The team of international researchers hope their work, published in Nature, will lead to new treatments.
Studying more than 2,000 children – 994 patients with childhood onset asthma and 1,243 non-asthmatics – they pinpointed a gene called ORMDL3, which was found at higher levels in the blood cells of children with asthma.
Carrying a specific variant of this gene may increase the risk of developing asthma by up to 70%.
Researcher Dr Miriam Moffatt, from Imperial College London, said “We are confident that we have discovered something new and exciting about childhood asthma. These novel findings do not explain completely how asthma is caused, but they do provide a further part of the gene-environment jigsaw that makes up the disease.”
The combination of genetic and environmental factors which cause asthma has previously been poorly understood.
Dr Victoria King, of the charity Asthma UK, said: “This is an exciting development in determining how genetics affects the chance of developing asthma in childhood, which currently affects one in 10 children in the UK.”
Asthma is the most common chronic disease of childhood.