When compared with all control CSF samples (mean 1.1, s.d. 1.0, range 0.55–7.50), CSF:diluent ratios in sporadic ALS (P < 0.0001), symptomatic C9orf72 mutation carriers (P < 0.001) and presymptomatic C9orf72 mutation carriers (P = 0.008) were significantly higher (Holm–Bonferroni correction; Extended Data Table 1 and Extended Data Fig. 5). This evidence concerns the gene C9orf72 and amyotrophic lateral sclerosis.