C9orf72 and amyotrophic lateral sclerosis: Conversely, in Asia, the overall incidence of ALS is lower than Europe and North America but, interestingly, the total prevalence is only second to that of West Europe [6], which may be in part linked to genetic differences, such as the lower prevalence of the C9orf72 hexanucleotide repeat expansion in Asian countries [2, 12, 13].