ADHD Causes
Most of the time ADHD is inherited, but it can also be caused by problems with the pregnancy, the delivery, early childhood severe illness, environmental toxins, etc
Genetic Factors
According to a majority of medical research in the United States, as well as other countries, ADHD is today generally regarded as a chronic disorder for which there are some effective treatments, but no true cure. Evidence suggests that hyperactivity has a strong heritable component, and in all probability ADHD is a heterogeneous disorder, meaning that several causes could create very similar symptomology. Candidate genes include dopamine transporter (DAT), dopamine receptor D4 (DRD4), dopamine beta-hydroxylase (DBH), monoamine oxidase A (MAOA), catecholamine-methyl transferase (COMT), serotonin transporter promoter (SLC6A4), 5-hydroxytryptamine 2A receptor (5-HT2A), and 5-hydroxytryptamine 1B receptor (5-HT1B). Researchers believe that a large majority of ADHD arises from a combination of various genes, many of which affect dopamine transporters. Suspect genes include the 10-repeat allele of the DAT1 gene, the 7-repeat allele of the DRD4 gene, and the dopamine beta hydroxylase gene (DBH TaqI).
Genome wide surveys have shown linkage between ADHD and loci on chromosomes 7, 11, 12, 15, 16, and 17. If anything, the broad selection of targets indicates the likelihood that ADHD does not follow the traditional model of a “genetic disease” and is better viewed as a complex interaction among genetic and environmental factors. As the authors of a review of the question have noted, “Although several genome-wide searches have identified chromosomal regions that are predicted to contain genes that contribute to ADHD susceptibility, to date no single gene with a major contribution to ADHD has been identified.”
Studies show that there is a familial transmission of the disorder which does not occur through adoptive relationships. Twin studies indicate that the disorder is highly heritable and that genetics contribute about three quarters of the total ADHD population. While the majority of ADHD is believed to be genetic in nature, roughly one-fifth of all ADHD cases are thought to be acquired after conception due to brain injury caused by either toxins or physical trauma prenatally or postnatally.
Environmental Factors
The estimated contribution of non genetic factors to the contribution of all cases of ADHD is 20 percent.
Pre-Natal
The environmental factors implicated are common exposures and include alcohol, in utero tobacco smoke and lead exposure, believed to stress babies prenatally. Lead concentration below the Center for Disease Control’s action level account for slightly more cases of ADHD than tobacco smoke (290 000 versus 270 000, in the USA, ages 4 to 15). Complications during pregnancy and birth—including premature birth—might also play a role. It has been observed that women who smoke while pregnant are more likely to have children with ADHD. This could be related to the fact that nicotine is known to cause hypoxia (lack of oxygen) in utero, but it could also be that ADHD women have more probabilities to smoke both in general and during pregnancy, being more likely to have children with ADHD due to genetic factors.
Another factor that may be correlated with ADHD is mobile phone usage. A study surveying over 13,000 children found use of mobile phone handsets by pregnant mothers raised the risk of hyperactivity, emotional problems, and conduct problems, much to the researchers’ surprise.
Diet
Studies have found that malnutrition is also correlated with attention deficits. Diet seems to cause ADHD symptoms or make them worse. Many studies point to synthetic preservatives and artificial coloring agents aggravating ADD & ADHD symptoms in those affected. Older studies were inconclusive quite possibly due to inadequate clinical methods of measuring offending behavior. Parental reports were more accurate indicators of the presence of additives than clinical tests. Several major studies show academic performance increased and disciplinary problems decreased in large non-ADD student populations when artificial ingredients, including artificial colors were eliminated from school food programs. Professor John Warner stated, “significant changes in children’s hyperactive behaviour could be produced by the removal of artificial colourings and sodium benzoate from their diet.” and “you could halve the number of kids suffering the worst behavioural problems by cutting out additives”. In 1982, the NIH had determined, based on research available at that time, that roughly 5% of children with ADHD could be helped significantly by removing additives from their diet. The vast majority of these children were believed to have food allergies. More recent studies have shown that approximately 60-70% of children with and without allergies improve when additives are removed from their diet, that up to almost 90% of them react when an appropriate amount of additive is used as a challenge in double blind tests, and that food additives may elicit hyperactive behavior and/or irritability in normal children as well.
Head Injuries
Head injuries can cause a person to present ADHD-like symptoms, possibly because of damage done to the patient’s frontal lobes. Because these types of symptoms can be attributable to brain damage, one earlier designation for ADHD was “Minimal Brain Damage”.
Social Factors
There is no compelling evidence that social factors alone can create ADHD. Many researchers believe that attachments and relationships with caregivers and other features of a child’s environment have profound effects on attentional and self-regulatory capacities. It is noteworthy that a study of foster children found that an inordinate number of them had symptoms closely resembling ADHD. An editorial in a special edition of Clinical Psychology in 2004 stated that “our impression from spending time with young people, their families and indeed colleagues from other disciplines is that a medical diagnosis and medication is not enough. In our clinical experience, without exception, we are finding that the same conduct typically labelled ADHD is shown by children in the context of violence and abuse, impaired parental attachments and other experiences of emotional trauma.” Furthermore, Complex Post Traumatic Stress Disorder can result in attention problems that can look like ADHD, as can Sensory Integration Disorders.
