The aim of the present study was to assess the risk conferred by HLA-DRB1, INS-VNTR and PTPN22 loci on the onset of T1D and the joint risk conferred by all these three susceptibility loci, using the Bayesian Network (BN) approach in both population-based case-control and family clustering data sets [15]. The gene discussed is PTPN22; the disease is type 1 diabetes mellitus.