Attention Deficit Hyperactivity Disorder Health Article

Definition

Attention deficit hyperactivity disorder (ADHD) is a neurological disorder that presents in various forms, with no two ADHD disorders having exactly the same characteristics. ADHD is classified as a disruptive behavior disorder characterized by ongoing difficulty with attention span, hyperactivity, and/or impulsivity. These difficulties occur more frequently and severely than is typical for individuals in the same stage of development.

Description

ADHD is a neurological condition, frequently familial, that affects specific types of brain functioning. The term ADHD is further divided into subcategories that describe the type of ADHD. The three categories recognized by the scientific community are ADHD inattentive type, ADHD impulsive-hyperactive type, or ADHD combined type. Some individuals, including many professionals, still refer to the condition as ADD (attention deficit disorder). However, this term is no longer in widespread use. For individuals who have been diagnosed with ADD in the past, the corresponding current terminology is most likely to be predominantly ADHD, inattentive type.

It is possible to meet the accepted diagnostic criteria for ADHD without displaying any symptoms of hyperactivity or impulsivity. Each ADHD individual will display a unique combination of symptoms. They will not necessarily have all of the symptoms associated with ADHD, and the levels of severity or impairment are varied from individual to individual. There are mild forms of ADHD in addition to the severe forms that result in significant impairment. Symptoms of ADHD usually begin before seven years of age, and can cause problems in school, jobs and careers, family life, and other relationships. ADHD can be managed through behavioral or medical interventions, or a combination of the two. Despite public controversy over the legitimacy of the disorder's existence, the National Institutes of Health (NIH), the Surgeon General of the United States, and the international community of clinical researchers and physicians have affirmed that ADHD is a valid disorder that may result in severe, lifelong consequences if left untreated. The Senate of the United States designated September 7, 2004, as National Attention Deficit Disorder Awareness Day.

Genetic profile

The exact cause of ADHD is unknown, although abnormal neurotransmitter levels, genetics, and complications occurring around the time of birth have been implicated. According to the National Resource Center on ADHD, heredity makes the largest contribution to the prevalence of ADHD in the population. ADHD occurs frequently in families, and inheritance is an important risk factor. Between 10–35% of children diagnosed with ADHD have a first-degree relative with ADHD. Approximately 50% of parents who have ADHD have a child with the disorder. ADHD is significantly more likely to be present in an identical (monozyogotic) twin than in a fraternal (dizygotic) twin.

ADHD is not a form of gross brain damage. Because the symptoms of ADHD respond well to treatment with stimulants that increase the availability of the neuro-transmitter dopamine, the dopamine hypothesis has gained acceptance. The dopamine hypothesis suggests that ADHD is due to inadequate availability of dopamine in the central nervous system. Dopamine plays a key role in initiating focused movement, increasing motivation and alertness, and preventing sleepiness in response to boredom. Multiple genes have been implicated in ADHD, including genes affecting dopamine usage by the brain.

The male to female ratio is 8:1. Despite the strong genetic linkage, research also suggests that non-genetic factors may play a role in ADHD. Hyperactivity and inattention are more common in children who have had exposure to toxins such as lead, alcohol, or cigarette smoke, or episodes of fetal oxygen deprivation during complications of pregnancy. These factors may adversely affect dopamine-rich areas of the brain.

In addition to dopamine, research has shown that glucose usage may also be involved in ADHD. Brain-imaging studies, using a technique called magnetic resonance imaging (MRI), have demonstrated differences between the brains of children with and without ADHD. A link has been established between an individual's ability to pay continued attention and the brain's use of glucose as a fuel. In adults with ADHD, the brain areas that control attention span may use less glucose and be less active, suggesting that a lower level of activity in this part of the brain may cause the inattention symptoms associated with ADHD.

By 2002, the NIMH Child Psychiatry Branch had performed a decade-long controlled study that demonstrated ADHD children having 3–4% smaller brain volumes in multiple critical brain regions affecting the types of behaviors associated with ADHD. The study also demonstrated that ADHD children receiving medication had developed volume of white matter that was the same as normal children. Individuals who had ADHD but were never medicated had an abnormally small volume of white matter. Whether or not genetic differences are responsible remains to be determined. As of 2004, the NIMH is conducting clinical trials examining the MRI of identical twins with ADHD.