In fact, knockdown of Arf6 blocked the enhanced Rac1 activation observed in induced pluripotent stem cell-derived motor neurons from ALS patients with C9ORF72 repeat expansion, and coexpression of Arf6T27N in C9ORF72-knockdown mouse motor neurons rescued the inhibitory effect of C9ORF72 knockdown on axonal elongation. Here, C9orf72 is linked to amyotrophic lateral sclerosis.