Brain may grow too fast, too early in autism

Last Updated: 2002-07-22 17:00:16 -0400 (Reuters Health)

By Merritt McKinney

NEW YORK (Reuters Health) - Two new reports provide more evidence that people with autism have slightly enlarged brains in childhood. But by adolescence, the differences in brain size between people with and without autism largely disappear, according to the research.

If investigators can figure out what causes the brain to go into overdrive early in life, it may be possible to develop treatments to prevent this abnormal development, Dr. Nancy J. Minshew of the University of Pittsburgh in Pennsylvania told Reuters Health.

Autism, which impairs a person's ability to communicate and form relationships with other people, usually begins within the first few years of life. Autism may also affect the ability to respond to sights, sounds and touch. Though some children with the disorder are mentally impaired, about one third are "high-functioning," meaning that they have a normal or near-normal IQ.

Although several studies have found that people with autism tend to have larger-than-average brains, the evidence is not conclusive. Some research has linked the disorder to abnormalities in several brain regions, including the hippocampus, amygdala and cerebellum.

In one of two studies published in the July 22nd issue of the journal Neurology, Minshew and her colleagues measured brain size in autistic individuals aged 8 to 46 and compared them with similarly aged people who did not have autism. Among people younger than 12, average brain volume was 5% larger in autistic individuals. After age 12, however, autistic and normal participants had similarly sized brains, but the average head circumference was 1% to 2% larger in autistic individuals.

In a second study reported on in the same issue, a team led by Dr. Stephen R. Dager of the University of Washington in Seattle found that among 3- to 4-year-old children, brain volume was 10% to 13% greater in autistic children than in normal children and in children who had delayed development but who were not autistic.

The findings of the two studies are "very significant" for understanding the causes of autism, according to Minshew.

"They establish that there is a premature overgrowth of the brain in the first 2 years of life and then brain growth essentially plateaus in autism," she said. "By adolescence, it is the same as in normal individuals because of brain growth in the normal population." She noted that the adults with autism had increased head circumference, suggesting that their brain volume had been larger when they were children.

What is significant about the findings, Minshew said, is that the increase in brain growth coincides with the beginning of autism symptoms and "reflects a disruption of normal brain development." During childhood when the intricate wiring in the brain must form so that social, language and reasoning skills will develop, the wiring grows too quickly in a disordered way, she noted.

"It is like all the planes that land at (Chicago's) O'Hare airport in 24 hours landing at the same time," Minshew explained.

Since this developmental process is under the control of genes, the goal of this type of research, Minshew said, is to define the brain abnormalities as precisely as possible so that future therapies can be designed that correct the genetic signal that triggers the overgrowth.

"The hunt is on for the cure, which will be found in the lifetime of children born today--not in mine--but in theirs if research like this continues its course," Minshew stated.

In an editorial that accompanies the studies, Dr. Jonathan W. Mink of the University of Rochester in New York, and Dr. Robert C. McKinstry of Washington University in St. Louis, Missouri, point out that the increase in brain size in autistic children "is slight and the volume of autistic brains is within the normal range of human brain volume."

Although several studies have found that the brains of autistic individuals differ in size from those of other people, because of the variations in how the studies were conducted, it is difficult to know whether the findings are due to actual brain differences or to differences in the study techniques, according to the editorialists.

SOURCE: Neurology 2002;59:158-159, 175-192.

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