Granuloma formation in a patient with GNE myopathy: A case report

Beyond sialylation: Exploring the multifaceted role of GNE in GNE myopathy

Defects in sialic acid metabolism disrupt the sialylation of glycoproteins and glycolipids, contributing to a spectrum of diseases, including GNE myopathy (GNEM). This rare disorder is caused by mutations in the GNE gene that encodes for a bifunctional enzyme required for sialic acid biosynthesis, resulting in progressive muscle atrophy and weakness. There is no approved treatment for GNEM, and the number of affected individuals is underestimated. Although hyposialylation is considered the hallmark of GNEM, evidence showed lack of consistent correlation with GNEM severity and unveiled additional roles of GNE that contribute to the onset and/or progression of GNEM. Recent findings indicate that these mechanisms extend beyond glycosylation, encompassing cytoskeletal dynamics, oxidative stress, and muscle regeneration pathways. Understanding how GNE mutations result in a cascade of cellular and molecular dysregulations is crucial for developing targeted therapies aimed at improving the quality of life of patients. This review comprehensively examines GNEM's pathophysiology, clinical presentation, and therapeutic strategies, highlighting key findings on non-canonical GNE functions that account to GNEM clinical outcomes and emerging therapeutic targets. We propose future research directions to explore alternative target pathways that can ultimately support clinical development.

A case report: identification of a novel exon 1 deletion mutation in the GNE gene in a Chinese patient with GNE myopathy

RATIONALE

GNE myopathy is caused by mutations in the UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase(GNE) gene and is clinically characterized by progressive weakness and atrophy of the lower-limb muscles with quadriceps sparing. Nearly all GNE mutations that have been reported thus far in various ethnic populations around the world have been missense or nonsense mutations.

PATIENT CONCERNS

We describe the case of a 32-year-old woman with GNE myopathy. The patient presented with progressive weakness of the lower-limb muscles that had spread to her legs. Her serum creatine kinase level was higher than the normal range. Mild myogenic changes were detected in the tibialis anterior muscles on electromyography, and moderate fatty infiltration was observed in various lower-limb muscles on magnetic resonance imaging. Histopathological examination of a skeletal muscle biopsy specimen revealed variation in muscle fiber size, rimmed vacuoles, and disorganized intermyofibrillar networks. DNA sequencing testing revealed a compound heterozygous mutation consisting of a known mutation (c.620A > T in exon 3) and a novel (exon 1 deletion) mutation.

DIAGNOSES

Taken together, the clinical features, laboratory testing and DNA findings eventually made the diagnosis of GNE myopathy.

INTERVENTIONS AND OUTCOMES

Based on the diagnosis of the GNE myopathy, the patient was administered sialic acid 6 g a day for 1 year, and up to now, her symptoms did not progress further.

LESSONS

We have reported the case of a GNE myopathy patient with compound heterozygous GNE gene mutations. This case expands the genotypic spectrum of GNE myopathy.