Itchy, painful, cracked skin that won’t go away… crumbling nails, inflamed scalp…. these are just some of the problems that people with psoriasis deal with every day.
The National Psoriasis Foundation estimates that about 7.5 million people in the US have psoriasis. There is a strong genetic component to psoriasis, and it tends to run in families. Along with the skin condition, there are other autoimmune conditions, such as Crohn’s disease, psoriatic arthritis, and uveitis, that are found more often in people with psoriasis.[ref][ref]
Psoriasis is an autoimmune condition that causes dry, sometimes itchy patches of skin. It is caused by the immune system attacking your skin cells, speeding up the turnover of the cells.
Everyone’s skin cells are constantly being replaced, and normal skin cells are replaced about once a month. For people with psoriasis, the turnover rate for skin cells can be as fast as three to four days, with the dead cells building up and flaking off in itchy, dry patches.[ref]
The HLA genes code for proteins that are a big part of our immune system known as the major histocompatibility complex(MHC), which helps the body identify foreign invaders. There are six different HLA class I genes (A, B, C, E, F, and G) and four different HLA class I genes (DM, DO, DQ, DP, and DR). (Here is a good video on the HLA family for those who want to learn more.)
There are a lot of genetic differences within the HLA genes, which leads to some people being more susceptible to one thing along with being less susceptible to something else.
This variability of HLA genes is a tradeoff that keeps our population as a whole thriving — some of us are great at fighting off a herpes virus while others are less susceptible to getting tuberculosis or leprosy.
In fact, some hypothesize that the HLA type susceptible to psoriasis is prevalent in humans because it is preventative for leprosy.
Different HLA genes are often associated with autoimmune diseases. For example, HLA-DQ2 is implicated in susceptibility to celiac disease (check your genes here) and HLA-B27 is tied to several different autoimmune diseases (check your genes here).
Susceptibility to psoriasis is linked to a couple of HLA genes. Just carrying the HLA type is not enough to cause psoriasis by itself, so the genetic variants act together with other genes or environmental factors in causing psoriasis.
Over 60% of psoriasis patients carry a specific HLA variant called HLA-Cw*0602. This variant is found in about 10% of the population as a whole. Therefore, just carrying the variant isn’t enough to cause psoriasis, but it does make a person much more susceptible to it.
A doctor (or lab) can do a test to see if you carry the HLA-Cw*0602 variant for sure, but there are a couple of variants of the HLA-C gene that are available through 23andMe and linked to significantly increased psoriasis risk.
Check your genetic data for rs10484554 (23andMe v4, v5; AncestryDNA):
Check your rs1265181 (23andMe v4, v5; AncestryDNA):
*Note that the orientation on this is flipped to match 23andMe (plus strand) orientation. If you are looking at the older studies on the SNP, you will see G as the risk allele (minus strand orientation).
Research studies show a connection between strep throat and psoriasis, which may be increased due to HLA-Cw*0602:
There is also a link between IBD and psoriasis.[ref]
A variant of the HCP5 gene predicts the HLA-B*5701 genotype for Caucasians and Hispanics with 99.9% accuracy.
Check your genetic data for rs2395029 (23andMe v4, v5; AncestryDNA):
IL23 gene: codes for interleukin-23, a component of the immune system
Check your genetic data for rs11209026 (23andMe v4, v5; AncestryDNA):
Check your genetic data for rs1217414 (23andMe v4; AncestryDNA):
Certain psoriasis medications work better for people with certain HLA types. So take your genetic information to your doctor along with the research studies showing which medications may work best. A recent study (full study – .take to your doc) shows that the type of psoriasis medication known as biologics works better for those who carry the HLA-Cw*0602 serotype. Although the study only included a few hundred people, a couple of the biologics were clearly more likely to be effective based on HLA type.
Breaking this down even further, the type of biologic that is an anti-TNF-alpha drug was found in a study to be more likely to be effective in those who carry the rs1799724 C/C genotype (TNF -857C).
Check your genetic data for rs1061622 (23andMe v4, v5):
The same study found that those carrying the TNF receptor variant rs1061622 T/T genotype (TNFRSF1B 676T) were also more likely to have a good response to the anti-TNF-alpha biologic.
Check your genetic data for rs1061622 (23andMe v4, v5; AncestryDNA):
Another study found that other TNF-alpha variants could also be used to help predict who would respond well to anti-TNFalpha biologics.
Check your genetic data for rs1800629 (23andMe v4, v5; AncestryDNA):
Check your genetic data for rs361525 (23andMe v4, v5; AncestryDNA):
Talk with your doctor, of course, on which medicine is best for your situation.
Dietary interventions: A study of 1206 psoriasis patients found that several dietary modifications were effective. Reducing alcohol helped 54% of patients. Cutting out gluten and/or nightshades helped over half of the patients. Adding in fish oil, more vegetables, and vitamin D helped around 40% of the patients. [ref]
Quercetin has been shown in several mouse studies to reduce levels of TNF-alpha and NF-kappa beta.
Curcumin has been shown in studies to reduce the inflammation of psoriasis. The human studies are using oral curcumin, and animal studies use topical curcumin (stains the skin yellow?). Curcumin is found in the spice turmeric, or it is available as a supplement. [ref]
Vitamin B12 may help, especially if you are low in B12. [ref]
Genetic link to nightshade sensitivity (BChE variant)
COMT gene variant can point towards the right vitamin B12
Some people are more likely to need fish oil
Updated and expanded on 11/04/2019