Research has been carried out using identical twins, non- identical twins, adopted children and their adopted brothers and sisters, as well as their parents. It has been discovered that there is a 72-83% chance of the identical twins both having ADHD and only a 21-45% for the non-identical. Parents and siblings of ADHD children are 5 times more likely to have the disorder than others. This is evidence of a heritable connection.
Researchers now believe that there are several genes which influence the development of ADHD. These genes influence the production of the particular neurotransmitters called dopamine and noradrenalin in the brain which influences the way one learns. This occurs by how effective glucose can be used in the brain. It has been discovered that those with ADHD since childhood only efficiently use glucose in some parts of their brains, whilst the others have a lower amount being used. This creates an imbalance and thus, ADHD symptoms.
56 families who had a sufferer of ADHD were studied and a consistency in the presence of these genes were found. This however, only opens more doors for research. It is possible that there is a specific combination of these genes and other genes which influence development of this disorder.
Ed Cook, the associate professor of psychiatry and of pediatrics at the University of Chicago says: “If we can establish a link between abnormal forms of this gene and ADHD, it could provide us with a powerful new tool for precise diagnosis and early identification of children at risk, and a signpost toward designing better drug treatment,"
The genes now thought to affect ADHD have also been found to influence the development of schizophrenia.
http://www.schizophreniaforum.org/new/detail.asp?id=500
http://www.uchospitals.edu/news/1995/19950000-adhd-gene.html
http://www.rps.psu.edu/sep96/hyper.html
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