1.What is HLA-B27? HLA is a three-letter acronym for Human Leukocyte Antigen. The main function of HLA is to help the body identify the “self” or “non-self” component, so patients receiving organ transplants are checked for a match before surgery, i.e. whether the human leukocyte antigen of the organ donor is compatible with the human leukocyte antigen of the patient receiving the organ. antigens of the recipient. The degree of compatibility will determine the severity of the rejection reaction. There are hundreds of human leukocyte antigens, each named by a letter plus a number, and HLA-B27 antigen is only one of them. 2.Does HLA-B27 run in families? The HLA-B27 antigen is a protein molecule that is encoded by the HLA-B27 gene, which is located on the short arm of human chromosome 6. The HLA-B27 gene is a dominant gene, and if one parent is HLA-B27 positive, the probability of their next generation being HLA-B27 positive is at least 50%. 3. Does HLA-B27 positivity necessarily lead to ankylosing spondylitis? Since the discovery of the association between HLA-B27 and ankylosing spondylitis in 1973, scientists have done considerable research on the two. In China, more than 90% of patients with ankylosing spondylitis are positive for HLA-B27, compared to about 5% of the general population, but the overall prevalence of ankylosing spondylitis in China is only about 0.3%. In other words, only about 6% of those who are HLA-B27 positive end up with ankylosing spondylitis. However, if you have a parent or sibling with ankylosing spondylitis and you are positive for HLA-B27, your chance of developing ankylosing spondylitis is as high as 10-30%. The above information also indirectly suggests that the vast majority of HLA-B27-positive people do not develop ankylosing spondylitis. However, if you are HLA-B27 positive and have symptoms of ankylosing spondylitis, such as low back pain or hip pain that worsens after prolonged sitting or lying and/or a feeling of stiffness, you probably have ankylosing spondylitis. Scientists transferred the human HLA-B27 gene into mice that did not develop spondylitis if they were kept in a germ-free environment, but only when they were kept in an environment with normal flora. This phenomenon provides strong evidence that a combination of genetic and environmental factors are involved in the development of ankylosing spondylitis. It is now believed that Chlamydia trachomatis infection of the genitourinary tract or pathogens such as Yersinia enterocolitica, Salmonella and Shigella may trigger the onset of ankylosing spondylitis. 4. Why is it necessary to test for HLA-B27 to diagnose ankylosing spondylitis? Before the association of HLA-B27 with ankylosing spondylitis was discovered, doctors often made the diagnosis only after inflammatory changes in the sacroiliac joints were found on X-rays. It often took years from the time a patient became symptomatic to the time the lesion appeared on the X-ray, thus missing the optimal window of treatment. As mentioned above, the vast majority of people with ankylosing spondylitis are positive for HLA-B27. If you are negative for HLA-B27, then your doctor will consider it less likely that you have ankylosing spondylitis and will need to look for additional causes. If you are positive for HLA-B27 and have symptoms consistent with ankylosing spondylitis, your doctor will diagnose you with “undifferentiated spondyloarthropathy” (understood as the early stages of ankylosing spondylitis) until the lesions are visible on X-rays or even CT. By giving appropriate treatment at this time, it is possible to prevent complications of ankylosing spondylitis such as spondylolisthesis and hip ankylosis. In addition, patients who are HLA-B27 positive are a little more likely to have complications compared to those who are HLA-B27 negative. Therefore, doctors often ask suspected patients to have HLA-B27 tested before making a diagnosis. Because the HLA-B27 gene is inherited from your parents, it is unlikely to turn negative if you are positive for HLA-B27, and similarly it is unlikely to turn positive in the future if you were negative for HLA-B27, so there is no need to repeat HLA-B27 testing. In summary, HLA-B27-positive people are at higher risk of developing ankylosing spondylitis than the general population, and in the absence of predisposing factors in their living environment (the nature of which is still unknown to scientists), HLA-B27-positive people will not develop ankylosing spondylitis. A small number of HLA-B27-negative individuals are also at risk for developing ankylosing spondylitis.