Ankylosing Spondylitis. The disease you can’t pronounce and likely had never heard of—until you or a loved one got diagnosed. It’s relatively rare, but for the 300,000 people in the U.S. (less than one percent of the adult population) who have it, it can be a real pain—literally. The disease, which affects the joints primarily in the lower back, can cause pain, stiffness, and damage, and not because of wear and tear, but thanks to inflammation, says Martin Bergman, M.D., chief of the division of rheumatology at Taylor Hospital in Ridley Park, PA, and clinical professor of medicine at Drexel University College of Medicine. “One of the hallmark symptoms we look for is back pain that’s worse in the morning and gets better throughout the day; another is back pain that awakens you at night.”