It has been demonstrated that children who have at least one parent diagnosed with ADHD are more likely to be diagnosed with ADHD. Scientific evidence suggests most strongly that, in many cases, the disorder is genetically transmitted, and is caused by an imbalance or deficiency in certain chemicals that regulate the efficiency with which the brain controls behavior. Current research is examining which genes may be involved. A team at the University of California suggest that genes contributing to (ADHD) overlap an area of chromosome 16p13 where the genes for autism are. The two conditions appear related, with both (ADHD) and autism, frequently involving inattentiveness and/or hyperactivity.
This investigative path also suggests an associated hypothesis that environmental factors, handed down from generation to generation, may trigger the symptoms associated with ADHD. There also exists a possibility that a family with one diagnosed member may have a heightened awareness of the disorder, along with a willingness to seek formal diagnosis, which would make detection and diagnosis more likely, thus skewing the data on heritability.