Same genes in same organs may behave differently simply depending on whom the genes belong to-men or women, a new study released on Friday said.

The researchers at the University of California, Los Angeles, said the gender gap in thousands of genes could explain the differences of men and women in their reactions to disease risk and

drug response. The findings will be published in the August issue of the journal Genome Research.

The team examined brain, liver, fat and muscle tissue from mice to search genetic clues related to mental illnesses, diabetes, obesity and atherosclerosis. They focused on gene expression, a process by which a gene's DNA sequence is converted into cellular proteins.

Scrutinizing more than 23,000 genes to measure their expression level in male and female tissue, the researchers found a direct correlation between gender and the amount of gene expressed.

In fact, more than half of the inspected genes have shown striking and measurable differences in expression patterns between males and females, the researchers reported.

Even in the same organ, the researchers identified scores of genes that varied in expression levels between the sexes. Gender consistently influenced the expression levels of thousands of genes in the liver, fat and muscle tissue.

Earlier studies have identified roughly 1,000 sex-biased genes in the liver and brain, but the new study is the first to uncover a gender difference in gene expression in fat and muscle tissue.

The gender differences in gene expression also varied by tissue.

Affected genes were typically those most involved in the organ's function, suggesting that gender influences important genes with specialized roles, not the rank-and-file.

In the liver, for example, the expression of genes involved in drug metabolism differed by sex. The findings mean that male and female livers function the same, but work at different rates.

"Our findings in the liver may explain why men and women respond differently to the same drug," said Jake Lusis, co-investigator and professor of human genetics.

"Studies show that aspirin is more effective at preventing heart attack in men than women. One gender may metabolize the drug faster, leaving too little of the medication in the system to produce an effect."

The findings also support the importance of gender-specific clinical trials, and even gender-specific drugs, the researchers said.

(Xinhua News Agency July 8, 2006)