The word comes from Greek ankylos meaning 'fused', spondylos meaning 'vertebra' and -itis meaning 'inflammation'.
Ankylosing Spondylitis a kind of spondyloarthopathy with chronic arthritis and inflammation of spine and other joints.
The immune system and genetics are said to play a major role.
It mainly affects the back bone and sacrum, later leading to fusion and complete rigidity of the spine known as "bamboo spine".
The disease is most prevalent in Northern European countries.