Studies Point to Autism Cause

July 22, 2002 -- Out-of-synch brain growth may cause autism, according to studies of brain and head size in autistic children and adults.

Nobody's sure exactly why, in early childhood, some children suddenly start to show signs of autism. Their interactions with others are bizarre. Their emotional reactions are abnormal. They have very little ability to communicate. Their behavior becomes repetitive. Yet physically they seem like other children.

New imaging techniques now make it possible to look at the brains of autistic people. Data from two studies, published side by side in the July 23 issue of the journal Neurology, now point toward an answer. The findings suggest that the timing of brain growth seems all wrong in autistic children. Early in childhood, the brains of autistic children grow faster and larger than those of normal children. Later, when normal children's brains get bigger and better organized, autistic kids' brains grow more slowly.

Nancy J. Minshew, MD, director of the autism program at the University of Pittsburgh School of Medicine, is co-author of one of the studies. She says the early growth spurt happens at age 2 to 3 years -- about the same time symptoms of autism kick in. And it happens at a time when normal children's brains are getting the wiring they need to support language skills, social interactions, and reasoning ability.

"This is a very significant finding," Minshew tells WebMD. "It's like if all the planes scheduled to come in at O'Hare airport came in all at once instead of in an orderly fashion. That is what is happening. This brain wiring develops at a certain pace so the brain can make the proper circuits in an organized way. If they overgrow, there is the chaos of autism."

Minshew and colleague Elizabeth H. Aylward, PHD, professor of radiology at the University of Washington in Seattle, hope the findings will point to treatments for autism.

"I think these studies say maybe it is an abnormality in the timing of what is going on rather than something prenatal," Aylward tells WebMD. "In a lot of disorders like Down syndrome you assume the brain abnormality takes place and then is set. In autism we are saying maybe not. Maybe it happens after birth and the abnormality is continuing throughout childhood."

An editorial in the same issue of Neurology warns against reading too much into brain size. The editorial's lead author is Jonathan W. Mink, MD, PhD, chief of child neurology at the University of Rochester in New York.

"Phrenology was the art of trying to divine functions of the brain, personality strengths, and mental weaknesses based on bumps on the head," Mink tells WebMD. "In our opinion, if you just look at the brain and say, 'Oh, this part of the brain is bigger in autism,' it is not too different from phrenology. These two studies are among the best. As far as we are concerned, this issue is now settled. Yes, the brain is bigger at one age -- but it doesn't get us to the underlying [problem] of autism. If there is some surge in brain chemicals, we have no evidence. What is making the brains larger? We need studies that propose specific hypotheses that can be tested."