Henoch-Schonlein purpura (HSP), also called immunoglobulin A vasculitis (IgAV), is a vascular disease that primarily affects small blood vessels. The disease is characterized by abnormal deposits of immunoglobulin A (an antibody) in the blood vessels, leading to their inflammation (vasculitis). The small vessels of the skin, joints, kidneys, and digestive organs are particularly involved. Signs and symptoms usually begin suddenly (and progress over days) and may include purple-colored spots on the skin (purpura); joint pain; and gastrointestinal problems such as abdominal pain, nausea, bloody stools, and rarely, severe complications requiring surgery. People with HSP may also develop glomerulonephritis (injury to the kidneys caused by inflammation) and poor kidney function, which may result in swelling of parts of the body or face (edema), and blood and protein in the urine (hematuria and proteinuria). Most cases of HSP occur in children and go away without causing serious or long-term health problems. Less commonly, the disease affects adults and may be more severe, leading to chronic kidney disease and kidney failure. The cause of HSP is not completely understood, but research indicates that genes (especially those involved in regulating the immune system) may play a key role in predisposing a person to HSP, as well as its severity. However, while genes may increase the risk of developing the disease (and in some cases more than one family member has HSP), the disease itself is not inherited. The diagnosis of HSP may be made based on symptoms, blood and urine tests, imaging studies, and/or a biopsy of the skin or kidney.