What+are+the+causes+of+ADHD?

Is not an exact cause for ADHD but, researchers still studying the brains for clues. They do believe there are several factors that could contribute to it.
 * // What are the causes of ADHD? //**
 * Hereditary- runs in the family
 * Chemical imbalance- brain chemicals that transmit nerve impulse could be a factor for ADHD
 * Brain changes- areas of the brain that control attention are less active.
 * Head injuries- children with head injuries specially concussions develop behavior problems
 * Mother use of cigarrets,alcohol or other drugs during pregnacy