We have studied the distribution of the different HLA-B51 alleles amo
ng patients with Behcet's disease (BD) and ethnically matched healthy
controls in a Spanish population. The serological B51 specificity was
increased in BD patients (37.5% versus 15.5% in controls), Among the B
51-associated alleles, the frequencies of B5101 (32%) and 5108 (5.5%)
were increased in BD patients with respect to the control frequencies
(13% and 1.2% respectively). The fact that different HLA-B51 subtypes
are as sociated with ED could suggest that common motifs shared by HL
A-B51-related alleles are involved in the susceptibility to BD or, in
the light of recent studies, that a mutation causing the susceptibilit
y to BD occurred in the B5101 haplotype, close to HLA-B gene, before
the divergence of B5108 from the B*5101 allele.