It's not just genes, environmental exposure too determines if a person would develop asthma, says a leading expert.
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.
Saturday, November 7, 2009
Both genetics and environmental factors determine asthma risk
Wednesday, September 16, 2009
Changes in humidity, temperature trigger asthma
Changes in humidity and temperature may trigger asthma among kids, suggests a report.
Published in the journal Annals of Allergy, Asthma and Immunology, the report says that such weather changes have been hound to result in a rise in Emergency Department (ED) visits for paediatric asthma exacerbations.
“We found a strong relationship between temperature and humidity fluctuations with pediatric asthma exacerbations, but not barometric pressure,” said Dr. Nana A. Mireku, an allergist at Dallas Allergy Immunology private practice in Dallas, formerly at Children’s Hospital of Michigan, Wayne State University School of Medicine, Detroit.
“To our knowledge, this is the first study that demonstrated these correlations after controlling for levels of airborne pollutants and common aeroallergens.
“Our study is also one of the few to examine the possibility that the weather one or two days before the asthma exacerbation may be as important as that on the day of admission, as the additional ED visits occur one to two days after the fluctuation,” she added.
The authors of the report write that patients experiencing an asthma attack often complain that weather fluctuations are a major trigger.
Dr. Mireku said: “the latest National Institutes of Health guidelines list ‘change in weather’ as a possible precipitating factor for asthma, but no previous studies have really examined this potential trigger in a rigorous fashion.”
According to the report, the retrospective 2-year study was performed at a large urban hospital of 25,401 children visiting the ED for an asthma exacerbation.
The researchers collected data on climactic factors, pollutants and aeroallergens on a daily basis.
They used time series analysis to evaluate the relationship of daily or between-day changes in climactic factors and asthma ED visits, controlling for seasonality, air pollution and aeroallergen exposure.
The effects of climactic factors were evaluated on the day of admission and up to five days before admission.
The researchers found that a 10 percent daily increase in humidity on a day or two before admission was associated with approximately one additional ED visit for asthma.
The authors write that between-day changes in humidity from two to three days prior to admission were also associated with more ED visits.
Daily changes in temperature on the day of or the day before admission increased ED visits, with a 10 degree F increase being association with 1.8 additional visits.
“Asthma is the most common chronic illness in childhood. Allergists have long known that weather conditions such as extremely dry, wet or windy weather can affect asthma symptoms. This study further defines the role of temperature and humidity on children’s asthma and confirms the importance of working with patients to identify the source of their symptoms and develop treatment plans that help prevent them,” said allergist Richard G. Gower, president of the American College of Allergy, Asthma and Immunology (ACAAI).
Friday, April 24, 2009
Family History raises asthma risk up to six times
Asthma risk is up to six times higher for those with a strong family history, says a new study.
"Our findings showed that a family history of asthma is an important risk factor for asthma, and that familial risk assessments for asthma can he
Asthma prevalence increased from 9.4 per cent for people at average risk, to 20.4 per cent for those at moderate risk, to 37.6 per cent for those at high risk. Asthma risk was 2.5 times higher in the moderate-risk group and 5.8 times higher in the high-risk grou
The new study suggests that asthma risk is at least two times higher in people with a moderate family history (for example, one parent or sibling with asthma), and up to six times higher for those with a strong family history (for example, both parents affected).
The researchers have called for more research into the role of family history in diagnosing asthma, and whether this information can help to reduce the disease’s harmful effects.
The study has been reported in the May issue of Genetics in Medicine.
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After adjustment for other factors, risk was 2.4 times higher in the moderate-risk group and 4.8 times higher in the high-risk group, compared to people at average risk.
Other asthma risk factors included African American race, low income, obesity, smoking or living with a smoker, and physical inactivity.
Asthma occurred at younger ages in people with a family history. Average age at onset decreased from 22 years in the average-risk group, to 19 years in the medium-risk group, to 17 years in the high-risk group.
lp identify people at highest risk for developing asthma," said lead author Tiebin Liu, MSPH, and colleagues of The US Centres for Disease Control and Prevention.
For the study, the researchers analyzed 1999 to 2004 data on 1,500 adults (20 or older) from the National Health and Nutrition Examination Survey (NHANES) study.
Based on the number and closeness of relatives with asthma, participants were classified as being at high, moderate, or average risk of asthma.
About two per cent of people were at high risk and thirteen per cent at moderate risk; the remaining 85 per cent were at average risk
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