HLAB51

HLAB51, also written as HLA-B51 or HLA-B*51, designates a family of alleles at the HLA-B gene, part of the human leukocyte antigen class I region on chromosome 6. The HLA-B51 proteins present peptide antigens to CD8+ T cells and are highly polymorphic, with B*51:01 being the most common allele worldwide. Allele frequencies vary widely by ethnicity, generally higher in populations along the historical Silk Road, including parts of the Middle East, the Mediterranean, and Central Asia, and lower in some sub-Saharan African and East Asian groups.

The most notable clinical association is with Behçet's disease. Numerous studies have shown that HLA-B51 is one of the strongest genetic risk factors for Behçet's, with increased prevalence among patients compared with the general population. However, many HLA-B51 carriers never develop the disease, and Behçet's can occur without HLA-B51, so the allele is not diagnostic and does not by itself determine disease if present.

In clinical practice, HLA-B51 testing is mainly used in research settings and as part of population-based risk assessments rather than as a stand-alone diagnostic test. HLA typing for various B alleles is performed for transplant compatibility in some contexts, though there is no specific clinical guideline that requires testing for HLA-B51 alone. Ongoing research continues to examine how HLA-B51 contributes to disease susceptibility and expression in Behçet's disease.