HLA-B27 Carriage in the General Population
Roughly 6–8% of people carry the HLA-B27 allele without any disease.
- ~8%: General population (carry HLA-B27 (varies by ancestry))
- ~0.15%: Lifetime AS risk (overall population baseline)
- Chr 6: Allele location (MHC class I region)
- >100: Subtypes known (HLA-B*27 alleles catalogued)
Carrier frequency varies by ancestry
Placeholder: carriage rates differ widely across populations and regions.
Placeholder: most HLA-B27 carriers never develop spondyloarthritis.
HLA-B27 Carriage Among Ankylosing Spondylitis Patients
About 90% of diagnosed AS patients carry the HLA-B27 allele.
- ~90%: AS patients HLA-B27+ (strongest known HLA-disease link)
- ~80–100x: Relative risk (carriers vs non-carriers)
- ~2–3:1: Male:female ratio (classic AS presentation)
- <45 yrs: Typical onset (age at first symptoms)
Strongest HLA-disease association known
Placeholder: HLA-B27 shows one of the strongest genetic disease links.
Placeholder: carriage alone is not sufficient for diagnosis.
Positive Predictive Value with Inflammatory Back Pain
Combining genotype with symptom pattern sharply improves prediction.
- ~80–90%: IBP + HLA-B27+ (referral criteria sensitivity)
- ~15%: IBP alone (PPV without genotype)
- 2009: ASAS criteria (axial spondyloarthritis classification)
- >3 mo: Chronic pain cutoff (defines inflammatory pattern)
Symptom pattern sharpens the estimate
Placeholder: chronic inflammatory back pain narrows the diagnosis substantially.
Placeholder: night pain and morning stiffness are key symptom clues.
Family History as a Risk Multiplier
A first-degree relative with AS meaningfully raises personal risk.
- ~10–20%: Sibling risk (HLA-B27+) (with affected first-degree relative)
- ~90%: Heritability estimate (twin studies of AS)
- >30: Non-HLA genes (additional loci implicated)
- epistatic: ERAP1 interaction (modifies HLA-B27 effect)
Genetics beyond a single allele
Placeholder: family clustering reflects shared HLA-B27 and other risk genes.
Placeholder: family history refines risk beyond genotype alone.
Combined Ankylosing Spondylitis Risk Estimate
Genotype, symptoms, and family history combine into one risk gauge.
- 3: Model inputs (genotype, symptoms, family history)
- >50%: High-risk threshold (triggers MRI + referral)
- 20–50%: Moderate threshold (consider X-ray, routine referral)
- <20%: Low threshold (primary care monitoring)
A composite decision-support estimate
Placeholder: combined score guides imaging and referral decisions.
Placeholder: this simulator is educational, not a diagnostic tool.