The significance of this is controversial due to the differences between people with ADHD and the difficulty determining the influence of symptoms, such as distractibility, on lower scores rather than intellectual capacity. In studies of ADHD, higher IQs may be over-represented because many studies exclude individuals who have lower IQs despite those with ADHD scoring on average nine points lower on standardized intelligence measures. In individuals with high intelligence, there is increased risk of a missed ADHD diagnosis, possibly because of compensatory strategies in highly intelligent individuals.Studies of adults suggest that negative differences in intelligence are not meaningful and may be explained by associated health problems. Causes
ADHD is generally claimed to be the result of neurological dysfunction in processes associated with the production or use of dopamine and norepinephrine in various brain structures, but there are no confirmed causes. It may involve interactions between genetics and the environment. Genetics
ADHD has a high heritability of 74%, meaning that 74% of the presence of ADHD in the population is due to genetic factors. There are multiple gene variants which each slightly increase the likelihood of a person having ADHD; it is polygenic and arises through the combination of many gene variants which each have a small effect. The siblings of children with ADHD are three to four times more likely to develop the disorder than siblings of children without the disorder.Arousal is related to dopaminergic functioning, and ADHD presents with low dopaminergic functioning. Typically, a number of genes are involved, many of which directly affect dopamine neurotransmission.
Medical pseudosciences, particularly those that targeted African American populations during the period of slavery in the US, lead to a distrust of medical practices within certain communities. The combination of ADHD symptoms often being regarded as misbehavior rather than as a psychiatric condition, and the use of drugs to regulate ADHD, result in a hesitancy to trust a diagnosis of ADHD. Cases of misdiagnosis in ADHD can also occur due to stereotyping of non-caucasian individuals. Due to ADHDs subjectively determined symptoms, medical professionals may diagnose individuals based on stereotyped behavior or misdiagnose due to differences in symptom presentation between Caucasian and non-Caucasian individuals. History
Hyperactivity has long been part of the human condition. Sir Alexander Crichton describes "mental restlessness" in his book An inquiry into the nature and origin of mental derangement written in 1798. He made observations about children showing signs of being inattentive and having the "fidgets". The first clear description of ADHD is credited to George Still in 1902 during a series of lectures he gave to the Royal College of Physicians of London. He noted both nature and nurture could be influencing this disorder.Alfred Tredgold proposed an association between brain damage and behavioral or learning problems which was able to be validated by the encephalitis lethargica epidemic from 1917 through 1928.The terminology used to describe the condition has changed over time and has included: minimal brain dysfunction in the DSM-I (1952), hyperkinetic reaction of childhood in the DSM-II (1968), and attention-deficit disorder with or without hyperactivity in the DSM-III (1980).