Study overview. (A) Study design. (B) Frequency of study patients by their HLA-DRB1 and -DQB1 alleles, with alleles ordered from most to least frequent. (C) Heat map of genetic linkage detected between HLA-DRB1 and -DQB1 alleles. Intensity (overlap) equals the number of patients having both DRB1 and DQB1 alleles divided by the number of patients having at least 1 of the alleles.