Autistic Characteristics Before and After the Age of Three in Children with Autism Spectrum Disorder

Background: Autism Spectrum Disorder (ASD) is a group of disorders characterized by social impairment, communication impairment, and behavioral abnormalities. ASD is a heterogeneous disorder and manifests as various characteristics that constitute the DSM-IV-TR criteria for ASD diagnosis. Research on the occurrence and appearance of autistic characteristics is necessary to better understand the etiology of ASD as ASD prevalence has dramatically increased over the past decade.  

Objectives: This study investigated the frequency of autistic characteristics before and after age three to determine if autistic characteristics increase or decrease in frequency with age, to determine if there are significant race or sex differences, and to examine if ASD children met the DSM-IV-TR criteria for ASD before the age of three.

Methods: Data were collected as part of a population-based ASD surveillance investigation carried out in Essex, Union, Hudson and Ocean Counties.  Current findings represent 8-year olds (1998-born) in 2006. ASD ascertainment was by an active, retrospective, multiple-source, case-finding method, developed by the Centers for Disease Control and Prevention (CDC), based on review and analysis of information contained in health and education records.   Demographic variables and case-specific data, contained in professional evaluations were analyzed before and after the age of 3.  DSM-IV-TR criteria for autistic characteristics were observed in this sample of ASD children. T tests and Chi square tests were used to test associations. 

Results: In a sample of 232 ASD children who had an average of 4 professional evaluations before age 3, significant increases in the frequency of seven out of twelve DSM-IV-TR autistic characteristics were found.  Of those, 163 children (70%) met the DSM criteria for ASD before the age of 3.  The following characteristics changed significantly: DSM-1a, non-verbal social behavior impairment, increased from 67% before the age of 3 to 81% after the age of 3 (p<.001) ; DSM-1b, peer interaction impairment, increased from 46% to 60% (p<.001); DSM 2b, communication/receptive language impairment, increased from 86% to 93% (p<.05); DSM-2c, repetitive language impairment, increased from 51% to 70% (p<.001); DSM-3a, restricted pattern of interest, increased from 28% to 46% (p<.001); DSM-3b, rigid non-functional routines, increased from 47% to 65% (p<.001); DSM-3c, stereotyped behaviors, increased from 50% to 65% (p<.001).  There were no race differences; however, sex differences were observed. DSM 1b was more frequent in males before the age of 3 (M= 64%, F=37%; p<.01). DSM-1a and DSM-3c were more frequent in females after the age of 3 (M= 64%, F=83% and M=48%, F=70; p<.05 respectively).

Conclusions: Autistic characteristics are not static and some may increase over time. Tracking autistic characteristics over time may aid in the development of targeted interventions aiming to improve functioning. Early identification of ASD is a worthy goal, however, more specific approximation of the ASD characteristics manifesting before age 3 may be needed to guide identification efforts.