C9orf72 and mild neurocognitive disorder: Strengthening this assumption, Behler et al. (2021) (which was not included in this review due to the lack of inclusion of a symptomatic MND group) observed that asymptomatic C9orf72 carriers made more antisaccade errors than healthy controls (non-gene carriers), thus, suggesting that antisaccade task metrics may serve as a useful indicator of specific cognitive functions in the asymptomatic/earliest stages of MND.