MICA gene and ankylosing spondylitis: linkage analysis via a transmembrane-encoded triplet repeat polymorphism.

In order to address the possibility that the MICA gene located 47 kb upstream from HLA-B is involved in the pathogenesis of ankylosing spondylitis (AS), we have investigated microsatellite polymorphism in the transmembrane region of MICA in Caucasian patients with AS. The microsatellite allele consisting of 4 repetitions of GCT/AGC was present at significantly higher frequency in the patient group (Pc<0.0000001) than in the ethnically matched control group. However, the frequency of the (GCT/AGC)4 allele was significantly low in the B27-positive patients than in the B27-positive healthy controls (Pc=0.0145). These observations suggest that B27 itself remains the primary genetic marker for AS, although the significantly dissimilar phenotype frequency of the (GCT/AGC)4 allele in B27-positive patients and healthy individuals may reflect the existence of other genetic factor(s) in the HLA-B27 haplotype involved in the development of AS.