The only good is knowledge and the only evil is ignorance. Socrates

The cause(s) of ADHD like its existence and treatment remain an area of controversy. There are many causes or risks factors attributed to the disease. The list is long and ranges from one extreme of having no cause, not being a disease , but natural variation to social and environmental causes, e.g. exposure to lead and other environmental toxins. 

Genetics: Common sense dictates that any disease like ADHD starting as early as age 4 or earlier could have a genetic cause. Genetic research on ADHD started with the finding that hyperactivity tends to aggregate in families. Since then, family studies have shown that ADHD has familial clustering both within and across generations. Increased rates of ADHD among the parents and siblings of ADHD children have been observed. In addition, strongly increased risks for ADHD (57%) among the offspring of adults with ADHD have been reported.  Twin studies indicate that the disorder is highly heritable and that genetics are a factor in about 75 percent of all cases. Genetic factors are also believed to be involved in determining whether ADHD persists into adulthood or ends in childhood or adolescence.  Molecular genetic studies have shown a combination of various genes, many of which affect dopamine transporters.

Environmental Causes: In brief and in the mist of all controversies, environmental factors, e.g. alcohol and other substances, toxins and poisons, such as exposure to lead and PCB, infections during pregnancy,at birth and early childhood, premature and low birth weight, food and diet, including food colours an additives, and finally social factors, e.g. caused by reading environment seem to be only triggering and exacerbating factors superimposed on a genetic base.

Dopamine and other Neurotransmitters deficiency: Genetics perhaps in some associations with environmental factors, cause deficiency in some neurotransmitter of cognition in the brain, giving rise to ADHD symptoms. The most important theory of the disease rely mainly on the “dopamine deficiency” from the first days of discovery of the psychostimlants, e.g. methylphenidate (Ritalin, Concerta,..) and amphetamine (Vyvanse, biphentin,..) that are still the mainstay of ADHD treatment. But other neurotransmitters are probably contributing to the disease, e.g. Serotonin and Norepinephrine, underlying newer drugs, e.g. Atomoxetine (Stratera) and  . Guanfacine (Tenex, and Intuniv).

To learn more about the causes of ADHD in detail and its pathophysiology and that in fact the ADHD brain is not deficient in any neurotransmitters, but need more than normal, read the book “ADHD:Revisited” available at Amazon, Kindle books.