Objective. To determine if the co-presence of genetic polymorphisms related to ALS has additive effects on the course of the disease in a population-based cohort of Italian patients. Methods. The study population includes 1245 ALS patients identified through the Piemonte Register for ALS, diagnosed between 2007 and 2016 and not carrying SOD1, TARDBP and FUS mutations. Controls were 766 age, sex, and geographically matched Italian subjects. We considered UNC13A (rs12608932), CAMTA1 (rs2412208), SLC112A (rs407135) and ZNF512B (ZNF512B) polymorphisms, as well as ATXN2 polyQ intermediate repeats and C9ORF72 GGGGCC intronic expansion. Results. The variants in C9orf72 (p=0.016), ATXN2 (p<0.001) and UNC13A (p<0.001) were significantly related to survival in univariate analysis, while the other considered variants did not influence ALS outcome. However, in the Cox multivariable analysis, also CAMTA1 emerged to be independently related to survival. When assessing the interaction by pairs of genes, we found that the presence of both detrimental alleles/expansion was correlated with significantly shorter survival compared to subjects non-carrying both detrimental alleles/expansions. Each association of pairs of detrimental alleles was characterized by specific clinical phenotypes. Conclusions. We demonstrated that gene polymorphisms acting as genetic modifiers of ALS survival can act on their own or in unison. Overall, 54% of patients carried at least one detrimental common polymorphism or repeat expansion, highlighting the clinical impact of our findings. In addition, the identification of the synergic effects of modifier genes represents an essential clue for explaining ALS clinical heterogeneity and should be considered in designing and interpreting clinical trials.

Adriano Chio serves on scientific advisory boards for Mitsubishi Tanabe, Biogen, Roche, Denali Pharma, Cytokinetics, Lilly, and Amylyx Pharmaceuticals and has received a research grant from Biogen. Cristina Moglia, Antonio Canosa, Umberto Manera, Maurizio Grassano, Rosario Vasta, Francesca Palumbo, Salvatore Gallone, Maura Brunetti, Fabiola De Marchi, Clifton L. Dalgard, Ruth Chia, Gabriele Mora, Lucia Corrado, Sandra DAlfonso, Letizia Mazzini no disclosures. Dr Traynor holds the US, Canadian, and European patents on the clinical testing and therapeutic intervention for the hexanucleotide repeat expansion in C9orf72. Andrea Calvo has received a research grant from Cytokinetics.

This work was supported by the Italian Ministry of Health (Ministero della Salute, Ricerca Sanitaria Finalizzata, grant RF201602362405); the Progetti di Rilevante Interesse Nazionale program of the Ministry of Education, University and Research (grant 2017SNW5MB); the European Commission Health Seventh Framework Programme (FP7/20072013 under grant agreement 259867); the Horizon 2020 Programme (project Brainteaser under grant agreement 101017598); and the Joint Programme Neurodegenerative Disease Research (Strength, ALSCare and BrainMend projects), granted by Italian Ministry of Education, University and Research. This work was supported in part by the Intramural Research Programs of the National Institute on Aging (grant Z01-AG000949-02). This study was performed under the Department of Excellence grant of the Italian Ministry of University and Research to the Rita Levi Montalcini Department of Neuroscience, University of Torino, Italy, and to the Department of Health Sciences, University of Eastern Piedmont, Novara, Italy. The funders had no role in data collection or analysis and did not participate in writing or approving the manuscript.

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