As with most autoimmune diseases the cause of JDM is unknown and it is believed to be multifactorial. Many doctors and researchers across the world are looking at JDM in detail and are trying to find what causes it. There is likely to be a genetic (hereditary) predisposition to all autoimmune diseases and children who have JDM may have a relative who suffers from another autoimmune disease such as diabetes or arthritis.
We know some of the genes (messages that are passed on from parents to children) are more common in children with JDM than children without the disease but these do not explain the whole story. We think autoimmune diseases start due to contact with a ‘trigger’, which makes the body’s immune system overreact. Research has not yet identified one specific trigger but it is thought that triggers could include infection (viruses, bacteria) or an environmental factor (such as sunlight).