Ankylosing Spondylitis

Ankylosing spondylitis (AS) - also known as Bechterew's disease, is long-term degenerative inflammatory type of arthritis attacking spine and sacroiliac joint. It causes fusion of the spine which can lead to condition known as "mamboo spine". AS has genetic nature.
It affects young people usually under the age of 30 including chronic pain in the lower region of the spine. It more oftenly occur in man then in women. Other symptoms may fatique and aphthae (mouth ulcers). Also very early symptoms may occur at very young age about third year of life through pain in joints, usually knees and elbows.
Diagnosis is usually made by examination of spine using X-ray and some blood tests.

Process of Ankylosis (taken from Wikipedia).

Unfortunatelly there is no known cure for Ankylosing spondylitis but treatments and medications can reduce its hardness. Those treatments usually consist of exercises.
In some types of AS surgery can help, especially in the knees and hips.