Which HLA allele is associated with ankylosing spondylitis?

• A. HLA-DR4
• B. HLA-B8
• C. HLA-B27
• D. HLA-A3

Answer: (C)

Genetic predisposition in ankylosing spondylitis is most strongly tied to HLA-B27, a class I MHC molecule that presents peptides to T cells. Across populations, a large majority of people with ankylosing spondylitis carry HLA-B27, making it the most consistent genetic marker for the disease. However, carrying HLA-B27 isn’t enough to cause the condition—many healthy individuals have this allele, and not all people with HLA-B27 develop AS. So, it supports the diagnosis in the right clinical context but isn’t definitive on its own. The other alleles listed are linked to different autoimmune diseases and do not have the same strong association with ankylosing spondylitis, which is why HLA-B27 is the best match for this question.