How Can Sex Make Men Mentally Disabled?

Here is the answer to why men act dumber than women: mutations in genes located on the X sex chromosome that provoke mental retardation. This is the result of a study made by Australian researchers, collaborating with colleagues from Katholieke Universiteit Leuven in Belgium and the Wellcome Trust Sanger Institute in Cambridge, England, and published in the "American Journal of Human Genetics."

"A change involving duplication of a small part of the 'X' chromosome was discovered in six families out of more than 550 in a worldwide study of mental health problems. Although the figure sounds relatively low, because of the complexity of the change, the number is actually very high. Another three families where a gene had been lost from the same section of the chromosome also suffered mental retardation," said co-author Jozef Gecz, geneticist of the University of Adelaide.

Women have two "X" sex chromosomes; men have one X and a small Y. That's why bad genes on the "X" chromosome manifest more frequently in boys than in girls, because women, having a double set of X, need to have a double set of bad genes to manifest them (which is statistically less possible), but they can "silently" carry a bad gene which can manifest in their sons. This is the case of the hemophilia gene. And now it appears that it is also a mutation causing mental disability.
"The finding adds weight to arguments that the 'X' chromosome plays a key role in human brain function. Around 30 individuals were affected, mostly boys or men," Gecz told AFP.

"To some extent they can dress and feed themselves. They don't necessarily require 24/7 care but they still need supervision. Visually these people look exactly like you and I. They just don't have the learning and memory working properly to allow them to lead a normal life," explained Gecz.

The impaired genes were HSD17B10 and HUWE1 (tumor suppressor gene), involved in the renewal of neurons.

"Clearly the amount you produce of this gene has to be just right. We are making an educated guess that this is in control of growth of cells in the human brain," said Gecz.

The team even developed a test allowing women to know if they possess the mutations before getting pregnant.

"So far about 85 genes have been discovered on the "X" chromosome which are involved in various forms of mental disability. There are about 800 genes on the chromosome," said Gecz.