The 48-base pair variable number tandem repeat (VNTR) inexon 3 range from 2 to 11 repeats.[16] Dopamine is more potent at the D4 receptor with 2 allelic repeat or 7 allelic repeats than the variant with 4 allelic repeats.[22]
DRD4-7R, the 7-repeat (7R) variant ofDRD4 (DRD4 7-repeat polymorphism), has been linked to a susceptibility for developingADHD in several meta-analyses and other psychological traits and disorders.[23][24] Adults and children with the DRD4 7-repeat polymorphism show variations in auditory-evokedgamma oscillations, which may be related to attention processing.[25][26]
The frequency of the alleles varies greatly between populations, e.g., the 7-repeat version has high incidence in America and low in Asia.[27] "Long" versions of polymorphisms are the alleles with 6 to 10 repeats. 7R appears to react less strongly to dopamine molecules.[28]
The 48-base pair VNTR has been the subject of much speculation about its evolution and role in human behaviors cross-culturally. The 7R allele appears to have been selected for about 40,000 years ago.[27] In 1999 Chen and colleagues[29] observed that populations who migrated farther in the past 30,000 to 1,000 years ago had a higher frequency of 7R/long alleles. They also showed that nomadic populations had higher frequencies of 7R alleles than sedentary ones. More recently it was observed that the health status of nomadicAriaal men was higher if they had 7R alleles. However, in recently sedentary (non-nomadic) Ariaal those with 7R alleles seemed to have slightly deteriorated health.[30]
Despite early findings of an association between theDRD4 48bp VNTR andnovelty seeking (a normal characteristic of exploratory and excitable people),[31][32] a 2008meta-analysis compared 36 published studies of novelty seeking and the polymorphism and found no effect. Results are consistent with novelty-seeking behavior being acomplex trait associated with many genes, and the variance attributable toDRD4 by itself being very small. The meta-analysis of 11 studies did find that another polymorphism in the gene, the-521C/T, showed an association with novelty seeking.[21] While human results are not strong, research in animals has suggested stronger associations[33][34][35][36][37][38] and new evidence suggests that human encroachment may exert selection pressure in favor ofDRD4 variants associated with novelty seeking.[39][clarification needed]
Several studies have shown thatagonists that activate the D4 receptor increase working memory performance and fear acquisition in monkeys and rodents according to a U-shapeddose response curve.[40][41][42] However,antagonists of the D4 receptor reverse stress-induced or drug-induced working memory deficits.[43][44]Gamma oscillations, which may be correlated with cognitive processing, can be increased by D4R agonists, but are not significantly reduced by D4R antagonists.[45][46][47]
Several studies have suggested that parenting may affect thecognitive development of children with the 7-repeat allele ofDRD4.[39] Parenting that has maternal sensitivity, mindfulness, and autonomy–support at 15 months was found to alter children's executive functions at 18 to 20 months.[39] Children with poorer quality parenting were more impulsive and sensation seeking than those with higher quality parenting.[39] Higher quality parenting was associated with betterexecutive control in 4-year-olds.[39]
Michael Connelly's 2020 crime novelFair Warning (ISBN 978-0-316-53942-5) revolves around a serial killer who uses DNA profiles obtained on theDark Web to target female victims, specifically those whose DRD4 profiles allegedly make them more susceptible to risk taking and sexual promiscuity.
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"Dopamine Receptors: D4".IUPHAR Database of Receptors and Ion Channels. International Union of Basic and Clinical Pharmacology. Archived fromthe original on 5 March 2012. Retrieved4 December 2008.