HLA-DR3 is composed of the HLA-DR17 and HLA-DR18 split 'antigens' serotypes. DR3 is a component gene-allele of the AH8.1 haplotype in Northern and Western Europeans. Genes between B8 and DR3 on this haplotype are frequently associated with autoimmune disease. Type 1 diabetes mellitus is associated with HLA-DR3 or HLA-DR4. Nearly half the US population has either DR3 or DR4 (only 1–3% have both), yet only a small percentage (about 0.5%) of these individuals will develop type 1 diabetes.