G>A conversion, also known as TaqIA (or Taq1A), in the gene dopamine D2 receptor (DRD2).
G = DRD2*A2 = Wild-type allele
A = DRD2*A1 = Alternate allele
G:G (46.6%) = Normal levels of dopamine D2 receptors = reduced dopamine
G:A (41.7%) = Lower levels of dopamine D2 inhibitory receptors = increased dopamine
A:A (11.7%) = Lower levels of dopamine D2 inhibitory receptors = increased dopamine
The minor allele, A (A1), creates a dominant effect.
Findings for the Minor Allele, A1 (A:A) and (G:A):
More likely to be extraverted (R)
Impaired ability to learn from mistakes
Increased risk of drug abuse
Increased risk of obesity
Increased association between obesity and substance abuse
Findings for the Major Allele, A2 (G:G):
Increased risk of depression following stressful life events
Leftward orientation bias
In a probabilistic learning task, A1-allele carriers (A:A and G:A) with reduced dopamine D2 receptor densities learned to avoid actions with negative consequences less efficiently [R].
Individuals with the A1 allele (A:A and G:A) showed increased improvements in a working memory training program [R].
Obese individuals who also had a substance abuse disorder were significantly more likely to have the A1 allele (A:A and G:A). This association increased when considering cases of severe substance abuse [R].
From 282 Dutch adolescents a correlation between risky alcohol use and the A1 allele (A:A and G:A) was reported [R].
Following administration of cocaine, participants with the A1 allele (A:A and G:A) reported a greater ‘high’ and ‘like’ for the experience [R].
Two studies found association between the A1 allele (A:A and G:A) and substance (opioid and heroin) use. One study compared 6,846 opioid dependence cases with 4,187 controls [R] while the other compared 303 heroin dependent subjects and 555 healthy controls [R].
Individuals carrying the A1 allele (A:A and G:A) were more likely to display emotional eating habits in adolescence as a response to parental psychological control [R].
An increased risk of tumor (adenoma) recurrence was reported for individuals who carry two copies of the A1 allele (A:A) [R].
Subjects with the A1 allele (A:A and G:A) recovered slower after a traumatic brain injury as assessed by memory and attention tests [R].
In a study of Han Chinese diagnosed with schizophrenia, female carriers of the A1 allele (A:A and G:A) showed a decreased age of onset [R].
A Finnish study of 1,611 young adults reported an increased risk of depression following stressful life events for individuals carrying two copies of the A2 allele (G:G) [R].
Healthy young Israeli Jewish individuals with two copies of the A2 allele (G:G) displayed an orientation bias towards the left [R].
An increased use of the striatum and proficiency at concatenative grammar learning was reported for individuals with two copies of the A2 allele (G:G) [R].