GAD1 and type 2 diabetes mellitus: In the UK, all children with negative GAD, IA2 and ZnT8 islet autoantibodies and detectable C-peptide and adults diagnosed <35 years with >20% prior probability of MODY are recommended to have genetic testing (25) with the aim of identifying the majority of patients with MODY at the expense of a lower positive predictive value due to the testing of polygenic atypical type 1 and type 2 diabetes cases.