Children with autism spectrum disorder (ASD) have larger resting pupil size and generally steadier, higher levels of a salivary enzyme linked to the neurotransmitter norepinephrine, according to University of Kansas researchers.
The levels of the enzyme, called salivary alpha-amylase (sAA), were lower than those of typically-developing children in samples taken in the afternoon in the lab.
However, samples taken at home throughout the day showed that sAA levels were higher in general across the day and far less variable on children with ASD.
“What this says is that the autonomic system of children with ASD is always on the same level,” Christa Anderson, assistant research professor, said. “They are in overdrive.”
The study compared children between the ages of 20 and 72 months of age diagnosed with ASD to a group of typically developing children and a third group of children with Down Syndrome.
In typically-developing children, sAA levels gradually rise and fall over the course of the day, said Anderson, who co-directed the study with John Colombo, professor of psychology.
Although norepinephrine (NE) is present in the blood plasma levels of individuals with ASD, some researchers suggest that perhaps these levels are related to the stress caused by the blood draw.
The KU study eliminated this possibility by collecting saliva through a no-stress method by putting a highly absorbent sponge swab under the child’s tongue. Collecting sAA levels may help physicians screen children for ASD much earlier, noninvasively and relatively inexpensively, said Anderson.
Researchers believe that pupil size and sAA levels could be biomarkers, or physiological signatures, of a possible dysfunction in the autonomic nervous system.
“Many theories of autism propose that the disorder is due to deficits in higher-order brain areas,” said Colombo. “Our findings, however, suggest that the core deficits may lie in areas of the brain typically associated with more fundamental, vital functions.”
The study is published online in Developmental Psychobiology.
Source: University of Kansas