C9orf72 and amyotrophic lateral sclerosis: It is also evident that the MS-ALS cases with a C9orf72 repeat expansion described by Ismail et al. (2013) [63] are characterized by more rapid progression of the disease than occurs in patients with pure C9orf72-ALS, raising the hypothesis that penetrance and progression of the C9orf72 expansion may be affected by MS-associated neurodegeneration or neuroinflammation.