By SANDRA BLAKESLEE
February 8, 2005
Within the last year, several laboratories have reported finding important new clues about the mysterious syndrome that derails normal childhood brain development.
For the first time, they say, a coherent picture is emerging.
In autism, subtle brain abnormalities are present from birth. Infants and toddlers move their bodies differently. From 6 months to 2 years, their heads grow much too fast. Parts of their brain have too many connections, while other parts are underconnected.
Moreover, their brains show signs of chronic inflammation in the same areas that show excessive growth. The inflammation appears to last a lifetime.
"Autism is still a confusing disorder, but one thing is now clear," said Dr. Pat R. Levitt, a neuroscientist who is the director of the Kennedy Center for Research on Human Development at Vanderbilt University in Nashville. "There is a specific disruption of circuitry in brain development. We can really dig in and begin to explain the splintered brains of autistic children."
To that end, Dr. Levitt and two dozen leading brain researchers held a three-day "autism summit" in Malibu, Calif., sponsored by the Cure Autism Now Foundation, to discuss this emerging view and to plan collaborative studies. The meeting ended Sunday.
"Up to now, there was no theory to link one anatomical study to the next," said Dr. William T. Greenough of the University of Illinois, an expert on brain development. "We now have a theoretical framework that can generate predictions to test."
People with autism have great difficulty with social interaction. Some cannot speak. Many are clumsy. A common trait is obsessive attention to certain details. Symptoms can be severe to mild.
Diagnoses of the disorder have increased in recent years, although no one knows why. One child in 166 born today may fall on the autism spectrum.
Researchers agree that an unknown number of genes interact with unidentified environmental factors to produce the disorder. The new clues focus on brain development and circuitry, and especially on the brain's white matter. White matter contains fibers that connect neurons in separate areas of the brain, whereas gray matter contains the neurons themselves. "You can think of this distinction as analogous to that between cables, or white matter, and circuit boards, or gray matter, inside a computer," said Dr. Matthew Belmonte, an autism researcher at the University of Cambridge in England. "Even though each individual circuit board may be intact, if the cables are disrupted then the computer can't function."
Using a new technique called morphometric analysis, in which post-mortem brain tissue is divided into tiny parcels and examined, Dr. Martha Herbert, a pediatric neurologist at Harvard Medical School, found an anomaly in the white matter of autistic brains - it is asymmetrical.
In autism, white matter grows normally until 9 months, Dr. Herbert said. Then it goes haywire. By 2 years, excessive white matter is found in the frontal lobes, the cerebellum and association areas, where higher-order processing occurs.
The right side of the brain, the nonverbal hemisphere, is especially encased in white matter. The two sides of the brain are poorly connected. Moreover, small functional regions in each hemisphere tend to be prematurely insulated by excess white matter.
Another clue was reported last year by Dr. Eric Courchesne, a neuroscientist at the University of California, San Diego. Using a simple tape measure, he found that newborns who later developed autism had smaller head circumferences than average. From 1 to 2 months of age, their brains suddenly begin to grow rapidly. Another spurt occurs between 6 months and 2 years, giving rise to exceptionally large heads.
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