Summary of RA
Rheumatoid arthritis (RA) is a long-term disease that leads to inflammation of the joints and surrounding tissues.
PubMed Health : D001172
OMIM : #180300
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.
- 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%.