Genetic alterations of VWA1: a new link between extracellular matrix and neuromuscular diseases

Proteomic studies in VWA1-related neuromyopathy allowed new pathophysiological insights and the definition of blood biomarkers

Bi-allelic variants in VWA1, encoding Von Willebrand Factor A domain containing 1 protein localized to the extracellular matrix (ECM), were linked to a neuromuscular disorder with manifestation in child- or adulthood. Clinical findings indicate a neuromyopathy presenting with muscle weakness. Given that pathophysiological processes are still incompletely understood, and biomarkers are still missing, we aimed to identify blood biomarkers of pathophysiological relevance: white blood cells (WBC) and plasma derived from six VWA1-patients were investigated by proteomics. Four proteins, BET1, HNRNPDL, NEFM and PHGDH, known to be involved in neurological diseases and dysregulated in WBC were further validated by muscle-immunostainings unravelling HNRNPDL as a protein showing differences between VWA1-patients, healthy controls and patients suffering from neurogenic muscular atrophy and BICD2-related neuromyopathy. Immunostaining studies of PHGDH indicate its involvement in apoptotic processes via co-localisation with caspase-3. NEFM showed an increase in cells within the ECM in biopsies of all patients studied. Plasma proteomics unravelled dysregulation of 15 proteins serving as biomarker candidates among which a profound proportion of increased ones (6/11) are mostly related to antioxidative processes and have even partially been described as blood biomarkers for other entities of neuromuscular disorders before. CRP elevated in plasma also showed an increase in the extracellular space of VWA1-mutant muscle. Results of our combined studies for the first time describe pathophysiologically relevant biomarkers for VWA1-related neuromyopathy and suggest that VWA1-patient derived blood might hold the potential to study disease processes of clinical relevance, an important aspect for further preclinical studies.

Upper motor neuron signs and early onset gait abnormalities in young children with bi-allelic VWA1 variants

Bi-allelic loss-of-function variants in Von Willebrand factor type A (VWA1) were recently discovered to lead to an early onset motor neuropathy or neuromyopathy. What makes this discovery particularly notable is the high frequency of one of the VWA1 (NM_022834.5) founder variants, c.62_71dup (p.Gly25ArgfsTer74), which nears 0.01% in European populations, and suggests that there may be a wide spectrum of disease features and severity. Here, we report two cases from nonconsanguineous families in North America that presented in early childhood with lower extremity weakness and prominent foot deformities, and were found to carry bi-allelic variants in VWA1. We draw focus to upper motor neuron signs and abnormal gait phenotypes as presenting symptoms in VWA1-related disorder and expand the clinical and molecular spectrum.

Hereditary motor neuropathies

PURPOSE OF REVIEW

Distal hereditary motor neuropathies (dHMN) are a clinically and genetically diverse group of disorders that are characterized by length-dependent axonal degeneration of lower motor neurons. In this review, we will provide an overview of dHMN, and we will correlate the distinct clinical subtypes with their causative genes, focusing on the most recent advances in the field.

RECENT FINDINGS

Despite the massive use of new-generation sequencing (NGS) and the discovery of new genes, only a third of dHMN patients receive a molecular diagnosis. Thanks to international cooperation between researchers, new genes have been implicated in dHMN, such as SORD and VWA1 . Mutations in SORD are the most frequent cause of autosomal recessive forms of dHMN. As a result of these findings, the potential benefits of some pharmacological compounds are being studied in cell and animal models, mainly targeting axonal transport and metabolic pathways.

SUMMARY

Despite the wide use of NGS, the diagnosis of dHMN remains a challenge. The low prevalence of dHMN makes international cooperation necessary in order to discover new genes and causal mechanisms. Genetic diagnosis of patients and identification of new pathomechanism are essential for the development of therapeutical clinical trials.