A new gene called LPHN3 which is responsible for about 9% of the incident of ADHD, a condition with a very high heritable component (about 80%), has been discovered. ADHD cases in persons with the gene are particularly responsive to stimulant medication, and it shows a dose-response relationship to the conditions with persons having two copies of the ADHD risk version of the gene impacted more than those having one only copy of it.
The discovery, which used a large international sample and started with a focused analysis of genetic inheritances within families in the Paisa population in Antioquia, Colombia where ADHD is unusually common, presumably due to founder effects. My Basque readers may be familiar with the region as it is a place with one of the highest concentrations of Basque ancestry in the Americas. Once discovered, the gene was found to play a role "in key brain regions related to attention and activity, [and to] affect metabolism in neural circuits implicated in ADHD."
The discovery comes out of nowhere as no prior studies had identified LPHN3 as a a gene to investigate for a relationship to ADHD, which has to date focused on half a dozen other genes with possible links to ADHD.