Children Diagnosed with Autism Spectrum Disorders before and after the Age of 6 Years: A Comparison Study

Background: The symptoms of autism spectrum disorders (ASD) become manifest in infancy or early childhood. However, many children are not diagnosed until well into elementary school age and therefore do not benefit from specialized early intervention.

Objectives: To describe and to compare the characteristics of children diagnosed with ASD before and after the age of 6 years.  

Methods: Participants were 99 Icelandic children born 1992-1995 who had been diagnosed with ASD, based on ICD-10 criteria. The children were divided into two groups based on their age at initial ASD diagnosis: 58 children were diagnosed before age 6 (group 1) and 41 after age 6 (group 2). Comparisons between the groups addressed autistic behaviors, cognitive- and adaptive measures, language status and other variables. In addition, a questionnaire was administered to parents regarding early concerns of their child’s development.

Results: Children diagnosed with childhood autism were more likely to receive their diagnosis before 6 years of age compared with children with other ASDs who were more likely to be recognized later (p < 0.001). Comparing groups 1 and 2 did not reveal differences on ADI-R (p = 0.255) or adaptive behavior (p = 0.944), but group 1 had lower mean IQ scores (p < 0.001) and lower verbal status (p < 0.001) than group 2. Group 1 was less likely to have received other diagnoses prior to the ASD diagnosis than group 2 (p < 0.001). The majority of parents (76.2%) had developmental concerns prior to their child’s third birthday. Upon hindsight, 83.3% of the parents thought that their children had shown autistic behaviors at or before 2 years of age.  

Conclusions: ASD was recognized later in children with higher IQ scores and with higher verbal status, although the groups did not differ on measures of autistic or adaptive behaviors.