Abstract: A method for the diagnosis of Type 1 diabetes, or a predisposition towards Type 1 diabetes, or to monitor the efficacy of a therapy to prevent or treat Type 1 diabetes, said method comprising contacting a sample from a subject with a reagent selected from Tetraspanin-7 or a fragment, or a modified form thereof, and detecting an interaction indicative of the presence of an autoimmune response to Tetraspanin-7. Tetraspanin-7 is now understood to be the protein recognised by Glima 38 specific antibodies. Reagents and kits for use in the method and therapies associated with these form further aspects of the invention.