The cause of ankylosing spondylitis is not very clear, mainly related to the following factors: a. Genetic factors According to the survey, the incidence of compulsory spondylitis in relatives of patients is about 3O times higher than the general population. The study found that multiple twin brothers have developed ankylosing spondylitis. Ankylosing spondylitis patients HLA-B27 (human leukocyte antigen B27 positive rate of up to 90% or more, children HLA-B27 positive pieces accounted for 50%, the occurrence of ankylosing spondylitis accounted for 25%. Ankylosing spondylitis has a stronger tendency to run in families than rheumatoid arthritis. This suggests that genetic factors play a decisive role in this disease. I have counted 100 cases of compulsory spondylitis patients, HLA-B27 positive rate of 88%, found that 15 cases have a family history, including 11 cases of fathers and brothers have suffered from the disease. It should be clear that 4% to 6% of the normal population is HLA-B27 positive, so people who are HLA-B27 positive do not necessarily have ankylosing spondylitis, and doctors never diagnose the disease on the basis of HLA-B27 positivity alone. It also indicates that there are other factors that play a role in the pathogenesis of the disease. Some scholars of compulsive spondylitis have made numerous observations and found that many men with compulsive spondylitis have a combination of urinary tract infections. In addition, some studies have found a higher incidence of ulcerative colitis and restrictive enteritis in patients with this disease than in the general population, leading to the speculation that the causative isotope may be an infection. Some recent studies have suggested that the source of infection may be Klebsiella enterica pneumoniae. They found in their experiments that both the fecal Klebsiella pneumoniae culture positivity rate and the serum anti-Klebsiella pneumoniae antibody level were significantly higher in patients with ankylosing spondylitis than in controls. Third, other causative factors include viral infections, trauma, thyroid disease, tuberculosis, and local infections, but all lack sufficient evidence. Although there is no definitive answer to the cause of compulsory spondylitis, most experts can identify genetic and infectious factors that predispose to the disease.