Early Behavioral Fear in Infants and Preschoolers at High Risk for Autism: Fragile X Syndrome Versus Autism

Background: Young males with fragile X syndrome (FXS) are at high risk for both autism spectrum disorders (ASD) and anxiety disorders with up to 70% and 80% meeting diagnostic criteria, respectively. Likewise, infants with an older sibling with ASD of unknown etiology are at high risk for ASD and anxiety with nearly 20% meeting criteria for ASD and 40% of those with ASD diagnosed with an anxiety disorder. Despite the high association of anxiety with FXS and infants with siblings, few studies have examined early indicators of anxiety in either group, and no work has examined the specificity of early anxiety indicators in FXS to those in infant siblings. Given that features of ASD and anxiety overlap considerably, disentangling the association of ASD and anxiety features in FXS and infant siblings is important to address the latent heterogeneity in ASD and to direct targeted treatments in both high risk groups.

Objectives:   To investigate social and non-social fear in infants and young children with FXS, contrasted with infant siblings of children with ASD and typically developing controls.

Methods: 76 boys (2-5 years) participated in our initial preschool study representing 29 with FXS, 11 with idiopathic ASD, and 36 typical controls. An additional 68 infants (12–24 months) completed our infant extension, representing 25 with FXS, 22 infant siblings, and 29 typical controls with 20 having data coded at this time and coding scheduled to be completed by 12/2015. Social and non-social fear were measured using gaze from the Stranger and Scary Spider epochs of the Laboratory – Temperament Assessment Battery at 12 and 24 months and at preschool age (stranger only). Autism symptoms were assessed using the severity score from the Autism Diagnostic Observation Schedule 2 and Childhood Autism Rating Scale -2 with anxiety symptoms estimated using the anxiety subscale of the Child Behavior Checklist. We anticipate increased sample sizes for the presentation.

Results: Data indicate that preschool males with FXS display a similar proportion of gaze towards the stranger as the ASD group (32% and 25% of time, respectively) with both being lower than typical controls (45%; p=.01). There were nonsignificant relationships between stranger gaze and autism symptom severity or parent rated anxiety symptoms in the preschoolers (p>.05). For infants, no differences were found between FXS (48%), autism siblings (58%), and typical infants (83%) on the proportion of time spent looking at the spider (p>.05). In contrast, results approached significance for the FXS group to gaze longer to the stranger (52%) than the autism siblings (32%; p=0.07); FXS and autism siblings were both similar to typical controls (p>.05).

Conclusions: Results from this study suggest that children with FXS and siblings of children with ASD may demonstrate different developmental trajectories of social and non-social fear. Though non-social fear does not appear to discriminate children with FXS from other children in infancy, children with FXS and children with ASD do demonstrate elevated social fear later in development, at preschool age.