C9orf72 and amyotrophic lateral sclerosis: Nonetheless, when it is accompanied with an additional cellular protein stressor, in this case, the overexpression of Ataxin2, a protein with polyglutamine expansions (~30) and a risk factor for ALS, C9ORF72 deficiency was toxic for motor neurons in culture and led to motor dysfunction in zebrafish (Sellier et al., 2016).