LONDON--Women with a single copy of the X chromosome from their mothers are more likely than those with a copy from their fathers to have problems coping with social situations, scientists reported at a press conference here today. And men, who get their X chromosome solely from the mother, are also more likely to have problems with social interactions than are normal women. The provocative findings, to appear in tomorrow's issue of Nature, are the first indication that a cognitive difference between the sexes might be inherited.
A team led by David Skuse of London's Institute of Child Health examined 80 young women with Turner's syndrome, a condition that affects one in 2500 females that is marked by short stature and social problems at school and through adolescence. Using genetic markers, the researchers found that 55 subjects had received the chromosome from their mother and 25 from their father. After collecting information from school counselors about any social difficulties experienced by the girls, Skuse's group found that 40% with the maternal X chromosome were likely to have problems at school, versus only 16% of girls with the paternal X. "It seemed to us there could only be a genetic explanation for that," Skuse says, because he says there were no other differences between the two sets of girls. The researchers next asked parents of three groups of children--Turner's females, normal females, and normal males, who get their single X chromosome from the mother--to rate their children's cognitive skills, such as awareness of other people's feelings and interpreting body language. Dysfunction in these skills was highest in two groups--Turner's females with a maternal X chromosome and normal males. Other tests revealed that Turner's females with a maternal X and males were more likely to be impulsive.
The findings suggest that Turner women who receive a copy of the X chromosome from the father (and normal women, who get a copy from each parent) are more adept at social skills, although it's unclear which genes might be at work. But because men never receive the father's X chromosome with the active genes, they are born with a disadvantage in social settings. Such a scenario may also help explain developmental disorders such as autism that are more prevalent in men than women.
Prevailing theories hold that social conditioning or sex hormones is responsible for behavioral differences between the sexes. "This is an entirely different mechanism that we're proposing," Skuse says. In a commentary accompanying the article, Peter McGuffin and Jane Scourfield of the University of Wales College of Medicine in Cardiff point out that the work may have even broader implications. "This raises the very real possibility," they write, that genes underlying intelligence will soon be found.