HLA and psoriasis (with or without arthropathy)

30 probands affected by psoriasis, with or without arthropathy, and their relatives were typed for HLA-A, -B and -C antigens. Association of HLA-B16 and HLA-B17 with psoriasis was confirmed. One third of probands was without any known HLA-A, -B, -C marker. Considering probands with at least one HLA-B marker, we found that 50% of their sibs carrying marker is affected and the remaining 50% is healthy. To explain the weak association observed, an attempt to propose a model is made: such a model postulate a gene interaction between the HLA marker gene and an hypothetic "Ps (Psoriasis susceptibility) gene". The model, described in detail in this work, tries to explain why a large part (1/3) of probands is affected even if they do not carry any HLA marker and why 50% of marker positive sibs of marker positive probands are healthy.