http://www.jyi.org/volumes/volume4/issue1/art...grove.html

Because these symptoms have a higher incidence in the offspring of infected individuals, the genetic basis for the pathogenesis of psoriasis has been studied using varied approaches, including twin studies. Results indicate that it is a genetically modulated disease (Cooper et al. 1999; Capon et al. 2000). Several specific human lymphocyte antigen (HLA) alleles have been associated with the disorder, as well gene products from chromosomes 1, 3, 4, 6, 8, 16, and 17, clearly identifying psoriasis as a multifactorial disease (Bhalero et al. 1998; Allen et al. 1999; Capon et al. 2000; Cooper et al. 1999).