SNPwatch gives you the latest news about research linking various traits and conditions to individual genetic variations. These studies are exciting because they offer a glimpse into how genetics may affect our bodies and health; but in most cases, more work is needed before this research can provide information of value to individuals. For that reason it is important to remember that like all information we provide, the studies we describe in SNPwatch are for research and educational purposes only. SNPwatch is not intended to be a substitute for professional medical advice; you should always seek the advice of your physician or other appropriate healthcare professional with any questions you may have regarding diagnosis, cure, treatment or prevention of any disease or other medical condition.
Millions of Americans suffer from the itchy, scaly skin brought on by psoriasis. In mild cases the condition is only a nuisance, but in the most severe cases it can be painful, disfiguring, and disabling.
Although the what of psoriasis is largely understood –immune cells mistakenly attack healthy skin cells, triggering further immune responses that lead to an overproduction of skin cells — – the why is not. Environmental factors, such as infections and injuries, may play a part, but twin studies have suggested that genetics has an even larger role.
Recent studies have started to unravel the genetics of psoriasis, showing that variations in several immune system genes can increase the odds of developing the disease. Now three studies, published online yesterday in the journal Nature Genetics, add to the list of variations associated with psoriasis and expand previous findings among Europeans to an Asian population.
Using data from more than 6,000 psoriasis patients with European ancestry and an equal number of unaffected controls, Rajan Nair and colleagues from the Collaborative Association Study of Psoriasis found seven genetic variations that were significantly associated with increased odds of developing psoriasis. All of these variations were in immune system-related genes, in keeping with previous research.
(Two of the variations identified by Nair et al are equivalent to SNPs already included in the 23andMe Health and Traits Clinical Report on psoriasis. Details of the four of the other five SNPs, and all others discussed here, are included in a table at the end of this post. Data on one SNP, near the TNIP1 gene, is not currently available from 23andMe.)
The second report, authored by Rafael de Cid and colleagues from several institutions in the United States and Europe, found a deletion of about 32,000 DNA bases that increases the odds of psoriasis. Their study used data from about 2,800 psoriasis patients and controls from the U.S., Spain, the Netherlands and Italy.
This deletion compromises two genes, LCE3C and LCE3B, which are part of a larger group of genes called the LCE gene cluster that are involved in the proper development of skin cells. de Cid et al speculate that other LCE genes are usually able to make up for the loss of LCE3C and LCE3B, but not perfectly. The result is skin that can become “leaky” due to injuries, allowing allergens and bacteria to penetrate the protective barrier of the skin. In someone with other risk factors for psoriasis, this could be enough to set off the inflammation characteristic of the disease.
(23andMe customers can use data for a SNP located near the deletion as a proxy for this variation.)
This week’s final Nature Genetics report on psoriasis comes from Xue-Jun Zhang and colleagues, who looked at SNPs in a large group of Han Chinese people (more than 5,000 patients and 6,500 controls) and a smaller group of Chinese Uygurs (539 patients and 824 controls). According to the authors this is the first study of its kind to examine genetic variations linked to psoriasis in the Chinese population.
Zhang et al. found three genetic variations associated with psoriasis in the Chinese population. Two of these – located in the HLA and IL23A genes – were replications of well-established associations in Europeans. The third association was in the LCE gene cluster, supporting the association in this same region found by de Cid in Europeans.
The results of all three studies may help scientists better understand psoriasis, but as Nair et al point out, they are only the beginning of a long road. Researchers will need to look more closely at the regions of the genome identified in these and other studies to find the true causes of the risk increases they have seen. The SNPs found so far are likely to only be signposts pointing the way. Further studies, using larger sample sizes and drawing together the findings of multiple research groups, will also be needed to uncover the many other genetic variations that likely contribute to psoriasis.
*”Effect” is the increase in odds compared to someone with two copies of the non-risk version of each SNP.
|SNP||Nearby Gene||Risk Version||Effect||Notes|
|rs2201841||IL23R||G||1.13||Distinct from IL23R SNP in psoriais Clinical Report|
|rs4112788||LCE||G||1.41||Proxy SNP for LCE deletion|
|SNP||Nearby Gene||Risk Version||Effect||Notes|
|rs1265159||HLA||A||22.62||Proxy SNP for rs1265181 in paper|