Adenosine deaminase 2 deficiency

Adenosine deaminase 2 (ADA2) deficiency is a disorder characterized by abnormal inflammation of various tissues. Signs and symptoms can begin anytime from early childhood to adulthood. The severity of the disorder also varies, even among affected individuals in the same family.

Inflammation is a normal immune system response to injury and foreign invaders (such as bacteria). However, ADA2 deficiency causes abnormal, unprovoked inflammation that can damage the body's tissues and organs, particularly blood vessels. (Inflammation of blood vessels is known as vasculitis.) Other tissues affected by abnormal inflammation can include the skin, gastrointestinal system, liver, kidneys, and nervous system. Depending on the severity and location of the inflammation, the disorder can cause disability or be life-threatening.

Signs and symptoms that can occur with ADA2 deficiency include fevers that are intermittent, meaning they come and go; areas of net-like, mottled skin discoloration called livedo racemosa; an enlarged liver and spleen (hepatosplenomegaly); and recurrent strokes affecting structures deep in the brain that can start in the first few years of life. In some people, ADA2 deficiency causes additional immune system abnormalities that increase the risk of bacterial and viral infections.

ADA2 deficiency is sometimes described as a form of polyarteritis nodosa (PAN), a disorder that causes inflammation of blood vessels throughout the body (systemic vasculitis). However, not all researchers classify ADA2 deficiency as a type of PAN.