How Much Genetic Influence Is There for ADHD?

Gene effects are not hardwired. They depend on gene expression. Environments can influence those. How much they influence them for ADHD is an open question. We now know it's nature and nurture for complex conditions and traits like ADHD. It depends in part on the environment for its activation. Nothing as simple as an infection for ADHD, unfortunately; a complex mix of many environments work together to enhance or activate genetic liability or genetic propensity.