ADHD is caused by differences in neurotransmitter patterns in certain parts of the brain. Neurotransmitters are chemicals that make it possible for nerve impulses to travel from one nerve cell to another, and therefore play an essential role in the functioning of the brain.
The brain performs a vast range of tasks or functions, allowing us, for instance, to see, hear, think, speak and move. Each function is performed by a different part of the brain.
In individuals with ADHD there are lower than normal levels of certain neurotransmitters (especially dopamine) in the regions of the brain that are responsible for regulating behaviour and attention.
Research also confirms that the norepinephrine system is also involved in some patients.
ADHD has a genetic component and a group of genes involved has been identified. The genetic component is confirmed with epidemiological studies looking at family groups. Research has shown that in the case of identical twins, if one of the twins has ADHD there is an almost 100% chance that the other twin will show symptoms of ADHD.
ADHD can also be present in some patients with neurological damage occurring either before or after birth. Certain developmental disorders or syndromes, like foetal alcohol syndrome, are associated with a higher incidence of ADHD.
Diet is often cited as the cause for ADHD. Patients with malnutrition or a poor diet may manifest some of the symptoms. In a small subgroup, dietary factors may play a role in the worsening of symptoms, especially that of impulsivity/hyperactivity in younger children.
Ongoing research is looking at the role that essential fatty acids play in some patients. Poisoning with heavy metals like lead will create a similar clinical picture in some patients.
Although environmental factors do not play a causal role in ADHD, a disorganised, chaotic and stressful environment can cause behaviour which mimics that of ADHD.
What is ADHD?
Reviewed by Dr A van der Walt, MMed (Paed) BSc Hon (Human Genetics) April 2015.