Epidemiology And Etiology

RA affects approximately 1% of the U.S population and 1% to 2% of the world s pop-1 2

ulation. ' RA arises from an immunologic reaction, and there is speculation that it is in response to a genetic or infectious antigen. Risk factors associated with the development of RA include the following:

• Female gender (3:1 females to males)

• Increasing age (peak onset 35-50 years of age)

• Current tobacco smoking. Studies have identified a direct relationship between tobacco use and RA disease severity. Tobacco users also have an increased risk of pulmonary manifestations of RA. This risk is reduced when a patient has remained tobacco-free for at least 10 years.

• Family history of RA. Genetic studies demonstrate a strong correlation between RA and the presence of major histocompatibility complex class II human leukocyte antigens (HLA), specifically HLA-DR1 and HLA-DR445 HLA is a molecule associated with the presentation of antigens to T lymphocytes.

• Potential environmental exposures. The number of RA cases has increased during industrialization, although a specific link to environmental factors has not been de-termined.6

• Oral contraceptive use and high ingestion of vitamin D and tea are associated with a decreased risk of RA.

• Fewer than 300,000 children in the United States under age 16 are affected by JIA. There are no known risk factors for JIA.

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