JIA is a disease of the immune system. In JIA, the immune system attacks the body's own healthy cells, mistaking them for cells that don't normally belong to the body. This causes inflammation in the lining and connective tissues of the joints.
JIA affects 1 in 1,000 Canadian children under the age of 16. Generally, it affects girls more than boys. JIA itself is not inherited. What can be inherited are the genes that may make someone more likely to develop the disease, including those genes that control your immune system, although scientists believe it is unlikely that genetics alone bring about JIA.