The quantitative nature of autistic social impairment

Abstract

Autism, like intellectual disability, represents the severe end of a continuous distribution of developmental impairments that occur in nature, that are highly inherited, and that are orthogonally related to other parameters of development. A paradigm shift in understanding the core social abnormality of autism as a quantitative trait rather than as a categorically defined condition has key implications for diagnostic classification, the measurement of change over time, the search for underlying genetic and neurobiologic mechanisms, and public health efforts to identify and support affected children. Here, a recent body of research in genetics and epidemiology is presented to examine a dimensional reconceptualization of autistic social impairment-as manifested in clinical autistic syndromes, the broader autism phenotype, and normal variation in the general population. It illustrates how traditional categorical approaches to diagnosis may lead to misclassification of subjects (especially girls and mildly affected boys in multiple-incidence autism families), which can be particularly damaging to biological studies and proposes continued efforts to derive a standardized quantitative system by which to characterize this family of conditions.

Figure 1

Distribution of Teacher-Report Social Responsiveness Scale scores (raw scores on x-axis, corresponding T-scores across the top of the figure) for male siblings of children with autism in single-incidence () and multiple-incidence (■) families.

Figure 2

Reciprocal Social Behavior in the General Population: Distribution of score for reciprocal social deficits, parent-report Social Responsiveness Scale. males (■); females (□). Adapted from Constantino JN and Todd RD Arch Gen Psychiatry 60:524-530; Copyright © 2003 American Medical Association, with permission.

Figure 3

Scree plot of principal components analysis of SRS sample of 1,799 boys from 1,799 separate families, representing the full range of variation in autistic severity from unaffected to severely affected by clinical autistic syndromes,

Figure 4

Percentage of subjects with clinically significant autistic traits, stratified by presence or absence of DSM-IV attention-deficit/hyperactivity disorder (ADHD) and by endorsement of Child Behavior Checklist (CBCL) motor problem items. N = 851. Number of subjects in each group is shown above each bar. DAMP = deficits in attention, motor control, and perception. Reprinted from Reiersen AM et al. J Am Acad Child Adolesc Psychiatry 47:662-672; Copyright © 2008 Elsevier, Ltd., with permission.