(U-WIRE) LOS ANGELES – To their surprise, University of California-Los Angeles scientists found that males and females really are not as different as they thought, particularly when it comes to the degree of differences in the expression of genes in their brains.

“Males and females think and behave differently and have different risks for neuropsychiatric diseases, but we found that the degree of differences in genetic expression in the brain is much less than that of other types of tissue,” said Xia Yang, lead author of the study and postdoctoral fellow in cardiology at the David Geffen School of Medicine.

However, the analysis was done on the basis of the brain as a whole and not on separate structures.

The study, published in the August issue of the journal Genome Research, examined the expression of genes in the fat, liver, muscle and brain tissues of mice, who share 99 percent of our genes. Human males and females have exactly the same genetic code, yet each gender expresses different genes.

“Males and females have the same genes but the differences come from what genes are turned on, and on what level,” said Dr. Arthur Arnold, chair of the department of physiological science, who also participated in the study.

The prolactine gene, which affects maternal behavior, is expressed three times higher in females, Yang said.

On the other hand, the PINK1 gene expression level, which plays a role in Parkinson’s disease, is slightly higher in male mice, Yang added.

But the question surrounds the cause of the differences in gene expressions.

“We believe that most of the sex differences in gene expression are secondary to hormonal effects, yet only a limited number of these are directly controlled by sex hormones,” said Dr. Thomas A. Drake, UCLA professor of pathology. “What we think is happening is something of a ripple effect.”

Compared to brain tissue, where hundreds of genes showed different expression patterns based on the gender, the study found that the other types of bodily tissue contained thousands of differences in gene expression.

“Thousands of genes behave differently in the same organs of males and females — something never detected to this degree,” said Drake.

“Three-quarters of the genes in the liver are expressed differently based on the gender,” Arnold said. “Lots of these small differences add up, creating an overall effect,” he said.

These findings imply that male and female livers function the same but work at different rates, Yang said.

“If one gender metabolizes a particular drug faster, it could leave too little of the medication in the system,” she said. “Most medication dosages for women have been based on clinical trials that are primarily conducted on men.”

“Our ultimate goal is to link specific sexually dimorphic genes or pathways with specific traits influenced by sex,” said Yang.

“This is important because of their potential relevance to the common diseases and physiological processes such as lipid metabolism, drug response, and neurological and psychiatric diseases,” Yang said. “Once we understand the gender gap in disease mechanisms, we can create new strategies for designing and testing new sex-specific drugs.”

Copyright ©2006 Daily Bruin via CSTV U-Wire