This document discusses the etiology and causes of attention deficit hyperactivity disorder (ADHD). It notes that ADHD affects 3-7% of school-aged children and is more common in boys. The causes are thought to include both genetic and environmental factors. Genetically, ADHD has been linked to mutations in dopamine receptor genes and damage to the frontal lobe of the brain. Environmental factors mentioned include toxins, mercury exposure, lack of proper prenatal care and nutrition, and dietary deficiencies or excesses. More research is still needed to fully understand the genetic and environmental contributions to the development of ADHD.