Evaluation of postmortem tissue of C9ORF72 ALS/FTD patients has identified a significant decrease in total C9ORF72 transcript levels (DeJesus-Hernandez et al., 2011; van Blitterswijk et al., 2015) and C9ORF72 protein levels (Waite et al., 2014; Frick et al., 2018) compared to healthy controls. Here, C9orf72 is linked to amyotrophic lateral sclerosis.