Atypical Sensory Processing in Individuals with ASD and Their Relatives: An Intermediate Phenotype?

Background: Genetic heterogeneity (e.g. copy number variants, single nucleotide polymorphisms) and additive effects are likely to contribute to the liability for ASD in a majority of cases. As a consequence, most parents and siblings of a child with ASD should be carriers of some of those risk factors without having ASD themselves, but possibly resulting in subclinical traits. Although they are not part of the diagnostic criteria, sensory symptoms are quite common in individuals with ASD. The Adolescent/Adult Sensory Profile (Brown & Dunn, 2002) is a self-report questionnaire for individuals aged 11 years or above, that results in scores on four sensory quadrants: Low Registration, Sensation Seeking, Sensory Sensitivity and Sensation Avoidance.

Objectives: 1) To replicate the findings that individuals with ASD show atypical sensory processing.
2) To find out whether first degree relatives of individuals with ASD show atypical sensory processing, in-between ASD subjects and controls. If so, atypical sensory processing may be an intermediate phenotype candidate.

Methods: We requested children with ASD  as well as parents and siblings to fill out the Dutch version of the Adolescent/Adult Sensory Profile as a part of a larger family study. We calculated Z-scores for the quadrant scores based on the normative means and standard deviations as described in the manual. Z-scores of participants with ASD were compared with those of the relatives and Z-scores of both groups were compared to 0 (as to compare with the normative scores).

Results: 96 subjects with ASD (79 male, 17 female; 89 adolescents, 7 adults) and 277 relatives (119 male, 158 female; 217 parents, 60 siblings), from 123 different families, filled out the questionnaire. Mean Z-scores for the ASD subjects on the 4 quadrants were .33, -1.28, .47 and .48, and for the relatives -.58, -.68, -.26, -.48. All calculated differences (ASD versus relatives, relatives versus normative data, ASD versus normative data, for each AASP quadrant) were significant at p<.001 (except ASD versus normative data quadrant 1 p=.0084). Most of the differences remained significant if we analysed the results of males and females separately.

Conclusions: These results demonstrate that individuals with ASD show atypical sensory processing: they register more stimuli, are more sensitive to them, seek less sensations and avoid them more than control participants. Since the Sensation Seeking quadrant results in in-between scores for first degree relatives (between ASD cases and controls), this might be an intermediate phenotype candidate. The results for the other three quadrants were not conform our expectations: normative data were in-between scores of ASD participants and their relatives. One major drawback of this study is that we used the normative data from the American manual, the Dutch version of the AASP has not been standardized yet.