Attention deficit hyperactivi... Health Article

Definition

Attention deficit hyperactivity disorder, or ADHD, is a behavioral disorder, characterized by poor attention, inability to focus on specific tasks, and excessive activity. ADHD is thought to have a strong genetic component, although studies are still ongoing to determine what role specific genes play in ADHD.

Description

Attention deficit hyperactivity disorder (ADHD) was first described by a pediatrician, Dr. George Still, in 1902. At the time, he gave an account of 43 children who exhibited such symptoms as aggressiveness, defiance, and limited attention spans. He stated that he felt these symptoms indicated a lack of "moral control" in these children and others exhibiting similar characteristics.

Until the 1950s, it was felt that the symptoms of ADHD were caused by either infections, toxins, or trauma to the head. During that time, ADHD was referred to as "minimal brain damage," or minimal brain dysfunction." In the 1960s and 1970s, when more was learned about brain functioning, scientists and doctors changed the name of the disorder to "hyperkinetic reaction to childhood" in response to the recognition of the prominent role of hyperactivity with the disorder. It was also during this time that the use of stimulants such as amphetamines began to be used to treat children diagnosed with the disorder. The term "attention deficit disorder," and finally, attention deficit hyperactivity disorder, was applied to the disorder in the 1980s and 1990s.

From the time it was first clinically described by Dr. Still, the diagnosis of ADHD has included certain basic characteristics, such as easy distractibility, hyperactivity, impulsivity, and a short attention span, especially when related to specific tasks. Early in its history, ADHD was thought of as a purely childhood disorder; however, it is now recognized that ADHD can continue well into adulthood. Current studies indicate that ADHD affects between six and nine million adults in the United States and is seen in both males and females, with males having the condition about twice as often as females.

Genetic profile

There is good evidence to suggest that genetic factors play an important role in ADHD. From early studies to the present, it has been recognized that ADHD tends to run in families. Multiple studies have shown that patients who have first or second degree relatives with ADHD are at higher risk for developing ADHD then patients who do not have close relatives with the condition. It has also been shown that children who are adopted are at higher risk for ADHD if their biologic parents have the condition, rather than their adoptive parents. Children whose parents have ADHD have a 50% chance of developing the condition.

While genetics certainly plays a role in ADHD, the specific genes responsible for the condition have yet to be identified. In 1993, a study reported that ADHD was seen in 40% of adults and 70% of children in a rare thyroid autosomal dominant disorder located on chromosome 3. However, later studies have been unable to confirm this initial study.

More convincing research points to a particular form of a gene called DRD4-7, which codes for dopamine transport in the brain. Dopamine is one of several very important brain neurotransmitters, and a certain type, or allele of DRD4-7 is thought to decrease the amount of dopamine in the brain. Studies have shown that about 30% of patients with ADHD have this certain DRD4-7 allele. In people who do not have ADHD, this allele is only seen about 15% of the time.

Demographics

Studies on the occurrence of ADHD within different ethnic, racial, and sociological groups is somewhat limited. Early studies pointed to families on the lower end of the socioeconomic scale and minority racial groups as having a higher incidence of ADHD. However, later studies have not bore these studies out, and in fact there was obvious ethnic and racial bias built into these initial studies.

More recent studies have focused on possible enviromental factors in the development of ADHD. Childhood exposure to certain toxins, such as lead, alcohol, and cigarette smoke, seemed to be linked to a higher occurrence of ADHD. Other studies point to childhood hypersensitivity to certain food additives as a contributing factor in the development of ADHD. Nutritional deficiencies in iron, zinc, and essential fatty acids have also been implicated in ADHD, but studies in this area are limited.