Children diagnosed with autism spectrum disorder before or after the age of 6 years

This study compared children with early and late diagnosis of autism spectrum disorder (ASD). All children in four consecutive birth cohorts in Iceland diagnosed with ASD were divided into two groups based on their age at initial ASD diagnosis: 58 children were diagnosed before age 6 (group 1) and 41 children after age 6 (group 2). Children in group 1 were more likely to receive a diagnosis of childhood autism (p ≤ 0.001), their average IQ/DQ was lower (p < 0.001), verbal status was lower (p < 0.001), and a history of autistic regression was more common (p < 0.01) than in group 2. Half of the children in group 2 had received other developmental diagnoses prior to the ASD diagnosis, but this applied to only a few of the children in group 1 (p < 0.001). There was no difference between the groups with regard to autistic symptoms as measured by the Autism Diagnostic Interview-Revised (p = 0.224), frequency of associated medical conditions (p = 0.640), age of first parental concern (p = 0.244), and age of first autistic symptoms on hindsight (p = 0.540). The majority of parents (76.2%) had developmental concerns before age 3, and with hindsight 83.3% thought that autistic symptoms had been present before age 2.