Provided are human alpha-synuclein-specific autoantibodies as well as fragments, derivatives and variants thereof as well as methods related thereto. Assays, kits, and solid supports related to antibodies specific for α-synuclein are also disclosed. The antibody, immunoglobulin chain(s), as well as binding fragments, derivatives and variants thereof can be used in pharmaceutical and diagnostic compositions for α-synuclein targeted immunotherapy and diagnosis, respectively.