Increased frequency of HLA-B 27 is seen in all the following diseases except
HLA-B27 is strongly associated with spondyloarthropathies. The main ones I remember are ankylosing spondylitis, reactive arthritis, psoriatic arthritis, and enteropathic arthritis (like in inflammatory bowel disease). Also, Behçet's disease might be linked, though it's less common.
The question asks for the exception. Let's think about the options. If the options include something like systemic lupus erythematosus (SLE) or rheumatoid arthritis (RA), those are not typically associated with HLA-B27. SLE is more linked to HLA-DR3 and DR2, while RA is associated with HLA-DR4 and DR1. So if one of the options is RA or SLE, that would be the correct answer.
Wait, the user didn't provide the options, but the correct answer is given as an example. Let me check the original question again. The user's example had the correct answer as "D. Systemic lupus erythematosus", so I need to structure the explanation around that.
Core Concept: HLA-B27 is a major histocompatibility complex class I antigen linked to spondyloarthropathies. It's a key marker for conditions like ankylosing spondylitis.
Why the correct answer is right: SLE isn't associated with HLA-B27. Its HLA associations are different.
Why the wrong options are wrong: Ankylosing spondylitis, reactive arthritis, psoriatic arthritis, etc., are all linked to HLA-B27.
Clinical pearl: Remember that HLA-B27 is a red flag for spondyloarthropathies. If a question asks for the exception, SLE fits here.
Now, structure this into the required sections, making sure each part is concise and fits within the character limit. Use bold for section headings and key terms. Avoid markdown except for the specified formatting.
**Core Concept**
HLA-B27 is a class I major histocompatibility complex (MHC) antigen strongly associated with spondyloarthritides, including ankylosing spondylitis, reactive arthritis, psoriatic arthritis, and enteropathic arthritis. It is not linked to systemic autoimmune diseases like lupus.
**Why the Correct Answer is Right**
Systemic lupus erythematosus (SLE) is associated with HLA-DR2 and HLA-DR3 alleles, not HLA-B27. SLE is a B-cell-driven autoimmune disorder with distinct HLA associations, whereas HLA-B27 mediates immune dysregulation in spondyloarthropathies via mechanisms involving misfolded proteins and innate immune activation.
**Why Each Wrong Option is Incorrect**
**Option A:** *Ankylosing spondylitis* is **strongly** linked to HLA-B27 (90% of cases).
**Option B:** *Reactive arthritis* has a