In C9orf72+ tissue the average proportion of neurons containing nuclear RNA foci was 39% (range 21–63%); in three C9orf72− cases with ALS the average proportion of neurons containing foci-like staining was 1.6% (range 1.1–2.5%); in normal controls the average proportion of neurons containing foci-like staining was 1.4% (range 1.3–1.6%). Here, C9orf72 is linked to amyotrophic lateral sclerosis.