No association between dopamine D2 receptor gene (DRD2) and human intelligence

Assessment of association between the dopamine D2 receptor (DRD2) polymorphism and neurodevelopment of children exposed to lead

The mechanism of lead (Pb) neurotoxicity has not been illustrated over the years. People pay more attention to dopaminergic neurotransmission, specifically dopamine receptor-2 (DRD2) Taq IA polymorphism, but no consensus has been reached. A total of 258 three-year-old children in Guiyu (exposed group) and Nanao (reference group), China were examined and their concentrations of blood lead (BPb) were determined. Cognitive and language scores of children were assessed using the Bayley Scales of Infant Development, third edition (BSID-III). Genotyping for the DRD2 polymorphism was carried out using a polymerase chain reaction (PCR) re-sequencing platform. The logistic stepwise regression analysis and stepwise regression analysis was used to explore associations among lead, neurodevelopment of children, and DRD2 Taq IA categories. Median values of Pb in Guiyu was higher than that of the reference group (11.30 ± 5.38 μg/dL vs. 5.77 ± 2.51 μg/dL, P < 0.001). Compared with the reference group, children from e-waste exposed area have lower cognitive scale scores (100 ± 25 vs 120 ± 20, P < 0.001) and lower language scale scores (99.87 ± 7.52 vs 111.39 ± 7.02, P < 0.001). The three kinds of genotype, A1/A1, A1/A2, and A2/A2, had no significant influences on BPb, cognitive scores and language scores (P > 0.05). Exposure of inhabitants, especially children to Pb from informal e-waste recycling activities might have contributed to higher levels of BPb and reduced cognitive and language scores observed in local children, however, the result obtained showed no significant association between DRD2 polymorphism and neurodevelopment of children exposed to lead.

Dopamine DRD2/ANKK1 Taq1A and DAT1 VNTR polymorphisms are associated with a cognitive flexibility profile in pathological gamblers

Like drug addiction, pathological gambling (PG) has been associated with impairments in executive functions and alterations in dopaminergic functioning; however, the role of dopamine (DA) in the executive profile of PG remains unclear. The aim of this study was to identify whether the DRD2/ANKK1 Taq1A-rs1800497 and the DAT1-40 bp VNTR polymorphisms are associated with cognitive flexibility (measured by Wisconsin Card Sorting Test (WCST) and Trail Making Test (TMT)) and inhibition response (measured by Stroop Color and Word Test (SCWT)), in a clinical sample of 69 PG patients. Our results showed an association between DA functioning and cognitive flexibility performance. The Taq1A A1+ (A1A2/A1A1) genotype was associated with poorer TMT performance (p<0.05), while DAT1 9-repeat homozygotes displayed better WCST performance (p<0.05) than either 10-repeat homozygotes or heterozygotes. We did not find any association between the DRD2 or DAT1 polymorphisms and the inhibition response. These results suggested that pathological gamblers with genetic predispositions toward lower availability of DA and D2 receptor density are at a higher risk of cognitive flexibility difficulties. Future studies should aim to shed more light on the genetic mechanisms underlying the executive profile in PG.

A dopamine receptor (DRD2) but not dopamine transporter (DAT1) gene polymorphism is associated with neurocognitive development of Mexican preschool children with lead exposure

OBJECTIVE

To investigate the effects of prenatal and postnatal lead exposure and polymorphisms in dopamine metabolism genes on neurocognitive development of Mexican children at 24 months (n = 220) and 48 months (n = 186) of age.

STUDY DESIGN

We genotyped the dopamine transporter gene (DAT1; SLC6A3) variable nucleotide tandem repeat and the dopamine receptor D2 (DRD2) Taq1A single nucleotide polymorphism. Children were assessed at 24 months with Bayley Scales of Infant Development (Mental Development Index and Psychomotor Development Index) and at 48 months with McCarthy Scales of Children's Abilities.

RESULTS

Blood lead concentration (BLL) in umbilical cord was 6.6 ± 3.3 μg/dL (measured in 1995-96), 8.1 ± 4.4 μg/dL at 24 months, and 8.1 ± 3.6 μg/dL at 48 months. Cord BLL was negatively associated with Mental Development Index (P < .01) and Psychomotor Development Index (P < .1), but not McCarthy scores. The 48-month BLL, but not the 24-month BLL, was negatively associated with children's scores. Children with DRD2 TT genotype (variant) scored higher than children with CC genotype (wild type) on the Mental Development Index and McCarthy memory scale. Neither polymorphism modified the relationship between BLL (either prenatal or postnatal) and neurocognitive development.

CONCLUSION

Lead exposure was adversely associated with neurocognitive measures, whereas the DRD2 Taq1A TT variant was positively associated with neurocognitive measures. We found no evidence of gene-environment interactions on developmental outcomes in early childhood.

Genetic lotteries within families

Drawing on findings from the biomedical literature, this paper introduces the idea that specific exogenously inherited differences in the genetic code between full biological siblings can be used to test within-family estimators and potentially improve our understanding of economic relationships. These points are illustrated with an application to identify the causal impact of several poor health conditions on academic outcomes. We present evidence that family fixed effects estimators by themselves cannot fully account for the endogeneity of poor health when estimating education production functions. Further, our analysis elucidates the situations under which genetic markers can serve as instrumental variables for specific health conditions.

Association between the A1 allele of the DRD2 gene and reduced verbal abilities in adolescence and early adulthood

Behavioral genetic research has consistently revealed that genetic factors explain at least one half of the variance in measures of cognitive skills. However, the specific DNA markers involved in the etiology of cognitive abilities have remained elusive. The current study examined the association between the TaqI polymorphism in the dopamine D2 receptor gene (DRD2) and verbal skills. Analysis of data drawn from the National Longitudinal Study of Adolescent Health (Add Health) revealed that the A1 allele was associated with group membership in high-, average-, and low-verbal skills groups for Caucasians. The results suggest that DRD2 may be related to domain specific cognitive abilities, such as verbal skills.

Thinking outside a less intact box: thalamic dopamine D2 receptor densities are negatively related to psychometric creativity in healthy individuals

Several lines of evidence support that dopaminergic neurotransmission plays a role in creative thought and behavior. Here, we investigated the relationship between creative ability and dopamine D2 receptor expression in healthy individuals, with a focus on regions where aberrations in dopaminergic function have previously been associated with psychotic symptoms and a genetic liability to schizophrenia. Scores on divergent thinking tests (Inventiveness battery, Berliner Intelligenz Struktur Test) were correlated with regional D2 receptor densities, as measured by Positron Emission Tomography, and the radioligands [¹¹C]raclopride and [¹¹C]FLB 457. The results show a negative correlation between divergent thinking scores and D2 density in the thalamus, also when controlling for age and general cognitive ability. Hence, the results demonstrate that the D2 receptor system, and specifically thalamic function, is important for creative performance, and may be one crucial link between creativity and psychopathology. We suggest that decreased D2 receptor densities in the thalamus lower thalamic gating thresholds, thus increasing thalamocortical information flow. In healthy individuals, who do not suffer from the detrimental effects of psychiatric disease, this may increase performance on divergent thinking tests. In combination with the cognitive functions of higher order cortical networks, this could constitute a basis for the generative and selective processes that underlie real life creativity.

The impact of poor health on academic performance: New evidence using genetic markers

This paper examines the influence of health conditions on academic performance during adolescence. To account for the endogeneity of health outcomes and their interactions with risky behaviors we exploit natural variation within a set of genetic markers across individuals. We present evidence that specific genetic markers have good statistical properties to identify the impacts of ADHD, depression and obesity. These markers help reveal a new dynamism from poor health to lower academic achievement with substantial heterogeneity in their impacts across genders. Our investigation further exposes the considerable challenges in identifying health impacts due to the prevalence of comorbid health conditions, with clear implications for the health economics literature.

“Scientific roots” of dualism in neuroscience

Although the dualistic concept is unpopular among neuroscientists involved in experimental studies of the brain, neurophysiological literature is full of covert dualistic statements on the possibility of understanding neural mechanisms of human consciousness. Particularly, the covert dualistic attitude is exhibited in the unwillingness to discuss neural mechanisms of consciousness, leaving the problem of consciousness to psychologists and philosophers. This covert dualism seems to be rooted in the main paradigm of neuroscience that suggests that cognitive functions, such as language production and comprehension, face recognition, declarative memory, emotions, etc., are performed by neural networks consisting of simple elements. I argue that neural networks of any complexity consisting of neurons whose function is limited to the generation of electrical potentials and the transmission of signals to other neurons are hardly capable of producing human mental activity, including consciousness. Based on results obtained in physiological, morphological, clinical, and genetic studies of cognitive functions (mainly linguistic ones), I advocate the hypothesis that the performance of cognitive functions is based on complex cooperative activity of "complex" neurons that are carriers of "elementary cognition." The uniqueness of human cognitive functions, which has a genetic basis, is determined by the specificity of genes expressed by these "complex" neurons. The main goal of the review is to show that the identification of the genes implicated in cognitive functions and the understanding of a functional role of their products is a possible way to overcome covert dualism in neuroscience.

Investigating cognitive genetics and its implications for the treatment of cognitive deficit

Cognitive impairment in the elderly, caused by either normal ageing process or dementia, is an increasing problem in developed countries that has enormous social and economic considerations. Research investigating the genetic basis of cognition is a new and rapidly developing field that may aid in the development of new treatments for age-related cognitive deficit. Over the past 6 years, a number of quantitative trait loci (QTLs) have been associated with cognitive functioning in humans including loci within the genes catechol-o-methyltransferase, brain-derived neurotrophic factor, muscle segment homeobox 1, serotonin transporter 2A (HTR2A), cholinergic muscarinic receptor 2, cathepsin D, metabotrophic glutamate receptor and most recently the class II human leukocyte antigens. Unfortunately, inconsistency within the literature, which is a hallmark of almost all association studies investigating complex diseases and traits, is casting doubt as to which genes are truly associated with cognition and which are a result of Type 2 error. This review will highlight implicated intelligence QTLs, examine the probable reasons for the current discrepancies between reports and discuss the potential advantages that may be procured from the study of cognitive genetics.