DR4 and DR3 are in strongest linkage disequilibrium with IDDM susceptibility genes, and DR1 demonstrates a lesser degree of positive disequilibrium. DR3/DR4 heterozygotes have the highest risk. The DR1 increase occurs almost exclusively in DR4/DR1 heterozygotes, suggesting that DR1 may be in disequilibrium with the same susceptibility gene as DR3. Homozygotes for DR4 and especially DR3 have a higher risk than heterozygotes of either with DRX. GLO-2 is increased in diabetic haplotypes carrying DR4, DR3 or DR1.