ADHD is a neurodevelopmental disorder, typically diagnosed during early childhood (age 4 to 6) and is associated with an increased risk of depression during adolescence 31. The current study demonstrated that there was a significant genetic correlation between ADHD and depression. The cadherin 13 (CDH13) gene, which codes for cell adhesion molecules, was found to be putatively associated with depression and has also been implicated in ADHD 32. CDH13 was included in the putative GO_NEURON_PART and GO_NEURON_PROJECTION gene-sets. A further gene involved in cell adhesion, astrotactin 2 (ASTN2), which we found to be putatively associated with depression is also involved in ADHD aetiology 32 and plays a role in neuronal development in the brain 33. Dopamine transmission may also underlie ADHD and depression with both the DRD2 and ankyrin repeat and kinase domain containing 1 (ANKK1) genes implicated in our analysis of depression and in ADHD 34.
