PITTSBURGH – The corpora callosa of individuals with autism are smaller than those of healthy controls both during early childhood and after age 30 years, according to data presented during a poster session at the annual meeting of the Child Neurology Society.
The differences are especially obvious in the genu, rostrum, and splenium–areas with a high density of thin fibers, which are important in higher-order cortical processing.
“Our findings provide new evidence that, in autism, differences in the pattern of neurological development may continue into the aging process,” said Diane L. Williams, Ph.D., who presented the findings.
Dr. Williams of Duquesne University, Pittsburgh, and her colleagues used magnetic resonance imaging to examine the corpora callosa of 80 high-functioning males with autism (aged 9–53 years) and 80 healthy age-matched male controls. Because corpus callosum anatomy has been reported to be affected by handedness and gender, the investigators used only males, and the groups were matched for handedness.
The researchers divided each group into five age categories (10–15.4 years, 15.5–20.4 years, 20.5–25.4 years, 25.5–30.4 years, and 35 years and older). On imaging, the corpus callosum was divided into seven subregions (rostrum, genu, rostral body, anterior midbody, posterior midbody, isthmus, and splenium), and was measured at the midsagittal slice.
After controlling for IQ, age, and total brain volume, the group with autism had reliably smaller corpora callosa than did controls.
The overall difference was driven by significant differences in the youngest and oldest groups compared with their corresponding control groups. Both autism groups had significantly smaller measurements for the total corpus callosum and the rostrum and genu; the oldest group also had reduced measurements in the splenium.
During adolescence and young adulthood, the size differences normalized. “This should not be interpreted, however, to mean that the integrity and composition of the neural structures are the same at that time,” the researchers noted.
Rather, the structure size differences in childhood and later adulthood may reflect a different developmental trajectory, with later maturing and earlier decline than normal controls experienced.
“The suggestion of group differences for the rostrum and genu at early and late ages is consistent with what is known about normal development of these subregions. In normal adults, the anterior white matter, including the genu of the corpus callosum, is the first to decline. In autism, this same developmental pattern may occur, only with a timing difference,” the investigators said.