Increased risk of developing ankylosing spondylitis among first‐born children

• Published in: Arthritis and rheumatism 2000-12, Vol.43 (12), p.2818-2822
• Main Authors: Baudoin, P., Van Der Horst‐Bruinsma, I. E., Dekker‐Saeys, A. J., Weinreich, S., Bezemer, P. D., Dijkmans, B. A. C.
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Biological and medical sciences; Birth Order; Diseases of the osteoarticular system; Female; Histocompatibility Testing; Humans; Inflammatory joint diseases; Male; Maternal Age; Medical sciences; Middle Aged; Pregnancy, High-Risk; Risk Factors; Spondylitis, Ankylosing - epidemiology; Spondylitis, Ankylosing - etiology
• ISSN: 0004-3591; 1529-0131
• DOI: 10.1002/1529-0131(200012)43:12<2818::AID-ANR23>3.0.CO;2-F

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.