RAB5A and amyotrophic lateral sclerosis: Thus the correlation between vesicle trafficking defects and ALS is obvious since the affected gene for familial ALS2 Alsin was found to encode a guanine-nucleotide exchange factor for the vesicle traffic associated protein Rab5 [16,17] and ALS8 encodes the vesicle associated membrane protein B (VAPB, [18]).