Researchers believe the genetic flaws lead to an excessive inflammatory response, causing asthma.
This may be treatable using a drug already licensed for rheumatoid arthritis, they said.
Previous studies have suggested genetic traits may predispose people to asthma.
Early candidate DNA markers pointed to flaws in the way cytokines – proteins associated with inflammation response – signal the immune system when the body detects a foreign substance.
However, the causes of the disease remain poorly understood.
Researchers led by Manuel Ferreira of the Queensland Institute of Medical Research in Brisbane, Australia examined the DNA of 2,669 asthmatics and 4,528 people without the disease.
They identified two sections of DNA common to people with asthma.
As expected, one of these rests within a gene that encodes a cytokine called interleukin-6 receptor (IL6R).
Researchers found this genetic variant increased production of the cytokine protein in asthmatics. It suggests that this trait leads to an excessive inflammatory response, causing asthma.
Existing drugs that block the receptor such as tocilizumab, licensed for the treatment of rheumatoid arthritis, could be used to treat asthma, researchers concluded.
The other genetic trait discovered in asthmatics may affect a gene with a role in allergic sensitisation, which increases the risk of developing allergic asthma.
Authors concluded: ‘The IL6R findings further support the hypothesis that a genetic dysregulation of cytokine signalling increases disease risk and raise the possibility that tocilizumab may be effective to treat asthma, perhaps in a genotype-dependent manner. Studies that address this possibility are warranted.’
However, researchers said there may be hundreds or thousands of gene variants affecting asthma risk.