Evangelista, Teresinha

Abstract GNE myopathy (GNEM) is a neuromuscular disorder caused by biallelic mutations in the gene GNE , which encodes a bifunctional enzyme essential for the biosynthesis of sialic acid. Despite extensive characterization, no effective therapies or validated biomarkers exist, and the molecular mechanisms driving disease pathology remain poorly understood. This study identifies the proteoglycan serglycin as a preliminary candidate biomarker in GNEM and investigates the mechanisms underlying its dysregulation. Proteomic analysis of serum samples from GNEM patients revealed reduced circulating serglycin levels. In contrast, increased intracellular serglycin was observed in GNE knockout and GNEM patient iPSC-derived myoblasts, suggesting impaired secretion and/or degradation. To investigate the basis of this accumulation, intracellular trafficking and autophagic pathways were examined. Proteomic profiling from HEK GNE knockout cells revealed alterations in pathways involved in membrane trafficking, Golgi function, and glycoprotein processing, consistent with broader disruptions in the secretory system that may impair serglycin export and contribute to its intracellular retention. In GNEM iPSC-derived myoblasts, serglycin overlapped with LAMP1-positive lysosomal compartments and the ER-phagy receptor FAM134B, suggesting association with lysosomal and ER-phagy related pathways. Functional assays further indicated impaired autophagic flux in mutant cells. Together, these findings support a model in which combined defects in secretion and autophagic clearance contribute to intracellular serglycin accumulation and reduced circulating levels. This study identifies serglycin as a potential circulating biomarker for GNEM and highlights dysregulation of secretory and degradative pathways as converging features of disease pathology.

AbstractValosin‐containing protein (VCP)‐associated multisystem proteinopathy (MSP) is a rare genetic disorder with abnormalities in the autophagy pathway leading to various combinations of myopathy, bone diseases, and neurodegeneration. Ninety percent of patients with VCP‐associated MSP have myopathy, but there is no consensus‐based guideline. The goal of this working group was to develop a best practice set of provisional recommendations for VCP myopathy which can be easily implemented across the globe. As an initiative by Cure VCP Disease Inc., a patient advocacy organization, an online survey was initially conducted to identify the practice gaps in VCP myopathy. All prior published literature on VCP myopathy was reviewed to better understand the different aspects of management of VCP myopathy, and several working group sessions were conducted involving international experts to develop this provisional recommendation. VCP myopathy has a heterogeneous clinical phenotype and should be considered in patients with limb‐girdle muscular dystrophy phenotype, or any myopathy with an autosomal dominant pattern of inheritance. Genetic testing is the only definitive way to diagnose VCP myopathy, and single‐variant testing in the case of a known familial VCP variant, or multi‐gene panel sequencing in undifferentiated cases can be considered. Muscle biopsy is important in cases of diagnostic uncertainty or lack of a definitive pathogenic genetic variant since rimmed vacuoles (present in ~40% cases) are considered a hallmark of VCP myopathy. Electrodiagnostic studies and magnetic resonance imaging can also help rule out disease mimics. Standardized management of VCP myopathy will optimize patient care and help future research initiatives.