ImmunologyTier 1Medical Sciences concept

Risk factors for rheumatoid arthritis development

Core concept

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*Shared epitope (HLA-DRB104:01/04:04/01:01)**

+ an environmental source of citrullination (smoking, periodontitis)

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The gene-environment interaction is the mechanism, not a coincidence: smoking raises ACPA-positive RA risk only modestly on its own, but ~20-40x in shared-epitope homozygotes
Risk factors are largely for ACPA-POSITIVE RA - seronegative RA has a different, weaker risk profile

Genetic (~60% heritability)

HLA-DRB1 shared epitope - the largest single contributor (~30-40% of genetic risk)
PTPN22 R620W - a lymphoid tyrosine phosphatase variant; also T1DM, SLE, autoimmune thyroid disease
STAT4 - the JAK-STAT gene classically implicated in RA (not STAT1); also SLE
PADI4 - stronger in Asian populations; TRAF1-C5, CTLA4, IL6R, TNFAIP3

Environmental / behavioural

Factor	Effect
Smoking	The strongest modifiable risk factor - dose-dependent, risk persists ~10-20 yr after quitting; also predicts worse disease, nodules, ILD, poorer MTX/anti-TNF response
Periodontitis (Porphyromonas gingivalis)	The only bacterium known to express PAD -> citrullinates host proteins directly; Aggregatibacter actinomycetemcomitans also implicated
Silica, textile and mineral dust exposure	Occupational RA risk
Obesity	Modest increase; worse treatment response
Microbiome	Gut dysbiosis (Prevotella copri), mucosal origin hypothesis

Host

Female (~3:1), peak onset 40-60 yr
Parity and breastfeeding are protective; the postpartum year is high-risk; RA often remits in pregnancy
Family history - first-degree relative ~3-5x
Alcohol in moderation is consistently associated with LOWER risk - a rare protective association

Smoking cessation is a disease-modifying intervention and should be framed that way - it reduces incidence in at-risk relatives and improves treatment response
ACPA can be present 10-14 years before symptoms - the "pre-RA" window
- Arthralgia + ACPA positivity + no synovitis = clinically suspect arthralgia, with high conversion risk -> refer early; treat-to-target from the first weeks of synovitis is what preserves joints
Ask about dental health and treat periodontitis
Screen for latent TB and hepatitis B before biologics, and address the same cardiovascular risk factors - RA itself carries CV risk equivalent to diabetes

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