The present invention relates to a method for diagnosing a disease comprising the step detecting in a sample comprising antibodies from a patient and also antibody binding to RGS8, a method for diagnosing a disease comprising the step detecting in a sample from a patient the level or activity of RGS8, a polypeptide comprising RGS8 or a variant thereof, a use of set polypeptide for the diagnosis of a disease, an antibody binding to RGS8, a use of the antibody for the diagnosis of the disease, a method for isolating an autoantibody binding to RGS8, a pharmaceutical composition or medical device comprising the polypeptide according to the present invention, a kit for the diagnosis of a disease comprising the polypeptide or the medical device according to the present invention and a use of the polypeptide, the antibody or the antibody for the manufacture of a kit or medical device.