However, these genes add only a small amount to the frequency of the genetic association in this disease, and there are certain caveats that must be considered, Dr. Weisman said. For example, the ERAP1 association with AS is not seen in the Chinese population, and the ERAP1 association is only found in those with HLA-B27 positivity, which implies a gene-gene interaction.
There remains a great deal of work to be done to define the genetic bases of AS, he said.
In the meantime, efforts to better determine AS prevalence based on newer classification criteria are underway.
Unlike the modified New York criteria, which used clear-cut radiographic sacroiliitis, new classification criteria for axial spondyloarthritis developed by the Assessments in Ankylosing Spondylitis Working Group uses additional features to increase sensitivity. One set of criteria uses HLA-B27 plus two additional features of spondyloarthritis for AS classification, and one uses sacroiliitis on imaging plus one spondyloarthritis feature to make a diagnosis. This increases sensitivity of screening to over 80%, he said (Ann. Rheum. Dis. 2009;68:777–83).
Furthermore, a screening questionnaire developed and published last year by Cedars-Sinai Medical Center to help improve diagnosis and to identify more patients on a population basis using various clinical features will be applied to National Health and Nutrition Examination Survey data for 2009–2010, which included a new survey on inflammatory back pain and spondyloarthritis. Together these seek to provide the first U.S. national inflammatory back pain estimate, and the first national U.S. study of HLA-B27 prevalence, Dr. Weisman said.
“With these two, we'll be able to find the lower bound of the true prevalence of ankylosing spondylitis in the United States,” he said.
Dr. Weisman had no financial disclosures to report.