Any person can develop psoriasis. This common skin condition does not spare any gender, ethnicity, or those with other skin diseases. For most people, psoriasis is diagnosed in their teens or 20s. Men and women are equally affected. Some children may be diagnosed with psoriasis, but the disease may look different from adult psoriasis. Some people are at increased risk for psoriasis. Specifically, a person’s risk increases if a first-degree relative (parent, grandparent, or sibling) has psoriasis.
Other risk factors for psoriasis include psoriasis in other family members (aunts, uncles, and cousins), psoriatic arthritis in family members, or a family history of autoimmune diseases. When people with psoriasis are surveyed about having family members with the dis-ease, 40% to 65% of individuals know of an affected family member.
Many studies have investigated how a person’s genetic background affects psoriasis. The genes that seem to be common in psoriasis sufferers—and less common in people without psoriasis—are those in the immune system. Although this information may be therapeutically useful in the future, at the present time no test is commercially available to determine the genotype or genetic fingerprint of psoriasis sufferers, and no changes in prognosis or therapy would be needed based on the results.
In studies of siblings, twins, and first-degree relatives (siblings, parents, and children), relative risks have been estimated. When one twin has psoriasis, the chance of the second twin being diagnosed was 58% in one study, based on 141 sets of twins. If a sibling has psoriasis, the chance of another sibling developing the disease is lower, around 6%. When one parent has psoriasis, the chance of a child acquiring the disease is below 20%, but if both parents have psoriasis the chance increases to 65%. The severity of disease varies within families, and not every related person with psoriasis has the same amount or location of the disease.