Amphiphysin is associated with the cytoplasmic surface of synaptic vesicles. A subset of patients with stiff man syndrome who were also affected by breast cancer are positive for autoantibodies against this protein. Alternate splicing of this gene results in two transcript variants (Amphiphysin 1 and Amphiphysin 2) encoding different isoforms. Additional splice variants have been described, but their full length sequences have not been determined.