What Causes Psoriasis?
What we do know about the causes of psoriasis is this:
Healthy skin cells are attacked by a particular type of immune cell called a T lymphocyte. This triggers a cascade of immune responses that leads to the over production of skin cells. The life cycle of a skin cell is typically around 30 days – they form, mature and are then sloughed off. But in psoriasis the process is so fast that it takes under six days.
T cells secrete chemicals that are usually of benefit to the skin, but here they are produced in abnormally large quantities which irritates and inflames the skin and some joints. This autoimmune reaction has a number of triggers such as stress, skin injuries, some medications and chest infections.
Psoriasis is seen to run in families which indicates that there is a genetic involvement. A number of genes have now been linked to the condition.
Genetics of Psoriasis
Scientists studying the genetics of psoriasis have uncovered a number of genes that are likely to contribute to the onset of the skin disease. Research into its genetic basis didn't really get underway until the 1970s when increased funding and technological advances made the search possible.
Over the years there have been a number of landmark studies that have pinpointed a number of genetic causes:
- A study performed by scientists from the Washington University School of Medicine in St. Louis and published in 2008 found 7 common DNA variations in psoriasis patients. The researchers scanned parts of the genome of 223 psoriasis patients and compared the results with the DNA of 519 healthy patients. They were looking for differences between the groups and found the variations, some of which were linked to psoriatic arthritis.
- In May 2006 scientists from the University of Michigan published research that showed a common genetic variation in an immune system gene of people with psoriasis. The variation was not seen in people without the condition. The gene is PSORS1 (SORE-ESS-1), which stands for psoriasis susceptibility 1. This gene is one of the many different varieties of the gene called HLA-C, which is located on chromosome 6. This gene is involved in regulating how the immune system fights infection.
- In February 2009 scientists from the University of Nottingham in the UK announced that psoriasis could be caused by two missing genes – LCE3B and LCE3C. In a paper in the journal Nature Genetics they revealed that people who lack these genes are more likely to develop psoriasis. The genes appear to be involved in how the skin responds to damage, and the Nottingham researchers postulated that when they are missing, the skin is more vulnerable to the damaging effects of an overactive immune system.
Understanding the genetics of psoriasis, and why some people are affected and others are not could lead to more effective treatments. They could work by blocking the action of contributory genes, correcting their behavior or by replacing mutated genes with healthy ones via gene therapy.
1) University of Michigan Health System (2006, March 18). Scientists Identify Major Psoriasis Susceptibility Gene. ScienceDaily
2) PLoS Genet 4(3): e1000041.Liu Y, Helms C, Liao W, Zaba LC, Duan S, et al. A Genome-Wide Association Study of Psoriasis and Psoriatic Arthritis Identifies New Disease Loci
3) University of Nottingham (2009, February 2). Missing Genes Link To Psoriasis. ScienceDaily
4) Picture credit – permission granted under GNU Free Documentation License.