Supporting evidence for genetic predisposition includes:
There is a higher-than-average incidence of psoriasis in relatives of people with psoriasis, indicating "familial tendency" to develop the disease; however, in some people with psoriasis no family history is evident.
There is an increased incidence of psoriasis in children when one or both parents has psoriasis.
In studies of identical and nonindentical twins, psoriasis is much more likely to appear in both identical twins than in both nonidentical twins, a finding that also confirms that more than one gene must be inherited to establish genetic predisposition for psoriasis.
There is a higher than expected frequency of certain white cell antigens (Class I human leucocyte antigens or HLAs) on cells of people with psoriasis and their close relatives; this finding also supports psoriasis inheritability and also suggests that the gene(s) involved in psoriasis may be on the same chromosome that holds the genes for HLA. There are many types of HLA in the HLA complex, and studies have shown that HLA type may be associated in some degree with timing of disease onset, type of psoriasis, and disease severity.
While the genetics of psoriasis remain to be worked out in detail, much is already known about patterns of inheritability. Persons with psoriasis who are worried about "passing it on" to children may wish to ask their dermatologist for genetic counseling.
