Attention deficit hyperactivity disorder is thought to be neuro-developmental disorder that is thought to have a genetic component since it is heritable as shown from the twin and family studies. There are 3 core features that are used in diagnosis since it is not a single type of disorder but rather defined by DSM-5 classification based on the presentation. The 3 features are inattention, hyperactivity and impulsivity.
Typically it has been ascribed to dopamine and norepinephrine neuro transmitter systems which are involved and ADHD is usually treated by modulation these systems. Many gene signals are involved in these pathways and deal with dopamine/serotonin pathways or synaptic function. Some common genes involved are DRD2/4 (dopamine signaling), SLC6A3 (dopamine reuptake), SNAP25 (synaptic vesicle release) and about 27 common variants have been associated with the disease.
Though the exact cause is not known, it is a polygenic disease with many loci and gene’s involved though studies looking at polygenic risk scores have shown some correlation.
However, environment may also play a role since there has been association of ADHD with lead prevalance, phthalates or bisphenal A (BPA). Environmental effects with genetic background may make it difficult to isolate exact etiology in ADHD.
Treatment is usually be behavioral modification such as CBT, lifestyle changes, monitoring and medication. Medication is usually as stimulants (Methylphenidate or Amphetamine) to block dopamine/norepinephrine reuptake to increase extracellular dopamine, or with non-stimulants (Atomoxetine, alpha-2 agonists) which modulates norepinephrine to improve attention. Sometimes these are combined to get a better response.
