A comprehensive study recently published in the open-access journal RMD Open has established correlations between the presence of older siblings, the surgical removal of tonsils during childhood, and an elevated risk of developing ankylosing spondylitis (AS), a form of chronic inflammatory arthritis. Utilizing data from Swedish health registries, the research points to a 12-15% increased risk for individuals with older siblings, and a 30-36% risk for those who had tonsillectomies during their formative years. Despite the observational nature of the study, which limits its capacity to definitively prove causality, it lends weight to the notion that infections during early years of life might be a contributory factor in the onset of AS.
Table of Contents
Study Overview and Examination of Early Life Risk Factors
To delve deeper into the subject, the investigators employed health and familial data from Swedish national population registries. They conducted a comparison between adults who had been diagnosed with AS and those who had not, based on multiple early-life risk factors.
To be included in the case-control study, individuals had to have at least one documented visit to an inpatient or outpatient specialist clinic with a diagnosis of AS between January 2001 and December 2022.
For each case, approximately four controls from the general population were matched by sex, birth year, and geographic location, none of whom had been diagnosed with AS.
The study considered a wide array of early-life risk factors, such as maternal age at childbirth, Body Mass Index (BMI) during early pregnancy, smoking status of the mother; length of gestation; birth weight; occurrence of multiple births; type of delivery (Caesarean or natural); infections in the mother during pregnancy; and season of birth. Other variables like the total number of siblings, occurrence of severe infections from birth until the age of 15, and surgical removal of tonsils or appendix prior to the age of 16 were also examined.
Findings Concerning Risk Factors and Analysis of Sibling Impact
The study found that 6771 individuals born after 1973 were diagnosed with AS between the years 2001 and 2022. Among these, 5612 were born in Sweden and were chosen as the cases for the study.
Certain factors correlated with an increased likelihood of receiving an AS diagnosis. Notably, individuals with one or more older siblings had a 12-15% increased risk. The study also discovered that serious infections during childhood correlated with a 13% elevated risk, whereas tonsillectomy before the age of 16 was linked to a 30% increased risk.
In a sub-analysis focused on sibling comparisons—accounting for 3965 individuals with AS and 6070 siblings without—the data suggested an 18% increased risk for those with one older sibling, escalating to 34% for those with two or more older siblings. This analysis was adjusted for variables such as sex, maternal age, and year of birth.
Limitations and Final Observations
It is essential to note that the study is observational and therefore cannot definitively establish causation. Additionally, the researchers did not have access to primary care records; thus, they relied on hospital data for identifying severe infections and tonsillectomies. The study only included individuals born after 1973.
The concluding remarks of the researchers affirm that the presence of older siblings and a history of tonsillectomy during childhood are independently correlated with a higher likelihood of developing AS. These findings further substantiate the hypothesis that infections during early life could be influential in the development of this condition.
Funding and Reference
The research was financially supported by the Swedish Research Council and the Swedish Rheumatism Association.
Reference: “Association of childhood infections and perinatal factors with ankylosing spondylitis: a Swedish nationwide case–control and sibling study” by Matilda Morin, Karin Hellgren, Ulf Lindström, and Thomas Frisell, published on 1 September 2023 in RMD Open.
DOI: 10.1136/rmdopen-2023-003438
Frequently Asked Questions (FAQs) about Ankylosing Spondylitis Risk Factors
What is the main finding of the study regarding ankylosing spondylitis?
The main finding of the study is that having older siblings and undergoing tonsil removal during childhood are associated with an increased risk of developing ankylosing spondylitis, a chronic inflammatory arthritis.
What data sources did the researchers use for this study?
The researchers utilized health and familial information from national Swedish population registries to conduct this study.
What were the early-life risk factors considered in the study?
The early-life risk factors considered include maternal age at childbirth, Body Mass Index during early pregnancy, length of gestation, birth weight, occurrence of multiple births, type of delivery, maternal infections during pregnancy, and the season of birth. Other variables such as the total number of siblings, serious infections from birth until age 15, and surgical removal of tonsils or appendix before the age of 16 were also examined.
What is the significance of the sibling comparison sub-analysis?
The sibling comparison sub-analysis aimed to adjust for potentially influential environmental factors shared within families. It indicated an 18% increased risk for those with one older sibling and a 34% increased risk for those with two or more older siblings in developing ankylosing spondylitis.
Can this study definitively establish causation between these factors and ankylosing spondylitis?
No, the study is observational in nature and therefore cannot definitively establish causation. It can, however, identify associations and contribute to the body of evidence supporting the role of early-life infections in the development of ankylosing spondylitis.
Who funded the research?
The study was financially supported by the Swedish Research Council and the Swedish Rheumatism Association.
Are there any limitations to the study?
Yes, the study has several limitations. It is observational and cannot establish causation. Additionally, the researchers relied only on hospital data to identify severe infections and tonsillectomies, and the study included only individuals born after 1973.
