The risk of your child developing asthma just because it’s hiding somewhere in your family tree isn’t as threatening as scientists once thought it was. In one of the largest genetic asthma studies to date, researchers from the University of Chicago Medical Center examined the real risks of hereditary asthma and published their findings in the journal Nature Communications.

"Previous studies have likely overestimated the heritability of asthma," said the study’s lead author Dr. Carole Ober, chair of the Department of Human Genetics at the University of Chicago, in a press release. "This could be because those estimates are based on correlations between family members that share environment as well as genes, which could inflate the heritability. Gene-environment interactions are not considered in these large scale association studies, and we know that these are particularly important in establishing individual risks for asthma."

Researchers studied more than 33,000 different possible mutations in more than 11,000 people with a variety of ethnicities, including European, African, and Latino. They combed through their DNA to search for any mutations people had in common with one another, and discovered three genes that were markers for asthma risk — the GRASP, GSDMB, and MTHFR genes. These rare mutations were found in less than five percent of the population, which means there is only a small portion of people who are at risk of inheriting asthma from their mom or dad.

"It was assumed that there would be rare mutations with larger effect sizes than the common variants we have been studying," Ober said. "Surprisingly, we found that low frequency mutations explain only a very small amount of asthma risk."

The first genes they discovered were found primarily in Latino individuals, while the last gene was found in those with African ancestry. When researchers took a closer look on how the genes worked, they found they were involved in the process of protein building, regulating cell death, and metabolizing vitamin B9. Researchers believe that, although these gene mutations only affect a small number of asthma cases, they could still serve as windows into how and why asthma develops in certain people and not others.

Asthma is a disease of the lungs that causes the airways to become blocked or narrowed, according to the Asthma and Allergy Foundation of America, and the blockage kills approximately nine people every single day. Children who are obese and pregnant women who are exposed to city air pollutants have both recently been found to have an increased risk of asthma. However those with inflamed airways will be abnormally sensitive to irritants that don’t bother other people, such as cigarette smoke, wood fires, pollens, molds, dust mites, pet dander, household sprays, paint, perfumes, and scented soaps.

More than 25 million adults and children suffer from asthma in the United States, according to the Centers for Disease Control and Prevention. The number of people who have asthma is increasing every year. Between 2001 and 2009, an additional 4.3 million more people were diagnosed with asthma, and greater access to medical care is necessary to catch up with the rapid growth.

Source: Ober C, Igartua C, Myers RA, Mathias RA, Eng C, and Graves PE. Ethnic-specific associations of rare and low-frequency DNA sequence variants with asthma. Nature Communications. 2015.