The exclusion of individuals with learning or developmental disabilities may have further obscured the identification of cognitive endophenotypes, particularly in families with the C9orf72 repeat expansion, where ALS is increasingly viewed as a neurodevelopmental disorder.38 This is possibly reflected in the relatively low sampling of C9orf72 positive family members from C9orf72 families (n = 16/44, 36%). This evidence concerns the gene C9orf72 and neurodevelopmental disorder.