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.