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Increased risk of developing ankylosing spondylitis among first-born children
P Baudoin1, I E van der Horst-Bruinsma, A J Dekker-Saeys
1University Hospital, Vrije Universiteit, Amsterdam, The Netherlands.
Insights
First-born children have a higher risk of developing ankylosing spondylitis (AS). Lower maternal age at delivery is also associated with increased AS risk in offspring. This study highlights birth order as a significant factor in AS development.
Area of Science:
- Rheumatology
- Genetics
- Epidemiology
Background:
- Studies in mice suggest a link between litter order and ankylosing enthesopathy.
- Previous human studies have not explored birth order or maternal age as risk factors for ankylosing spondylitis (AS).
Purpose of the Study:
- To investigate if first-born children have a higher risk of AS compared to later-born children.
- To determine if maternal age at delivery is a risk factor for AS.
Main Methods:
- Compared birth order of 162 AS patients with their healthy siblings.
- Stratified analysis by maternal age at first delivery.
- Compared maternal age at delivery for first-born AS patients with population data.
Main Results:
- Significantly higher number of first-born children among AS patients compared to expected rates (P = 0.004).
- Mean maternal age at first delivery was lower for AS patients (24.8 years) versus controls (26.1 years).
Conclusions:
- Low birth order is identified as a risk factor for ankylosing spondylitis in humans.
- Maternal age at first delivery may also play a role in AS development.
Objective:
Studies in mice have demonstrated an increased risk of ankylosing enthesopathy in earlier litters compared with later-born offspring. In humans, birth order and maternal age as risk factors for ankylosing spondylitis (AS) have not been investigated previously. This study was undertaken to investigate whether first-born children have a higher risk of AS than later-born children and whether maternal age at delivery is another risk factor.
Methods:
The birth order of 162 AS patients was compared with that of their healthy siblings, both for the total group and with stratification for maternal age at first delivery. Maternal age at the time of delivery of AS patients who were first-born children was compared with the mean maternal age at first delivery in the Dutch population.
Results:
The number of first-born children with AS was significantly higher than would be expected in case of an equal risk between first-born and later-born children (26 versus 20 for families with 2 children [P = 0.029] and 63 versus 47.6 for all families [P = 0.004]). Also, the mean maternal age at first delivery was lower in mothers of AS patients (24.8 years) compared with mothers of healthy controls (26.1 years).
Conclusion:
Low birth order is a risk factor for AS in humans.