HLA-DRB1 and type 1 diabetes mellitus: Despite these similarities, there are some notable disease-specific differences in the association with the HLA between the two conditions: i) the DRB1*04 allele, one of the strongest risk factor in T1D, is not associated with IgAD; ii) unlike T1D, the DRB1*0301 association with IgAD is restricted to the extended B*0801-DRB1*0301-DQB1*02 haplotype; iii) the DRB1*0701 allele, which is associated with increased risk of IgAD is protective in T1D, while the DRB1*0102 allele shows no evidence for association with T1D [34], [35].