C9orf72 and amyotrophic lateral sclerosis: When evaluating the frequency of positive cryptic HDGFL2 signal (CSF:diluent ratio >1) in the cohort, sporadic ALS (19 of 44, 43.2%; P = 0.005), symptomatic C9orf72 mutation carrier (20 of 52, 38.5%; P = 0.010) and presymptomatic C9orf72 mutation carrier (16 of 44, 36.4%; P = 0.011) groups all had significantly higher frequencies of cryptic HDGFL2-positive individuals than the control group (nine of 62, 14.5%, Holm–Bonferroni correction; Extended Data Table 1).