Summary of RA

  • Rheumatoid arthritis (RA) is a long-term disease that leads to inflammation of the joints and surrounding tissues.
  • PubMed Health : D001172 Link, OMIM : #180300 Link, MESH : D001172 Link
  • The heritability of RA is estimated to be 53-65% in the Finnish and UK data.
  • Factors known to increase risk of RA.

Genetic risk factors
  • The main genetic factor is HLA-DRB1*04 and *01 clusters which encode the "shared-epitope" sequences in MHC region.
  • Polymorphisms of PTPN22, TRAF1-C5 and TNFAIP3 have also been described in RA.
  • However more than half of the genetic risk factors remain to be identified.
Environmental risk factors
  • Smoking is the main environmental risk factor associated with RA.
  • Several microorganisms have been implicated in the development of RA.
  • Pollutants may affect the risk of developing RA. Women living within 50m of a road had an increased risk of RA (hazard ratio,1.31) compared to 200m.
  • High birth weight was positively associated with RA(OR, 3.3).
Other risk factors
  • RA is far more common in women then in men (3:1).
  • Gene-environment interactions may have a synergistic effect on RA. In a population-based case-control study, the risk was higher in smokers carrying two copies of shared-epitope genes (RR, 15.7) than in smokers with no copies (RR, 2.4).
  • The peak age at RA onset is the fifth decade. However, recent studies suggest a shift toward an older age at onset.
  • North America and Northern Europe populations are at higher risk for RA than others.
Protective factors
  • Hormone replacement therapy (HRT) may decrease the RA risk in women who carry the HLA-DRB1 alleles.
  • Breast feeding was protective to RA (OR, 0.3).
  • A diet rich in fish, olive oil, and cooked vegetables has been shown to protect against RA.
Genetic vs Environmental factors

The world prevalence of RA is approximately 1.0%.

Country Males (%) Females (%) Overall (%)
United States 0.74 1.4 1.07
United Kingdom 0.44 1.16 0.81
Spain 0.2 0.8 0.5
Italy 0.13 0.51 0.33
France 0.09 0.51 0.31
Greece 0.3 1 0.68
Russia - - 0.61
China - - 0.2-0.37
Taiwan - - 0.93
Japan 0.62 1.25 1.04
India - - 0.75
Argentina 0.6 3.2 1.97
Pima Indians 3.23 6.95 5.3