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Matters arising
Role of HLA genes in familial spondyloarthropathy
  1. M A Brown1,
  2. A M Crane1,
  3. B P Wordsworth1
  1. 1Wellcome Trust Centre for Human Genetics, Spondyloarthritis and Bone Disease Research Group, Roosevelt Drive, Headington, OX3 7BN, UK
  1. Correspondence to:
    Dr M A Brown;
    mbrown{at}well.ox.ac.uk

https://doi.org/10.1136/ard.61.8.764

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    Said-Nahal and colleagues report an intriguing finding of an association with HLA-DR4 independent of B27 in families with ankylosing spondylitis (AS),1 a finding highlighted by an accompanying editorial.2 The approach of studying B27 positive and B27 negative haplotypes may prove powerful in identifying further cis or trans encoded genes involved in AS. However, the reported association of DR4 with AS is quite a surprising finding given that no difference was noted in B27-DR4 haplotype frequencies in patients and ethnically matched healthy controls. Many previous studies have not reported any such association,3–9 including a similar preliminary study by the same authors.10 Although these studies were mainly case-control studies, population stratification is highly unlikely to cause a false negative finding if the effect size of the reported association with DR4 is as high as Said-Nahal and colleagues describe.

    We are concerned that both the family and case-control results are biased by the statistical approach employed. Multicase families were used in the study, yet a form of transmission test for linkage disequilibrium (TDT) was used11 which is only suitable for single affected families, and …

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