🖐 HLA-B27 Ankylosing Spondylitis Risk Association Simulator

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.