As an intern at COSMOS Online:
What makes someone male and another female? A new genetic study looks past the clothing, body parts and behaviour to reveal the real gender divide.
Thousands of genes have been found to behave differently in the same organs of males and females. The difference had never before been detected to this degree, and may explain differences in how males and females respond to certain drugs and their susceptibility to certain diseases.
A research team led by Xia Yang of the David Geffen School of Medicine at the University of California, Los Angeles, scrutinised more than 23,000 genes in the brain, liver, fat and muscle tissue from mice, with whom humans share 99 per cent of our genes.
"We previously had no good understanding of why the sexes vary in their relationship to different diseases," Yang explained. "Our study discovered a genetic disparity that may explain why males and females diverge in terms of disease risk, rate and severity."
The study aimed to find genetic clues related to mental illnesses, diabetes, obesity and atherosclerosis by focussing on ‘gene expression', which is the process by which a gene's DNA sequence is converted into cellular proteins. While individual genes were observed to function similarly in both sexes, the team was surprised to find a direct correlation between gender and the amount of gene expressed.
"Males and females share the same genetic code, but our findings imply that gender regulates how quickly the body can convert DNA to proteins," said Yang. "This suggests that gender influences how disease develops."
Gender consistently influenced the expression levels of thousands of genes in the liver, fat and muscle tissue. The effect was slightly more limited in the brain, where hundreds, not thousands of genes showed different expression patterns. Affected genes were typically those most involved in the organ's function, suggesting that gender influences important genes with specialised roles, not the rank-and-file.
The gender differences in gene expression also varied by tissue.
In the liver, for example, the expression of genes involved in drug metabolism differed by sex. The findings imply 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 at the same university. "Studies show that aspirin is more effective at preventing heart attack in men than women. One gender may metabolise the drug faster, leaving too little of the medication in the system to produce an effect."
Researchers say that their results support the importance of gender-specific clinical trials.
"Many of the genes we identified relate to processes that influence common diseases," said Yang. "This is crucial, because once we understand the gender gap in these disease mechanisms, we can create new strategies for designing and testing new sex-specific drugs."
The study will be published in the August 1 issue of the international journal Genome Research.
