Novel POMT2 variants associated with limb-girdle muscular dystrophy R14: genetic, histological and functional studies.

BACKGROUND: The POMT2 gene, which encodes protein O-mannosyltransferase 2, is essential for α-dystroglycan glycosylation. Variants in POMT2 cause various disorders, including the relatively rare presentation of limb-girdle muscular dystrophy R14 (LGMDR14). METHODS: This study retrospectively analyzed the clinical, pathological, and genetic data of three LGMDR14 patients. And we investigated the pathogenic mechanisms of POMT2 variants through aberrant mRNA processing analysis and molecular dynamics simulations to assess their impact on protein structure and function. RESULTS: We recruited three LGMDR14 patients from unrelated Chinese families, all presenting with adult-onset proximal muscle weakness. All of these patients showed a myopathic pattern on electromyography and decreased α-dystroglycan expression on muscle biopsy. One patient had severe cardiomyopathy and mild cognitive impairment. Genetic sequencing revealed compound heterozygous variants in the POMT2 gene in all three patients: c.1006 + 1G > A and c.295 C > T in patient 1, c.1261 C > T and c.700_701insCT in patient 2, and c.812 C > T and c.170G > A in patient 3. Variants c.700_701insCT, c.812 C > T, and c.170G > A are novel. Splicing and cDNA analysis revealed that the c.1006 + 1G > A variant could cause retention of the first 26 bp of intron 8 by inducing recognition of new donor splice sites. Pyrosequencing revealed that both frameshift variant c.700_701insCT and splicing variant c.1006 + 1G > A triggered a nonsense-mediated mRNA decay. Molecular dynamics indicated that c.1006 + 1G > A, c.700_701insCT, and c.170G > A variants could lead to truncated proteins, altering stability and function. CONCLUSIONS: Our study summarizes the clinical, pathological and genetic characteristics of three adult-onset LGMDR14 patients, expanding the genetic spectrum of POMT2 variants. Moreover, the finding reinforces the impact of POMT2 splicing defects on mRNA regulation, and molecular dynamics simulations predict the structural consequences of POMT2 variants, providing additional evidence for their functional effects.