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SUMMARYAmyotrophic lateral sclerosis (ALS) is a devastating progressive neurodegenerative disease that affects 1 in 400 people. Almost 40 genes have been associated with ALS, currently explaining about 15% of the ALS risk. These genes tend to cluster in certain disease pathways such as protein quality control, RNA metabolism and axonal function. Despite these advances, adequate treatments for ALS patients are still missing. In this study, we investigate the role of a newly discovered ALS gene, C21orf2, in ALS pathology. We show that C21orf2 is localized to the basal body of the primary cilium and plays an important role in ciliogenesis in vitro and in vivo. Knock down of C21orf2 also lowers cilia frequency and length in human iPSC-derived spinal motor neurons (sMNs). Furthermore, we show that intraflagellar transport is impaired, causing primary cilia to fail in transducing extracellular signals essential in the sonic hedgehog pathway. ALS-associated mutations in C21orf2 lead to loss of binding to centrosomal proteins, loss of proper localization at the basal body and hereby prevent C21orf2 from carrying out its normal function in cilia by loss-of-function. Finally, we confirm that sMNs derived from iPSCs from ALS patients with C21orf2 mutations display similar cilia dysfunction and have disturbed sonic hedgehog signaling. Collectively, our data reveal impaired cilia homeostasis as a novel disease mechanism at play in ALS, opening new avenues for further research.

BACKGROUND AND PURPOSE: With the advent of gene therapies for amyotrophic lateral sclerosis (ALS), the importance of gene testing in ALS is increasing. This will likely lead to the identification of new variants for which the pathogenicity is not established. We aimed to study the pathogenicity of a newly identified variant in superoxide dismutase 1 (SOD1). METHODS: Gene testing was performed using Sanger sequencing. SOD1 activity in erythrocytes was measured using spectrophotometry. Postmortem brain and spinal cord sections were stained with antibodies against phospho-TDP-43 and SOD1. RESULTS: We identified a novel c.416G>T (p.Gly139Val) mutation in SOD1, which caused a rapidly progressive respiratory onset form of ALS. The mutation resulted in a 50% drop of SOD1 activity. Postmortem examination confirmed the absence of TDP-43 pathology and displayed typical SOD1 inclusions in remaining motor neurons, confirming the pathogenic nature of the mutation. CONCLUSIONS: Novel variants of unknown pathogenicity will be identified as a result of a surge in gene testing in people with ALS. An in-depth study of a newly identified p.Gly139Val mutation in SOD1 confirmed the pathogenicity of this mutation. Future patients with this particular mutation should qualify for SOD1 silencing or editing therapies. ispartof: EUROPEAN JOURNAL OF NEUROLOGY vol:29 issue:4 pages:1279-1283 ispartof: location:England status: published