REVIEW - Epidemiology and genetics of RA

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Arthritis Res. 2002;4 Suppl 3:S265-72. Epub 2002 May 9.

Epidemiology and genetics of rheumatoid arthritis.

Silman AJ, Pearson JE.

ARC Epidemiology Unit, School of Epidemiology & Health Sciences,

University of Manchester, UK.

The prevalence of rheumatoid arthritis (RA) is relatively constant in

many populations, at 0.5-1.0%. However, a high prevalence of RA has

been reported in the Pima Indians (5.3%) and in the Chippewa Indians

(6.8%). In contrast, low occurrences have been reported in populations

from China and Japan. These data support a genetic role in disease

risk. Studies have so far shown that the familial recurrence risk in

RA is small compared with other autoimmune diseases. The main genetic

risk factor of RA is the HLA DRB1 alleles, and this has consistently

been shown in many populations throughout the world. The strongest

susceptibility factor so far has been the HLA DRB1*0404 allele. Tumour

necrosis factor alleles have also been linked with RA. However, it is

estimated that these genes can explain only 50% of the genetic effect.

A number of other non-MHC genes have thus been investigated and linked

with RA (e.g. corticotrophin releasing hormone, oestrogen synthase,

IFN-gamma and other cytokines). Environmental factors have also been

studied in relation to RA. Female sex hormones may play a protective

role in RA; for example, the use of the oral contraceptive pill and

pregnancy are both associated with a decreased risk. However, the

postpartum period has been highlighted as a risk period for the

development of RA. Furthermore, breastfeeding after a first pregnancy

poses the greatest risk. Exposure to infection may act as a trigger

for RA, and a number of agents have been implicated (e.g. Epstein-Barr

virus, parvovirus and some bacteria such as Proteus and Mycoplasma).

However, the epidemiological data so far are inconclusive. There has

recently been renewed interest in the link between cigarette smoking

and RA, and the data presented so far are consistent with and

suggestive of an increased risk.

PMID: 12110146

http://www.ncbi.nlm.nih.gov/pubmed/12110146

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