VAPB Vesicle-associated membrane protein (VAMP)-associated protein B (aka VAPB) is a type IV transmembrane protein and belongs to the VAP family of proteins. VAPB may have a role in vesicle trafficking. VAPB is found in plasma and intracellular vesicle membranes as a homodimer and heterodimer with VAPA, and interacts with VAMP1 and VAMP2. VAPB defects are the basis for the amyotrophic lateral sclerosis type 8 and spinal muscular atrophy autosomal dominant Finkel type.