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Like adult rheumatoid arthritis, JRA is an autoimmune disease, which means the body's immune system attacks its own healthy cells and tissues.
JRA is considered to be a multifactorial condition. Multifactorial inheritance means that many factors are involved in causing a health problem. The factors are usually both genetic and environmental, where a combination of genes from both parents, in addition to unknown environmental factors, produce the trait or condition. Often one gender (either males or females) is affected more frequently than the other in multifactorial traits. Multifactorial traits do recur in families because they are partly caused by genes.
A group of genes on chromosome 6 codes for the HLA (human leukocyte antigens) antigens play a major role in susceptibility and resistance to disease. Specific HLA antigens influence the development of many common disorders. Some of these disorders, like JRA, are autoimmune related and inherited in a multifactorial manner. When a child has the specific HLA antigen type associated with the disease, he/she is thought to have an increased chance to develop the disorder.
The HLA antigen associated with JRA is called DR4. Children with the DR4 HLA antigen are thought to have an increased chance (or genetic susceptibility) to develop JRA; however, it is important to understand that a child without this antigen may also develop JRA. This means HLA antigen testing is not diagnostic or accurate for prediction of the condition. Females are affected with JRA more often than males.