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
G:A (41.7%) = Lower levels of dopamine D2 receptors
A:A (11.7%) = Lower levels of dopamine D2 receptors
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
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].
Of 202 severely obese individuals who participated in a weight loss program, young individuals with the A1 allele (A:A and G:A) exhibited problems in maintaining weight loss during the program [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].