Learning Objectives
Master the HLA Subtype Associations with chronic diseases. Learn to identify which Human Leukocyte Antigen (HLA) genes predispose individuals to specific autoimmune, inflammatory, and endocrine disorders, and utilize high-yield mnemonics for the USMLE Step 1.
1. HLA-B27 (MHC Class I)
HLA-B27 is strongly associated with a group of inflammatory joint diseases known as Seronegative Spondyloarthropathies. These conditions are often grouped because they are rheumatoid factor (RF) negative.
| HLA Subtype | Associated Diseases | Mnemonic |
|---|---|---|
| B27 | Psoriatic arthritis, Ankylosing spondylitis, IBD-associated arthritis, Reactive arthritis | PAIR |
2. HLA-DR3 and DR4 (MHC Class II)
These subtypes are primarily associated with endocrine and systemic autoimmune pathologies. Note that DM Type 1 is uniquely associated with both.
| HLA Subtype | Associated Diseases | Mnemonic / Logic |
|---|---|---|
| DR3 | Diabetes Mellitus Type 1, SLE, Graves disease, Hashimoto thyroiditis, and Addison’s disease | SL3 (for SLE)DM Type 1: DR3 and DR4( ) |
| DR4 | Rheumatoid arthritis, Diabetes Mellitus Type 1, Addison’s disease | “There are 4 walls in 1 rheum (room.” |
Activity:
3. Summary of Additional High-Yield Associations
| Disease | HLA Association | Mnemonic |
|---|---|---|
| Celiac Disease | DQ2 / DQ8 | “I ate 2 much at DQ [Dairy Queen] at 8.” |
| Multiple Sclerosis | DR2 | MS has 2 letters. |
| Goodpasture Syndrome | DR2 | 2 organs involved (Lung + Kidney). |
Activity:
High-Yield Clinical Pearls:
- MHC Class Match: Remember that B subtypes are MHC Class I, while D subtypes (DR, DQ, DP) are MHC Class II.
- Addison Disease: This is a classic “cross-over” disease; it is linked to both DR3 and DR4, making it a common distractor in DM Type 1 questions.
- Negative Selection: HLA-associated diseases often occur because the body’s T cells fail to be “negatively selected” against these specific self-antigens during maturation in the thymus.