July 15, 2003 -- Small head size at birth followed by an abnormally rapid and excessive growth in head size during the first year of life may be an early-warning sign of autism, new research suggests. The findings could lead to earlier diagnosis of the condition, before symptoms occur, and the development of better ways to study it.
The findings also argue against the theory that certain childhood immunizations -- most notably the mumps, measles, and rubella (MMR) vaccine -- cause autism, say the University of California, San Diego, investigators who conducted the study. That is because children typically get their MMR vaccinations between 12 and 18 months of age, but the increase in head size and accelerated brain growth tended to occur earlier.
Writing in the July 16 issue of The Journal of the American Medical Association, the researchers note that the "degree, rate and/or duration" of the excessive brain growth may be predictive of the severity of later symptoms of autism. But in an accompanying editorial, pediatrician and psychiatrist Janet Lainhart, MD, writes that it is "premature to conclude that increased rate of head growth is a universal feature of autism."
"On its own this marker is not specific, so it certainly can't tell if a child is going to develop autism," Lainhart tells WebMD. "But the hope is that it can be combined with subtle developmental differences that might be present during infancy to aid in early identification."
Diagnosis of Autism
Children are usually diagnosed with autism between the ages of 2 and 4, when behavioral signs and symptoms such as delayed speech and unusual social and emotional reactions become apparent.
"By 18 months there are very clear warning signs in most children who develop autism," study co-author Natacha Akshoomoff, PhD, tells WebMD. "The hope is that suspicions will be raised even earlier if this pattern of head growth is proven to be a biological marker of autism."
In earlier work, lead author Eric Courchesne, PhD, and colleagues with UCSD and the Center for Autism Research at Children's Hospital reported that 90% of 2- and 3-year-old autistic children they studied had brains that were larger than normal. In their latest study, they examined the medical records of 48 2- to 5-year-olds who had been diagnosed with autism and compared head growth measurements with those of average children, as defined by Centers for Disease Control and Prevention growth charts. They were also compared with 51 non-autistic infants born between 1980 and 2001 who took part in a separate head circumference study.
Head size at birth among the autistic children was, on average, smaller than the children who did not develop autism. But during the first year of life, these children experienced sudden and excessive brain growth such that their brains were larger than all but 15% of all children measured. This excessive growth in head size occurred well before the onset of behavioral symptoms.
"Those infants having the most extreme rate of accelerated head (and brain) growth had the poorest clinical outcome -- being at the severe end of the autism spectrum, while those infants with a slower rate of accelerated growth had a relatively better outcome," Courchesne said in a news release.
Explaining the Symptoms
Though it is widely believed that autism is a genetic disorder, Akshoomoff says the rapid, early brain growth could explain why autistic children develop the symptoms they do. The hypothesis, she says, is that the brain growth occurs in an autistic child before that child is developmentally ready for it.
"There is a vast overproduction of connections in a young child's brain," she says. "But as children start to develop skills between 2 and 5 years of age, there is a pruning back of these connections. They keep what they need and get rid of those that are not meaningful."
The early brain growth in autistic children could mean that they are losing these extra connections too soon, Akshoomoff says, and as a result their emotional and intellectual development is impaired.
She says that the findings must be confirmed in a larger sample of children followed from infancy in the hopes of identifying a clinically useful model of brain growth and autism risk. Such research could also lead to better animal models to study the disorder.
"If there is ever going to be a useful pharmaceutical or genetic intervention in autism it will have to be delivered early in a child's life," she says. "If we wait until the child is 2 to 5 years old, there is only so much that can be done to correct what has already taken place."