Rheumatoid arthritis (RA) is a complex disease that affects approximately 0.5% of the adult population worldwide, and occurs in 20-50 cases per 100 000 annually, mainly in women after their 40s. The onset of the disease has important diagnostic, prognostic and therapeutic implications and is yet to be defined. The distribution of the disease, in terms of both occurrence and clinical expression, has unclear geographical borders that may reflect differences in genetic admixture, environmental factors and socio-demographic determinants. Some diseases co-occur more frequently than expected with RA, as it is the case of cardiovascular disease, infections or lymphoma, but others in lower frequency than expected, such as cancer or schizophrenia. RA is associated with increased mortality rates compared with the general population in the majority of cohorts published, and the expected survival of RA patients is likely to decrease 3-10 years. As in the general population, the leading cause of death among patients with RA is cardiovascular disease, and deaths due to malignancy occur at a comparable incidence; however, patients with RA are at greater risk of mortality due to infection. Many genes have been implicated in the susceptibility of RA, all of which with a modest effect on isolation. Gene-environment interactions appear as the most plausible underlying cause of RA. Age, sex, smoking, shared epitope and others correlate with its RA. The most important determinants of prognosis in RA are the severity at presentation and the management of the disease, both of which are subject to inequalities.
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