These potentially include the PTPN22 gene on chromosome 1, which encodes for proteins involved in T cell and B cell activation. However, the contribution of HLA-DRB1 status to the heritability of RA is approximately one third, indicating that there are non-HLA associations. Individuals who are homozygous for the shared epitope have a substantially higher risk of developing RA than those who are heterozygous. Studies have shown that many people with RA possess particular HLA-DR alleles (eg, HLA-DR1, HLA-DR4 and HLA-DR10) that share a common sequence in the third hypervariable region of their DRB1 chains. The MHC locus, otherwise known as the HLA (human leukocyte antigen) region, is involved in the presentation of antigen to T вЂњhelperвЂќ cells. Variations in the alleles in the major histocompatibility complex (MHC) on chromosome 6 contribute to the risk of developing almost all of the autoimmune diseases. Genetic clustering in families has been confirmed through observations in twin studies, where concordance among monozygotic twins is approximately 15%, which is up to five times greater than that in dizygotic twins. First-degree relatives of those with RA are two to 10 times more likely to have the condition than the general population. It has long been established that RA tends to run in families. This difference may be explained by genetic or environmental factors.

There is some evidence to suggest a possible gradient in prevalence going from south to north (eg, in Finland the prevalence of RA in men is 0.6% and in France it is 0.32%). The prevalence in the UK is approximately 1%. For example, in some Native American groups, the prevalence is 5вЂ“6%, whereas one large study in Nigeria failed to identify a single case RA is also rare in rural China and Indonesia. There has also been a shift towards an increased age of onset, which is potentially related to the so-called вЂњbirth cohort effectвЂќ, ie, women born in a particular period might carry a high risk of RA throughout their lives and women from later generations might have a lower risk.ДЄlthough the condition affects all populations to some extent, it is more prevalent in some groups than others. It is also possible that the decline in incidence is a result of RA becoming less severe and therefore less likely to be diagnosed. 1,2 The initial fall was attributed to a protective effect of the oral contraceptive pill (see later). However, several studies have shown a decrease in the incidence of RA, particularly in women, over the past few decades. The annual incidence of RA in the UK is approximately three cases per 10,000 population. Many of these have been undertaken in geographically and ethnically diverse populations and have shown variations in the incidence and prevalence of RA, highlighting the dynamic nature of RA epidemiology. The most reliable estimates of the incidence and prevalence of RA are those derived from population-based studies. Many facets of a patientвЂ™s life are affected by the condition (see Figure 1), which exerts a considerable financial burden on society both directly (eg, medical care) and indirectly (eg, potential loss of social and financial independence).ДЇigure 1: Aspects of patientsвЂ™ health and lifestyle impacted on by rheumatoid arthritis Epidemiology

As a systemic disease, it is also associated with an increased risk of myocardial infarction and cerebrovascular accident. If left untreated, it leads to joint destruction and, potentially, deformity and disability. It is a chronic, progressive, systemic inflammatory disorder affecting synovial joints. Rheumatoid arthritis (RA) is one of the most common autoimmune diseases. Common comorbidities include heart disease, cancer and infection. However, this is not always easy because a variety of clinical, radiological and serological test results are needed before the condition can be confirmed. Early diagnosis (and hence prompt treatment) can prevent progression to joint destruction, disability and systemic effects. Inflammation of the synovial joints characterises the condition. Environmental and genetic factors contribute to this disparity.

Journal of Pharmaceutical Health Services ResearchДЄround 1% of the UK population has rheumatoid arthritis but it would be hard to find people with the condition in Nigeria, rural China or Indonesia.

International Journal of Pharmacy Practice.

Antimicrobial resistance and stewardship.

Rheumatoid arthritis diagnosis criteria