C9orf72 and amyotrophic lateral sclerosis: Penetrance by age was modestly higher among C9orf72 carriers presenting with pure ALS (median age of onset = 57.0 years of age, 95% CI: 56.0–58.0) compared to those presenting with pure FTD (median age of onset = 58.0 years of age, 95% CI: 57.0–60.0; Log-rank test = 4.4, p-value = 0.04; see Fig. 3B).