New hypotheses in the genetics of psoriasis and other 'complex' diseases.

Psoriasis is a complex genetic disorder in which the disease, according to the current concept, is caused by the interplay of many different genes. However, recent genetic studies indicate that the location of these genes varies considerably among populations and families, raising the question of how the same phenotype can be induced by such variable genetic linkages. To circumvent these discrepancies we propose that psoriasis could be induced by the same repetitive DNA sequence, an endogenous retroviral element present at different locations in the genome. The occurrence of the disease could be linked to an abnormal activation of one or more endogenous retroviral element copies due to their location and/or to modification of their sequence. This unifying concept would simplify our understanding of genetically complex diseases.