Science of Psoriasis: The Role of Genetics
Genes hold the key to understanding how the immune system becomes activated in people who have psoriasis or psoriatic arthritis. When a specific gene is found to be linked to psoriasis, researchers work to determine what the gene does under "normal" conditions. Next they try to determine how the gene is behaving differently in psoriasis. This is a very difficult and time-consuming process, because researchers believe that more than one gene is responsible for causing psoriasis.
How do genes work?
Genes control everything from height to eye and hair color. Differences between people result from different versions of the gene. Genes determine how cells act. When genes are working normally, the body and its cells function normally. When a misstep occurs in the way a gene works, a genetic disease, such as psoriasis, may result.
How are genes different in people with psoriasis?
Researchers are investigating how the genes in people with psoriasis make them more likely to get the disease than others. There are some possible genetic changes that could explain why psoriasis occurs.
Some chemicals in the DNA may have errors. This could lead to missing proteins. It could also lead to the proteins being misshapen or in the wrong place.
Some genes may be turned on or off at the wrong rate, because of errors in the regions of DNA that control the production of proteins.
Are there more people who carry the genes for psoriasis than are actually affected by it?
It is known that some people are more likely to have psoriasis than others, and this "susceptibility" may lie in the genes themselves. Researchers believe that for a person to develop psoriasis, certain steps must happen.
Genes are essential for the body to perform the functions necessary for life. These are coded for by 3 billion units of genetic material that make up "deoxyribonucleic acid" (DNA). DNA provides the information to direct the "synthesis," or making, of proteins. Proteins are large molecules that perform a wide variety of very specific functions in the body. Researchers now know that we have approximately 30,000 to 40,000 genes.
The individual must receive a combination of different genes (a combination which is likely to be different for different people) that work together to cause psoriasis.
The individual must then be exposed to specific factors that can trigger his or her particular combination of genes to cause disease. These triggers are not yet fully understood or defined. However, certain types of infection and stress have been identified as potential triggers.
What does heredity have to do with it?
Scientists now believe that at least 10 percent of the general population inherits one or more of the genes that create a predisposition to psoriasis. However, only 2 percent to 3 percent of the population develops the disease.
This is thought to be because only 2 percent to 3 percent of people encounter the "right" mix of genetics and triggers that lead to the development of psoriasis. Those who have a genetic disease but don't have a family history of it, for example, may have "inherited" two genes from their father and two from their mother—neither of whom had all four and therefore never developed the disease.
What is happening with genetic research?
Research into the genetics of psoriasis didn't begin until the early 1970s. Recently, it has exploded in scope, thanks to improvements in medical and genetic technology, and increased funding. In 2006, the Foundation began collecting DNA samples for the National Psoriasis Victor Henschel BioBank. The BioBank is slated to be the world's largest collection of psoriasis-related DNA in the world available to qualified researchers. The first BioBank DNA samples were released to researchers in 2010. Read about current studies using BioBank samples »
The predecessor to the BioBank was the National Psoriasis Tissue Bank. Launched in 1994, it was the first public source of genetic material for researchers investigating psoriasis. Just weeks after it opened, a research team from the University of Texas Southwestern and Baylor University Medical Center in Dallas announced the first genetic marker (a section of DNA that tracks with a disease) for psoriasis on chromosome 17.
If a marker exists in families with a genetic disease, the marker and the disease gene are said to be "linked," meaning they are located quite close to each other in the genetic sequence. Because each chromosome contains thousands of genes, with 10 to 100 of them close enough to the marker to be "linked" to it, the identification of linkagesets the stage for the identification of the disease gene. However, linkage does greatly narrow down the list of genes that are candidates for psoriasis. Markers for psoriasis have been identified on at least 11 chromosomes (1, 3, 4, 6, 8, 10, 16, 17, 18, 19 and 20).
What happens after the genes are found?
Discovering the genes that cause psoriasis will help identify the cause of this disease. It will go beyond showing that the immune system is activated to telling us why it is activated and causes defects in the skin. This will further open the door to better control of psoriasis through more precise and more effective treatments.
Once all the genetic factors causing the disease are found, researchers will be able to study why some people get psoriasis and others don't. By understanding how people who develop psoriasis are genetically different than people who do not, scientists may be able to create treatments that "correct" the behavior of cells. Or, they may be able to fix this difference in the genes themselves.