Infants at High Familial Risk for Autism May Show Signs as Early as 6 Months Old

A study in the Journal of Neurodevelopmental Disorders has found that infants as young as 6 months old reveal atypical sensorimotor development that can be associated with autism spectrum disorder (ASD) at 24 months. These differences precede the development of cognitive and adaptive deficits and behavioral features of autism.

The timing and pattern of symptoms associated with emergence of ASD may hold clues for better understanding of the underlying pathogenesis of ASD and lead to earlier identification of affected individuals. Current research indicates that ASD recurrence risk for siblings of children with ASD may be as high as 18.7%. Previous longitudinal studies have suggested that high-risk siblings may show the hallmark symptoms of ASD at 12 months or later. But, the study authors note, “…there is growing evidence that other developmental differences associated with ASD emerge earlier, in the first year of life.” Such signs may include reduced motor control, as indexed by persistent head lag at 6 months of age.

Study participants included 210 high-risk (HR) and 98 low-risk (LR) infants with comparable behavioral data at age 6, 12, and 24 months assessed in the domains of cognitive development (Mullen Scales of Early Learning), adaptive skills (Vineland Adaptive Behavioral Scales), and early behavioral features of ASD (Autism Observation Scale for Infants). Participants evaluated were further stratified by empirically derived cutoff scores using the Autism Diagnostic Observation Schedule yielding four groups: HR-ASD-High, HR-ASD-Moderate (HR-ASD-Mod), HR-ASD-Negative (HR-Neg), and LR-ASD-Negative (LR-Neg).

The four groups demonstrated different developmental trajectories that became increasingly distinct from 6 to 24 months. At 6 months, the HR-ASD-High group demonstrated less advanced Gross Motor and Visual Reception skills compared with the LR-Neg group. By 12 months, the HR-ASD-High group demonstrated increased behavioral features of ASD and decreased cognitive and adaptive functioning compared to the HR-Neg and LR-Neg groups.

This is not a new area of study, but there is an ongoing question about whether early atypical motor function ability represent non-specific phenomena associated with general risk for developmental difficulties, are specific to vulnerability for ASD.

For this study, adaptive functioning was evaluated by parent interview, and all participants were assessed using the Mullen Scales of Early Learning, which provides an overall index of cognitive ability and delay, and other evaluation criteria. While there was no evidence of atypical social-communication or repetitive behavior at 6 months in the HR-ASD-High group, such features were evident at 12 months relative to other HR and LR infants. The study authors note that “…these data illustrate a pattern of unfolding symptoms in children with ASD, starting in the sensorimotor domain at 6 months and moving to the social-communication domain in the second year of life.”

Limitations of the study include the fact that a recent report on high-risk infants who do not go on to develop ASD, followed through 36 months, suggests that over a quarter of high-risk infants without a diagnosis of ASD will nonetheless demonstrate significant developmental difficulties such as ASD symptoms or lower developmental skills. “Thus, a follow-up of high-risk infants into preschool and school-age is clinically indicated and may reveal additional information about developmental trajectories, risk, and protective factors in ASD,” the researchers note.

The study authors also caution that, “Although it is well known that an ASD diagnosis has strong predictive validity, especially in comparison with other childhood psychiatric diagnoses, this should not be taken to suggest that an ASD classification, especially in very young children, is immutable…changes in symptom expression over the course of a psychiatric disorder should not be unexpected or invalidate a diagnosis at an earlier age.”