Attention deficit hyperactivity disorder
Attention deficit hyperactivity disorder (ADHD, similar to hyperkinetic disorder in the ICD-10) is a neurodevelopmental psychiatric disorder in which there are significant problems with executive functions (e.g., attentional control and inhibitory control) that cause attention deficits, hyperactivity, or impulsiveness which is not appropriate for a person's age. These symptoms must begin by age six to twelve and persist for more than six months for a diagnosis to be made. In school-aged individuals inattention symptoms often result in poor school performance. Although it causes impairment, particularly in modern society, many children have a good attention span for tasks they find interesting.
Despite being the most commonly studied and diagnosed psychiatric disorder in children and adolescents, the cause in the majority of cases is unknown. The World Health Organization estimates that it affected about 39 million people as of 2013. It affects about 6–7% of children when diagnosed via the DSM-IV criteria and 1–2% when diagnosed via the ICD-10 criteria. Rates are similar between countries and depend mostly on how it is diagnosed. ADHD is diagnosed approximately three times more in boys than in girls. About 30–50% of people diagnosed in childhood continue to have symptoms into adulthood and between 2–5% of adults have the condition. The condition can be difficult to tell apart from other disorders as well as that of high normal activity.
ADHD management recommendations vary by country and usually involves some combination of counseling, lifestyle changes, and medications. The British guideline only recommends medications as a first-line treatment in children who have severe symptoms and for them to be considered in those with moderate symptoms who either refuse or fail to improve with counseling. Canadian and American guidelines recommend that medications and behavioral therapy be used together as a first-line therapy, except in preschool-aged children. Stimulant therapy is not recommended as a first-line therapy in preschool-aged children in either guideline. Treatment with stimulants is effective for up to 14 months; however, its long term effectiveness is unclear. Adolescents and adults tend to develop coping skills which make up for some or all of their impairments. ADHD, its diagnosis, and its treatment have been considered controversial since the 1970s. The controversies have involved clinicians, teachers, policymakers, parents, and the media. Topics include ADHD's causes and the use of stimulant medications in its treatment. Most healthcare providers accept ADHD as a genuine disorder, and the debate in the scientific community mainly centers on how it is diagnosed and treated. Before 1987 the condition was known as attention deficit disorder (ADD)
Cause
The cause of most cases of ADHD is unknown; however, it is believed to involve interactions between genetic and environmental factors. Certain cases are related to previous infection of or trauma to the brain.
Genetics
Twin studies indicate that the disorder is often inherited from one's parents with genetics determining about 75% of cases. Siblings of children with ADHD are three to four times more likely to develop the disorder than siblings of children without the disorder. Genetic factors are also believed to be involved in determining whether ADHD persists into adulthood. Typically, a number of genes are involved, many of which directly affect dopamine neurotransmission. Those involved with dopamine include DAT, DRD4, DRD5, TAAR1, MAOA, COMT, and DBH. Other genes associated with ADHD include SERT, HTR1B, SNAP25, GRIN2A, ADRA2A, TPH2, and BDNF. A common variant of a gene called LPHN3 is estimated to be responsible for about 9% of cases and when this variant is present, people are particularly responsive to stimulant medication.
As ADHD is common, natural selection likely favored the traits, at least individually, and they may have provided a survival advantage. For example, some women may be more attracted to males who are risk takers, increasing the frequency of genes that predispose to ADHD in the gene pool. As it is more common in children of anxious or stressed mothers, some argue that ADHD is an adaptation that helps children face a stressful or dangerous environment with, for example, increased impulsivity and exploratory behavior. Hyperactivity might have been beneficial, from an evolutionary perspective, in situations involving risk, competition, or unpredictable behavior (i.e. exploring new areas or finding new food sources). In these situations, ADHD could have been beneficial to society as a whole even while being harmful to the individual. Additionally, in certain environments it may have offered advantages to the individuals themselves, such as quicker response to predators or superior hunting skills.
People with Down syndrome are more likely to have ADHD.
Environment
Environmental factors are believed to play a lesser role. Alcohol intake during pregnancy can cause fetal alcohol spectrum disorders which can include ADHD or symptoms like it. Exposure to tobacco smoke during pregnancy can cause problems with central nervous system development and can increase the risk of ADHD. Many children exposed to tobacco do not develop ADHD or only have mild symptoms which do not reach the threshold for a diagnosis. A combination of a genetic predisposition with tobacco exposure may explain why some children exposed during pregnancy may develop ADHD and others do not. Children exposed to lead, even low levels, or polychlorinated biphenyls may develop problems which resemble ADHD and fulfill the diagnosis. Exposure to the organophosphate insecticides chlorpyrifos and dialkyl phosphate is associated with an increased risk; however, the evidence is not conclusive.
Very low birth weight, premature birth and early adversity also increase the risk as do infections during pregnancy, at birth, and in early childhood. These infections include, among others, various viruses (measles, varicella, rubella, enterovirus 71) and streptococcal bacterial infection. At least 30% of children with a traumatic brain injury later develop ADHD and about 5% of cases are due to brain damage. Some children may react negatively to food dyes or preservatives. It is possible that certain food coloring may act as a trigger in those who are genetically predisposed but the evidence is weak. The United Kingdom and European Union have put in place regulatory measures based on these concerns; the FDA has not.
Society
The diagnosis of ADHD can represent family dysfunction or a poor educational system rather than an individual problem. Some cases may be explained by increasing academic expectations, with a diagnosis being a method for parents in some countries to get extra financial and educational support for their child. The youngest children in a class have been found to be more likely to be diagnosed as having ADHD possibly due to their being developmentally behind their older classmates. Behavior typical of ADHD occurs more commonly in children who have experienced violence and emotional abuse.
Per social construction theory it is societies that determine the boundary between normal and abnormal behavior. Members of society, including physicians, parents, and teachers, determine which diagnostic criteria are used and, thus, the number of people affected. This leads to the current situation where the DSM-IV arrives at levels of ADHD three to four times higher than those obtained with the ICD-10. Thomas Szasz, a supporter of this theory, has argued that ADHD was "invented and not discovered."