It has long been considered that psoriasis has a genetic component. What that means is there might be something in your DNA that makes it more likely that you could develop psoriasis. There are several specific DNA abnormalities that have been linked with various conditions, and it now looks like psoriasis may be added to the list.

A report from the University of Utah has found a genetic variation that "stands alone as a high risk for psoriasis". This genetic variation, called HLA-Cw*0602, appears to be a major factor in developing psoriasis. Just as there are many forms of psoriasis there are almost certainly various other genetic variations that determine how psoriasis might manifest itself in any particular individual, but this is a big step forward.

Gene Variation Is ‘Major Genetic Determinant of Psoriasis’ (08/27/2009)

(this links to the article posted on the University of Utah Health Care web site)