Q-Bank Breakdown: HLA associations with disease — Why Every Answer Choice Matters

You’re cruising through a Q-bank and hit the classic: “Which HLA is associated with this disease?” These questions feel like pure memorization—until you realize the test-writers are also checking whether you can recognize the vignette and avoid distractors that sound immunology-ish. Let’s break down a high-yield stem and then do what top scorers do: squeeze points out of every answer choice.

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Tag

Immunology > Transplant & Autoimmune

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The Clinical Vignette (Q-bank style)

A 27-year-old man presents with 3 months of low back pain that is worse in the morning and improves with activity. He also reports intermittent pain in his heels when he first gets out of bed. Exam shows decreased lumbar flexion and tenderness at the Achilles tendon insertion. Pelvic radiograph demonstrates bilateral sacroiliitis. Which HLA allele is most strongly associated with this condition?

Answer choices: A. HLA-A3
B. HLA-B27
C. HLA-DR2
D. HLA-DR3
E. HLA-DQ2

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Step-by-Step: Identify the Diagnosis First

This is ankylosing spondylitis (AS)—a seronegative spondyloarthropathy.

Clues:

• Inflammatory back pain: morning stiffness, improves with exercise
• Enthesitis: heel pain at Achilles insertion (enthesopathy)
• Bilateral sacroiliitis on imaging
• Typical demographic: young adult male

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Correct Answer: B. HLA-B27

Why it’s correct

HLA-B27 is a Class I MHC allele strongly associated with:

• Ankylosing spondylitis
• Reactive arthritis
• Psoriatic arthritis (axial)
• Enteropathic arthritis (IBD-associated)

High-yield immunology tie-in

• MHC Class I presents endogenous peptides to CD8+ T cells
• Expressed on all nucleated cells
• AS is part of the “B27 family” of seronegative spondyloarthropathies

Classic associations to remember

• AS complications: anterior uveitis, aortitis → aortic regurgitation, syndesmophytes (“bamboo spine”)
• Reactive arthritis triad: conjunctivitis + urethritis + arthritis (often post-Chlamydia or GI infection)

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Why Every Distractor Is Wrong (and what it actually goes with)

A. HLA-A3 — the sneaky one

Why it’s tempting: It’s an MHC Class I allele (like B27), so it “feels” plausible.

What it’s actually associated with (high yield):

• Hereditary hemochromatosis is most classically HLA-A3 (and also linked with HFE mutation on chromosome 6 near the HLA locus—this is why A3 shows up in memory banks)

How to avoid the trap:

• Hemochromatosis vignettes scream bronze diabetes, cirrhosis, cardiomyopathy, hypogonadism, high transferrin saturation—not inflammatory back pain.

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C. HLA-DR2 — autoimmune/neuro “DR” bucket

Why it’s tempting: DR alleles are frequently autoimmune-associated.

What DR2 is associated with:

• Multiple sclerosis
• Goodpasture syndrome
• (Often taught also with narcolepsy associations in some resources, but MS/Goodpasture are the classic Step associations.)

How to avoid the trap:

• MS is CNS demyelination (optic neuritis, internuclear ophthalmoplegia); Goodpasture is pulmonary hemorrhage + rapidly progressive glomerulonephritis with anti-GBM. Not sacroiliitis/enthesitis.

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D. HLA-DR3 — endocrine & junctional autoimmune

What DR3 is associated with:

• Type 1 diabetes mellitus
• Graves disease
• SLE
• Myasthenia gravis
• Addison disease
• Often paired with DR4 for T1DM risk

Why it’s wrong here:

• Nothing about AS suggests antibody-mediated endocrine disease or NMJ weakness (ptosis, fatigability).

Quick mental anchor:
DR3 = “autoimmune endocrine + SLE + MG”

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E. HLA-DQ2 — the GI malabsorption standout

What DQ2 is associated with:

• Celiac disease (also DQ8)

Why it’s wrong here:

• Celiac disease presents with diarrhea, weight loss, iron deficiency, dermatitis herpetiformis, villous atrophy, anti–tTG/anti-endomysial antibodies.

Important nuance for Step 2:

• Celiac can be associated with other autoimmune disease—but the question asks for the allele most strongly tied to this condition (AS), which is B27.

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The High-Yield Table: HLA Associations You Should Know Cold

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Mini-Framework: How to Answer HLA Questions Fast (Without Pure Memorization)

1) Class I vs Class II can narrow choices

• Class I (A, B, C) → often tied to CD8+ T cell-linked patterns, including seronegative spondyloarthropathies (B27)
• Class II (DP, DQ, DR) → many classic autoimmune diseases (T1DM, celiac, MS, SLE, Graves)

2) The vignette usually screams one diagnosis

If the vignette is:

• Axial back pain + sacroiliitis + enthesitis → think B27
• Diarrhea + malabsorption + dermatitis herpetiformis → think DQ2/DQ8
• Neuro deficits separated in time/space → think DR2

3) Distractors are often “right” for something else

The test isn’t just asking “Do you know B27?”
It’s asking, “Do you know that DR3 is also a real thing with real diseases—and can you avoid mislabeling AS as ‘generic autoimmune’?”

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Transplant Tie-In (Quick but Testable)

Even though this question is autoimmune-focused, remember why HLA matters in transplant:

• HLA matching reduces graft rejection risk, especially:
  • HLA-A, HLA-B (Class I) and HLA-DR (Class II) are commonly matched in solid organ transplantation
• Rejection types (high yield patterns):
  • Hyperacute (minutes–hours): preformed anti-ABO/HLA antibodies → thrombosis, ischemia
  • Acute (days–weeks to months): T-cell mediated ± antibodies → endotheliitis
  • Chronic (months–years): fibrosis, vascular narrowing

USMLE loves linking HLA fundamentals to both autoimmune predisposition and transplant immunology—same system, two different testing angles.

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Final Takeaways (What to memorize and how to use it)

• Ankylosing spondylitis = HLA-B27 (Class I)
• Celiac = DQ2/DQ8 (Class II)
• MS/Goodpasture = DR2
• T1DM/Graves/SLE/MG = DR3 (± DR4 for T1DM)
• Learn HLA questions by vignette pattern recognition, then use Class I vs II as your safety net.