HLA-B27

HLA-B27 is a specific allele (or variant) of the HLA-B gene, which is part of the human leukocyte antigen (HLA) system. The HLA system plays a crucial role in the immune system’s functioning, particularly in the presentation of peptides to immune cells. Certain HLA alleles have been associated with susceptibility to specific diseases.

HLA-B27, in particular, has been associated with an increased risk for several inflammatory conditions, the most prominent of which are:

  1. Ankylosing Spondylitis (AS): This is a chronic inflammatory disease that primarily affects the spine, leading to pain, stiffness, and in severe cases, fusion of the vertebrae. HLA-B27 is strongly associated with AS; however, not everyone with the allele will develop the disease.
  2. Reactive Arthritis (Reiter’s Syndrome): This condition can develop after certain infections, particularly of the gastrointestinal or genitourinary systems. It can lead to joint pain, eye inflammation, and urinary symptoms.
  3. Psoriatic Arthritis: This is an inflammatory arthritis seen in some people with psoriasis, a skin condition. The presence of HLA-B27 might influence the specific joint patterns affected in psoriatic arthritis.
  4. Juvenile Idiopathic Arthritis (specific subtypes): HLA-B27 is associated with certain subtypes of juvenile idiopathic arthritis, a term for various inflammatory joint diseases that start in childhood.
  5. Uveitis: This refers to inflammation of the uveal tract of the eye. HLA-B27 is associated with a specific type called acute anterior uveitis.
  6. Inflammatory Bowel Disease-Associated Arthritis: Patients with conditions like Crohn’s disease or ulcerative colitis sometimes develop joint symptoms. The presence of HLA-B27 may influence the pattern of joint involvement.

It’s essential to note that while HLA-B27 is associated with these conditions, it is not the sole determinant of disease. Many people with the HLA-B27 allele do not develop any of these diseases, and conversely, many people with these conditions do not have the HLA-B27 allele. Genetic predisposition, combined with environmental factors, immune responses, and other genes, likely contribute to the actual development and expression of these diseases.