Later Age of Autism Diagnosis in Children with Multiple Co-Occurring Psychiatric Disorders

PURPOSE: In children with autism spectrum disorder (ASD), early diagnosis permits early access to therapeutic interventions which may improve outcomes. Factors affecting the age of diagnosis in ASD are not fully understood. METHODS: Here, two large independent datasets were analyzed to investigate age of autism diagnosis and co-occurring psychiatric conditions, including bipolar disorder, depressive disorder, anxiety disorder, obsessive-compulsive disorder, attention deficit hyperactivity disorder, oppositional defiant disorder, and conduct disorder. Clinical characteristics examined included demographics, verbal status, intellectual disability, restricted/repetitive behaviors, adaptive behaviors, and psychiatric medication use. RESULTS: Over 50,000 participants with ASD were analyzed from the Rhode Island Consortium for Autism Research and Treatment study (RI-CART; n=823) and the Simons Foundation Powering Autism Research for Knowledge (SPARK) database (n=52,611). In RI-CART, age of diagnosis differed between those with no co-occurring conditions (mean age at diagnosis = 4.3 years), those with one or two co-occurring conditions (7.1 years), and those with three or more co-occurring conditions (8.5 years; p<.001). This pattern was observed in the SPARK database (age of diagnosis 4, 7.1, and 10 years, respectively; p<.001). Controlling for age, sex, and symptom severity, more co-occurring psychiatric conditions was associated with later age of ASD diagnoses in both samples. Depression and ADHD were associated with later ASD diagnoses; OCD and ID were associated with earlier ASD diagnoses. CONCLUSION: These findings indicate that those children with high co-occurring psychiatric conditions, who are ultimately diagnosed with ASD, experience later diagnosis. This group of children may represent a distinct subtype of autism.