HLA B-27 has > 90% association with?
**Core Concept**
The HLA-B27 antigen is a **human leukocyte antigen** subtype that plays a significant role in the immune system, particularly in the context of autoimmune diseases. It is strongly associated with certain **spondyloarthropathies**. The underlying principle being tested here involves the relationship between specific HLA alleles and autoimmune conditions.
**Why the Correct Answer is Right**
HLA-B27 has a strong association with **Ankylosing Spondylitis (AS)**, a type of arthritis that primarily affects the spine, although other joints can also be involved. This association is well-documented, with more than 90% of patients with AS testing positive for HLA-B27. The exact mechanism of how HLA-B27 contributes to the development of AS is not fully understood, but it is believed to involve the presentation of **autoantigens** to T-cells, triggering an immune response.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because, while HLA-B27 can be associated with other conditions, its strongest and most well-known association is not with this option.
**Option B:** Incorrect as it does not have the strongest association with HLA-B27 compared to the correct answer.
**Option C:** Incorrect because, although HLA-B27 can be found in patients with various spondyloarthropathies, this option does not specify the condition with the highest association.
**Clinical Pearl / High-Yield Fact**
Remembering that HLA-B27 is strongly associated with Ankylosing Spondylitis is crucial for diagnosing and managing this condition. A significant proportion of patients with AS will test positive for HLA-B27, although the presence of the antigen does not guarantee the development of the disease.
**Correct Answer:** D. Ankylosing Spondylitis.