Psoriasis is a chronic inflammatory skin disorder. Although the aetiology and pathogenesis of
psoriasis are unproven, it is hypothesised that the major histocompatibility complex (MHC) gene/haplotype contributes to the susceptibility of
psoriasis in many populations. MHC class I chain-related gene A (
MICA), located 46-kb centromeric of
HLA-B, is expressed on keratinocytes and fibroblasts.
MICA is in linkage disequilibrium with
HLA-B and is involved in natural killer-cell functions. To investigate the relative contribution of the
MICA gene in the pathogenesis of
psoriasis, extracellular polymorphisms of
MICA were studied by polymerase chain reaction-sequence specific primers in 128 Thai
psoriasis patients (87 and 41 were Types I and II, respectively) from Srinagarind Hospital, Faculty of Medicine, Khon Kaen University. The control group included 255 healthy, unrelated Northeast Thais. We observed 11
MICA alleles (or groups of alleles) in the patients. A comparison of the
psoriasis patients and the control group revealed that
MICA*010 and
MICA*017 were associated with Type I
psoriasis whereas only
MICA*010 was associated with Type II. The haplotype analysis revealed that
MICA*008-
HLA-B*13-Cw*0602 and
MICA*010-
HLA-B*4601-Cw*01 were significantly increased in both Types I and II, whereas
MICA*002-
HLA-B*38-Cw*07 (01-03) and
MICA*017-
HLA-B*57-Cw*0602 were elevated only in Type I.
MICA*010 was in strong linkage with Cw*01. Analysis of independent association of
MICA*010 in individuals lacking Cw*01 failed to maintain an association. Our results suggest that a significant increase of the
MICA alleles in the patient group is a part of
HLA-B-Cw haplotypes. It is conceivable that an unknown susceptibility gene, on certain
HLA-B-Cw haplotypes, is responsible for the development of
psoriasis.