Previous research suggests that individuals with ASD overlap in motor impairment with those with DCD. But these two conditions may differ significantly in some areas, as children with ASD tend to show weaker skills in social motor tasks such as imitation, wrote Emil Kilroy, PhD, of the University of Southern California, Los Angeles, and colleagues.
The neurobiological basis of autism remains unknown, despite many research efforts, in part because of the heterogeneity of the disease, said corresponding author Lisa Aziz-Zadeh, PhD, also of the University of Southern California, in an interview.
Comorbidity with other disorders is a strong contributing factor to heterogeneity, and approximately 80% of autistic individuals have motor impairments and meet criteria for a diagnosis of DCD, said Dr. Aziz-Zadeh. “Controlling for other comorbidities, such as developmental coordination disorder, when trying to understand the neural basis of autism is important, so that we can understand which neural circuits are related to [core symptoms of autism] and which ones are related to motor impairments that are comorbid with autism, but not necessarily part of the core symptomology,” she explained. “We focused on white matter pathways here because many researchers now think the underlying basis of autism, besides genetics, is brain connectivity differences.”
In their study published in, the researchers reviewed data from whole-brain correlational tractography for 22 individuals with autism spectrum disorder, 16 with developmental coordination disorder, and 21 normally developing individuals, who served as the control group. The mean age of the participants was approximately 11 years; the age range was 8-17 years.
Overall, patterns of brain diffusion (movement of fluid, mainly water molecules, in the brain) were significantly different in ASD children, compared with typically developing children.
The ASD group showed significantly reduced diffusivity in the bilateral fronto-parietal cingulum and the left parolfactory cingulum. This finding reflects previous studies suggesting an association between brain patterns in the cingulum area and ASD. But the current study is “the first to identify the fronto-parietal and the parolfactory portions of the cingulum as well as the anterior caudal u-fibers as specific to core ASD symptomatology and not related to motor-related comorbidity,” the researchers wrote.
Differences in brain diffusivity were associated with worse performance on motor skills and behavioral measures for children with ASD and children with DCD, compared with controls.
Motor development was assessed using the Total Movement Assessment Battery for Children-2 (MABC-2) and the Florida Apraxia Battery modified for children (FAB-M). The MABC-2 is among the most common tools for measuring motor skills and identifying clinically relevant motor deficits in children and teens aged 3-16 years. The test includes three subtest scores (manual dexterity, gross-motor aiming and catching, and balance) and a total score. Scores are based on a child’s best performance on each component, and higher scores indicate better functioning. In the new study, The MABC-2 total scores averaged 10.57 for controls, compared with 5.76 in the ASD group, and 4.31 in the DCD group.
Children with ASD differed from the other groups in social measures. Social skills were measured using several tools, including the Social Responsivity Scale (SRS Total), which is a parent-completed survey that includes a total score designed to reflect the severity of social deficits in ASD. It is divided into five subscales for parents to assess a child’s social skill impairment: social awareness, social cognition, social communication, social motivation, and mannerisms. Scores for the SRS are calculated in T-scores, in which a score of 50 represents the mean. T-scores of 59 and below are generally not associated with ASD, and patients with these scores are considered to have low to no symptomatology. Scores on the SRS Total in the new study were 45.95, 77.45, and 55.81 for the controls, ASD group, and DCD group, respectively.