Studies reveal that children with a lot of brain connections clustered in the frontal lobe often tend to have learning difficulties. However, they had fewer connections to other parts of the brain.

The frontal lobe is that part of the brain important for learning.

"This is a key piece of the puzzle we've been searching for," said Dr. Daniel Geschwind of the University of California, Los Angeles, who worked on the study published in Science Translational Medicine.

"Now we can begin to unravel the mystery of how genes rearrange the brain's circuitry not only in autism, but in many related neurological disorders."

Experts note that the complex brain disorder often diagnosed in early childhood is characterized by mild to serious difficulties in interacting with the society.

A magnetic resonance imaging was used to scan and scrutinize brains of 32 kids as they had learning difficulties. Half of them were autistic, the other half was not.

The team noted that those kids with contactin associated protein-like 2 or CNTNAP2 had strong brain connections within the frontal lobe, but weaker connections to the rest of the brain.

"In children who carry the risk gene, the front of the brain appears to talk mostly with itself," Ashley Scott-Van Zeeland, now at Scripps Translational Science Institute, said in a statement.

"It doesn't communicate as much with other parts of the brain and lacks long-range connections to the back of the brain," she said.

As the gene is also found in healthy people, researchers are studying how it had any effect on the 40 children who did not have autism.

"We actually saw the same pattern," Scott-Van Zeeland said in a telephone interview.

"Kids who carried the risk version of the gene had the same extra connections in the frontal lobe as the first group. Of course, they didn't have autism," she said.

Scott-Van Zeeland said researchers know that autism is caused by more than one gene, but the CNTNAP2 gene helps explain part of the picture.

One in 110 kids in the U.S. might have autism spectrum disorders. It could affect four times as many boys as girls.

"One third of the population carries this variant in its DNA," Geschwind cautioned. "It's important to remember that the gene variant alone doesn't cause autism -- it just increases risk."