Large international study finds new risk genes for hay fever

In a large international study involving almost 900,000 participants, researchers from the University of Copenhagen and COPSAC have found new risk genes for hay fever. It is the largest genetic study so far on this type of allergy, which affects millions of people around the world.

Hay fever is the most common type of allergy, affecting up to a million people in Denmark every spring and summer and more than 400 million worldwide. It is steadily spreading in the western world, but its underlying mechanisms are still unknown. However, a large international study led by researchers from the University of Copenhagen has now brought us a little closer to understanding its causes.

The study, which has just been published in the scientific journal Nature Genetics, includes data from more than 30 studies and almost 900,000 participants from Europe. Based on this data, the researchers have mapped 41 genes that increase the risk of developing hay fever. Of these, 20 are new to science.

"This is the largest genetic study ever conducted into hay fever. The scope of the study has allowed us to learn more about the allergy, and it has only been possible with the help of many other research groups from around the world. The risk genes we have mapped can help us understand what causes hay fever. And in the longer term this will be helpful when it comes to developing drugs and better treatments for the allergy", says Klaus Bønnelykke, Clinical Research Associate Professor at the Department of Clinical Medicine, University of Copenhagen. He is also associated with Copenhagen Prospective Studies on Asthma in Childhood (COPSAC), where he has headed the study together with Professor Hans Bisgaard and senior researcher Johannes Waage.

Ten percent of hay fever explained

Hay fever is triggered by airborne allergens such as pollen, pet hair and dust mites. The number of people with allergies is increasing, particularly in western countries, among them Denmark. It is not yet known exactly why hay fever is beginning to reach epidemic proportions. But it seems likely that part of the explanation lies in our lifestyles, says Klaus Bønnelykke.

"Genes are very important, and twin studies show that in more than half of sufferers, the allergy is caused by genetics. We can also see that a great many cases must be due to environmental factors, since the number of people with hay fever has increased over the past 100 years. The allergy is not spreading that fast due to genetic changes. It takes tens of thousands of years for genetic makeups to change. Therefore, I believe that the rise is likely to be caused by an interplay between risk genes like the ones we have found in this study and various environmental factors that trigger the allergy in people with risk genes", says Klaus Bønnelykke.

Even though the study is the largest and most comprehensive of its kind, it does not fully explain why some people develop hay fever and others don't. It only explains about ten percent of the illness. The next step for Klaus Bønnelykke, therefore, is not just to add more participants, but also to start looking at how the genes interact with environmental factors such as pollen, pollution and pets.

Genetic commonality with autoimmune diseases

In the study, the researchers also found an overlap between risk genes for hay fever and risk genes for autoimmune diseases such as type 1 diabetes, rheumatoid arthritis and inflammatory bowel disease. As with allergies, the number of people with autoimmune diseases has risen sharply in recent years. According to Klaus Bønnelykke, the overlap of genes can help explain why.

"Our study helps identify genetic commonalities which may be a key to understanding why these illnesses are all on the rise. It seems there are some common factors in the western lifestyle that are causing these illnesses to become more widespread, but we haven't yet understood why. The genetic overlap we have observed seems to suggest that it is the same genes that trigger these illnesses, at least in part. This is important information when trying to understand the mechanisms and causes. It may matter not just to understanding hay fever but also to understanding autoimmune diseases", says Klaus Bønnelykke.