What Do Genetics Have to Do with Psoriasis?
Scientists still don’t know exactly what causes psoriasis, but the general consensus is that the most likely cause of this chronic autoimmune disorder is a combination of specific immune-related gene mutations (changes) and environmental triggers. But just how much does having a family member with psoriasis increase one’s risk of developing the condition? Science offers a lot of information and theories, but some questions remain.
When a Parent Has Psoriasis
While psoriasis can occur in people who don’t have a known family history of the condition, doctors believe having a family member with psoriasis increases the risk.
According to the National Psoriasis Foundation, you have about a 10 percent chance of getting psoriasis if one of your parents has it. And if both of your parents have it, the risk increases to 50 percent. It’s estimated that one third of people with psoriasis (that’s 125 million worldwide, equal to 2 to 3 percent of the population—including more than 8 million in the U.S. alone) have a relative who has it, too.
Cracking the Genetic Code
“Classic psoriasis [known as plaque psoriasis] has a strong genetic component, but there is no specified pattern of inheritance,” says board-certified dermatologist Daniel P. Friedmann, M.D., from Westlake Dermatology & Cosmetic Surgery in Austin, Texas.
Immediate family and extended family members of a person with psoriasis are at increased risk of developing psoriasis, Friedmann explains, but the fact that one or both parents have psoriasis in no way guarantees that any of their children will develop the disease. “In fact, the risk of an identical twin developing psoriasis (when the other twin is affected) is only 2- to 3-fold higher than that of a fraternal twin,” he says.
The issue of genetics in psoriasis is complex, and it’s only one part of a bigger picture. Research suggests that around 10 percent of the population inherit one or more of the genes that increase the chance of developing psoriasis, but only 2 to 3 percent of the population will actually end up with the condition. Those who don’t may not have the right collection of genetic features and/or they may not have had exposure to specific environmental triggers.
In other words, both environmental triggers and genes come into play when it comes to the development of psoriasis. This means that without a specific trigger (such as a chronic infection; the use of certain medications, including lithium and beta-blockers; smoking; or, stress, to name a few), a person who has psoriasis-related genetic features may never develop the condition.
Typically, scientists focusing on the genetic component of psoriasis begin with the premise that an immune system malfunction is the underlying issue. Research published in the journal Current Dermatology Report in March 2014 showed that psoriatic skin has large quantities of immune cells that produce inflammatory molecules called cytokines.
And there’s not just one gene that may be responsible for an increased likelihood of psoriasis; scientists have discovered about 25 genetic variants that could be linked to the condition, per the National Psoriasis Foundation.
Psoriatic skin also contains gene mutations (changes) known as alleles, and back in the 1980s some researchers thought a single allele might be responsible for the hereditary nature of psoriasis. But a study published in the journal Trends in Genetics in September 2010 found that this allele alone (HLA-Cw6) wasn’t enough to make someone develop the condition. A more recent study, published in the British Journal of Dermatology in April 2018, concluded that more research is needed to determine the role of HLA-Cw6 in the development of psoriasis. It also confirmed that across the world, the gene mutation was generally higher in white people than in other ethnicities.
According to Genetics Home Reference from the U.S. National Library of Medicine, CARD14, another gene mutation linked to psoriatic disease, may lead to additional inflammation. Scientists believe that it produces plaque psoriasis following exposure to an environmental trigger, such as an infection. A study published in the journal AJHG in May 2012 found CARD14 present in two large families containing many members with both plaque psoriasis and psoriatic arthritis.
No True Way to Measure Risk
Without a doubt, the relationship between genetics and psoriasis is interesting. But it’s not something that should be a cause for concern, whether you have a relative with psoriasis and are worried about your risk for developing the condition, or you have it yourself and want to do everything you can to prevent your children developing it, too.
“There is also no genetic testing that can be performed to reliably determine whether the child of a psoriatic parent will develop psoriasis,” Friedmann says. This is largely due to the fact that at least 60 genes have been implicated in increased susceptibility to the disease.
Focus on What You Can Do
There’s also the fact that chance may play a part. It’s probable that a person needs a very specific combination of genetic mutations for psoriasis to develop. And even then, the condition might never manifest unless that person is exposed to a particular trigger.
Of course, some triggers are avoidable. You can get vaccinations and practice good personal hygiene to reduce the risk of infection. There’s also a theory that smoking may be a trigger for psoriasis (there’s a higher incidence of smoking among people with psoriasis), and that’s one thing you can choose to avoid. Other triggers, such as stress, are more difficult to avoid.
As research into the relationship between genes and psoriasis continues, experts in the field will discover new ways of treating and preventing the condition. One day their work may even lead to a cure.