C9orf72 and immune system disorder: In order to explore our hypothesis, we compared C9orf72 repeat size, allele distribution and frequency with those observed in a historical cohort of genetically characterized patients with ALS (n = 93), harboring no C9orf72 pathogenic large expansions, without clinically defined disorders related to immune dysfunctions, mostly Caucasian and from the same geographical region (Lombardy, Italy) of COVID-19 patients.