Association between the estrogen receptor TA polymorphism and Harm avoidance.

In the last decade a large number of studies focused on the recognition of gene variants modulating temperamental traits. The gene coding for the estrogen receptor alpha (ESR1) appears to be an interesting candidate and it has been found to be linked to Harm avoidance (HA). The aim of the present study was to investigate whether the ESR1 TA dinucleotide repeat polymorphism is associated with HA temperamental trait in a sample of Caucasian University students. One hundred ninety healthy subjects were genotyped for ESR1 TA dinucleotide repeat polymorphism and were administered the Temperament and Character Inventory (TCI). ESR1 TA repeat lengths were dichotomized into short and long categories. ANOVA was used to examine the influence of ESR1 variants (short/long) on the means of the TCI HA scores. HA was significantly associated with age and gender in our sample, being higher in older and female subjects. In the global sample as well as in men and women separately, individuals carrying the S/S variant showed significantly higher HA scores. Further analysis on the HA subscales revealed that specific differences could exist between men and women. Our results further suggest a possible role of ESR1 variants on HA. Further research is needed to replicate our findings as well as to better explore the neuro-biological mechanisms of the modulation of ESR1 on HA.

A "line item" approach to the identification of genes involved in polygenic behavioral disorders: the adrenergic alpha2A (ADRA2A) gene.

The usual approach for using single base pair polymorphisms (SNPs) for the investigation of the genetics of behavioral disorders is to examine a single diagnostic syndrome or personality trait based on variables relating to a cluster of behavioral symptoms. However, since some of these variables may address behaviors that are associated with one allele while others are associated with the other allele, the overall association may be non-significant and significant sub-syndromal associations may be missed. Thus, we have reversed the process in a technique we term a "line item" approach. As a test of the technique we have examined the association between genotypes of a C- > G-1291 Msp I promotor SNP of the ADRA2A gene and 390 individual symptoms from a structured review of DSM-IV criteria for twelve different groups of symptoms. We examined 334 individuals consisting of controls and subjects with Tourette syndrome (TS). Based on the mean scores for each genotype, those symptoms that were individually significant at alpha < or = 0.05 fell into three major groups by mode of inheritance: allele 1 codominant (11 > 12 > 22), allele 2 codominant (22 > 12 > 11), and negative heterosis (12 < 11, 22). Within each mode of inheritance group, the number of symptoms that were significant for the twelve symptom clusters was compared by chi-square analysis. This showed that symptoms were drawn from the diagnostic groups in a significantly non-random fashion. Thus, the allele 1 codominant symptoms came from the anxiety, affective, schizoid, and somatization diagnostic groups (internalizing symptoms) (chi(2) = 80.0, d.f. = 11, P < or = 0.0000001), while the allele 2 codominant symptoms came from the ADHD and oppositional defiant/conduct disorder diagnostic groups (externalizing symptoms) (chi(2) = 81.0, d.f. = 11, P < or = 0.0000001). The questions that fell in the negative heterosis type of inheritance were not significantly associated with specific diagnostic groups (P = 0.87). These results showed that the ADRA2A gene was associated with symptoms of autonomic, sympathetic dysfunction from different diagnostic groups. The advantages of the "line item" approach include (a) the identification of the symptoms associated with each allele, (b) the identification of symptom clusters independent of DSM diagnoses, (c) the elucidation of heterosis and other mode of inheritance effects, (d) the distinction between an association with a primary disorder versus a comorbid disorder, (e) the identification of associations with sub-syndromal symptom clusters that do meet full DSM-IV criteria, and (f) the identification of symptom clusters across databases.

The additive effect of neurotransmitter genes in pathological gambling.

As access to gambling increases there is a corresponding increase in the frequency of addiction to gambling, known as pathological gambling. Studies have shown that a number of different neurotransmitters are affected in pathological gamblers and that genetic factors play a role. Polymorphisms at 31 different genes involved in dopamine, serotonin, norepinephrine, GABA and neurotransmitters were genotyped in 139 pathological gamblers and 139 age, race, and sex-matched controls. Multivariate regression analysis was used with the presence or absence of pathological gambling as the dependent variable, and the 31 coded genes as the independent variables. Fifteen genes were included in the regression equation. The most significant were the DRD2, DRD4, DAT1, TPH, ADRA2C, NMDA1, and PS1 genes. The r(2) or fraction of the variance was less than 0.02 for most genes. Dopamine, serotonin, and norepinephrine genes contributed approximately equally to the risk for pathological gambling. These results indicate that genes influencing a range of brain functions play an additive role as risk factors for pathological gambling. Multi-gene profiles in specific individuals may be of assistance in choosing the appropriate treatment.

Cholecystokinin (CCK) gene as a possible risk factor for smoking: a replication in two independent samples.

BACKGROUND: CCK is a satiety neuropeptide. Animal studies have shown that both acute and chronic exposure to nicotine results in weight loss which is associated with an increase in hypothalamic CCK and that CCK antagonists ameliorate symptoms of nicotine withdrawal. A major detriment to smoking cessation, especially in women, is the fear of gaining weight. These observations suggested that genetic variants in the CCK gene might be a possible risk factor for smoking. METHODS: To test this hypothesis we examined the association of the C-45T promoter polymorphism in the Sp1 binding region of the CCK gene with smoking and BMI in two independent groups of subjects. RESULTS: Group 1 consisted of 191 Caucasian women participating in an obesity study. The T allele was present in 15% of women who had never smoked, 20% of ex-smokers, and 58% of current smokers, P < or = 0.0014. The T allele was present in 26.8% of ever-smokers (ex-smokers + current smokers). There was no association with BMI. Group 2 consisted of 725 parents of twins from the Minnesota Twin and Family Study of substance abuse. Logistic regression analysis showed that a diagnosis of nicotine dependence was significantly associated with the T allele (P < or = 0.002) and with gender (males > females) (P < or = 0.001), but not with BMI (P < or = 0.68). The T allele was present in 15.9% of parents who had never smoked and 24.7% of ever-smokers, very similar to the results for group 1. INTERPRETATION: These results are consistent with a role of the CCK gene as a risk factor for smoking.

Clinical and molecular genetics of ADHD and Tourette syndrome. Two related polygenic disorders.

ADHD is a polygenic disorder due to the additive effect of genes affecting dopamine, norepinephrine, serotonin, GABA, and other neurotransmitters. Some of the specific loci involved are dopamine genes--DRD2, DRD4, DRD5, and the dopamine transporter; norepinephrine (NE) and epinephrine (EPI) genes--dopamine beta-hydroxylase, ADRA2A, ADRA2C, PNMT, norepinephrine transporter, MAOA, COMT; serotonin genes--TDO2, HTR1A, HTR1DA, serotonin transporter; GABA genes--GABRB3; androgen receptor and other genes. This model is consistent with all of the present knowledge about ADHD including (a) the increased frequency of ADHD in the relatives of ADHD probands, (b) the presence of a wide spectrum of comorbid behaviors (depression, anxiety, learning, conduct, oppositional-defiant, conduct and substance abuse disorders) in ADHD probands and their relatives on both parental sides, (c) the close relationship to Tourette syndrome (TS), (d) the failure to find the genes for TS using linkage analysis, (e) the brain imaging studies showing hypometabolism of the frontal lobes, (f) the relationship between dopamine D2 receptor density and regional blood flow, (g) the correlation between tics and dopamine D2 receptor density in TS, (h) the motor hyperactivity of dopamine transporter and dopamine D3 receptor gene knockout mice, (i) the LeMoal and Shaywitz dopamine deficiency animal models of ADHD, (j) the NE models of ADHD, (k) the failure to explain ADHD on the basis of any single neurotransmitter defect, (l) the response of ADHD to dopamine and alpha 2-adrenergic agonists, (m) the small percentage of the variance of specific behaviors accounted for by each gene, and numerous other aspects of ADHD. The implications of the polygenic model for the understanding, diagnosis and treatment of ADHD and TS, as well as other psychiatric disorders, are reviewed.

The LEP gene and age of menarche: maternal age as a potential cause of hidden stratification in association studies.

Leptin has a powerful effect on fertility and the initiation of puberty in addition to its effect on obesity. It has been suggested that that in times of fasting, infertility induced by low leptin levels protect the female from the energy demands of pregnancy. Despite this there have been no studies of the potential role of LEP gene variants on the age of onset of menarche. We genotyped 183 non-Hispanic Caucasian adult females at the LEP D7S1875 dinucleotide repeat polymorphism. The alleles were placed into three genotypes, <208/<208 bp, heterozygotes, and > or =208/> or =208 bp. A hierarchical ANOVA was performed with age of menarche as the dependent variable and LEP(1875) genotypes and maternal age (age of the mothers at birth of the subject) as independent variables. There was a significant (P or =30 years. If maternal age effects prove to be generalized, failure to take them into consideration could provide a source of hidden stratification that could significantly alter the replication of association studies.

Stress as a mediating factor in the association between the DRD2 TaqI polymorphism and alcoholism.

Results of earlier studies have shown that rating of prior stress exposure in preadolescent boys influenced the association between DRD2 genotypes and alcoholism risk factors, suggesting that variability in stress exposure, either in patient or control samples, could readily account for at least part of the confusion in DRD2 study outcomes. In order to test the hypothesis that the DRD2 A1 allele is only associated with alcoholism in subjects with elevated stress exposure, we examined the gene-stress interactional model in a sample of males of Mayan descent in the Olancho district of Honduras. Ascertainment was based on an epidemiologic, observational cross-sectional design, and the study was approved by the Institutional Review Board. A total of 309 adult males (age range 18-87 years) were interviewed by a physician or a public health nurse, blood samples were obtained for genetic studies, and participants were administered the short version of the Michigan Alcoholism Screening Test (S-MAST) and the Hispanic Stress Inventory (HSI). Three explanatory models were evaluated. The first model tested the effect of the demographic variables alone as predictors of MAST scores, the second tested the effects of stress and DRD2 genotypes separately, and the third tested the effect of the interaction between stress and the DRD2 genotypes. Neither model 1 nor model 2 yielded significant results; neither MAST scores nor HSI scores were found to be associated with DRD2 genotypes. However, Model 3 was confirmed reflecting a significant (P<.05) interaction between DRD2 genotype and stress score as a predictor of MAST score. Additionally, this difference was found to be largely accounted by the HSI occupational/economic stress score, which had a highly significant (P=.003) interaction with DRD2 genotype as a predictor of MAST score. This stress score was the only one of four that showed levels of stress as high as HSI scores in a US population. The MAST scores of A2A2 genotype participants were found to be nearly identical in low stress and high stress participants, whereas the MAST scores of A1A2 participants increased modestly with stress (P=.01) and that of A1A1 participants increased markedly with stress (P=.001). These findings support the hypothesis that DRD2 genotype-phenotype associations depend on the magnitude of stress exposure, and they lend support to the view that variability in DRD2 study outcomes may in part be explained by this gene-environment interaction.

Phenylethanolamine N-methyltransferase (PNMT) gene and early-onset Alzheimer disease.

The activity of human phenylethanolamine N-methyltransferase (PNMT) is reduced in the neurons of those cells in many subcortical areas of the brain that are known to undergo neurodegeneration in Alzheimer disease (AD). Others have reported that PNMT is decreased in brains of persons with AD and that the decrease in enzymatic activity is due to a reduced amount of the enzyme protein. We have previously described two polymorphisms, G-353A and G-148A, in the promoter region of the gene coding for PNMT. These markers were tested for their association with the occurrence of sporadic AD. Genotyping of 131 necropsy confirmed AD cases, and 947 adult nondemented controls were completed. We observed a significant association between both of the PNMT gene polymorphisms and early-onset AD (EOAD) (P < or = 0.007), but not in late-onset AD (LOAD). These data suggest that genetic variation in the promoter of the PNMT gene is associated with increased susceptibility to the sporadic form of EOAD.

Serotonin transporter gene polymorphisms in alcohol dependence.

The serotonin transporter (5-HTT) gene is a candidate gene in alcohol dependence because serotonin reuptake inhibitors (SRIs) can alleviate alcohol withdrawal. Studies of the 5-HTT gene in alcohol dependence have not resulted in a consensus. Recent studies have examined the transcriptionally active promoter polymorphism, a 44-bp deletion resulting in short (S) or long (L) alleles. In this study, 131 alcohol-dependent patients of Northern and Western European descent were genotyped. Seventy of these patients were diagnosed with alcohol dependence without comorbid disorders. Sixty-one patients were diagnosed with alcohol dependence comorbid with Tourette syndrome (alcoholic-TS). We found an excess of the S allele in alcohol-dependent patients (47%) compared with 125 ethnically matched controls (39%). A similar trend was found in 150 ethnically matched TS patients without alcohol dependence comorbidity (51%). However, the statistical significance of this trend in the data was not present after Bonferroni correction. The data presented suggests a trend toward increased frequency of the S promoter allele in alcohol-dependent, alcoholic-TS and TS patients.

Reward deficiency syndrome: genetic aspects of behavioral disorders.

The dopaminergic and opioidergic reward pathways of the brain are critical for survival since they provide the pleasure drives for eating, love and reproduction; these are called 'natural rewards' and involve the release of dopamine in the nucleus accumbens and frontal lobes. However, the same release of dopamine and production of sensations of pleasure can be produced by 'unnatural rewards' such as alcohol, cocaine, methamphetamine, heroin, nicotine, marijuana, and other drugs, and by compulsive activities such as gambling, eating, and sex, and by risk taking behaviors. Since only a minority of individuals become addicted to these compounds or behaviors, it is reasonable to ask what factors distinguish those who do become addicted from those who do not. It has usually been assumed that these behaviors are entirely voluntary and that environmental factors play the major role; however, since all of these behaviors have a significant genetic component, the presence of one or more variant genes presumably act as risk factors for these behaviors. Since the primary neurotransmitter of the reward pathway is dopamine, genes for dopamine synthesis, degradation, receptors, and transporters are reasonable candidates. However, serotonin, norepinephrine, GABA, opioid, and cannabinoid neurons all modify dopamine metabolism and dopamine neurons. We have proposed that defects in various combinations of the genes for these neurotransmitters result in a Reward Deficiency Syndrome (RDS) and that such individuals are at risk for abuse of the unnatural rewards. Because of its importance, the gene for the [figure: see text] dopamine D2 receptor was a major candidate gene. Studies in the past decade have shown that in various subject groups the Taq I A1 allele of the DRD2 gene is associated with alcoholism, drug abuse, smoking, obesity, compulsive gambling, and several personality traits. A range of other dopamine, opioid, cannabinoid, norepinephrine, and related genes have since been added to the list. Like other behavioral disorders, these are polygenically inherited and each gene accounts for only a small per cent of the variance. Techniques such as the Multivariate Analysis of Associations, which simultaneously examine the contribution of multiple genes, hold promise for understanding the genetic make up of polygenic disorders.

Molecular heterosis: a review.

Molecular heterosis occurs when subjects heterozygous for a specific genetic polymorphism show a significantly greater effect (positive heterosis) or lesser effect (negative heterosis) for a quantitative or dichotomous trait than subjects homozygous for either allele. At a molecular level heterosis appears counterintuitive to the expectation that if the 1 allele of a two-allele polymorphism is associated with a decrease in gene expression, those carrying the 11 genotype should show the greatest effect, 12 heterozygotes should be intermediate, and 22 homozygotes should show the least effect. We review the accumulating evidence that molecular heterosis is common in humans and may occur in up to 50% of all gene associations. A number of examples are reviewed, including those for the following genes: ADRA2C, C3 complement, DRD1, DRD2, DRD3, DRD4, ESR1, HP, HBB, HLA-DR DQ, HTR2A, properdin B, SLC6A4, PNMT, and secretor. Several examples are given in which the heterosis is gender-specific. Three explanations for molecular heterosis are proposed. The first is based on an inverted U-shaped response curve in which either to little or too much gene expression is deleterious, with optimal gene expression occurring in 12 heterozygotes. The second proposes an independent third factor causing a hidden stratification of the sample such that for in one set of subjects 11 homozygosity is associated with the highest phenotype score, while in the other set, 22 homozygosity is associated with the highest phenotype score. The third explanation suggests greater fitness in 12 heterozygotes because they show a broader range of gene expression than 11 or 22 homozygotes. Allele-based linkage techniques usually miss heterotic associations. Because up to 50% of association studies show a heterosis effect, this can significantly diminish the power of family-based linkage and association studies.

Association of the neutral endopeptidase (MME) gene with anxiety.

Enkephalins have been implicated in the regulation of mood, anxiety, reward, euphoria and pain. One of the major enzymes for enkephalin degradation is neutral endopeptidase [enkephalinase, membrane metalloendopeptidase (MME)]. We identified a dinucleotide polymorphism in the 5' region of the MME gene. Subjects were placed into three genotypes, 3/3, 3/x, and x/x since the 3 allele was the most common of the six alleles. Using one-way analysis of variance, we examined the association of these genotypes with the mean SCL-90 scores for anxiety, depression, obsessive-compulsive and phobic anxiety symptoms in 120 Caucasian males from an addiction treatment unit. There was a significant association between the MME genotypes and the SCL-90 scores for phobic anxiety, obsessive-compulsive and anxiety at a Bonferroni corrected alpha value of 0.0125. These results support a role of genetic variants of enkephalin metabolism in anxiety.

Multivariate analysis of associations of 42 genes in ADHD, ODD and conduct disorder.

In a previous study (Comings DE et al. Comparison of the role of dopamine, serotonin, and noradrenergic genes in ADHD, ODD and conduct disorder. Multivariate regression analysis of 20 genes. Clin Genet 2000: 57: 178-196) we examined the role of 20 dopamine, serotonin and norepinephrine genes in attention deficit hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), and conduct disorder (CD), using a multivariate analysis of associations (MAA) technique. We have now brought the total number of genes examined to 42 by adding an additional 22 candidate genes. These results indicate that even with the inclusion of these additional genes the noradrenergic genes still played a greater role in ADHD than any other group. Six other neurotransmitter genes were included in the regression equation - cholinergic, nicotinic, alpha 4 receptor (CHNRA4), adenosine A2A receptor (ADOA2A), nitric oxide synthase (NOS3), NMDAR1, GRIN2B, and GABRB3. In contrast to ADHD and ODD, CD preferentially utilized hormone and neuropeptide genes These included CCK, CYP19 (aromatase cytochrome P-450), ESR1, and INS (p = 0.005). This is consistent with our prior studies indicating a role of the androgen receptor (AR) gene in a range of externalizing behavors. We propose that the MAA technique, by focusing on the additive effect of multiple genes and on the cummulative effect of functionally related groups of genes, provides a powerful approach to the dissection of the genetic basis of polygenic disorders.

Association between the adrenergic alpha 2A receptor gene (ADRA2A) and measures of irritability, hostility, impulsivity and memory in normal subjects.

The noradrenergic system has been implicated in arousal, vigilance, irritability hostility, and memory. This suggests the hypothesis that genetic variants at noradrenergic receptors may be risk factors of these behaviors. To test this hypothesis, the potential association between measures of these traits and genetic variation at the adrenergic2A receptor gene (ADRA2A), using a common single nucleotide polymorphism (SNP) polymorphism of the promoter region, were examined in two independent sets of subjects: university students (student group), and parents of twins in the Minnesota Twin Study (twin group). In the student group, there was a significant linear association by genotype (11 > 12 > 22) for the total Brown ADD score (BADD), and BADD subscores of memory and irritability, and with the total Buss-Durkee Hostility Inventory (BDHI) score and BDHI subscores of indirect hostility, irritability, negativity, and verbal aggression. A multiple analysis of variance (MANOVA) of all the BADD and BDHI subscores was significant at P < or = 0.009. For the twin group, the same genotype associations were significant for the Multidimensional Personality Questionnaire (MPQ) impulsivity scores but not for the MPQ aggression or harm avoidance scores. The ADRA2A gene accounted for 1.8-8.3% of the variance of these scores.

Association of the N-acetyltransferase I gene (NATI) with mild and severe substance abuse.

We observed a significant increase in the number subjects carrying the NAT1* 10 allele of the N-acetyl transferasel (NAT1) gene in controls with a MAST-R score of > or = 4 and in subjects with drug and/or alcohol dependence (p=0.003), compared with controls with a MAST-R <4. These results suggest that alterations in the acetylation of one or more CNS compounds may be related to both mild and severe substance abuse.

Comparison of the role of dopamine, serotonin, and noradrenaline genes in ADHD, ODD and conduct disorder: multivariate regression analysis of 20 genes.

The present study is based on the proposal that complex disorders resulting from the effects of multiple genes are best investigated by simultaneously examining multiple candidate genes in the same group of subjects. We have examined the effect of 20 genes for dopamine, serotonin, and noradrenergic metabolism on a quantitative score for attention deficit hyperactivity disorder (ADHD) in 336 unrelated Caucasian subjects. The genotypes of each gene were assigned a score from 0 to 2, based on results from the literature or studies in an independent set of subjects (literature-based scoring), or results based on analysis of variance for the sample (optimized gene scoring). Multivariate linear regression analysis with backward elimination was used to determine which genes contributed most to the phenotype for both coding methods. For optimized gene scoring, three dopamine genes contributed to 2.3% of the variance, p = 0.052; three serotonin genes contributed to 3%, p = 0.015; and six adrenergic genes contributed to 6.9%, p = 0.0006. For all genes combined, 12 genes contributed to 11.6% of the variance, p = 0.0001. These results indicate that the adrenergic genes play a greater role in ADHD than either the dopaminergic or serotonergic genes combined. The results using literature-based gene scoring were similar. An examination of two additional comorbid phenotypes, conduct disorder and oppositional defiant disorder (ODD), indicated they shared genes with ADHD. For ODD different genotypes of the same genes were often used. These results support the value of the simultaneous examination of multiple candidate genes.

A multivariate analysis of 59 candidate genes in personality traits: the temperament and character inventory.

Cloninger (Cloninger CR. Neurogenetic adaptive mechanisms in alcoholism. Science 1987: 236: 410-416) proposed three basic personality dimensions for temperament: novelty seeking, harm avoidance, and reward dependence. He suggested that novelty seeking primarily utilized dopamine pathways, harm avoidance utilized serotonin pathways, and reward dependence utilized norepinephrine pathways. Subsequently, one additional temperament dimension (persistence) and three character dimensions (cooperativeness, self-directedness, and self-transcendence) were added to form the temperament and character inventory (TCI). We have utilized a previously described multivariate analysis technique (Comings DE, Gade-Andavolu R, Gonzalez N et al. Comparison of the role of dopamine, serotonin, and noradrenergic genes in ADHD, ODD and conduct disorder. Multivariate regression analysis of 20 genes. Clin Genet 2000: 57: 178-196; Comings DD, Gade-Andavolu R, Gonzalez N et al. Multivariate analysis of associations of 42 genes in ADHD, ODD and conduct disorder. Clin Genet 2000: in press) to examine the relative role of 59 candidate genes in the seven TCI traits and test the hypothesis that specific personality traits were associated with specific genes. While there was some tendency for this to be true, a more important trend was the involvement of different ratios of functionally related groups of genes, and of different genotypes of the same genes, for different traits.

The DRD4 gene and the spiritual transcendence scale of the character temperament index.

Two hundred male subjects (81 college students and 119 subjects from an addiction treatment unit) were administered the Temperament and Character Inventory (TCI) and genotyped at the 48 base pair repeat polymorphism of the DRD4 gene. Subjects were divided by genotype into those carrying any < 4 repeat allele, those homozygous for the 4 repeat allele, and those with any > 4 repeat allele. The total MANCOVA of seven TCI summary scores, with age and diagnostic group as covariates, was significant (P < or = 0.001). The largest effect was with self-transcendence (P < or = 0.001). The total MANCOVA for the three self-transcendence subscores was significant (P < or = 0.017), with the spiritual acceptance subscore showing the most effect (P < or = 0.001, power = 0.91). These results suggest the DRD4 gene may play a role in the personality trait of spiritual acceptance. This may be a function of the high concentration of the dopamine D4 receptor in the cortical areas, especially the frontal cortex.

Reward deficiency syndrome: a biogenetic model for the diagnosis and treatment of impulsive, addictive, and compulsive behaviors.

The dopaminergic system, and in particular the dopamine D2 receptor, has been implicated in reward mechanisms. The net effect of neurotransmitter interaction at the mesolimbic brain region induces "reward" when dopamine (DA) is released from the neuron at the nucleus accumbens and interacts with a dopamine D2 receptor. "The reward cascade" involves the release of serotonin, which in turn at the hypothalmus stimulates enkephalin, which in turn inhibits GABA at the substania nigra, which in turn fine tunes the amount of DA released at the nucleus accumbens or "reward site." It is well known that under normal conditions in the reward site DA works to maintain our normal drives. In fact, DA has become to be known as the "pleasure molecule" and/or the "antistress molecule." When DA is released into the synapse, it stimulates a number a DA receptors (D1-D5) which results in increased feelings of well-being and stress reduction. A consensus of the literature suggests that when there is a dysfunction in the brain reward cascade, which could be caused by certain genetic variants (polygenic), especially in the DA system causing a hypodopaminergic trait, the brain of that person requires a DA fix to feel good. This trait leads to multiple drug-seeking behavior. This is so because alcohol, cocaine, heroin, marijuana, nicotine, and glucose all cause activation and neuronal release of brain DA, which could heal the abnormal cravings. Certainly after ten years of study we could say with confidence that carriers of the DAD2 receptor A1 allele have compromised D2 receptors. Therefore lack of D2 receptors causes individuals to have a high risk for multiple addictive, impulsive and compulsive behavioral propensities, such as severe alcoholism, cocaine, heroin, marijuana and nicotine use, glucose bingeing, pathological gambling, sex addiction, ADHD, Tourette's Syndrome, autism, chronic violence, posttraumatic stress disorder, schizoid/avoidant cluster, conduct disorder and antisocial behavior. In order to explain the breakdown of the reward cascade due to both multiple genes and environmental stimuli (pleiotropism) and resultant aberrant behaviors, Blum united this hypodopaminergic trait under the rubric of a reward deficiency syndrome.