More Clues to Autism's Origin

Study finds it closely linked to slow language development

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HealthDay Reporter

TUESDAY, March 23, 2004 (HealthDayNews) -- Researchers have pinned down more specifically the portions of the brain associated with autism, the developmental disorder that affects up to 1.5 million Americans.

Using imaging technology, the team narrowed down the link to specific areas of white matter, which is essentially the brain's wiring system.

In the process, the researchers also have obtained more clues about the timeline of the disorder, says study leader Dr. Martha R. Herbert, a pediatric neurologist at Massachusetts General Hospital and Harvard Medical School in Boston. Her report appears in the April issue of the Annals of Neurology.

The findings also strengthen experts' suspicions of a relationship between autism and developmental language disorder, she says, adding the two disorders may be on a spectrum rather than two clearly distinct conditions.

Herbert's findings build on research by her team and other experts. "It's already been established by a growing number [of researchers] that children with autism have a larger brain volume," she says. Herbert's team and one other have also reported previously that what makes the brain bigger in autistic children is more white matter.

Autism, a complex developmental disability, usually appears during the first three years of a child's life, according to the Autism Society of America. It is marked by a lack of normal social interaction, language abnormalities and repetitive, ritualistic behavior.

Developmental language disorder (DLD), as the name suggests, involves language impairments.

Using advanced techniques to analyze magnetic resonance imaging (MRI) studies, Herbert's team studied 63 children, including 13 with autism, 21 with DLD and 29 normal healthy controls. All were aged 8 to 9, had IQs above 80, and were considered high functioning.

In both the autistic and DLD children, the outer area of white matter was larger than that of the controls, they found, but the inner zones of white matter were no different.

The outer zone, called the radiate zone, "is the only part that showed a significant volume increase," Herbert says.

The children with DLD and autism showed the greatest white matter enlargement in the prefrontal area, the very front of the brain.

The areas showing the greatest volume increases are areas in which the white matter myelinates later, Herbert says. Myelination is the process in which portion of nerve cells called axons are covered with a material called myelin.

"Myelin travels up from deep to superficial [parts of the brain]," Herbert says, and also back to front of the brain. "Most of the fibers in the womb are nonmyelinated; they don't have the white sheath around them."

"This gives us a time interval to look for underlying disease mechanisms," she says.

Paul Thompson, an associate professor of neurology at the UCLA David Geffen School of Medicine in Los Angeles, says the research is significant because it pins down more specifically where in the brain autistic children are different and when things may go awry.

"This is a little bit like shining a flashlight on the area of the brain that will encourage researchers to look at this a little more," he says.

This research, he adds, points to the outer layer of white matter as the possible origin of the problem. "Her research also points to when it occurred," he adds, which could be valuable information. Eventually, the finding might help in the diagnosis of autism, he says.

More information

For more information about autism, visit the Autism Society of America and the Cure Autism Now Foundation. Learn about dealing with language development problems from the American Speech-Language-Hearing Association.

SOURCES: Martha R. Herbert, M.D., Ph.D., pediatric neurologist, Massachusetts General Hospital and Harvard Medical School, Boston; Paul Thompson, Ph.D., associate professor, neurology, UCLA David Geffen School of Medicine, Los Angeles; April 2004 Annals of Neurology

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