Discovering the causes of the development of ADHD has posed many problems for scientists from the very beginning. It is still not entirely possible to say with certainty what the cause of this type of disorder is. This is in part due to the complexity of the issue. ADHD (Attention Deficit Hyperactivity Disorder) is still a mysterious disorder. In the course of the research carried out on ADHD, many different hypotheses have been put forward as to what causes it.

Causes of ADHD

For many years, the predominant view was that the development of ADHD was due to disturbed relationships within the child’s family. The causes were attributed to parental mistakes. It is now known that this approach to the problem is wrong. It is true that disturbed family relationships, difficult family situations, parental impulsivity and a lack of a proper normative system can exacerbate the symptoms, but they are not the direct cause.

The second hypothesis for the development of ADHD made damage to the child’s brain tissue the main and direct cause of this condition. However, thanks to advances in medical diagnosis, it has become clear that this is not the most common reason for the symptoms characteristic of hyperkinetic syndrome.

So what is the cause of the development of ADHD? A number of studies have concluded that attention deficit hyperactivity disorder is written into a person’s DNA, i.e. genetic factors underlie the condition. This means that ADHD can be passed on from generation to generation. Finding the condition in at least one of a child’s parents increases the likelihood of the same disorder in the toddler. The heritability of ADHD reaches about 50%. In addition, if one child is diagnosed with ADHD, siblings are more likely to have the disorder (in about 35% of cases). For this reason, ADHD is said to have a familial occurrence.

It is already known that the cause of the described disorder lies in the human genetic material. However, it has not been possible to isolate the single gene responsible for this condition. Therefore, ADHD is said to be a multi-gene inherited disorder. This means that not one, but several different genes need to act together for the disorder to occur. Attention deficit hyperactivity disorder is therefore considered, in the light of modern research, to be a collection of genetically determined traits. Family studies have shown that the risk of ADHD is significantly (up to seven times) higher in families where someone already suffers from the disorder. Also, studies on monozygotic and dizygotic twins have confirmed the hypothesis of a genetic determinant of hyperactivity.

Symptoms of ADHD

What is the relationship between the occurrence of a particular gene configuration and the development of ADHD-specific symptoms? It has been found that genetic factors ‘specific’ to ADHD in people with the disorder cause them to have delayed nervous system development compared to healthy people. More figuratively speaking, in children with ADHD certain areas of the brain work less efficiently than in their peers. This includes areas such as the prefrontal cortex, subcortical structures, the great spiracle and the cerebellum.

In the 1950s and 1960s, the causes of ADHD were linked to microdamage to the central nervous system (CNS) caused by pathological factors during the perinatal period. However, it turned out that CNS microdamage actually occurs in a small group of children with ADHD, while also being recognised in healthy children. The source of the changes in information processing and response is the different structure and functioning of certain brain structures in individuals with attention deficit hyperactivity disorder. This difference in brain maturation is due to changes in the genetic material.

Frontal lobe function is impaired in children with ADHD. This area is responsible for emotions, planning, judgement, anticipating consequences, memory. At this point, it is possible to realise to some extent what happens when this part of the brain is not working properly. Such a condition can manifest itself in the form of a disorder of the child’s emotions, i.e. aggression, uncontrollable anger, for example, or being distracted and forgetting things.

Another part of the brain, whose dysfunction is undoubtedly important in the development of ADHD symptoms, is the so-called basal nuclei. The aforementioned part of the brain is responsible for motor control, emotions, learning, cognitive processes (e.g. speech, memory, attention, thinking). In such a case, the dysfunction will be observed as an inability to focus, learning problems, a sometimes occurring lack of motor coordination. The functioning of the areas responsible for the association of visual and auditory sensations may also be impaired. The cause of these abnormalities is a weakening of certain substances in the brain that are responsible for transmitting information between the different parts of the brain. These are the so-called neurotransmitters dopamine, noradrenaline and (less important in this case) serotonin.

  • Dopamine – is responsible for emotional processes, higher mental functions (e.g. memory, speech) and, to a lesser extent, motor processes. It is also called the ‘happiness hormone’ because its appearance in the relevant areas of the brain induces a state of euphoria.
  • Norepinephrine – a hormone secreted in the adrenal glands during stressful situations. It causes an accelerated heartbeat and an increase in muscle tension. In the brain, it is involved in, among other things, thermoregulation processes. Deficiency can cause underestimation of danger, constant agitation of the body. It is also called the ‘aggressiveness hormone’.
  • Serotonin – is essential for normal sleep patterns. Its levels also affect impulsive behaviour, appetite and sexual needs. Too low levels of serotonin are observed in aggressive people.

On the basis of research, it has been concluded that the levels of these substances are reduced in people with ADHD, resulting in an abnormal flow of information between different brain structures.

Factors contributing to ADHD symptoms

Before the starting point for the development of ADHD was considered to be genetic defects, attempts were made to find causes in other factors. It is now known that this was not entirely the wrong approach. Indeed, it has been shown that factors that are no longer considered to be the primary cause of ADHD can significantly contribute to or exacerbate the symptoms of the syndrome. A significant role in this process is attributed to the conditions in the child’s immediate environment.

Attention is drawn to the relationships between individual family members. Frequent disagreements, arguments, shouting and violent reactions can greatly exacerbate the symptoms in a child affected by ADHD. The environment in which the child is brought up is also very important. If the family situation is difficult, the child develops in an atmosphere of a lack of norms and rules and, as a consequence, symptoms can be expected to be more pronounced and therefore more troublesome for the child and those around him.

The role of environmental factors is also highlighted in the development and severity of ADHD symptoms. It is important to consider what may have affected the child during the foetal period and at birth. Complications during pregnancy, maternal alcohol consumption, exposure to toxic substances in food, and the child’s exposure to nicotine during fetal life may all be related to a higher susceptibility to the onset of the condition. Psychomotor hyperactivity is one of the symptoms of Fetal Alcohol Syndrome (FAS), which is caused by the mother’s alcohol consumption during pregnancy.

The role of perinatal hypoxia is also highlighted. The resulting micro-damage to the child’s brain can cause symptoms characteristic of behavioural disorders. However, this applies to a small group of young patients.

Psychosocial factors are certainly important in exacerbating ADHD symptoms, e.g. frequent changes of residence and problems at school, which make it difficult for a child with ADHD to function in a group of peers. A ‘vicious circle’ is created – the child with ADHD encounters non-acceptance from classmates, which exacerbates the symptoms and ultimately leads to an even more pronounced rejection of the child by the environment in which he or she lives. It is important to pay attention to the school situation of the child with ADHD, as appropriate preparation of those who interact with the pupil on a daily basis can minimise his/her difficulties related to functioning in society.

In addition, among the causes of exacerbation of symptoms, consideration is given to conditions that in healthy children generally do not cause behavioural disturbances, but in those with ADHD may cause imbalance. Factors such as asthma, diet and allergy have received attention. However, it is important to remember that these factors do not cause ADHD, but may only exacerbate the symptoms of the condition.

ADHD and pesticides

The causes of ADHD are not fully known. Genes are known to play a role in the condition, as well as alcohol, nicotine and lead exposure. Recent studies show that pesticides, present in certain fruit and vegetables, may increase the risk of developing ADHD. Pesticides, specifically organophosphates, are found in the highest concentrations in berries and celery – of course, only in those grown on a large scale and with pesticides.

The study involved 1 100 children aged between 8 and 15 years. Long-term exposure to large amounts of pesticides increased their risk of developing ADHD. Pesticide levels in the body were measured in a urine test. However, pesticide exposure alone was not found to be a cause of ADHD. According to the researchers conducting the study, pesticides can block an enzyme called acetylcholinesterase, which works in the nervous system, and disrupts neurotransmitters in the brain. However, further scientific research is needed to gain certainty about pesticides and their role in causing ADHD symptoms.