Study finds variant and protein it expresses may cause some cases of the disease
WEDNESDAY, April 9 (HealthDay News) -- Just a small change in one gene, called CHI3L1, can increase a person's risk of developing asthma.
The genetic variation in CHI3L1 causes the gene to release high levels of a protein known as YKL-40, and high levels of this protein have been associated with an increased risk of asthma in past research. The current study found that high levels of YKL-40 in four different population groups were linked to the development of asthma in all four groups, suggesting that YKL-40 and CHI3L1 are likely at the root of some cases of asthma.
That means if scientists can block YKL-40, they could create a novel, potentially more effective treatment for people with asthma.
"While there won't be one silver bullet for all asthma, we can start to think about tailoring medications to get at the cause, rather than just alleviating asthma symptoms," said study author Carole Ober, a professor of human genetics at the University of Chicago. "These findings give us optimism that one day there will be better treatments, more targeted to the specific cause of asthma."
The findings were published online April 9 by the New England Journal of Medicine and were expected to be in the journal's April 17 print issue.
It's believed that YKL-40 was originally produced by the body as a defensive mechanism against harmful parasitic worms, called helminths, according to Dr. Burton Dickey, chairman of pulmonary medicine at M.D. Anderson Cancer Center in Houston. Dickey said that helminths contained a substance called chitin that is also found in fungi, crustaceans and in insects such as dust mites and cockroaches. YKL-40 is what's known as a chitinase-like protein, because it attaches itself to chitin, possibly alerting the body that chitins are present.
But, Dickey pointed out that in the developed world, chitin infections simply aren't an issue any longer, so now this defense mechanism may be reacting to chitin in harmless settings.
In November 2007, Yale researchers reported that people with severe asthma had higher levels of YKL-40. This finding led to the current study, which measured levels of YKL-40 in an isolated population called the Hutterites. The Hutterites settled their isolated religious community in South Dakota in 1874. They live communally, share the same food, have the same education and socioeconomic status. About 11 percent of Hutterites have asthma, and 12 percent have hyperactive airways.
Working with the Yale team, Ober found that the Hutterites with asthma or overactive airways had elevated levels of YKL-40. After searching their genetic code, Ober and her colleagues found that one tiny change in the CHI3L1 gene was slightly different in Hutterites with asthma. When the researchers compared these findings to three different groups of people from Chicago; Madison, Wisc.; and Freiberg, Germany, they found an association with changes in CHI3L1 and YKL-40 levels, and the development of asthma. Some children were too young to have developed asthma, but already showed higher levels of YKL-40 if they had the genetic change.
Ober said that not everyone with high levels of YKL-40 develops asthma, but that someone with the CHI3L1 change inherited from both parents "was twice as likely to develop asthma as someone who doesn't have it."
"YKL-40 seems to be involved in many different diseases in which inflammation is a component, and so it is likely to be an important component of the innate immune response, and treatments directed at YKL-40 may be helpful in all of these diseases," said Dr. William Cookson, co-author of an accompanying editorial and a professor of respiratory genetics at the National Heart and Lung Institute at Imperial College in London.
Dickey said the Yale team is currently working on an animal model that doesn't produce YKL-40 to see if the protein is important in other functions in the body.
"If the protein doesn't contribute importantly to any other biological process, it's likely just involved as a parasitic defense, and inhibiting it may not cause any problems, yet could provide substantial benefit [in terms of asthma treatment]," said Dickey.
To learn more about the causes of asthma, visit the National Heart, Lung, and Blood Institute.
SOURCES: Carole Ober, Ph.D., professor, human genetics, University of Chicago; William Cookson, M.D., professor, respiratory genetics, National Heart and Lung Institute, Imperial College, London, U.K.; Burton F. Dickey, M.D., Clifton D. Howe Distinguished Professor, and chairman, pulmonary medicine, M.D. Anderson Cancer Center, Houston; April 17, 2008, New England Journal of Medicine
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