Scientists have found a renegade gene which could be the direct cause of severe asthma in young children.
The gene, CDHR3, is especially active in epithelial cells lining the inner surfaces of the airways.
Researchers studied and compared the complete genetic codes, or genomes, of 3,695 Danish children and adults with asthma, including a number of children under the age of six.
Lead researcher Dr Hakon Hakonarson, from the Children's Hospital of Philadelphia (Chop) in the US, said: "Because asthma is a complex disease, with multiple interacting causes, we concentrated on a specific phenotype - severe, recurrent asthma occurring between ages two and six.
"Identifying a risk-susceptibility gene linked to this phenotype may lead to more effective, targeted treatments for this type of childhood asthma."