MICA and arthritic joint disease: Thus, it has been postulated that there are two different susceptibility loci associated with PsA in the MHC region: HLA-C*06, which is associated with the skin lesions (present in the extended haplotypes-EH-13.1, 37.1, and 57.1) and another, MICA-A9, associated with susceptibility to arthritis and present in EH38.1, EH39.1, and EH57.1.