Clinical and molecular genetic analysis further delineates the phenotypic variability of POMT2-related limb girdle muscular dystrophy type R14

Abstract

Background The POMT2 gene, which encodes protein O-mannosyltransferase 2, is crucial for the initial stage of α-dystroglycan glycosylation. Mutations in POMT2 are responsible for severe congenital muscular dystrophies, such as Walker-Warburg syndrome, muscle-eye-brain disease, and limb-girdle muscular dystrophy R14 (LGMDR14). This article retrospectively analyzed the clinical, pathological and genetic data of three patients diagnosed with LGMDR14. Aberrant mRNA processing analysis was subsequently conducted to investigate the pathogenic mechanism of the mutation. We employed innovative bioinformatic techniques of molecular dynamics to assess the impact of identified POMT2 mutations on protein structure and function and sought to establish a connection between these variants and their phenotypic manifestations. Results Three LGMDR14 patients from unrelated Chinese families were recruited. Adult onset age and proximal muscle weakness were common in our patients. They all showed myopathic lesions on electromyography and decreased α-dystroglycan expression on muscle biopsy. One patient was found to have severe cardiomyopathy and mild cognitive impairment, highlighting the importance of monitoring both the heart and brain activity. Genetic sequencing revealed that patient 1 harbored compound heterozygous c.1006+1G>A and c.295C>T variants of the POMT2 gene, patient 2 harbored c.1261C>T and c.700_701insCT variants, and patient 3 harbored c.812C>T and c.170G>A variants. Among these mutations, the variants c.700_701insCT, c.812C>T and c.170G>A have never been reported before. RNA sequencing revealed that the c.1006+1G>A mutation could cause retention of the first 26 bp of intron 8 by inducing recognition of new donor splice sites. Pyrosequencing revealed that both the frameshift mutation c.700_701insCT and the splicing mutation c.1006+1G>A triggered nonsense-mediated mRNA decay. Molecular dynamics indicated that the c.1006+1G>A, c.700_701insCT and c.170G>A variants could generate truncated protein structures and change the stability and function of the POMT2 protein. Conclusions Our study summarizes the clinical and genetic characteristics of three newly diagnosed adult-onset LGMDR14 patients, expanding the genetic spectrum of POMT2mutations. Moreover, this study also broadens the understanding of the anomalous mRNA regulation of POMT2 caused by splicing mutations and introduces a new bionformatic method for predicting the effect of POMT2variants on protein structure using molecular dynamics.