Psoriasis, sacro-iliitis and peripheral arthritis occurring in patients with the same HLA haplotype. A preliminary family report and a hypothetical explanation of the interaction between MHS products.

The present family investigation has shown that genes within the MHS are mainly responsible for the development of psoriasis or psoriasis-associated arthritic lesions (peripheral arthritis and sacroiliitis). We have hypothetically discussed the possibility that multiple genes, all located within the MHS, act in concert to increase the risk of developing disease to very high levels. This implies that at least two MHS linked genes act in complementary fashion for the development of disease, these genes seem to be able to operate both in the cis and in the trans position. One of these genes would be situated in the chromosomal portion of the MHS which carries the HLA-D locus. Families with a high incidence of disease would show inheritance according to the cis position of genes, when it can be shown that most of the carriers of the specific disease-associated haplotype are affected by disease, whereas in other families, complementarity between two distinct HLA haplotypes with genes acting in the trans position would result in disease.