Siblings and Environmental Factors
Those who underwent the procedure when younger had an approximately one-third increased risk of developing ankylosing spondylitis, a form of chronic inflammatory arthritis.
Swedish researchers found that people with an older sibling were more likely to get the disease, suggesting early environmental effects.
Early Life Risk Factors
Almost 7,000 individuals with the disease who were diagnosed between January 2001 and December 2022 participated in the study.
Individuals were categorized based on early life risk factors, which comprised the age of the mother at the time of delivery, her weight during early pregnancy (BMI), the duration of her pregnancy, the birth weight of her baby, and the method of delivery performed.
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The number of siblings, the occurrence of severe childhood infections from birth to age 15, and tonsil and appendix removal prior to the age of 16 were additional factors that were taken into account.
Siblings Comparison Analysis
Studies found that older siblings and severe childhood illnesses increased risk by 12–15% and 13%, respectively.
In contrast, tonsil removal was found to be correlated with a 30% increased likelihood of developing the condition, which is commonly distinguished by inflammation of the tendons, spine, and joints, leading to symptoms such as fatigue, pain, and stiffness.
Multiple births increased risk by 23%, according to BMJ research. Whereas being born in the summer or autumn months posed a considerably lower risk than being born in the winter.
Childhood Infections Hypothesis
The increased risk may be due to older siblings’ higher risk of infancy infections. Whereas tonsillectomies were frequently performed as a response to infections, according to scientists.
Following this, the researchers conducted a sibling comparison analysis, which controls for potentially influential family-wide environmental factors.
Compared to having no elder sibling, this analysis revealed an 18% increased risk for those with one older sibling. This risk rose to 34% for those with two or more older siblings and 36% for those with tonsils removed.
A history of tonsillectomy in childhood and having elder siblings were found to be independently associated with the development of ankylosing spondylitis, the researchers conclude, even after controlling for family-shared factors in a sibling comparison analysis.
This provides additional support for the hypothesis that childhood infections contribute to the development of the condition.
