A novel mutation of Myotilin is associated with muscular dystrophy and postoperative respiratory failure

Mutations of myotilin (MYOT) have been identified in patients with muscular dystrophy. We identified a novel mutation (NM_006790: c.849G>A/p.W283X) of MYOT in a family with muscular dystrophy and postoperative respiratory failure. Functional studies revealed that the mutation led to a truncated protein, as the molecular weight was smaller, the expression level was reduced and the distribution of MYOT was altered. The Myotilin (MYOT) gene encodes a cystoskeletal protein and is located on chromosome 5q31.2. It consists of 10 exons spanning ∼19.9 kb.1 Previous studies have indicated that MYOT, which binds to F-actin and crosslinks actin filaments, plays a crucial role in the stability of thin filaments during muscle contraction and prevents latrunculin A-induced filament disassembly.1,2 In 2000, Hauser et al.3 first identified a pathogenic mutation in a large North American family of German descent expressing an autosomal dominant form of limb-girdle muscular dystrophy. After that, ∼21 mutations were detected in patients with multiple diseases, including myofibrillar myopathy, myotilinopathy, spheroid body myopathy, sudden arrhythmic death syndrome and abnormality of the nervous system. Here, we enrolled a Chinese family from Hunan Province, China (Figure 1A). Blood was obtained from eight family members, including three affected individuals. The proband (III-4), a 21-year-old female, was admitted to our hospital and underwent arthroscopy of the left patellar dislocation and reconstruction of the medial patellar ligament due to recurrent patellar dislocation of the left knee after general anesthesia. The patient presented with decreased oxygen saturation and respiratory muscle weakness after surgery. Via emergency rescue with tracheal intubation and assisted respiration, her oxygen saturation levels were normal with clear consciousness. However, her muscle tone was slightly poor. Multidisciplinary consultation preliminarily determined that the patient had slight muscular dystrophy. A family history survey indicated that her grandfather (I-1) suffered from paralysis before death. Her mother (II-3) presented with limb myasthenia two years prior. The electromyogram (EMG) of the proband was normal. For the proband’s mother, the nerve conduction velocity was normal, but EMG showed myogenic damage (Supplementary Table S1). The genetic analysis of the family. (A) Pedigree of the family. White circles/squares are unaffected, arrow indicates the proband. (B) Sanger DNA sequencing chromatogram demonstrates the heterozygosity for a MYOT nonsense mutation (c.849G>A/p.W283X) in the affected patients. (C) THE CONSURF SERVER program analyzed the evolutionary conservation profiles of MYOT protein. The site p. W283 was located in the conserved site and marker by red arrow. (D) Western blot analyzed the protein molecular weight and expression levels of transfected MYOT (HIS) from HSkMCs transfected with WT or mutated (p.W283X) plasmids. (E) The statistical results of MYOT in western blot. ***P < 0.001. (F) Immunofluorescence analyzed the distribution of transfected MYOT (HIS) in HSkMCs transfected with WT or mutated (p.W283X) plasmids. The arrow indicates the cells transfected the plasmids successfully. Whole exome sequencing was performed to explore the genetic profile of the patient. After data filtering, a novel nonsense mutation (NM_006790: c.849G>A/p.W283X) in MYOT was detected in the patient. Sanger sequencing further validated that the novel mutation was present in the proband and her mother (Figure 1B). The novel mutation, resulting in the truncation of the MYOT protein, was located in a highly evolutionarily conserved site (Figure 1C). The wild-type (WT) and mutated (p.W283X) MYOT CDS with an N-terminal HIS-tag in pEnter were designed and transfected into the human skeletal muscle cells (HSkMCs). Western blot analysis showed that the p. W283X mutation resulted in a truncated MYOT. The molecular weight was smaller, and its expression level was lower than that in cells transfected with the WT plasmid (Figure 1D and E). Immunofluorescence analysis showed that the novel mutation changed the distribution of MYOT in HSkMCs (Figure 1F). The relationship between MYOT mutations and multiple muscle diseases has been established. However, respiratory muscle damage in adults has rarely been reported in MYOT mutation carriers. The MYOT protein contains a serine-rich N-terminal region and a C-terminal tail. The N-terminal region consists of a hydrophobic stretch and two Ig-like domains.4 As a part of the Z-disc, MYOT can interact with several proteins, including α-actinin, actin and filamin C.5 The novel mutation (p.W283X) may lead to the deletion of two Ig-like domains and the C-terminal tail in MYOT, which may disrupt the function of the Z-disc. According to ACMG guidelines,6 the novel mutation is pathogenic (PVS1 + PS3 + PM2 + PM4 + PP1 + PP3). In summary, we identified a novel mutation (NM_006790: c.849G>A/p.W283X) in MYOT in a Chinese family with muscular dystrophy and postoperative respiratory failure. Functional studies further confirmed the harmfulness of the mutation. Our study may establish the relationship between MYOT mutations and respiratory muscle damage and expand the mutation and phenotype spectrum of MYOT. These findings may contribute to the genetic consultation of patients with muscular dystrophy and emphasize the need for potential disease diagnosis before general anesthesia. Supplementary material is available at QJMED online. This study was supported by the National Natural Science Foundation of China (82000427) and the National Natural Science Foundation of Hunan province (2023JJ20078). Ning Li (Data curation [lead], Methodology [lead], Validation [lead], Writing—original draft [equal]), Zhao-Jing Lin (Formal analysis [lead], Methodology [equal], Writing—original draft [equal]), Liang-Liang Fan (Conceptualization [lead], Funding acquisition [lead], Writing—review & editing [equal]), Jun-Mei Xu (Investigation [equal], Resources [equal]), and Rong Yu (Conceptualization [equal], Funding acquisition [equal], Writing—review & editing [equal]) The studies involving human participants were reviewed and approved by the Ethics Committee of the Second Xiangya Hospital of Central South University. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article. The authors declare that they have no conflict of interest.