Autoimmune diseases: Why our body sometimes turns on itself

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What role does our genetic makeup play in autoimmune diseases – diseases like lupus and multiple sclerosis wherein the body’s own immune system turns on itself? That question has plagued researchers for decades. However, a new gene mutation has been discovered that could help scientists map an autoimmune disease in the body and find out how the immune system is inappropriately triggered to attack the body.

Researchers in a study at the University of Edinburgh have honed in on five of 89 independent variations in human genetics that are believed to be responsible for autoimmune conditions, from celiac disease and multiple sclerosis to rheumatoid arthritis and asthma. Understanding how these mechanisms work could help scientists to develop new treatments.

The team found that a mutation in the ADAR1 gene causes a defect in an “alarm system” in cells that normally protects the body from viruses and other infections by triggering the body’s immune system to fight. The mutation causes this alarm system to be tripped by the cell’s own molecules, causing the immune system to attack – the uniting trait of all autoimmune diseases.

The ADAR1 mutation and the others identified by the researchers together helped reveal the system that helps the body to differentiate between normal RNA and RNA from foreign organisms. The exact problem with this mechanism that characterizes autoimmune disorders differs for each, as the body’s way of attacking itself is unique and presents no two symptoms that are exactly alike, even within families.

There are more than 80 types of autoimmune diseases affecting 5-8 percent of the American population. There are no obvious patterns in autoimmune disease; individuals of any age and sex may be affected, making the process of pin-pointing important genes extremely difficult.

Though autoimmune diseases vary wildly in their specifics, a family history of autoimmune disorders can indicate a genetic predisposition that may increase the risk to develop an autoimmune disease. This risk persists even when dealing with different autoimmune diseases. In a predisposed family, a woman may have rheumatoid arthritis and one of her siblings may develop lupus. While diseases can be passed down from parent to child, it doesn’t automatically mean someone will get the same disorders their family members suffer from. The exact nature of the immune response and how the body deals with it varies from case to case.

Though identifying genetic common ground is essential to a better understanding and treatment of autoimmune diseases, environmental factors can also play an important role in triggering the onset of disease. A few such triggers have been identified, including several drugs that are associated with some forms of lupus, thrombocytopenia, and hemolytic anemia. Sometimes infections can trigger an autoimmune disease, such as rheumatic fever caused by a streptococcal infection and Guillain-Barre syndrome caused by chlamydia. In addition, a great deal of circumstantial evidence suggests that viruses may play a role in initiating some autoimmune diseases. Despite these known triggers, most cases of autoimmune disease cannot be linked to clear evidence of a particular environmental trigger.

The new ability the researchers found to associate specific genetic variants with autoimmune disease broadly and to probe  will enable medical researchers to more precisely target therapeutic interventions in autoimmune diseases in order to dampen fired-up immune responses.

Finding the ADAR1 mutation is a huge step toward learning more about autoimmune diseases and what exactly they do to the human body when active. Mapping the relevant mutations and their chemical signatures in the body helps reveal the exact mechanisms by which autoimmune diseases occur and cause harm – hopefully providing new targets for doctors trying to treat these stubborn and pernicious disease.

Emily Sutherlin is a science journalist focusing on education and communication issues surrounding crop and animal biotechnology. Follow her @kimberlyvmonet.

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