A leading expert says that it's not just genes, environmental exposure too determines if a person would develop asthma.
Dr. Fernando D. Martinez, director of Arizona Respiratory Center, said that 39 potential "asthma genes" have already been identified.
But, for nearly every gene found to be negatively associated with asthma in one study, other studies have failed to replicate the findings.
"This suggests that the effect of these genes on allergic diseases is not direct and simple. Many genetic variants associated with asthma will not increase the risk of the disease in all persons. Most will modulate the effects of environmental exposures, making certain subjects more or less susceptible," he said.
With respect to environmental exposures worsening asthma, Martinez highlights viral infections, passive smoking and air pollution.
But the impact of all environmental factors is not necessarily obvious, as some exposures play a protective role.
"For example, in farming communities where exposure to microbial products is high, children have significantly less asthma and allergies," said Martinez.
In some cases, an allele (part of a gene) found to be a higher risk factor for allergic asthma in some individuals might be associated with less risk of developing asthma in others.
Martinez has pinpointed the CD14 gene as one such example, saying that when people with a variant of this gene are exposed to high levels of endotoxin (a product present in bacteria), it protects them from developing an allergic response.
But people with this same gene variant who are exposed to low levels of endotoxin are at higher risk of an allergy.
Research is going on to identify and understand the genes related to asthma.
"We have identified many genetic variants associated with asthma and allergies. However, only a fraction of the variants have been discovered. A lot of work still needs to be done to uncover how these diseases are inherited," said Marteniz.
Martinez suggests that the expectation that doctors will someday be able to predict asthma at birth should be replaced with an expectation that experts will be able to identify which children should or should not be exposed to certain environmental factors to lessen their risk of developing asthma.
"The hope is that by combining information on genetic markers and exposures, we will be able to identify even more accurately children at high-risk for different forms of asthma in the future," he said.
The findings were presented at the annual meeting of the American College of Allergy, Asthma and Immunology (ACAAI) in Miami Beach, Fla.