For all scientific objectives, we have achieved important results, among which are the following:
I) We found the comorbidity of ADHD and ASD as well as related traits to be largely due to genetic factors and (non-shared) environmental factors. We found cognitive deficits in executive functioning to be more relevant to ADHD. We also found that emotion recognition problems are similarly frequent in ADHD as they are in ASD. Investigating mind-wandering, emotional lability, and sleep quality in adults with ADHD, we observed that all three contributed to ADHD severity.
II) Investigating effects of medication for ADHD on the risk for injuries in children and adolescents with comorbid neurodevelopmental disorders in Swedish population registries, we found a significant reduction in injuries during periods of medical treatment for ADHD. We also studied effects of environmental risk factors on cellular models of ADHD using neurons derived from induced stem cells of people carrying mutations of PARK2, a gene linked to ADHD and ASD: we observed an increased sensitivity of processes related to neuronal maturation when studying effects of early exposure to nicotine. We also found alterations in the gut microbiome to be linked to inattention in individuals with ADHD and healthy individuals. Studying epigenetic factors that might mediate the effects of environmental factors, our studies identified several genes of interest for further study.
III) We worked both on human genetics approaches to find novel genes for (comorbidity) of ADHD and ASD as well as on different models systems. We obtained evidence for the influence of parent of origin effects on ADHD risk and studied evolutionary aspects of ADHD and ASD. Studying deficiency of the ADHD risk gene ADGRL3 in a mouse model, we found increased impulsivity and locomotive activity and impairments of memory and learning. Neurotransmission through dopamine and neurohormones/peptides seemed to be involved. In Drosophila, we studied an ASD-related gene network, for which reduction of gene expression resulted in habituation learning defects. In zebrafish we studied two genes implicated in ADHD and ASD, ywhaz and reelin, determining their expression across the lifespan and identifying alterations of dopaminergic and serotonergic neurotransmission.
IV) In a study of reaction time variability, we found that attentional fluctuation in children with high ASD traits may be due to co-occurring ADHD traits. We found persistence of ADHD to be linked to genetic burden and to low grey matter volumes in frontal/cerebellar regions involved in top-down cognitive control. We also identified potential biomarkers for ADHD based on gene expression in blood cells. In genome-wide genetic studies, we found genetic burden for ADHD to also predict cocaine dependence.
V) We explored the druggable genome in ADHD by utilizing genome-wide association studies on ADHD and its co-morbid conditions. We identified several promising genetic loci for potential drug development. We studied several additional potential candidate drugs for ASD and ADHD in our zebrafish and Drosophila models. To study non-pharmacological treatments for ADHD, we performed a randomized controlled trial (RCT) of the meditation technique mindfulness, which shows promising first results.
In addition to the scientific progress, we have also completed the planned training events.