Original articleLow frequency of HLA-B27 in ankylosing spondylitis patients from Turkey
Introduction
Ankylosing spondylitis (AS), the prototype of spondyloarthropathies (SpA) is strongly associated with HLA-B27. The frequency of HLA-B27 is over 90% in Caucasians with AS and the prevalence of AS goes parallel with the frequency of HLA-B27 in a population. The strength of the association varies among different racial and ethnic groups. The highest rates of AS have been found in native groups of North America. HLA-B27 positivity in Canadian Haida Indians reaches to 50% and the prevalence of AS among them is 4.2%, but both AS and HLA-B27 are very infrequent in black populations [1]. Along with the changes in the frequency of HLA-B27, there may be differences in the clinical characteristics of AS in different populations due to other genetic and environmental factors contributing to the disease. It is suggested that AS may develop at an earlier age and with a more frequent involvement of peripheral arthritis in developing countries [2].
Although AS and HLA-B27 interaction is one of the best-known disease associations and has been recognized since 1973 [3], [4], the role of HLA-B27 in the pathogenesis of AS is yet unknown. There are currently 45 alleles of HLA-B27 encoding 365 proteins (anthonynolan.org.uk, 10.05.2007). The distribution of HLA-B27 alleles also shows variations in different ethnic groups. Case control studies have determined that HLA-B*2705, B*2702, B*2704 and B*2707 are the alleles clearly associated with SpA [4]. Since HLA-B*2705 is found all around the world and is present in about 90% of B27 positive individuals with a Northern European descent, it is thought to be the origin of other HLA-B27 alleles [1]. Among B27 positive individuals, the prevalence of HLA-B*2702 is about 10% in Northern Europe, increases to 20% in Spain and Portugal and reaches up to 55% in Arabic and Jewish populations [1], [5], [6], [7]. HLA-B*2704 is common in Asia especially in China and Japan. HLA-B*2707 is a rare allele seen in India and Europe [1], [7], [8]. Further genetic studies of HLA-B27 and subtypes may provide a new clue to the pathogenesis of AS.
Owing to Turkey's geographical position like a bridge between Europe and Asia, disease characteristics and allele frequencies of AS patients may exhibit variations from previous studies. We planned this study to investigate the frequency and allelic distribution of HLA-B27 in AS patients from Turkey as well as its association with clinical manifestations.
Section snippets
Methods
Consecutive 112 patients according to the modified New York criteria for the classification of AS followed up at Istanbul University, Istanbul Faculty of Medicine, Department of Internal Medicine, Division of Rheumatology between February 2003 and February 2004 were included in the study [9]. None of the patients reported accompanying psoriasis (Ps), inflammatory bowel disease, Behçet's disease (BD), familial Mediterranean fever (FMF) or features of reactive arthritis.
Results
In this study 112 AS patients were evaluated for HLA-B27 status and its association with clinical findings. Demographic characteristics are shown in Table 1. Male to female ratio was 1.8, 27 (24.1%) patients described symptoms starting before 16 years of age (juvenile onset) and mean age at onset was 23. The most frequent symptoms were inflammatory back pain (IBP), buttock pain and pain due to enthesitis and was seen in 106 (94.6%), 102 (91.9%) and 87 (77.7%) patients, respectively (Table 2).
Discussion
The aim of this study was to assess the frequencies of HLA-B27 and its alleles in AS patients from Turkey as well as the clinical characteristics and to compare with other series. To our knowledge this is the first report about HLA-B27 and allele frequencies in AS patients from Turkey. Although main clinical characteristics of Turkish AS patients were comparable to earlier reports, some variations were noted in this study.
The male to female ratio (1.8) was lower than other studies in AS (M:F
Acknowledgement
This study was supported by RAED (The Society for Research and Education in Rheumatology, Turkey.)
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