Gene 'dial' changes may help explain why autism hits more boys
Autism is diagnosed about four times more often in boys than in girls. A new study points to small changes near a gene on the X chromosome. Boys have only one X, so they have no backup copy when that gene is turned down.
Autism is diagnosed about four times more often in boys than in girls. Scientists have long asked why. A study published this week offers part of an answer.
Researchers at Baylor College of Medicine and Texas Children's Hospital in Houston looked at a gene called MECP2. It sits on the X chromosome. Girls have two X chromosomes. Boys have one.
The gene makes a protein the brain needs in a "just right" amount. Earlier work showed that losing about half of it causes Rett syndrome, a severe disorder. Having twice as much causes a different condition. In mice, smaller changes, such as a 30% drop, led to autism-like behavior without the severe symptoms.
So the team studied the gene's control switches, the parts of DNA that act like dials and set how much protein is made. They used a lab method that tests many versions of these dials at once. Then they checked the same spots in people with autism.
They found two control regions where autistic boys had inherited a change from a mother who did not have autism. One change cut the gene's output by about 30% in human brain cells. The boy who carried it was diagnosed with autism and ADHD but had no signs of Rett syndrome.
The idea is simple. A girl with the same change has a second X chromosome that can make up for it. A boy has no backup.
Lead scientist Huda Zoghbi said the work reveals "just the tip of the iceberg" and gives a way to look for similar changes in other X chromosome genes. The study appeared in the American Journal of Human Genetics.
What we know: Small changes in MECP2's control regions lowered the gene's output and were found in autistic boys.
What we don't: How many autism cases this explains, since the finding rests on a small number of families.
Where outlets agree News-Medical and We are Healthy both report that MECP2 control-region changes on the X chromosome may help explain why autism is more common in males.
Where they differ We are Healthy says the study explains the male bias and that autistic males often inherit these variants, while News-Medical's account says the changes explain only part of the gap, found in two regions, and calls it the tip of the iceberg.