Loss-of-function of foxp2 in zebrafish larvae leads to behavioural changes resembling ADHD-like pathology

Introduction Attention-deficit/hyperactivity disorder (ADHD, OMIM #143 465) represents one of the most prevalent psychiatric disorders with 2 – 8% affected children and adolescents worldwide. The characteristic symptoms are diverse, ranging from hyperactivity and impulsivity over inattention to emotional dysregulation. Previous studies claimed a genetic heritability of 60 – 90% and thereby led to several genomic studies focusing on the identification of genetic variants contributing to ADHD susceptibility.

Making use of zebrafish (Danio rerio), a well-established model organism in genetic and (neuro-) developmental research with a rich behavioural repertoire, we aim to understand the genetic role as well as related neuro-developmental mechanisms of gene variants in the clinical picture of ADHD.

Methods Developmental expression analysis using RNA in situ hybridisation of foxp2, a forkhead box transcription factor present in the nervous system showing significant variability in ADHD patients (Demontis et al., 2019), is used to define foxp2 expression domains in the brain of zebrafish. In addition, genetic mutations are induced with CRISPR/Cas9 to generate a loss-of-function model. Using this model, various behavioural assays in zebrafish larvae are conducted to assess the developmental and functional role of foxp2.

Results foxp2 is already expressed during very early stages in the CNS of zebrafish larvae. Prominent domains of expression were seen in different brain regions, including parts of the forebrain, midbrain and hindbrain. Heterozygotic foxp2(±) larvae display a behavioural output in various assays which partly resembles human ADHD-like pathology. Currently, further characterisation of mutant animals is ongoing and will show, whether variability in foxp2 expression might affect downstream ADHD-specific gene networks.

Conclusion These results pave the way for the further characterisation of FOXP2 role in the development of ADHD.