Gender-specific molecular heterosis of dopamine D2 receptor gene (DRD2) for smoking in schizophrenia

Polymorphism in the LASP1 gene promoter region alters cognitive functions of patients with schizophrenia

Schizophrenia's pathogenesis remains elusive. Cognitive dysfunction is the endophenotype and outcome predictor of schizophrenia. The LIM and SH3 domain protein (LASP1) protein, a component of CNS synapses and dendritic spines, has been related to the N-methyl-D-aspartate receptor (NMDAR) dysfunction hypothesis and schizophrenia. A single-nucleotide polymorphism (rs979607) in the LASP1 gene promoter region has been also implicated in schizophrenia susceptibility. The aim of this study was to investigate the role of the LASP1 rs979607 polymorphism in the cognitive functions of patients with schizophrenia. Two hundred and ninety-one Han Taiwanese patients with schizophrenia were recruited. Ten cognitive tests and two clinical rating scales were assessed. The scores of cognitive tests were standardized to T-scores. The genotyping of the LASP1 rs979607 polymorphism was performed using TaqMan assay. Among the 291 patients, 85 were C/C homozygotes of rs979607, 141 C/T heterozygotes, and 65 T/T homozygotes, which fitted the Hardy-Weinberg equilibrium. After adjusting age, gender, and education with general linear model, the C/C homozygotes performed better than C/T heterozygotes in overall composite score (p = 0.023), Category Fluency test (representing processing speed and semantic memory) (p = 0.045), and Wechsler Memory Scale (WMS)-III backward Spatial Span test (p = 0.025), albeit without correction for multiple comparisons for the latter two individual tests. To the best of our knowledge, this is the first study suggesting that the genetic variation of LASP1 may be associated with global cognitive function, category verbal fluency, and spatial working memory of patients with schizophrenia. The finding also lends support to the NMDAR dysfunction hypothesis of schizophrenia. More studies with longitudinal designs are warranted.

Genetic Variation of the Mu Opioid Receptor (OPRM1) and Dopamine D2 Receptor (DRD2) is Related to Smoking Differences in Patients with Schizophrenia but not Bipolar Disorder

It is not known why mentally ill persons smoke excessively. Inasmuch as endogenous opioid and dopaminergic systems are involved in smoking reinforcement, it is important to study mu opioid receptor (OPRM1) A118G (rs1799971), dopamine D2 receptor (DRD2) Taq1A (rs1800497) genotypes, and sex differences among patients with schizophrenia or bipolar disorder. Smokers and nonsmokers with schizophrenia (n=177) and bipolar disorder (n=113) were recruited and genotyped. They were classified into three groups: current smoker, former smoker, and never smoker by tobacco smoking status self-report. The number of cigarettes smoked per day was used as the major tobacco smoking parameter. In patients with schizophrenia, tobacco smoking prevalence was greater in males than in females as expected, but women had greater daily cigarette consumption (p<0.01). Subjects with schizophrenia who had the OPRM1 *G genotype smoked more cigarettes per day than the AA allele carriers with schizophrenia (p<0.05). DRD2 Taq1A genotype differences had no effect on the number of cigarettes smoked per day. However, female smokers with schizophrenia who were GG homozygous of the DRD2 receptor smoked more than the *A male smokers with schizophrenia (p<0.05). In bipolar patients, there were no OPRM1 and DRD2 Taq1A genotype differences in smoking status. There also were no sex differences for smoking behavior among the bipolar patients. The results of this study indicate that single nucleotide polymorphism (SNP) of the less functional mu opioid receptor increases tobacco smoking in patients with schizophrenia. Alteration of DRD2 receptor function also increased smoking behavior in females with schizophrenia.

Effect of Functionally Significant Deiodinase Single Nucleotide Polymorphisms on Drinking Behavior in Alcohol Dependence: An Exploratory Investigation

BACKGROUND

Abnormalities of the hypothalamic-pituitary-thyroid (HPT) axis have been reported in alcoholism; however, there is no definitive agreement on the specific thyroid abnormalities and their underlying mechanisms in alcohol dependence. The biological activity of thyroid hormones or the availability of T3 is regulated by the three deiodinase enzymes: D1, D2, and D3. In the context of alcohol use, functionally significant single nucleotide polymorphisms (SNPs) of these deiodinase genes may play a role in HPT dysfunction.

METHODS

This study explored the effect of three functionally significant SNPs (D1: rs2235544, D2: rs225014, and rs12885300) of deiodinase genes on drinking behavior and thyroid-stimulating hormone (TSH) levels in alcohol-dependent (N = 521) and control subjects (N = 288).

RESULTS

Rs225014 was associated with significant differences in the amount of naturalistic alcohol drinking assessed by Timeline Follow Back. Alcohol-dependent subjects had significantly higher TSH levels compared to controls; however, there was no effect of genotype on TSH levels for either group.

CONCLUSIONS

These findings extend previous studies on thyroid dysfunction in alcoholism and provide novel, albeit preliminary, information by linking functionally significant genetic polymorphisms of the deiodinase enzymes with alcohol-drinking behavior.

Determination of genotype combinations that can predict the outcome of the treatment of alcohol dependence using the 5-HT(3) antagonist ondansetron

OBJECTIVE

The authors previously reported that the 5'-HTTLPR-LL and rs1042173-TT (SLC6A4-LL/TT) genotypes in the serotonin transporter gene predicted a significant reduction in the severity of alcohol consumption among alcoholics receiving the 5-HT3 antagonist ondansetron. In this study, they explored additional markers of ondansetron treatment response in alcoholics by examining polymorphisms in the HTR3A and HTR3B genes, which regulate directly the function and binding of 5-HT3 receptors to ondansetron.

METHOD

The authors genotyped one rare and 18 common single-nucleotide polymorphisms in HTR3A and HTR3B in the same sample that they genotyped for SLC6A4-LL/TT in the previous randomized, double-blind, 11-week clinical trial. Participants were 283 European Americans who received oral ondansetron (4 mg/kg of body weight twice daily) or placebo along with weekly cognitive-behavioral therapy. Associations of individual and combined genotypes with treatment response on drinking outcomes were analyzed.

RESULTS

Individuals carrying one or more of genotypes rs1150226-AG and rs1176713-GG in HTR3A and rs17614942-AC in HTR3B showed a significant overall mean difference between ondansetron and placebo in drinks per drinking day (22.50; effect size=0.867), percentage of heavy drinking days (220.58%; effect size=0.780), and percentage of days abstinent (18.18%; effect size=0.683). Combining these HTR3A/HTR3B and SLC6A4-LL/TT genotypes increased the target cohort from approaching 20% (identified in the previous study) to 34%.

CONCLUSIONS

The authors present initial evidence suggesting that a combined fivemarker genotype panel can be used to predict the outcome of treatment of alcohol dependence with ondansetron. Additional, larger pharmacogenetic studies would help to validate these results.

The role of dopamine transporter (SLC6A3) and dopamine D2 receptor/ankyrin repeat and kinase domain containing 1 (DRD2/ANKK1) gene polymorphisms in personality traits

Variations in personality traits are caused by interactions between multiple genes of small effect and environmental factors. To date, gender- and ethnicity-specific variations in personality have been established. In the present study, we aimed to test: (1) the effects of four polymorphisms of dopamine system genes: ANKK1/DRD2 Taq1A, DRD2 rs6275, SLC6A3 40-bp VNTR and rs27072, on personality traits; (2) whether these effects differ between men and women and between Russians and Tatars. A sample of 652 healthy individuals (222 men and 430 women) of Caucasian origin (233 Russians and 419 Tatars) from Russia was subjected to personality traits assessment with Eysenck Personality Inventory (EPI) and Temperament and Character Inventory-125 (TCI-125). The associations between each personality trait and polymorphisms were assessed with regression models adjusted for gender and ethnicity. There were significant effects of ANKK1/DRD2 Taq1A on Neuroticism (p=0.016) and of SLC6A3 rs27072 on Persistence (p=0.021) in both genders. The association between ANKK1/DRD2 Taq1A A2/A2-genotype and higher Novelty Seeking and lower Reward Dependence was shown in men only (p for gender interaction=0.018). In women only, there was a significant association between SLC6A3 10R*G-haplotype and higher Persistence (p=0.002). Our findings provide evidence for a modifying effect of gender on the associations between dopamine system genes and approach-related traits (in men) and Persistence (in women).

DRD2/ANKK1 TaqI A polymorphism affects corticostriatal activity in response to negative affective facial stimuli

DRD2/ANKK1 TaqI A polymorphism has been suggested to be involved in a reward-related psychiatric disorders. However, the effect of Dopamine receptor D2 (DRD2) on emotional processing has not been investigated yet. We investigated the possible relationship between DRD2/ANKK1 TaqI A polymorphism and corticostriatal response to negative facial stimuli using functional magnetic resonance imaging. All participants were genotyped with regard to the DRD2/ANKK1 TaqI A polymorphism. Our results suggest an association between the DRD2/ANKK1 TaqI A polymorphism and activations in the putamen, the anterior cingulate cortex, and amygdala in response to negative facial stimuli. Furthermore, molecular heterosis at the TaqI polymorphism of DRD2/ANKK1 may play an important role in affective regulation by corticostriatal pathway.

Prospective association of dopamine-related polymorphisms with smoking cessation in general care

AIMS

Genetic contributions to nicotine dependence have been demonstrated repeatedly, but the relevance of individual polymorphisms for smoking cessation remains controversial.

MATERIALS & METHODS

We examined genotypes at two dopamine-related loci, DRD2/ANKK1 (rs1800497) and DBH (rs77905), in 577 heavy smokers participating in a prospective study of smoking cessation in general care in Germany.

RESULTS

Smoking status after 1 year was significantly associated with DRD2/ANKK1, odds of abstinence being 4.4-fold (95% CI: 1.5-12.9) increased in TT- versus CC-homozygous subjects (p = 0.008). No effect was observed for the DBH genotype. The smoking cessation drug bupropion appeared to be particularly effective in CC-homozygotes (among CC subjects there was a 28% higher cessation probability among those taking buproprion; among T carrier subjects there was an increase only by 12%).

CONCLUSION

The large effects observed for DRD2/ANKK1 might be related to our study design, in which individual therapy was decided by the physician. Further studies are needed to clarify the genetic effects of DRD2/ANKK1 especially in 'real-life' settings outside clinical trials.

Multiple genetic tests for susceptibility to smoking do not outperform simple family history

AIMS

To evaluate the utility of using predictive genetic screening of the population for susceptibility to smoking.

METHODS

The results of meta-analyses of genetic association studies of smoking behaviour were used to create simulated data sets using Monte Carlo methods. The ability of the genetic tests to screen for smoking was assessed using receiver operator characteristic curve analysis. The result was compared to prediction using simple family history information. To identify the circumstances in which predictive genetic testing would potentially justify screening we simulated tests using larger numbers of alleles (10, 15 and 20) that varied in prevalence from 10 to 50% and in strength of association [relative risks (RRs) of 1.2-2.1].

RESULTS

A test based on the RRs and prevalence of five susceptibility alleles derived from meta-analyses of genetic association studies of smoking performed similarly to chance and no better than the prediction based on simple family history. Increasing the number of alleles from five to 20 improved the predictive ability of genetic screening only modestly when using genes with the effect sizes reported to date.

CONCLUSIONS

This panel of genetic tests would be unsuitable for population screening. This situation is unlikely to be improved upon by screening based on more genetic tests. Given the similarity with associations found for other polygenic conditions, our results also suggest that using multiple genes to screen the general population for genetic susceptibility to polygenic disorders will be of limited utility.

The interaction of DRD2 and violent victimization on depression: an analysis by gender and race

BACKGROUND

Recent research has shown that a polymorphism in the dopamine D2 receptor gene (DRD2) moderates the association between stressful life events and depression. The present study builds off this literature and examines whether DRD2 moderates the effect of violent victimization on depression. Furthermore, the current analyses investigate whether the effects of DRD2 and violent victimization vary by gender and by race for females.

METHODS

Respondents from waves II and III of the National Longitudinal Study of Adolescent Health (Add Health) completed questionnaires regarding their depressive symptoms and violent victimization experiences (n = 2380).

RESULTS

Multivariate regression results reveal that violent victimization has a strong independent effect on depressive symptoms for Caucasian females. In contrast, violent victimization is only associated with higher levels of depressive symptoms among African American females when they carry at least one A1 allele of DRD2. Results also show that DRD2 has a significant independent effect on depressive symptoms for males and African American females.

CONCLUSIONS

The results suggest that African American females who carry the A1 allele of DRD2 may be more vulnerable to the negative effects of violent victimization than African American females who do not carry at least one copy of the A1 allele.

LIMITATIONS

The current study's findings may not generalize to clinical populations, adults, and individuals residing in other countries. In addition, the effects of DRD2 may reflect other polymorphisms that are in linkage with DRD2.

Gender differences in 542 Chinese inpatients with schizophrenia

OBJECTIVE

To investigate gender differences in the onset and other clinical features of Han Chinese inpatients with schizophrenia.

METHODS

Five-hundred-and-forty-two Han Chinese inpatients with DSM-IV schizophrenia were assessed with the Positive and Negative Symptoms Scale (PANSS), the Brief Psychiatric Rating Scale (BPRS), the Global Assessment of Function scale (GAF) and locally-developed standardized data collection forms. Comparisons were made between male and female patients.

RESULTS

This is the largest study of gender differences in schizophrenia to be conducted in a Chinese population. In our sample, we found that schizophrenia onset occurred at a significantly earlier age in male patients compared to female patients and that late-onset schizophrenia (as defined by onset> or =45 years) was significantly more common in female patients. The paranoid subtype of schizophrenia was less common in male patients, males received higher daily doses of antipsychotics and demonstrated a different pattern of antipsychotic usage, being less likely to be treated with SGAs. Further, cigarette smoking was more common in male patients and male patients were more likely to be single or never married. By contrast, female patients showed a different pattern of ongoing symptoms and severity, being more likely to have persistent positive symptoms, more severe positive and affective symptoms, and a greater number of suicide attempts whereas male patients were more likely to show severe deterioration over time.

CONCLUSIONS

There are notable gender differences in the age at onset, treatment and a range of other clinical features in Han Chinese patients with schizophrenia. Such differences were largely consistent with those reported in Western studies. These gender differences need to be considered in the assessment and management of Chinese patients with schizophrenia.

Molecular heterosis in metamphetamine abusers

Objective. The aim of our study was to assess whether the catechol-O-methyltransferase (COMT) genetic background of patients dependent on metamphetamine is related to their non-abstinence in a 1-year follow-up. Methods. We examined COMT gene Val158Met polymorphism and 1-year abstinence in a group of 31 (women N=8) Czech Caucasian metamphetamine abusers (average age, 23.8±4.0years). Results. Non-abstinence was significantly (P=0.046, Fisher's exact test) associated with the heterozygous Val/Met genotype. Conclusion. The case where subjects heterozygous for a specific genetic polymorphism show a significantly greater or lesser effect for a phenotypic trait than subjects homozygous for either allele is described as molecular heterosis in the literature. We discuss several explanations and recommendations for further research.

Systematic search for single nucleotide polymorphisms in a lymphoid tyrosine phosphatase gene (PTPN22): association between a promoter polymorphism and type 1 diabetes in Asian populations

The protein tyrosine phosphatase, nonreceptor 22 gene (PTPN22) maps to human chromosome 1p13.3-p13.1 and encodes an important negative regulator of T-cell activation, lymphoid-specific phosphatase (Lyp). Recently, the minor allele of a single-nucleotide polymorphism (SNP) at nucleotide position 1858 (rs2476601, +1858C > T) was found to be associated with type 1 diabetes. However, the degree of the association is variable among ethnic populations, suggesting the presence of other disease-associated variants in PTPN22. To examine this possibility, we carried out a systemic search for PTPN22 using direct sequencing of PCR-amplified products in the Japanese population. Association and linkage studies were also conducted in 1,690 Japanese samples, 180 Korean samples, and 472 Caucasian samples from 95 nuclear families. We identified five novel SNPs, but not the +1858C > T SNP. Of these two frequent SNPs, -1123G > C, and +2740C > T were in strong linkage disequilibrium (LD), and the -1123G > C promoter SNP was associated with acute-onset but not slow-onset type 1 diabetes in the Japanese population (odds ratio [OR] = 1.42, 95% CI = 1.07-1.89, P = 0.015). This association was observed also in Korean patients with type 1 diabetes (Mantel-Haenszel chi2= 6.543, P = 0.0105, combined OR = 1.41 95% CI = 1.09-1.82). Furthermore, the affected family-based control (AFBAC) association test and the transmission disequilibrium analysis of multiplex families of European descent from the British Diabetes Association (BDA) Warren Repository indicated that the association was stronger in -1123G > C compared to +1858C > T. In conclusion, the type 1 diabetes association with PTPN22 is confirmed, but it cannot be attributed solely to the +1858C > T variant. The promoter -1123G > C SNP is a more likely causative variant in PTPN22.

Gender-specific molecular heterosis and association studies: dopamine D2 receptor gene and smoking

If the concept of the gender-specific molecular heterosis is not considered and tested, incorrect conclusions would easily be drawn in association studies. Therein, heterosis and its gender effect in the genetic effect of DRD2 gene for smoking were examined with 187 healthy Korean individuals. The male smokers showed a higher A1 allele frequency (P = 0.016) and prevalence (P = 0.049) than those of the male non-smokers, and the female smokers showed a lower frequency of heterozygotes (P = 0.018) than the female non-smokers. However, the association of DRD2 gene with smoking found in each gender disappeared when both males and females were considered as one group because of the opposite genetic effect of DRD2 gene for smoking: (1) while 75% of heterozygotes males were smokers, only 22% of female heterozygotes were; (2) males showed an excess of heterozygotes and the deviation from Hardy-Weinberg expectations in smokers, while these were true in the female non-smokers; and (3) in non-smokers, females were different from the males exhibiting a significantly higher prevalence (P = 0.005) and frequency (P = 0.015) of A1 allele, and significantly different genotype (P = 0.017) distribution, and higher frequency of heterozygotes (P = 0.055). Meanwhile, in smokers, males showed higher frequency of heterozygotes (P = 0.019) compared to females. The results indicate that gender-specific molecular heterosis at DRD2 gene for smoking is also applicable in healthy individuals as well as schizophrenics. Moreover, this concept has general applicability to other candidate genes and biological phenotypes.