Developmental course of autistic social impairment in males

Abstract

Recent research has suggested that autistic social impairment (ASI) is continuously distributed in nature and that subtle autistic-like social impairments aggregate in the family members of children with pervasive developmental disorders (PDDs). This study examined the longitudinal course of quantitatively characterized ASI in 3- to 18-year-old boys with and without PDD. We obtained assessments of 95 epidemiologically ascertained male-male twin pairs and a clinical sample of 95 affected children using the Social Responsiveness Scale (SRS), at two time points, spaced 1-5 years apart. Longitudinal course was examined as a function of age, familial loading for PDD, and autistic severity at baseline. Interindividual variation in SRS scores was highly preserved over time, with test-retest correlation of 0.90 for the entire sample. SRS scores exhibited modest general improvement over the study period; individual trajectories varied as a function of severity at baseline and were highly familial. Quantitative measurements of ASI reflect heritable traitlike characteristics. Such measurements can serve as reliable indices of phenotypic severity for genetic and neurobiologic studies, and have potential utility for ascertaining incremental response to intervention.

Figure 1. Scatter plot of maternal SRS Scores at baseline and follow-up

This plot incorporates both groups of study subjects (general population and clinic subjects) in order to represent the full range of SRS scores that occur in nature. When calculating the intraclass coefficient of correlation for the whole sample, icc = .90; when calculated separately for each study group, for twins (one per family, as incorporated in the scatter plot), icc = .71; for clinic subjects, icc = .76. Lower coefficients of correlation are expected when the range of trait variation within a sub sample is narrower.