Researchers from the University of California, Davis, MIND Institute used MRI scans to look at the brains of infants, to see if they could find early biological signs of autism spectrum disorder (ASD). The condition is not usually diagnosed until after the age of 4, according to the U.S. Centers for Disease Control and Prevention.
"Currently, there is no reliable biological marker of ASD for very young children. And, at 6 months of life, there is no behavioral test that distinguishes children who will go on to a diagnosis of ASD," explained study senior author Dr. David Amaral, a distinguished professor of psychiatry at the University of California, Davis, and research director at the MIND Institute.
Fifty-five babies, between 6 and 36 months old, were studied by the researchers. Thirty-three had an older sibling with autism, and 22 babies had no family history of autism. Amaral and his colleagues measured their extra-axial fluid, a cerebrospinal fluid that is located above the brain and between it and the bony skull.
Amaral said they were specifically interested in looking at the brains of very young children, aged 6 months to 9 months, who were siblings of older children already diagnosed with an autism spectrum disorder. He said the medical literature suggests that these youngsters are at a much higher risk for the condition (20 percent versus 1 percent).
Previous research by study co-author Dr. Sally Ozonoff, vice chair for research and a professor in the department of psychiatry and behavioral sciences, showed that autism risk is almost 20 times greater in siblings of children with autism than in the general population.
Eight of the 10 children in the study who went on to have a diagnosis of autism spectrum disorder at 24 to 36 months had increased volumes of extra-axial fluid, said Amaral.
The findings were published online July 9 in the journal Brain, and Amaral added that they are in the process of working with scientists at other institutions to see if they can replicate the findings.
"If the major finding is replicated and extra-axial fluid is associated with increased risk of ASD, I hope that structural MRIs would become standard of practice, especially for siblings of children with ASD who are showing rapid head growth, as an adjunct to determining risk of an ASD diagnosis," said Amaral.
He noted that earlier identification of autism might result in more positive long-term outcomes for a child.
Autism affects about one in 88 children, according to the CDC. Symptoms can vary widely, but kids with autism typically have a hard time communicating and interacting with others.
It's an important and relatively new finding, said Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at Steven and Alexandra Cohen Children's Medical Center in New Hyde Park, N.Y.
"The amount of extra-axial fluid detected as early as six months was predictive of more severe ASD symptoms at the time of outcome," said Adesman, who noted that the researchers found that infants who developed ASD also had significantly larger total cerebral volumes at 12 to 15 months of age, and again at 18 to 24 months of age.
But Adesman said that it's important to note that the study shows higher measurements of extra-axial fluid were not unique to kids later diagnosed with autism, and that it's too early to make recommendations for screenings this early in the game.
"It all sounds promising, to think we can do an MRI and figure out who's going to have bad autism, but it's the wrong conclusion. Before we go down that path, we have to see if this finding is relatively big -- if it's a unique finding in kids with ASD -- and then the question is, how does this help us and do you intervene?" said Adesman. "Since we don't understand what causes autism, you might be able to identify a child at higher risk. You could monitor them more closely for signs or absence of signs."
Amaral said while MRI is a safe, noninvasive technique that can be performed on very young kids without anesthesia, he doubts brain imaging like the type conducted in the study will become a routine screen in the general population. But he said its use may increase for children who have an abnormally rapidly growing head size -- another early hallmark of autism in some children.
The goal of finding an early biological marker is to figure out which children need early behavioral therapy, Amaral concluded. "We are hopeful that this may add to the clinician's database of information to help parents make that decision."
For more on autism, go to the U.S. National Institute of Neurological Disorders and Stroke.