Which genetic marker has been linked to reactive arthritis?

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

Answer: (A)

Reactive arthritis is most strongly linked to HLA-B27, a genetic marker associated with the seronegative spondyloarthropathies. Having HLA-B27 increases susceptibility and helps explain why some people develop arthritis after a gut or genitourinary infection. A positive HLA-B27 supports the diagnosis when the clinical story fits, but it isn’t by itself diagnostic, and many people without the marker can still have the condition while some with it never develop arthritis.

The other options fit poorly: HLA-DR4 is more commonly associated with rheumatoid arthritis; being negative for HLA-B27 argues against this predisposition; and HLA-A3 does not have a strong, established link to reactive arthritis.