Researchers said on Tuesday they had found a way to predict how people will respond to an asthma drug by looking at their genes.

Tiny differences called single nucleotide polymorphisms (SNPs) cannot dictate response on their own, but they combine in predictable ways to affect a patient's ability to use the drug, the team at Genaissance Pharmaceuticals, Inc. and the University of Cincinnati found.

These combinations of genetic variation are called genetic haplotypes, and the researchers found 12 different haplotypes that affected patients' response to the asthma drug albuterol.

"It appears that haplotype 4 is associated with depressed responsiveness and haplotype 2 with increased responsiveness," the researchers wrote in their study, published in the Proceedings of the National Academy of Sciences.

Genaissance, based in New Haven, Connecticut, was set up to find just such genetic differences. Doctors hope some day they can analyse a patient's genes to find out which medication would work best for an individual.

The Genaissance-University of Cincinnati team studied 121 patients with asthma. They found 13 different SNPs + which are a change in a single "letter" of the genetic code + that could have combined into more than 8,000 different haplotypes.

Instead, they found just 12 haplotypes actually occurred.

Some of them could be linked to ethnic group, the researchers said. "Four of the observed haplotypes occur in all populations sampled, although at markedly different frequencies," they wrote.

"Haplotype 2, the most frequent in Caucasians (48 percent), is seen only at frequencies of 6 percent, 10 percent and 27 percent in samples of African-Americans, Asians and Hispanic-Latinos," they added.

"Also, haplotype 6 is more common in African-Americans and Asians as compared with the two other groups."

The research could help shed light on other studies that suggest people in different ethnic groups sometimes respond differently to various medications.

Dr. Stephen Liggett of the University of Cincinnati, who led the study, said it showed that genetic response to drugs might be complicated.

"The drug response predictions could not have been made by using only the individual SNPs," he said in a statement.

Both public groups and private companies are racing to catalogue as many SNPs as possible in the human population. The National Institutes of Health said this week that 800,000 had been identified. There are more than 3 billion "letters" in the human genetic code.

No single SNP has been linked with any trait, and scientists have said it is likely that more than one difference would be needed to cause a measurable effect.

(From China Daily)