13 (Nelson) - Attention-Deficit/Hyperactivity Disorder

Question 1

Definition of
Attention-deficit/hyperactivity disorder (ADHD)

Answer 1

Attention-deficit/hyperactivity disorder (ADHD) is a chronic
neurobehavioral disorder characterized by symptoms of inattention,
hyperactivity, impulsivity, or a combination of these
symptoms. It is typically diagnosed in childhood but frequently
has long-term implications, including decreased likelihood of
high school and postsecondary graduation as well as poor peer
relations.

Question 2

Etiology of
Attention-deficit/hyperactivity disorder (ADHD)

Answer 2

ADHD is multifactorial in origin with genetic, neural, and
environmental contributions. There are many studies that
suggest variable degrees of genetic associations with ADHD,
yet overall, clear and definitive associations are not well defined.
Twin and family studies demonstrate high heritability (0.8)
and greater risk of developing ADHD in first-degree relatives,
especially those where ADHD persists into adolescence and
adulthood. Candidate genes include those involving the
dopaminergic and noradrenergic neurotransmitter systems.

Neuroimaging studies (functional magnetic resonance imaging
and positron emission tomography) have shown structural and
functional differences, particularly of the frontal lobes, inferior
parietal cortex, basal ganglia, corpus callus, and cerebellar
vermis. Neuroimaging studies have demonstrated delay in
cortical maturation and suggest that the pathophysiological
features include large-scale neuronal networks including frontal
to parietal cortical connections.

Environmental links have been
described with prenatal exposure to a variety of substances
including nicotine, alcohol, prescription medications, and illicit
substances. Environmental exposure to lead, organophosphate
pesticides, or polychlorinated biphenyls has also been shown
to be a risk factor. Additionally, damage to the central nervous
system from trauma or infection can increase the risk
of ADHD.