Research labs may be short-changing women by ignoring differences between male and female animals in experiments to discover new drugs, suggesting sexual equality in scientific studies is overdue, researchers said on Monday.
In research using mice of both sexes, scientists at Britain's Wellcome Trust Sanger Institute found that gender differences could impact results in more than half of their experiments.
Since these early-stage laboratory studies underpin research into treatments for human diseases, the scientists said sex differences should be an important factor in designing future studies.
"A person's sex has a significant impact on the course and severity of many common diseases, and the consequential side-effects of treatments—which are being missed," Natasha Karp, who co-led the study, wrote in the journal Nature Communications.
With an historic bias towards the scientific study of males, the common approach in biomedical research has been to ignore sex or to analyze only one sex and assume the results applied to the other.
"This was a scientific blindspot that we really thought needed exploration," Karp said.
U.S. regulations requiring that both sexes be included in human clinical trials were introduced 20 years ago. Yet in 2006, only 41 percent of people in U.S. trials were women, up from 9 percent in 1970, the researchers said.
Yet sex influences many common conditions, including heart diseases, autoimmune diseases and asthma.
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For animal studies, an international review in 2011 and 2012 found that 22 percent did not state the sex of the animals. Of those that did, 80 percent used only males and 3 percent both sexes.
In this latest study, Karp's team quantified the difference between male and female mice by analyzing around 230 physical characteristics of more than 50,000 mice.
They found that in the control group, their sex had an impact on 56.6 percent of quantitative traits, such as bone mass, metabolism and blood components, and on 9.9 percent of qualitative traits, such as whether their head shape, coat and paws were normal or abnormal.
In mutant mice that had a gene switched off for experimental purposes, gender modified the effect of the mutation in 13.3 percent of qualitative traits and up to 17.7 percent of quantitative ones.
Judith Mank of University College London, who worked with Karp, said the findings showed that "only studying males paints half the picture."