Homozygosity for HLA-B27. Impact on rheumatic disease expression in two families

The effect of homozygosity for HLA-B27 on the clinical expression of rheumatic disease was studied in two families. The 1 homozygous patient in each of two families demonstrated extraordinarily severe peripheral and axial arthritis compared to other affected heterozygous relatives. In addition, predominant peripheral or axial disease appeared to segregate with different B27 haplotypes. The 2 homozygous patients were not homozygous at the hla-a,c, or D loci.