Visual Scanning of Faces In Childhood Disintegrative Disorder

Background: Childhood disintegrative disorder (CDD) is a rare developmental disorder characterized by at least two years of normal development, followed by a loss of language, social and motor skills. Little research on the disorder exists, due mostly to its rare occurrence, with estimates ranging from .11 to .64 per 10,000. The unique natural history of the disorder, specifically the late age of onset, is the foundation of the definition and diagnosis of CDD. Otherwise, its clinical features, post regression, are very similar to those of the other Autism Spectrum Disorders (ASD) coupled with moderate to profound Intellectual Disability. However, the unique natural history of CDD raises the possibility that it may represent a different pathophysiological process than ASD, which might be marked by subtle behavioral differences. Eye-tracking studies have repeatedly identified disrupted facial scanning as a hallmark of ASD, but have yet to be applied to individuals with CDD. Eye-tracking may enable us to determine whether CDD is associated with the same behavioral phenotype as ASD.

Objectives: We sought to characterize the gaze behavior of children with CDD, relative to children with ASD and typically developing (TD) children, while scanning pictures of faces.

Methods: Two children with CDD (mean age = 149 months), 16 with ASD (mean age = 114 months) and 8 TD children (mean age = 129 months) were eye-tracked using a Tobii T60 XL. The stimuli included 14 adult faces from the NimStim Face Stimulus Set (shown three times expressing either a happy, fearful or neutral expression) and 14 houses. The task consisted of two, 4 minute 13 second runs of randomly ordered faces and houses with staggered fixations (in either the upper and lower left or right corners of the screen). Regions of interest were created for the eyes and the mouth on each face, using Tobii Studio 2.1, and were applied to every face in the stimulus set.

Results: Overall, children with CDD looked less at the faces (total fixation duration for eyes= 14.2 seconds and mouth= 3.37 seconds) compared to both TD children (eyes= 27.90 seconds and mouth= 9.40 seconds) and children with an ASD (eyes= 16.70 seconds and mouth= 12.64 seconds). Notably, the CDD group had the highest ratio of total fixation of eyes to mouth (4.29), compared to TD children (2.97) and children with ASD (1.32).

Conclusions: Children with CDD look less at faces than either the ASD, or TD groups. This may be related to some difference in their intellectual function. However, when they do attend to faces they look more at the eye region compared to the mouth region of the face. Although this work is limited to two subjects (data collection is ongoing), it raises the possibility that despite their low levels of intellectual function, children with CDD, in comparison to ASD, explore faces in a manner more similar to their TD counterparts. These results suggest that CDD represents a distinct pathophysiology from ASD despite the similarities in clinical presentation of these disorders.