C9orf72 and amyotrophic lateral sclerosis: Although more frequent bulbar onset has been reported in C9orf72 ALS patients compared to ALS patients without a C9orf72 repeat expansion mutation [14,15,16], this is still debatable, because a recent multi-center prospective natural history study on C9orf72 ALS cases reported a higher rate of limb (54%) than bulbar (39%) onset [13].