The genetics of psoriasis has been studied with a questionnaire requesting information on presence or absence of the disease in relatives of 698 probands and 104 controls (spouses of probands). A statistically significant familial concentration of the disease has been demonstrated which, together with twin studies, supports the concept that hereditary factors contribute to the etiology of psoriasis. Pedigree analysis and frequencies of psoriasis among siblings of probands were not consistent with inheritance of genetic differences at a single autosomal or x-linked locus, even with decreased penetrance due to delayed age of onset. These findings plus further analysis suggested that psoriasis is determined by multifactorial inheritance. Estimates of heritability of liability for psoriasis were consistent among parents (64%) and siblings (65%) of probands. Hereditary factors play an important role in the etiology of psoriasis.
Watson W, Cann HM, Farber EM, Nall ML. The Genetics of Psoriasis. Arch Dermatol. 1972;105(2):197-207. doi:10.1001/archderm.1972.01620050011002