Disclosed is a GAD65 mutant having a retained antigenicity to an autoantibody specific to pancreatic islet ß-cells and having thermal stability which is useful for early diagnosis of insulin-dependent diabetes mellitus. A GAD65 mutant having a thermal stability and an antigenicity can be produced by performing Error-prone PCR using a GAD65 gene as a template to give a random gene library, transforming a host microorganism with the library to express a protein, treating the protein with heating, and screening a protein based on the presence or absence of antigenicity to an autoantibody specific to pancreatic islet ß-cells to thereby yield the GAD65 mutant.
GLUTAMATE DECARBOXYLASE MUTANT