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Spectrum: Autism Research News

Why oh Y

by  /  24 April 2012

This article is more than five years old. Autism research — and science in general — is constantly evolving, so older articles may contain information or theories that have been reevaluated since their original publication date.

So why don’t we hear more about that Y?

The male chromosome only carries about 60 genes, of which 2 have been linked to autism. Nevertheless, some new research on children born with extra sex chromosomes suggests that there may be more than meets the Y.

About 1 in 1,000 boys are born with an extra X chromosome, a condition known as Klinefelter syndrome. The disorder is often not detected until adolescence because its effects are fairly mild, including some intellectual disability, speech and language delay, attention problems and low muscle tone. Around the same proportion of infants are born with an extra Y chromosome, and show a similar range of impairments.

In a study published earlier this month in Pediatrics, Judith Ross’s team at Thomas Jefferson University in Philadelphia studied 108 boys born with either condition, and 50 controls. The researchers found that half of the XYY group and 12 percent of the Klinefelter group met criteria for further autism evaluation on the Social Communication Questionnaire, a ten-minute parental survey.

In other words, carrying an extra copy of genes on the X chromosome increases autism risk slightly, and carrying an extra copy of Y genes boosts that risk significantly. Ross hypothesizes that there are hidden genetic culprits on the Y chromosome that could partially explain the preponderance of boys on the autism spectrum.

For example, neuroligin 4, one of the most talked-about autism candidate genes, has one version that’s found on the X chromosome and another that’s found only on the Y.

“There hasn’t been a lot of attention paid to the Y,” Ross says, partly because genetic linkage studies of years ago didn’t have the statistical power to look only at males. “But it’s starting to turn up.”

It could be that autism arises when the neuroligin 4 protein (or others on sex chromosomes) is expressed too much or too little. This gene dosage effect has been seen, for example, in individuals with autism who carry deletions or duplications in chromosome 16.