tertiary structure of the dysferlin transmembrane protein, illustrating the spatial arrangement of its domains. (a) The figure highlights the location of a mutation within the C2 domain. (b) The functional domains of dysferlin are arranged from the N-terminal to the C-terminal as follows: seven C2 domains, three FerA domains, and one DysF domain. The detected mutation is located in the C2G domain near the C-terminal. The structure was predicted using AlphaFold and visualized with the VMD tool [38].

Figure 3

Sanger sequencing validation of c.6001C>T variant discovered by WES in Exon 53 of the DYSF gene. The chromatograms indicate the sequences of this variant relative to (a) proband, (b) father, (c) mother, affected sisters (d) V-5 and (e) V-7, and (f) unaffected sister. The position of nucleotide substitution is displaced by an arrow.