HLA‑Cw6 is a genetic marker strongly associated with psoriasis, particularly early‑onset (type I) and guttate forms. It’s linked to family history and streptococcal‑triggered flares, tends to associate with specific clinical patterns (scalp and widespread lesions) and earlier onset, and can affect disease course. Presence of HLA‑Cw6 may also influence prognosis and response to some therapies.

The major HLA marker associated with Behçet’s disease is HLA‑B51 (part of the HLA‑B5 serotype). HLA‑B51 increases susceptibility, especially in Mediterranean, Middle Eastern and East Asian populations, but it is not diagnostic alone. Many affected individuals do not carry the marker, and many carriers never develop disease; clinical evaluation and other tests are required.

HLA-B27 is the HLA allele most commonly associated with psoriatic arthritis, particularly with axial involvement and sacroiliitis. Its presence increases the likelihood of spinal and joint inflammation and can influence disease pattern and prognosis. Other HLA class I alleles (for example HLA-B38 and B39) may also be implicated, but HLA-B27 is the principal genetic marker linked to psoriatic arthritis.

Systemic lupus erythematosus is most strongly associated with HLA class II alleles, particularly HLA-DR2 and HLA-DR3 (notably DRB1*15:01 and DRB1*03:01). These alleles correlate with higher susceptibility and autoantibody production, though associations vary by ethnicity and presence of these HLAs does not guarantee disease—genetic and environmental factors together determine risk. Testing may inform risk assessment in select cases.

Human leukocyte antigen (HLA) genes are linked to multiple autoimmune conditions. The clearest example is HLA-B27, which is strongly associated with ankylosing spondylitis and related spondyloarthropathies. Other HLA types (e.g., HLA-DR3, DR4) increase risk for diseases such as type 1 diabetes and rheumatoid arthritis. HLA testing can support diagnosis but is not definitive on its own.

HLA‑C alleles are linked most strongly to psoriasis (notably HLA‑C*06:02) and psoriatic arthritis. HLA‑C variation influences viral control in HIV infection. HLA‑C matching affects transplant outcomes and graft‑versus‑host disease risk. Certain HLA‑C types have been associated with spondyloarthropathies and other inflammatory conditions, though associations are allele‑specific and vary between populations.