Association Between Polymorphisms of the Dopamine Receptor D2 and Catechol-o-Methyl Transferase Genes and Cognitive Function

Lifespan longitudinal changes in mesocortical thickness and executive function: Role of dopaminergic genetic predisposition

Dopamine (DA) signaling is critical for optimal cognitive aging, especially in prefrontal-parietal and fronto-striatal networks. Single nucleotide polymorphisms associated with dopamine regulation, COMTVal158Met and DRD2C957T, stand to exert influence on executive function performance via neural properties. The current study investigated whether longitudinal thinning of mesocortical regions is related to COMT and DRD2 genetic predisposition and associated with decline in executive function over four-years. N=235 healthy adults aged 20-94 years were recruited, with n=124 returning 4-years later. Latent mixed effects modeling revealed dopamine-related thinning in several frontal, parietal, and cingulate regions as well as decline in verbal fluency category switching across 4-years. Mesocortical thinning was also related to switching performance. Greater cortical thinning interacted with DA-genotype risk for lower DA-availability to predict poorer switching performance in parietal and posterior cingulate cortex. These findings lend support to the notion that early-life factors, such as genetic influence on neurotransmitter function, play a role in cognitive and brain aging and their linked association.

Contributions of the Catechol-O-Methyltransferase Val158Met Polymorphism to Changes in Brain Iron Across Adulthood and Their Relationships to Working Memory

Ageing is associated with excessive free brain iron, which may induce oxidative stress and neuroinflammation, likely causing cognitive deficits. Lack of dopamine may be a factor behind the increase of iron with advancing age, as it has an important role in cellular iron homoeostasis. We investigated the effect of COMT Val 158 Met (rs4680), a polymorphism crucial for dopamine degradation and proxy for endogenous dopamine, on iron accumulation and working memory in a longitudinal lifespan sample (n = 208, age 20–79 at baseline, mean follow-up time = 2.75 years) using structural equation modelling. Approximation of iron content was assessed using quantitative susceptibility mapping in striatum and dorsolateral prefrontal cortex (DLPFC). Iron accumulated in both striatum and DLPFC during the follow-up period. Greater iron accumulation in DLPFC was associated with more deleterious change in working memory. Older (age 50–79) Val homozygotes (with presumably lower endogenous dopamine) accumulated more iron than older Met carriers in both striatum and DLPFC, no such differences were observed among younger adults (age 20–49). In conclusion, individual differences in genetic predisposition related to low dopamine levels increase iron accumulation, which in turn may trigger deleterious change in working memory. Future studies are needed to better understand how dopamine may modulate iron accumulation across the human lifespan.

Interdisciplinary Approach to Biological and Health Implications in Selected Professional Competences

Everyday life’s hygiene and professional realities, especially in economically developed countries, indicate the need to modify the standards of pro-health programs as well as modern hygiene and work ergonomics programs. These observations are based on the problem of premature death caused by civilization diseases. The biological mechanisms associated with financial risk susceptibility are well described, but there is little data explaining the biological basis of neuroaccounting. Therefore, the aim of the study was to present relationships between personality traits, cognitive competences and biological factors shaping behavioral conditions in a multidisciplinary aspect. This critical review paper is an attempt to compile biological and psychological factors influencing the development of professional competences, especially decent in the area of accounting and finance. We analyzed existing literature from wide range of scientific disciplines (including economics, psychology, behavioral genetics) to create background to pursuit multidisciplinary research models in the field of neuroaccounting. This would help in pointing the best genetically based behavioral profile of future successful financial and accounting specialists.

Dopamine, Cognitive Flexibility, and IQ: Epistatic Catechol-O-MethylTransferase:DRD2 Gene-Gene Interactions Modulate Mental Rigidity

Cognitive flexibility has been hypothesized to be neurochemically rooted in dopamine neurotransmission. Nonetheless, underpowered sample sizes and contradictory meta-analytic findings have obscured the role of dopamine genes in cognitive flexibility and neglected potential gene-gene interactions. In this largest neurocognitive-genetic study to date (n = 1400), single nucleotide polymorphisms associated with elevated prefrontal dopamine levels (catechol-O-methyltransferase; rs4680) and diminished striatal dopamine (C957T; rs6277) were both implicated in Wisconsin Card Sorting Test performance. Crucially, however, these genetic effects were only evident in low-IQ participants, suggesting high intelligence compensates for, and eliminates, the effect of dispositional dopamine functioning on flexibility. This interaction between cognitive systems may explain and resolve previous empirical inconsistencies in highly educated participant samples. Moreover, compensatory gene-gene interactions were discovered between catechol-O-methyltransferase and DRD2, such that genotypes conferring either elevated prefrontal dopamine or diminished striatal dopamine-via heightened striatally concentrated D2 dopamine receptor availability-are sufficient for cognitive flexibility, but neither is necessary. The study has therefore revealed a form of epistatic redundancy or substitutability among dopamine systems in shaping adaptable thought and action, thus defining boundary conditions for dopaminergic effects on flexible behavior. These results inform theories of clinical disorders and psychopharmacological interventions and uncover complex fronto-striatal synergies in human flexible cognition.

Cortical thickness mediates the relationship between DRD2 C957T polymorphism and executive function across the adult lifespan

Dopamine (DA) signaling is critical for optimal cognitive performance. Aging is accompanied by a change in the strength of this signaling, with a loss of striatal and extrastriatal D2 binding potential. The reduction in dopamine modulation with age negatively influences various aspects of cognition. DRD2 C957T (rs6277) impacts DA D2 receptor density and availability, with C homozygotes linked to lower striatal DA availability and reduced executive functioning (EF), but also high extrastriatal binding potential. Here, we investigated in 176 participants aged 20-94 years whether: (1) DRD2 C carriers differ from T carriers in cortical thickness or subcortical volume in areas of high concentrations of D2 receptors that receive projections from mesocortical or nigrostriatal dopaminergic pathways; (2) whether the DRD2*COMT relationship has any synergistic effects on cortical thickness; (3) whether the effect of DRD2 on brain structure depends upon age; and (4) whether DRD2-related regional thinning affects executive function performance. We show that DRD2 impacts cortical thickness in the superior parietal lobule, precuneus, and anterior cingulate (marginal after FDR correction), while statistically controlling sex, age, and COMT genotype. Specifically, C homozygotes demonstrated thinner cortices than both heterozygotes and/or T homozygotes in an age-invariant manner. Additionally, DRD2 predicted executive function performance via cortical thickness. The results highlight that genetic influences on dopamine availability impact cognitive performance via the contribution of brain structure in cortical regions influenced by DRD2.

The relationship of age and DRD2 polymorphisms to frontostriatal brain activity and working memory performance

Dopamine (DA) in both prefrontal cortex (PFC) and caudate nucleus is critical for working memory (WM) function. The C957T and Taq1A polymorphisms of the DRD2 gene are related to DA D2 receptor densities in PFC and striatum. Using functional MRI, we investigated the relationship of age and these 2 DRD2 gene polymorphisms to WM function and examined possible age by gene interactions. Results demonstrated less caudate activity for older adults (70-80 years; n = 112) compared with the younger age group (25-65 years; n = 191), suggesting age-related functional differences in this region. Importantly, there was a gene-related difference regarding WM performance and frontostriatal brain activity. Specifically, better WM performance and greater activity in PFC were found among C957T C allele carriers. Combined genetic markers for increased DA D2 receptor density were associated with greater caudate activity and higher WM updating performance. The genetic effects on blood oxygen level-dependent activity were only observed in older participants, suggesting magnified genetic effects in aging. Our findings emphasize the importance of DA-related genes in regulating WM functioning in aging and demonstrate a positive link between DA and brain activation in the frontostriatal circuitry.

COMT val158met is not associated with Aβ-amyloid and APOE ε4 related cognitive decline in cognitively normal older adults

The non-synonymous single nucleotide polymorphism (SNP), Val158Met within the Catechol-O-methyltransferase (COMT) gene has been associated with altered levels of cognition and memory performance in cognitively normal adults. This study aimed to investigate the independent and interactional effects of COMT Val158Met on cognitive performance. In particular, it was hypothesised that COMT Val158Met would modify the effect of neocortical Aβ-amyloid (Aβ) accumulation and carriage of the apolipoprotein E (APOE) ε4 allele on cognition in preclinical Alzheimer's disease (AD). In 598 cognitively normal older adults with known neocortical Aβ levels, linear mixed modelling revealed no significant independent or interactional associations between COMT Val158Met and cognitive decline. These findings do not support previous associations between COMT Val158Met and cognitive performance and suggest this variant does not influence Aβ-amyloid or APOE ε4 driven cognitive decline in a well characterised cohort of cognitively normal older adults.

Mechanisms of Cognitive Aging in the HIV-Positive Adult

PURPOSE OF REVIEW

As of the year 2016, an estimated 50% of the United States' HIV-Positive population is aged 50 years or older. Due to a combination of increased rates of infection in older adults, and successful anti-retroviral (ART) regimens allowing HIV-positive adults to survive for decades with the disease, we are now faced with a steadily graying HIV-positive population, with only limited knowledge of how the cognitive and physiological effects of aging intersect with those of chronic HIV-infection.

RECENT FINDINGS

Age-related changes to mood, cognition, and neurological health may be experienced differently in those living with HIV, and research concerning quality of life, mental health, and cognitive aging needs to account for and explore these factors more carefully in the coming years.

SUMMARY

This review will explore the topic of cognitive aging with HIV: 1. Central nervous system (CNS) infection of HIV and how the virus affects brain integrity and function; 2. Cognitive and behavioral symptoms of HIV-Associated Neurocognitive Disorders (HAND); 3. Neurobiological theories of Cognitive Aging and how these processes may be exacerbated by HIV-infection; 4: Clinical implications and complications of aging with HIV and factors that may result in poorer cognitive outcomes.

The effect of COMT Val158Met and DRD2 C957T polymorphisms on executive function and the impact of early life stress

INTRODUCTION

Previous research has indicated that variation in genes encoding catechol-O-methyltransferase (COMT) and dopamine receptor D2 (DRD2) may influence cognitive function and that this may confer vulnerability to the development of mental health disorders such as schizophrenia. However, increasing evidence suggests environmental factors such as early life stress may interact with genetic variants in affecting these cognitive outcomes. This study investigated the effect of COMT Val158Met and DRD2 C957T polymorphisms on executive function and the impact of early life stress in healthy adults.

METHODS

One hundred and twenty-two healthy adult males (mean age 35.2 years, range 21-63) were enrolled in the study. Cognitive function was assessed using Cambridge Neuropsychological Test Automated Battery and early life stress was assessed using the Childhood Traumatic Events Scale (Pennebaker & Susman, 1988).

RESULTS

DRD2 C957T was significantly associated with executive function, with CC homozygotes having significantly reduced performance in spatial working memory and spatial planning. A significant genotype-trauma interaction was found in Rapid Visual Information Processing test, a measure of sustained attention, with CC carriers who had experienced early life stress exhibiting impaired performance compared to the CC carriers without early life stressful experiences. There were no significant findings for COMT Val158Met.

CONCLUSIONS

This study supports previous findings that DRD2 C957T significantly affects performance on executive function related tasks in healthy individuals and shows for the first time that some of these effects may be mediated through the impact of childhood traumatic events. Future work should aim to clarify further the effect of stress on neuronal systems that are known to be vulnerable in mental health disorders and more specifically what the impact of this might be on cognitive function.

Effects of dopamine D2/D3 receptor antagonism on human planning and spatial working memory

Psychopharmacological studies in humans suggest important roles for dopamine (DA) D2 receptors in human executive functions, such as cognitive planning and spatial working memory (SWM). However, studies that investigate an impairment of such functions using the selective DA D2/3 receptor antagonist sulpiride have yielded inconsistent results, perhaps because relatively low doses were used. We believe we report for the first time, the effects of a higher (800 mg p.o.) single dose of sulpiride as well as of genetic variation in the DA receptor D2 gene (DA receptor D2 Taq1A polymorphism), on planning and working memory. With 78 healthy male volunteers, we apply a between-groups, placebo-controlled design. We measure outcomes in the difficult versions of the Cambridge Neuropsychological Test Automated Battery One-Touch Stockings of Cambridge and the self-ordered SWM task. Volunteers in the sulpiride group showed significant impairments in planning accuracy and, for the more difficult problems, in SWM. Sulpiride administration speeded response latencies in the planning task on the most difficult problems. Volunteers with at least one copy of the minor allele (A1+) of the DA receptor D2 Taq1A polymorphism showed better SWM capacity, regardless of whether they received sulpiride or placebo. There were no effects on blood pressure, heart rate or subjective sedation. In sum, a higher single dose of sulpiride impairs SWM and executive planning functions, in a manner independent of the DA receptor D2 Taq1A polymorphism.

Impact of DRD2/ANKK1 and COMT Polymorphisms on Attention and Cognitive Functions in Schizophrenia

BACKGROUND

Cognitive deficits such as poor selective attention and executive functions decline have been reported in patients with schizophrenia. Many studies have emphasized the role of dopamine in regulating cognitive functions in the general population as well as in schizophrenia. However, the relationship between cognitive processes, schizophrenia and dopaminergic candidate genes is an original approach given interesting results. The purpose of the current exploratory study was to examine the interaction of dopaminergic genes (coding for dopamine receptor D2, DRD2, and for Catecholamine-O-Methyl-Transferase, COMT) with the diagnostic of schizophrenia in (i) the executive control of attention, (ii) selective attention, and (iii) executive functions.

METHODS AND RESULTS

We recruited 52 patients with schizophrenia and 53 healthy controls who performed the Stroop Color-Word Test, the Attention Network Test and the Wisconsin Card Sorting test. Four single nucleotide polymorphisms (SNPs) in the DRD2 gene (rs6275, rs6277, rs2242592 and rs1800497) and two SNPs in the COMT gene (rs4680 and rs165599) have been genotyped. Patients with schizophrenia performed significantly worse than controls in all cognitive performance, taking into account demographic variables. A significant gene by disease interaction was found for the Stroop interference (p = 0.002) for rs6275 of the DRD2 gene. The COMT Val/Val genotype and schizophrenia were associated with increased number of perseverative errors (p = 0.01).

CONCLUSIONS

In our study, the DRD2 gene is involved in attention while the COMT gene is implicated in executive functions in patients with schizophrenia.

DRD2 C957T polymorphism is associated with improved 6-month verbal learning following traumatic brain injury

Traumatic brain injury (TBI) often leads to heterogeneous clinical outcomes, which may be influenced by genetic variation. A single-nucleotide polymorphism (SNP) in the dopamine D2 receptor (DRD2) may influence cognitive deficits following TBI. However, part of the association with DRD2 has been attributed to genetic variability within the adjacent ankyrin repeat and kinase domain containing 1 protein (ANKK1). Here, we utilize the Transforming Research and Clinical Knowledge in Traumatic Brain Injury Pilot (TRACK-TBI Pilot) study to investigate whether a novel DRD2 C957T polymorphism (rs6277) influences outcome on a cognitive battery at 6 months following TBI-California Verbal Learning Test (CVLT-II), Wechsler Adult Intelligence Test Processing Speed Index Composite Score (WAIS-PSI), and Trail Making Test (TMT). Results in 128 Caucasian subjects show that the rs6277 T-allele associates with better verbal learning and recall on CVLT-II Trials 1-5 (T-allele carrier 52.8 ± 1.3 points, C/C 47.9 ± 1.7 points; mean increase 4.9 points, 95% confidence interval [0.9 to 8.8]; p = 0.018), Short-Delay Free Recall (T-carrier 10.9 ± 0.4 points, C/C 9.7 ± 0.5 points; mean increase 1.2 points [0.1 to 2.5]; p = 0.046), and Long-Delay Free Recall (T-carrier 11.5 ± 0.4 points, C/C 10.2 ± 0.5 points; mean increase 1.3 points [0.1 to 2.5]; p = 0.041) after adjusting for age, education years, Glasgow Coma Scale, presence of acute intracranial pathology on head computed tomography scan, and genotype of the ANKK1 SNP rs1800497 using multivariable regression. No association was found between DRD2 C947T and non-verbal processing speed (WAIS-PSI) or mental flexibility (TMT) at 6 months. Hence, DRD2 C947T (rs6277) may be associated with better performance on select cognitive domains independent of ANKK1 following TBI.

Dissociable electrophysiological subprocesses during response inhibition are differentially modulated by dopamine D1 and D2 receptors

Action control is achieved through a multitude of cognitive processes. One of them is the ability to inhibit responses, for which the dopaminergic systems is known to play an important role. Many lines of psychophysiological research substantiate that two distinct response inhibition subprocesses exist, but it has remained elusive whether they can be attributed to distinct neurobiological factors governing the dopaminergic system. We, therefore, investigated this question by examining the effects of DRD1 (rs4532) and DRD2 (rs6277) receptor polymorphisms on electrophysiological correlates of response inhibition subprocesses (i.e., Nogo-N2 and Nogo-P3) in 195 healthy human subjects with a standard Go/Nogo task. The results show that response inhibition performance at a behavioral level is affected by DRD1 and DRD2 receptor variation. However, from an electrophysiological point of view these effects emerge via different mechanisms selectively affected by DRD1 and DRD2 receptor variation. While the D1 receptor system is associated with pre-motor inhibition electrophysiological correlates of response inhibition processes (Nogo-N2), the D2 receptor system is associated with electrophysiological correlates of outcome evaluation processes. Dissociable cognitive-neurophysiological subprocesses of response inhibition are hence attributable to distinct dopamine receptor systems.

Genetic variation and dopamine D2 receptor availability: a systematic review and meta-analysis of human in vivo molecular imaging studies

The D2 dopamine receptor mediates neuropsychiatric symptoms and is a target of pharmacotherapy. Inter-individual variation of D2 receptor density is thought to influence disease risk and pharmacological response. Numerous molecular imaging studies have tested whether common genetic variants influence D2 receptor binding potential (BP) in humans, but demonstration of robust effects has been limited by small sample sizes. We performed a systematic search of published human in vivo molecular imaging studies to estimate effect sizes of common genetic variants on striatal D2 receptor BP. We identified 21 studies examining 19 variants in 11 genes. The most commonly studied variant was a single-nucleotide polymorphism in ANKK1 (rs1800497, Glu713Lys, also called 'Taq1A'). Fixed- and random-effects meta-analyses of this variant (5 studies, 194 subjects total) revealed that striatal BP was significantly and robustly lower among carriers of the minor allele (Lys713) relative to major allele homozygotes. The weighted standardized mean difference was -0.57 under the fixed-effect model (95% confidence interval=(-0.87, -0.27), P=0.0002). The normal relationship between rs1800497 and BP was not apparent among subjects with neuropsychiatric diseases. Significant associations with baseline striatal D2 receptor BP have been reported for four DRD2 variants (rs1079597, rs1076560, rs6277 and rs1799732) and a PER2 repeat polymorphism, but none have yet been tested in more than two independent samples. Our findings resolve apparent discrepancies in the literature and establish that rs1800497 robustly influences striatal D2 receptor availability. This genetic variant is likely to contribute to important individual differences in human striatal function, neuropsychiatric disease risk and pharmacological response.

DRD2 and DRD4 genes related to cognitive deficits in HIV-infected adults who abuse alcohol

Background

HIV-infected individuals continue to experience neurocognitive deterioration despite virologically successful treatments. The causes of neurocognitive impairment are still unclear. However, several factors have been suggested including the role of genetics. There is evidence suggesting that neurocognitive impairment is heritable and individual differences in cognition are strongly driven by genetic variations. The contribution of genetic variants affecting the metabolism and activity of dopamine may influence these individual differences.

Methods

The present study explored the relationship between two candidate genes (DRD4 and DRD2) and neurocognitive performance in HIV-infected adults. A total of 267 HIV-infected adults were genotyped for polymorphisms, DRD4 48 bp-variable number tandem repeat (VNTR), DRD2 rs6277 and ANKK1 rs1800497. The Short Category (SCT), Color Trail (CTT) and Rey-Osterrieth Complex Figure Tests (ROCT) were used to measure executive function and memory.

Results

Results showed significant associations with the SNP rs6277 and impaired executive function (odds ratio = 3.3, 95 % CI 1.2–2.6; p = 0.004) and cognitive flexibility (odds ratio = 1.6, 95 % CI 2.0–5.7; p = 0.001). The results were further stratified by race and sex and significant results were seen in males (odds ratio = 3.5, 95 % CI 1.5–5.5; p = 0.008) and in African Americans (odds ratio = 3.1, 95 % CI 2.3–3.5; p = 0.01). Also, DRD4 VNTR 7-allele was significantly associated with executive dysfunction.

Conclusion

The study shows that genetically determined differences in the SNP rs6277 DRD2 gene and DRD4 48 bp VNTR may be risk factors for deficits in executive function and cognitive flexibility.

Association between Dopamine Receptor D2 (DRD2) Variations rs6277 and rs1800497 and Cognitive Performance According to Risk Type for Psychosis: A Nested Case Control Study in a Finnish Population Sample

Background

There is limited research regarding the association between genes and cognitive intermediate phenotypes in those at risk for psychotic disorders.

Methods

We measured the association between established psychosis risk variants in dopamine D2 receptor (DRD2) and cognitive performance in individuals at age 23 years and explored if associations between cognition and these variants differed according to the presence of familial or clinical risk for psychosis. The subjects of the Oulu Brain and Mind Study were drawn from the general population-based Northern Finland 1986 Birth Cohort (NFBC 1986). Using linear regression, we compared the associations between cognitive performance and two candidate DRD2 polymorphisms (rs6277 and rs1800497) between subjects having familial (n=61) and clinical (n=45) risk for psychosis and a random sample of participating NFBC 1986 controls (n=74). Cognitive performance was evaluated using a comprehensive battery of tests at follow-up.

Results

Principal components factor analysis supported a three-factor model for cognitive measures. The minor allele of rs6277 was associated with poorer performance on a verbal factor (p=0.003) but this did not significantly interact with familial or clinical risk for psychosis. The minor allele of rs1800497 was associated with poorer performance on a psychomotor factor (p=0.038), though only in those at familial risk for psychotic disorders (interaction p=0.049).

Conclusion

The effect of two DRD2 SNPs on cognitive performance may differ according to risk type for psychosis, suggesting that cognitive intermediate phenotypes differ according to the type (familial or clinical) risk for psychosis.

The DYX2 locus and neurochemical signaling genes contribute to speech sound disorder and related neurocognitive domains

A major milestone of child development is the acquisition and use of speech and language. Communication disorders, including speech sound disorder (SSD), can impair a child's academic, social and behavioral development. Speech sound disorder is a complex, polygenic trait with a substantial genetic component. However, specific genes that contribute to SSD remain largely unknown. To identify associated genes, we assessed the association of the DYX2 dyslexia risk locus and markers in neurochemical signaling genes (e.g., nicotinic and dopaminergic) with SSD and related endophenotypes. We first performed separate primary associations in two independent samples - Cleveland SSD (210 affected and 257 unaffected individuals in 127 families) and Denver SSD (113 affected individuals and 106 unaffected individuals in 85 families) - and then combined results by meta-analysis. DYX2 markers, specifically those in the 3' untranslated region of DCDC2 (P = 1.43 × 10(-4) ), showed the strongest associations with phonological awareness. We also observed suggestive associations of dopaminergic-related genes ANKK1 (P = 1.02 × 10(-2) ) and DRD2 (P = 9.22 × 10(-3) ) and nicotinic-related genes CHRNA3 (P = 2.51 × 10(-3) ) and BDNF (P = 8.14 × 10(-3) ) with case-control status and articulation. Our results further implicate variation in putative regulatory regions in the DYX2 locus, particularly in DCDC2, influencing language and cognitive traits. The results also support previous studies implicating variation in dopaminergic and nicotinic neural signaling influencing human communication and cognitive development. Our findings expand the literature showing genetic factors (e.g., DYX2) contributing to multiple related, yet distinct neurocognitive domains (e.g., dyslexia, language impairment, and SSD). How these factors interactively yield different neurocognitive and language-related outcomes remains to be elucidated.

Association study of dopamine receptor genes polymorphism with cognitive functions in bipolar I disorder patients

OBJECTIVE

To determine the correlation among the polymorphisms of dopamine receptor genes, cognitive function of Bipolar disorder (BD) patients, and BD.

METHODS

Twenty-three Single Nucleotide Polymorphisms (SNPs) of dopamine receptor genes were genotyped using Illumina GoldenGate genotyping assay in 375 patients with bipolar I disorder (BD-I) (patients group) and 475 healthy controls (control group). Cognitive function tests were performed in 158 patients who were clinically stable and 307 healthy controls who were matched with the patients in age, sex, and education.

RESULTS

The allele frequencies of rs3758653 in the promoter region of the DRD4 gene were significantly different between patients group and control group (χ(2)=9.386, Corrected P=0.046). This significant difference was also observed between BD-I patients with psychotic symptoms and healthy controls (χ(2)=9.27, Corrected P=0.049). Patients with BD-I performed significantly worse than healthy controls in all cognitive domains (p<0.01) except TMTA errors and illegal time. Significant interactions between polymorphisms of rs5326 in DRD1 gene and phenotype (affected or unaffected with BD-I) were found in non-perseverative errors (β=3.20 and Corrected P=0.0034) on the Wisconsin Card Sorting Test (WCST). The allele of this SNP denoted the positive effect on the WCST non-perseverative errors in BD-I patients group (β=2.80 and Corrected P=0.017). The genotypic association analyses also supported the findings (F=4.24 and P=0.007), but this effect was not found in controls.

LIMITATIONS

The sample size was relatively small and the SNP coverage was limited, making it very important to be cautious when drawing a conclusion.

CONCLUSIONS

DRD4 gene may play an important role in psychotic symptomatology rather than in unique diagnosis, BD, for example. A genetic association exists between DRD1 gene and impaired cognition in BD.

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.

DRD1 and DRD2 genotypes modulate processing modes of goal activation processes during action cascading

Dopamine plays an important role in action selection, but little is known about the influence of different dopamine receptor systems on the subprocesses occurring during the cascading of actions. Because action selection and cascading can be accomplished in a serial manner or a parallel manner, we investigated the potential effects of DRD1 (rs4531) and DRD2 (rs6277) receptor polymorphisms on this dimension. We gathered behavioral and neurophysiological data from healthy human subjects (n = 162) and applied mathematical constraints to quantify their action selection strategy on a serial-parallel continuum. The behavioral results show a more serial and more effective action cascading strategy in homozygous DRD1 G allele carriers, who are assumed to have a higher D1 receptor efficiency than carriers of the A allele. In the group of homozygous DRD2 T-allele carriers, who have a higher striatal density of D2 receptors than C-allele carriers, we found a less effective and more parallel action cascading strategy. These findings suggest that, within the same sample, a higher D1 efficiency seems to shift the action cascading strategy toward a more serial processing mode, whereas the D2 receptors seem to promote a shift in the opposite direction by inducing a more parallel processing mode. Furthermore, the neurophysiological analysis shows that the observed differences are not based on attentional differences or basic inhibition. Instead, processes linking stimulus processing and response execution seem to differentiate between more serial and more parallel processing groups.

Drug abuse relapse rates linked to level of education: can we repair hypodopaminergic-induced cognitive decline with nutrient therapy?

It is well known that athletes and other individuals who have suffered painful injuries are at increased risk for all reward deficiency syndrome (RDS) behaviors, including substance use disorder (SUD). Comparing patient demographics and relapse rates in chemical dependence programs is pertinent because demographics may affect outcomes. Increased risk for relapse and lower academic achievement were found to have a significant association in recent outcome data from a holistic treatment center (HTC) located in North Miami Beach, FL. Relapse outcomes from the Drug Addiction Treatment Outcome Study (DATOS; n = 1738) and HTC (n = 224) were compared for a 12-month period. Post-discharge relapse was reported by 26% of HTC patients and 58% of patients in DATOS. When broken out by education level-less than high school, high school diploma, college degree, and graduate degree-HTC patient relapse was 50%, 36%, 33%, and 16%, respectively, and demonstrated an inverse linear association (F = 5.702; P = 0.017). Looking at DATOS patient relapse rates broken down by educational grades/years completed, patients who attended school between 7th grade and 4 years of college also demonstrated an inverse linear association (F = 5.563; P = 0.018). Additionally, the lowest performers, patients who reported their academic performance as "not so good," had the highest relapse (F = 4.226; P = 0.04). Albeit certain limitations, compared with DATOS patients, HTC patients produced significantly larger net differences in relapse rates (X 2 = 84.09; P = 0.0001), suggesting that other variables, such as the treatment model may also affect patient relapse. Our results implicate the use of vitamin and mineral supplements coupled with a well-researched natural dopamine agonist nutrient therapy; both have been shown to improve cognition and behavior, and thus academic achievement. That relapse is highest among addicts who have less education and who report lower grades is a factor that can be useful when considering treatment type and controlled for when comparing treatment outcomes.

Catechol-O-methyltransferase (COMT) genotype affects age-related changes in plasticity in working memory: a pilot study

Objectives. Recent work suggests that a genetic variation associated with increased dopamine metabolism in the prefrontal cortex (catechol-O-methyltransferase Val158Met; COMT) amplifies age-related changes in working memory performance. Research on younger adults indicates that the influence of dopamine-related genetic polymorphisms on working memory performance increases when testing the cognitive limits through training. To date, this has not been studied in older adults. Method. Here we investigate the effect of COMT genotype on plasticity in working memory in a sample of 14 younger (aged 24–30 years) and 25 older (aged 60–75 years) healthy adults. Participants underwent adaptive training in the n-back working memory task over 12 sessions under increasing difficulty conditions. Results. Both younger and older adults exhibited sizeable behavioral plasticity through training (P < .001), which was larger in younger as compared to older adults (P < .001). Age-related differences were qualified by an interaction with COMT genotype (P < .001), and this interaction was due to decreased behavioral plasticity in older adults carrying the Val/Val genotype, while there was no effect of genotype in younger adults. Discussion. Our findings indicate that age-related changes in plasticity in working memory are critically affected by genetic variation in prefrontal dopamine metabolism.

The DRD2 C957T polymorphism and the attentional blink--a genetic association study

The attentional blink phenomenon (AB) describes a transient deficit in temporally selective visual attention regarding the processing of the second of two target stimuli in a rapid serial visual presentation (RSVP) task. The AB is a very prominent paradigm in the Cognitive Neurosciences that has been extensively studied by diverse psychophysiological techniques such as EEG or fMRI. Association studies from molecular genetics are scarce although the high heritability of higher cognitive functioning is proven. Only one seminal study reported an association between AB magnitude and the dopamine receptor D2 (DRD2) C957T polymorphism (Colzato et al., 2011). This functional polymorphism influences striatal D2 receptor binding affinity and thereby the efficacy of dopaminergic neurotransmission which is important for working memory and attentional processes. Colzato et al. (2011) reported that DRD2 C957T T/T-carriers exhibit a significant smaller AB than C-allele carriers. In the present study this influence of the DRD2 SNP on the AB could not be replicated in N=211 healthy participants. However, a significantly larger lag 1 sparing was observed for homozygous T/T-carriers. Moreover, carriers of at least one T-allele showed a significantly poorer performance in the identification of T1. In general, these results support the notion of a role of the dopaminergic system on the AB. However, as our results do not parallel previous findings the exact nature of this influence and its dependence on task parameters will have to be examined in further genetic association studies.

Associations of prenatal nicotine exposure and the dopamine related genes ANKK1 and DRD2 to verbal language

Language impairment (LI) and reading disability (RD) are common pediatric neurobehavioral disorders that frequently co-occur, suggesting they share etiological determinants. Recently, our group identified prenatal nicotine exposure as a factor for RD and poor reading performance. Using smoking questionnaire and language data from the Avon Longitudinal Study of Parents and Children, we first determined if this risk could be expanded to other communication disorders by evaluating whether prenatal nicotine exposure increases risk for LI and poor performance on language tasks. Prenatal nicotine exposure increased LI risk (OR = 1.60; p = 0.0305) in a dose-response fashion with low (OR = 1.25; p = 0.1202) and high (OR = 3.84; p = 0.0002) exposures. Next, hypothesizing that the effects of prenatal nicotine may also implicate genes that function in nicotine related pathways, we determined whether known nicotine dependence (ND) genes associate with performance on language tasks. We assessed the association of 33 variants previously implicated in ND with LI and language abilities, finding association between ANKK1/DRD2 and performance on language tasks (p≤0.0003). The associations of markers within ANKK1 were replicated in a separate LI case-control cohort (p<0.05). Our results show that smoking during pregnancy increases the risk for LI and poor performance on language tasks and that ANKK1/DRD2 contributes to language performance. More precisely, these findings suggest that prenatal environmental factors influence in utero development of neural circuits vital to language. Our association of ANKK1/DRD2 further implicates the role of nicotine-related pathways and dopamine signaling in language processing, particularly in comprehension and phonological memory.

C957T polymorphism of the dopamine D2 receptor gene is associated with motor learning and heart rate

Genetic variants that are related to the dopaminergic system have been frequently found to be associated with various neurological and mental disorders. Here, we studied the relationships between some of these genetic variants and some cognitive and psychophysiological processes that are implicated in such disorders. Two single nucleotide polymorphisms were chosen: one in the dopamine D2 receptor gene (rs6277-C957T) and one in the catechol-O-methyltransferase gene (rs4680-Val158Met), which is involved in the metabolic degradation of dopamine. The performance of participants on two long-term memory tasks was assessed: free recall (declarative memory) and mirror drawing (procedural motor learning). Heart rate (HR) was also monitored during the initial trials of the mirror-drawing task, which is considered to be a laboratory middle-stress generator (moderate stress), and during a rest period (low stress). Data were collected from 213 healthy Caucasian university students. The C957T C homozygous participants showed more rapid learning than the T allele carriers in the procedural motor learning task and smaller differences in HR between the moderate- and the low-stress conditions. These results provide useful information regarding phenotypic variance in both healthy individuals and patients.

Neuropsychopharmacology and neurogenetic aspects of executive functioning: should reward gene polymorphisms constitute a diagnostic tool to identify individuals at risk for impaired judgment?

Executive functions are processes that act in harmony to control behaviors necessary for maintaining focus and achieving outcomes. Executive dysfunction in neuropsychiatric disorders is attributed to structural or functional pathology of brain networks involving prefrontal cortex (PFC) and its connections with other brain regions. The PFC receives innervations from different neurons associated with a number of neurotransmitters, especially dopamine (DA). Here we review findings on the contribution of PFC DA to higher-order cognitive and emotional behaviors. We suggest that examination of multifactorial interactions of an individual's genetic history, along with environmental risk factors, can assist in the characterization of executive functioning for that individual. Based upon the results of genetic studies, we also propose genetic mapping as a probable diagnostic tool serving as a therapeutic adjunct for augmenting executive functioning capabilities. We conclude that preservation of the neurological underpinnings of executive functions requires the integrity of complex neural systems including the influence of specific genes and associated polymorphisms to provide adequate neurotransmission.