In a new study of more than 400 young children, those who were diagnosed with autism were more likely to have had difficulty falling asleep as infants. This sleep difficulty was associated with altered growth trajectories in the hippocampus.
The findings are published in the American Journal of Psychiatry.
Infants spend most of their first year of life sleeping, and these hours are vital for brain development, as neural connections are formed and sensory memories are encoded. But when sleep is disrupted, as occurs more often among children with autism, brain development may be affected.
In the new study, researchers at the University of Washington (UW) found that sleep problems in a baby’s first 12 months may not only precede an autism diagnosis, but also may be linked to an altered growth trajectory in a key part of the brain: the hippocampus.
“The hippocampus is critical for learning and memory, and changes in the size of the hippocampus have been associated with poor sleep in adults and older children,” said lead author Dr. Kate MacDuffie, a postdoctoral researcher at the UW Autism Center. “However, this is the first study we are aware of to find an association in infants as young as 6 months of age.”
As many as 80% of children with autism spectrum disorder (ASD) have sleep problems, said Dr. Annette Estes, director of the UW Autism Center and senior author on the study. But much of the existing research focus on behavior and cognition.
With sleep such a critical need for children and their parents, the researchers involved in the multicenter Infant Brain Imaging Study Network, or IBIS Network, believed there was more to be examined.
“In our clinical experience, parents have a lot of concerns about their children’s sleep, and in our work on early autism intervention, we observed that sleep problems were holding children and families back,” said Estes, who is also a UW professor of speech and hearing sciences.
The study was conducted because researchers had questions about how sleep and autism were related, Estes said. For example, do sleep problems exacerbate the symptoms of autism? Or is it the other way around, that autism symptoms lead to sleep problems? Or something different altogether?
“It could be that altered sleep is part-and-parcel of autism for some children. One clue is that behavioral interventions to improve sleep don’t work for all children with autism, even when their parents are doing everything just right. This suggests that there may be a biological component to sleep problems for some children with autism,” Estes said.
To investigate any associations among sleep, brain development and autism, researchers at the IBIS Network evaluated the MRI scans of 432 infants, surveyed parents about sleep patterns, and measured cognitive functioning using a standardized assessment.
Researchers at four institutions — UW, University of North Carolina at Chapel Hill, Washington University in St. Louis and the Children’s Hospital of Philadelphia — evaluated the children at 6, 12 and 24 months of age and surveyed parents about their child’s sleep, all as part of a longer questionnaire covering infant behavior. Sleep-specific questions addressed how long it took for the child to fall asleep or to fall back asleep if awakened in the middle of the night, for example.
At the beginning of the study, infants were classified according to their risk for developing autism. Those who were at higher risk of developing autism had an older sibling who had already been diagnosed (about two-thirds of the study sample). Infant siblings of children with autism have a 20 percent chance of developing autism spectrum disorder, a much higher risk than children in the general population.
A 2017 study by the IBIS Network found that infants who had an autistic older sibling and who also showed expanded cortical surface area at 6 and 12 months of age were more likely to be diagnosed with autism compared with infants without those indicators.
In the new study, 127 of the 432 infants were identified as “low risk” at the time the MRI scans were taken because they had no family history of autism. They later evaluated all of the participants at 24 months of age to determine whether they had developed autism. Of the roughly 300 children originally considered “high familial risk,” 71 were diagnosed with ASD.
The findings allow researchers to re-examine previously collected longitudinal brain scans and behavioral data and identify some patterns. Difficulties with sleep were more common among the infants later diagnosed with ASD, as were larger hippocampi.
No other subcortical brain structures were affected, including the amygdala, which is responsible for certain emotions and aspects of memory, or the thalamus, a signal transmitter from the spinal cord to the cerebral cortex.
The UW-led sleep study is the first to show an association between hippocampal growth and sleep problems in infants who are later diagnosed with autism. It is still unclear if there is a causal relationship, however.
Source: University of Washington