A 23-year-old man complains of stiffness and pain in his lower back that causes him to awaken at night. He first noticed morning stiffness in his lower back during his college years. He also describes occasional pain in his right eye and sensitivity to light. An X-ray of the sacroiliac region shows fusion of the small joint spaces in the posterior spine and ossification of the intervertebral discs. Serologic tests for rheumatoid factor and antinuclear antibodies are negative. This patient most likely expresses which of the following human leukocyte antigen (HLA) haplotypes?
A 23-year-old man complains of stiffness and pain in his lower back that causes him to awaken at night. He first noticed morning stiffness in his lower back during his college years. He also describes occasional pain in his right eye and sensitivity to light. An X-ray of the sacroiliac region shows fusion of the small joint spaces in the posterior spine and ossification of the intervertebral discs. Serologic tests for rheumatoid factor and antinuclear antibodies are negative. This patient most likely expresses which of the following human leukocyte antigen (HLA) haplotypes?
💡 Explanation
**Core Concept:** Rheumatoid arthritis (RA) is an autoimmune inflammatory disorder affecting joints, leading to pain, swelling, and stiffness. It is associated with specific human leukocyte antigen (HLA) haplotypes. The HLA-DRB1 shared epitope (SE) is a group of shared amino acids within the HLA-DRB1 gene, which increases the risk of developing rheumatoid arthritis.
**Why the Correct Answer is Right:** The patient described presents with classical symptoms of rheumatoid arthritis, such as morning stiffness, bilateral symmetrical joint pain, and sensitivity to light (photophobia) along with joint space narrowing in X-ray. The negative serologic tests for rheumatoid factor and antinuclear antibodies are also consistent with RA, as these tests are often positive in other forms of arthritis.
**Why Each Wrong Option is Incorrect:**
A. This option is incorrect as the patient does not express the HLA-DRB1*0101 haplotype, which is associated with juvenile idiopathic arthritis (JIA).
B. This option is incorrect as the patient does not express the HLA-DRB1*0401 haplotype, which is associated with psoriatic arthritis.
C. This option is incorrect as the patient does not express the HLA-DRB1*0104 haplotype, which is associated with ankylosing spondylitis (AS).
D. This option is incorrect as the patient does not express the HLA-DRB1*0405 haplotype, which is associated with psoriatic arthritis.
**Clinical Pearl:** The presence of the HLA-DRB1*0401 haplotype increases the risk of developing rheumatoid arthritis, but this option is incorrect in this case as the patient does not express this haplotype. The correct answer is HLA-DRB1*0404, which is associated with rheumatoid arthritis, as mentioned above. The SE is a genetic marker for RA and is associated with a higher risk of developing the disease.
✓ Correct Answer: C. B27
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