Causes+of+ADHD

Causes of ADHD.
The exact causes of ADHD are unknown; however, research has demonstrated that factors that many people associate with the development of ADHD do not cause the disorder. For example, ADHD is not caused by minor head injuries, damage to the brain from complications during birth, food allergies, excess sugar intake, too much television, poor schools, or poor parenting.7, 19 No single cause of ADHD has been discovered. Rather, a number of significant risk factors affecting neurodevelopment and behavior expression have been implicated. Events such as maternal alcohol and tobacco use that affect the development of the fetal brain can increase the risk for ADHD. Injuries to the brain from environmental toxins such as lack of iron have also been implicated. Scientists have investigated the role of the neurotransmitter dopamine in the development of ADHD because this neurotransmitter plays a key role in regulating movement, increasing motivation and alertness, and inducing insomnia. The observation that ADHD tends to run in families strongly suggests that the disease has a genetic component. Children who have ADHD usually have at least one close relative who also has the disorder.24 One group of researchers found that a child whose identical twin has ADHD is 11 to 18 times more likely to develop the disorder than a nontwin sibling. Investigations of particular genes involved in ADHD have focused on a dopamine receptor gene (DRD) on chromosome 11 and the dopamine transporter gene (DAT1) on chromosome 5.44 Ongoing studies continue to examine these genes and others as factors in ADHD. Most likely, a combination of several genes and environmental factors determines whether a person has ADHD. Imaging studies have shown differences in the brains of boys with ADHD compared with boys who do not have ADHD. Researchers found that certain parts of the brain are, on average, smaller in boys with ADHD.8 Other studies found that the total brain volume is smaller in girls who have ADHD than in control subjects; these results match similar findings about the brains of boys with ADHD.9 Scientists have speculated that the changes in the particular brain regions may be involved in the inability to inhibit thoughts, which is a symptom of ADHD.

http://science.education.nih.gov/Supplements/Nih5/Mental/guide/info-mental-c.htm