The University of North Carolina School of Medicine’s Joseph Piven, MD, and a team of researchers found through a national research network that many toddlers diagnosed with autism at 2 years old had substantially more extra-axial cerebrospinal fluid (CSF) at 6 and 12 months of age, before diagnosis is possible.

“The CSF is easy to see on standard MRIs and points to a potential biomarker of autism before symptoms appear years later,” said Piven, co-senior author of the study, the director of the Carolina Institute for Developmental Disabilities (CIDD) in a UNC, in a statement.

The work, published in Biological Psychiatry, showed the more CSF a patient had at 6 months old meant more severe the autism symptoms at 2 years old. Data suggests that the way CSF flows could be a possible cause of autism for a large subset of people.

“We know that CSF is very important for brain health, and our data suggest that in this large subset of kids, the fluid is not flowing properly,” said Mark Shen, PhD, the first author of the study, in the release. “We don’t expect there’s a single mechanism that explains the cause of the condition for every child. But we think improper CSF flow could be one important mechanism.”

The team of researchers studied 343 infants, 221 who were at high risk of developing autism due to having an older sibling with the condition. Some 47 of the participants were diagnosed with autism at 2 years old. Researchers compared these 47 infant brain MRIs to those of other infants who did not have autism at 2 years old.

The 6-month-olds who later developed autism had 18 percent more CSF than 6-month-olds who were not diagnosed with autism. The amount of CSF remained elevated at 12 and 24 months. Infants who developed more severe autism symptoms had 24 percent more CSF at 6 months, than those not diagnosed with autism.

“Normally, autism is diagnosed when the child is 2 or 3 years old and beginning to show behavioral symptoms, [because] there are currently no early biological markers,” said David G. Amaral, director of research at the UC Davis MIND Institute in a statement. “That there’s an alteration in the distribution of cerebrospinal fluid that we can see on MRIs as early as 6 months is a major finding.”