1. What is ankylosing spondylitis? Ankylosing Spondylitis (AS) is a chronic progressive disease that affects the sacroiliac joints, spondylolisthesis, paraspinal soft tissues and peripheral joints, and may be accompanied by extra-articular manifestations. AS is the prototype of spondylolisthesis or primary AS, while other spondylolisthesis complicated by sacroiliac arthritis is secondary AS, usually referred to as the former and referred to in this guideline. The prevalence of AS has been reported differently in various countries, with a preliminary survey of 0.26% in China. It was previously thought to be more common in men, with a male to female ratio of 10.6:1; now the male to female ratio is reported to be 5:1, except that the onset of the disease is slower and less severe in women. The age of onset is usually between 13 and 31 years old, with rare onset after 30 years of age and before 8 years of age. 2, ankylosing spondylitis pathogenesis: the cause of AS is unknown. Epidemiological investigations have revealed that genetic and environmental factors play a role in the development of the disease. It has been shown that the onset of AS is closely related to HLA-B27, and there is a clear familial tendency to develop the disease. The rate of HLA-B27 positivity in the normal population varies greatly by race and region, for example, 4%-13% in Caucasians in Europe and 2%-7% in China, but the rate of HLA-B27 positivity in AS patients in China is 91%. Other data show that the prevalence of AS is 0.1% in the general population, 4% in the family line of AS patients, and up to 11%-25% in the first-degree relatives of B27-positive AS patients, suggesting that HLA-B27-positive individuals or those with a family history of AS are at increased risk of developing AS. However, approximately 80% of HLA-B27-positive individuals do not develop AS, and approximately 10% of AS patients are HLA-B27-negative, suggesting that other factors are involved in the pathogenesis, such as intestinal bacteria and intestinal inflammation.