What could cause ankylosing spondylitis?

Unknown, genes: The exact cause is uncertain, but it does seem to have a genetic connection. It is more common in males. It usually starts in early adulthood (occasionally earlier or later), ofter with morning stiffness and back pain. Severe pain, stiffness in a young person in the absence of trauma may be a good reason to see your doctor. Consider a seeing a rheumatologist.