HLA class II (DR and DQ) antigen associations in idiopathic dilated cardiomyopathy. Validation study and meta-analysis of published HLA association studies 
 We previously reported antigen frequency differences for HLA-DR4 and HLA-DRw6 between idiopathic dilated cardiomyopathy (IDC) patients and healthy controls in a pilot study.
 To confirm these findings, we undertook an independent study with a prospective hypothesis regarding the frequencies of DR4 and DRw6; typing for a second family of class II antigens (HLA-DQ) was included because of the proximity of the DQ loci to the DR loci and the strong linkage disequilibrium between some of the DR and DQ alleles.
 Comparing a new consecutive series of IDC patients (n = 41) and healthy blood bank controls (n = 53), we confirmed an increase of DR4 antigen frequency in patients (49% versus 21%, p less than 0.005).
 A trend toward decreased expression of DRw6 among patients was also noted (10% of patients versus 23% of controls).
 HLA-DQw4 was significantly elevated in patients compared with controls (27% versus 6%, p less than 0.005; relative risk, 6.1; etiologic fraction, 0.22).
 We identified the combined DR4-DQw4 haplotype in five of 41 Caucasian IDC patients (12%) and none of 53 controls (p less than 0.007).
 A comparison of specific antigen frequencies between the preliminary and validation studies did not reveal significant differences; therefore, the data from the two studies were examined in combination.
 For the combined studies, DR4 was elevated (51% versus 27% in controls, p less than 0.001), and DRw6 was decreased (9% versus 24% in controls, p less than 0.01).
 The relative risk for DR4 was 2.8, and the etiologic fraction was 0.33.
