Relationship between cognitive ability and predictors for age at the time of autism spectrum disorder diagnosis

The rising prevalence of autism spectrum disorder (ASD) has increased awareness of the need for early diagnosis and intervention; however, not all children are diagnosed at preschool age. In the literature, findings regarding factors that may play a role in later diagnosis are inconsistent. Presence or absence of intellectual disability is a possible factor. This study aimed to identify factors associated with later diagnosis of ASD among children grouped according to low and high cognitive levels. Data of children who were previously diagnosed with ASD between 2002 and 2016 at a national autism center were analyzed. Better cognitive ability, having more siblings, and previous diagnosis of attention-deficit/hyperactivity disorder were predictors of later diagnosis among the entire cohort. Children exhibiting lower cognitive levels (LC-ASD; DQ/IQ < 70; n = 209) were diagnosed much earlier. Among this group, later ASD diagnosis was predicted by poorer adaptive behavior, more severe restricted and repetitive behaviors, and previous diagnosis of epilepsy. In the higher cognitive level group (HC-ASD; DQ/IQ ≥ 70; n = 321), familial variables and more severe social impairments were predictors of later ASD diagnosis. Clinicians should be aware of variables that may affect ASD diagnostic age among children with varying cognitive abilities.