C9orf72 and amyotrophic lateral sclerosis: The C9ORF72 mutation has been reported in approximately 6.3% and 5.8% of sporadic ALS and FTD cases, respectively,13 and 33% of familial ALS cases.14 An association between the presence of C9ORF72 and cognitive impairment has been reported in some, but not all, ALS studies.15 16 It is unclear whether these differences may relate to varying prevalence of genetic modifiers such as TMEM106B and UNC13A.