Spondyloarthropathies in eastern Asia

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Abstract
The association between HLA-B27 and the spondyloarthro-pathies (SpAs) is so strong that it is supposed that the HLA-B27 molecule plays a pathogenetic role. In whites and Indonesians, the frequency of HLA-B27 is about 10%; in Chinese it is about 8%; and in Japanese it is only about 1%. The prevalence of SpA in the Chinese is at least 0.2%, but in native Indonesians, Philippians, and Malaysians, SpA is rarely seen. Twenty-three subtypes (B*2701–B*2723) have been distinguished. These subtypes are not equally distributed over the world. In most countries the distribution of the subtypes among HLA-B27 SpA patients is the same as that among the normal HLA-B27-positive population. In China, the subtype B*2704 is frequent and the prevalence of SpA is high. Native Indonesians, however, mostly have subtype B*2706, and SpA is rarely seen in this population. It was shown that B*2706, probably like B*2709 in Sardinia, is not associated with SpA. The difference between the SpA-associated and non-SpA-associated subtypes is limited to only two amino acid residues (114 and 116) at the bottom of the peptide-binding groove of HLA-B27. This small difference between health and disease rewards studies for different peptide-binding capacities and may help us characterize the peptides that are involved in the pathogenesis of SpA. The differences in disease associations in these countries also have clinical implications. In Southeast Asia, HLA-B27 typing without subtyping has less clinical usefulness than in parts of the world where B*2706 is rarely seen. When native Indonesians, Malaysians, or Philippians are suspected of having ankylosing spondylitis or a related SpA, it is worth asking if they had white or Chinese ancestors. If native HLA-B27-positive Indonesians (with subtypes other than B*2706) develop SpA, the clinical features are not different from those in other parts of the world. In the Chinese population on the mainland and in Taiwan, juvenile SpA is frequently seen. The onset is often a peripheral arthritis or enthesitis.