Researchers at Karolinska Institutet have contributed to a major international study in the journal Nature Genetics that has identified more than 100 genetic risk factors for asthma, hay fever and eczema which explain why these conditions often coexist.

Previous studies have shown that the three conditions share many genetic risk factors, but it has not been known exactly where in the genome those shared genetic risk factors are located.

The new international study, led by researchers at QIMR Berghofer Medical Research Institute, Australia, aimed to determine which genes are involved in all three conditions by looking at data from the Swedish Twin Registry and analysing the genomes of more than 360,000 individuals.

The researchers pinpointed 136 separate positions in the genome that are risk factors for developing these conditions by influencing whether nearby genes are switched on or off. They believe that these genes in turn influence the risk of asthma, hay fever and eczema by affecting how the cells of the immune system work.

The study also found that environmental factors affect whether many of these genes are switched on or off. For example, the researchers found one gene that is more likely to be switched off in people who smoke. When the gene is switched off, the risk of developing allergies increases.

The mapping of genetic risk factors helps us understand why asthma, hay fever and eczema often coexist and provides new clues on how these conditions can be prevented or treated, according to co-author Catarina Almqvist Malmros, Professor at Karolinska Institutet’s Department of Medical Epidemiology and Biostatistics.

The study involved collaborators from Australia, Germany, the Netherlands, Norway, Sweden, the UK and the US.

The article is titled, “Shared genetic origin of asthma, hay fever and eczema elucidates allergic disease biology.”