GAD1 and type 1 diabetes mellitus: Over the last few decades, several study screening general population or families at risk showed that the clinical onset of T1D is preceded by a long pre-symptomatic phase characterized by the appearance of islet specific autoantibodies, including antibodies to GAD (GADA), insulin (IAA), IA-2 (IA-2A) and ZnT8 (ZnT8A), indicating that the measurement of islet autoantibodies is the most effective tool for identifying individuals at risk and stage pre-symptomatic T1D, ideal for screening purposes [4].