Attention deficit hyperactivity disorder (ADHD) is a complex disorder that has multiple causes, this includes genetics in combination with environmental factors.
ADHD has been blamed on bad parenting, or a “bad” attitude. However, brain-imaging studies have shown that children with ADHD have an underlying neurological dysfunction, which likely accounts for their behavior. In the one sense, these children’s brains have yet to come fully “on-line.”
It has been suggested that ADHD symptoms stem from a dysfunction in the “brain reward cascade,” a complex interaction among brain neurotransmitters in the reward centers of the brain. Neurotransmitters control feelings of well being and influence mood. In some ADHD individuals, the brain lacks sufficient neurotransmitters to be used in reward centers and thus dysregulation may occur.
In healthy people, neurotransmitters work together in a pattern of stimulation or inhibition, and the effects spread downward, like a cascade, from stimulus input to complex patterns of response leading to feelings of well-being. This neurotransmitter system is very complex and is still not completely understood.
Genetics also play an important component as related to ADHD. There are over 40 gene variants that have been associated with ADHD and contribute to the overall variance. ADHD can range from mild to severe depending on the number of variants as well as in combination with environmental factors. In many cases, these genes constitute the basis for the reward cascade including certain neurotransmitters such as dopaminergic, serotonergic, enkephalinergic, catecholaminergic, cholinergic, GABAergic, androgen receptors, as well as other putative transmitters, hormones, and their receptors and enzymes.
In recent years, a number of reviews of the neurochemical basis of ADHD have emphasized the involvement of multiple neurotransmitters and emphasized that one single genetic defect cannot explain all of the data.