SUMMARY HLA-B27 subtypes can be defined by cellular, serological, and biochemical techniques. The seven subtypes4 9 So far identified represent structural variants of B27 with limited variations in the amino acid sequence of the B27 molecule. The routinely typed B27 'antigen' remains a common (shared, public) determinant present on various B27 molecules. The distribution of the subtypes varies strongly among different ethnic groups and they occur in different linkage disequilibria.4 In the healthy Dutch population only two subtypes were found: B27W (B27*1, B27M2+) (90%) and B27K (B27-2, B27M2-) (10%). A similar distribution of B27 subtypes was observed in 91 unrelated Dutch patients with ankylosing spondylitis (AS)-namely, 92% B27W and 8% B27K. In Oriental populations the subtype distribution is quite different: B27W occurs in less than 50%, whereas more than 50% individuals are of the B27C and B27D subtypes. Preliminary data indicate that the distribution of subtypes in healthy and diseased Oriental individuals is similar. These results suggest that the B27 and disease (AS) association is not correlated with the structural variations of one of the B27 subtypes, but with a common B27 determinant shared by various B27 subtypes. Consequently, the disease is older than the B27 variants. Further studies on disease and subtype distribution in various ethnic groups might contribute to a better understanding of the origin of both.

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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.

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: Spondyloarthropathy (SpA) as observed in patients with idiopathic inflammatory bowel diseases is categorized according to the recently developed criteria of the European Spondylarthropathy Group, and belongs to a large complex of rheumatic disorders, encompassing ankylosing spondylitis, Reiter's disease, psoriatic arthritis, and reactive arthritis. It has been recognized for many years that patients with ulcerative colitis or Crohn's disease frequently have arthritic complications. The gastroenterologist should therefore carefully evaluate any symptom of peripheral or axial arthritis, in an attempt to provide an accurate diagnosis, to define a realistic prognosis, and to establish adequate therapy at an early stage. In this review, clinical and etiopathogenic aspects are analyzed, not only of patients with inflammatory bowel diseases and SpA, but also of patients developing arthritic symptoms after gastrointestinal bacterial infections (reactive arthritis). The significance of ileal mucosal inflammation as observed frequently in patients with SpA is discussed; the contribution of immunogenetic factors in the development of SpA, such as HLA-B27, is briefly reviewed. Finally, analysis is made of the different therapeutic options that are available at present.