New research suggests that having a tonsillectomy or older siblings may increase the risk of developing ankylosing spondylitis — a specific type of inflammatory arthritis.
Ankylosing spondylitis is a chronic inflammatory arthritis that mainly affects the spine and pelvic joints, leading to pain and stiffness. This type of arthritis typically appears in young adulthood, and in severe cases, it can cause the vertebrae to fuse.
While its exact cause remains unclear, genetic factors and conditions like Crohn's disease or psoriasis are believed to play a significant role.
In addition, scientists believe environmental and early-life factors may also contribute to the development of ankylosing spondylitis.
To investigate these potential risk factors, Swedish researchers conducted a nationwide, register-based case-control study using Swedish National Patient Register health and family data. From this information, the researchers identified 5,612 people with ankylosing spondylitis and matched them with 22,042 individuals without the condition.
Their research was published on October 16 in RMD Open.
What factors increase the risk of ankylosing spondylitis?
After analyzing the data, the scientists discovered several factors that appear to raise the risk of developing this type of arthritis.
- Having one or more older siblings increased the risk by 12% to 15%.
- Experiencing severe childhood infections led to a 13% increased risk.
- Tonsil removal before age 16 was linked to a 30% increased risk for ankylosing spondylitis.
Moreover, individuals from multiple births, such as twins, were 23% more likely to develop the condition, and people born in the winter also had an increased risk.
After adjusting for potential influential factors in a sibling comparison, the scientists found an 18% elevated risk of developing ankylosing spondylitis among people with one older sibling. However, the risk jumped to 34% among those with two or more older siblings. In addition, tonsil removal increased the risk of developing ankylosing spondylitis to 36%.
However, the risk level associated with severe childhood infections fell to 4% after adjusting for other influential factors in the sibling comparison.
While the study's results don't prove these factors cause ankylosing spondylitis, the authors conclude that older siblings and a history of tonsillectomy in childhood were independently associated with the development of the condition, even after they adjusted for family-shared factors.
They also offer some possible explanations. For example, the scientists note that children will likely have experienced repeated infections in the time leading up to a tonsillectomy, and younger siblings are more likely to be exposed to infections early in life than older siblings. These factors could explain the links between childhood infections or tonsil removal and ankylosing spondylitis.
They also suggest antibiotic use could play a role, as antibiotics interfere with the gut biome, which they suspect may contribute to developing ankylosing spondylitis. However, the researchers did not examine antibiotic use in this study.
Though the heightened risks of ankylosing spondylitis associated with severe infections fell after adjusting for family-shared factors, the scientists say these results add more weight to the hypothesis that childhood infections play a role in the development of the condition.