Changing ASD-ADHD symptom co-occurrence across the lifespan with adolescence as crucial time window: Illustrating the need to go beyond childhood

- Current literature on ASD-ADHD co-occurrence is strongly biased on childhood.
- ASD/ADHD constellations peak during adolescence, driven by those who still have the symptoms.
- Strong emphasis in this developmental periodon social adaptation and executive functioning may explain this pattern.
- Adolescence may be -after early childhood- a second crucial time window for change in symptoms (for better or worse).
- A full lifespan approach towards ASD-ADHD co-occurrence into old age brings novel opportunities.

Literature on the co-occurrence between Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD) is strongly biased by a focus on childhood age. A review of the adolescent and adult literature was made on core and related symptoms of ADHD and ASD. In addition, an empirical approach was used including 17,173 ASD-ADHD symptom ratings from participants aged 0 to 84 years. Results indicate that ASD/ADHD constellations peak during adolescence and are lower in early childhood and old age. We hypothesize that on the border of the expected transition to independent adulthood, ASD and ADHD co-occur most because social adaptation and EF skills matter most. Lower correlations in childhood and older age may be due to more diffuse symptoms reflecting respectively still differentiating and de-differentiating EF functions. We plea for a strong research focus in adolescence which may -after early childhood- be a second crucial time window for catching-up pattern explaining more optimal outcomes. We discuss obstacles and oppportunities of a full lifespan approach into old age.