Ankylosing Spondylitis (AS) is a painful and progressive form of spinal arthritis and symptoms of inflammatory back pain often first present in people before age 35. It typically begins in the late teens and early twenties and in severe cases may result in fusing spinal vertebrae and may cause structural damage to hips and other joints. Often misdiagnosed as "just back pain" or undifferentiated arthritis, AS is a systemic inflammatory disease that, in addition to its effect on the spine, can affect internal organs, peripheral joints and vision. The Arthritis Research Campaign, estimates that on the European continent, AS prevalence ranges from 0.2 to 1 percent of the entire population. The Spondylitis Association of America estimates that between 350,000 and one million people in the U.S. suffer from Ankylosing Spondylitis.