Dopamine beta-hydroxylase (DBH) gene and schizophrenia phenotypic variability: a genetic association study

Effect of rs1108580 of DBH and rs1006737 of CACNA1C on Cognition and Tardive Dyskinesia in a North Indian Schizophrenia Cohort

Genetic perturbations in dopamine neurotransmission and calcium signaling pathways are implicated in the etiology of schizophrenia. We aimed to test the association of a functional splice variant each in Dopamine β-Hydroxylase (DBH; rs1108580) and Calcium voltage-gated channel subunit alpha1 C (CACNA1C; rs1006737) genes in these pathways with schizophrenia (506 cases, 443 controls); Abnormal Involuntary Movement Scale (AIMS) scores in subjects assessed for tardive dyskinesia (76 TD-positive, 95 TD-negative) and Penn Computerized Neurocognitive Battery (PennCNB) scores (334 cases, 234 controls). The effect of smoking status and SNP genotypes on AIMS scores were assessed using ANOVA; health status and SNP genotypes on three performance functions of PennCNB cognitive domains were assessed by ANCOVA with age and sex as covariates. Association with Positive and Negative Syndrome Scale (PANSS) scores in the TD cohort and cognitive scores in healthy controls of the cognition cohort were tested by linear regression. None of the markers were associated with schizophrenia. Smoking status [F(2, 139) = 10.6; p = 5 × 10-5], rs1006737 [F(2, 139) = 7.1; p = 0.001], TD status*smoking [F(2, 139) = 8.0; p = 5.0 × 10-4] and smoking status*rs1006737 [F(4, 139) = 2.7; p = 0.03] had an effect on AIMS score. Furthermore, rs1006737 was associated with orofacial [F(2, 139) = 4.6; p = 0.01] and limb-truncal TD [(F(2, 139) = 3.8; p = 0.02]. Main effect of rs1108580 on working memoryprocessing speed [F(2, 544) = 3.8; p = 0.03] and rs1006737 on spatial abilityefficiency [F(1, 550) = 9.4; p = 0.02] was identified. Health status*rs1006737 interaction had an effect on spatial memoryprocessing speed [F(1, 550) = 6.9; p = 0.01]. Allelic/genotypic association (p = 0.01/0.03) of rs1006737 with disorganized/concrete factor and allelic association of rs1108580 (p = 0.04) with a depressive factor of PANSS was observed in the TD-negative subcohort. Allelic association of rs1006737 with sensorimotor dexterityaccuracy (p = 0.03), attentionefficiency (p = 0.05), and spatial abilityefficiency (p = 0.02); allelic association of rs1108580 with face memoryaccuracy (p = 0.05) and emotionefficiency (p = 0.05); and allelic/genotypic association with emotionaccuracy (p = 0.003/0.009) were observed in healthy controls of the cognition cohort. These association findings may have direct implications for personalized medicine and cognitive remediation.

Contrasting ABCB1 pharmacogenetics and psychotropic responses in child and adolescent psychiatry: a case comparison

This case comparison illustrates pharmacogenetic testing in psychotropic and clinical management in relation to the ABCB1 gene, which encodes the P-glycoprotein transporter affecting blood-brain barrier (BBB) permeability. Two pediatric patients (9 and 11 years old) were selected for similar clinical presentations with opposing ABCB1 genotype, while they were identically matched for key CYP450, dopaminergic and serotonergic genes (CYP2C9, CYP2C19, DRD2, SLC6A4, 5HTR2A). Case A was functional for the ABCB1 gene (G/G rs1045642), suggesting that the BBB had a functional P-glycoprotein transporter. Case B was subfunctional for the ABCB1 gene (A/A rs1045642), suggesting that the patient's BBB may be permeable to psychotropic drugs. Case A had more medication trials and dose adjustments than Case B. Case A had two inpatient admissions and interspersed emergency room visits, while case B had none.

Association of regulatory variants of dopamine β-hydroxylase with cognition and tardive dyskinesia in schizophrenia subjects

BACKGROUND

Dopamine-β-hydroxylase (DBH, EC 1.14.17.1), which converts dopamine to norepinephrine, is a candidate gene in neuropsychiatric diseases.

AIM

To assess the effect of regulatory variants in DBH on schizophrenia and its endophenotypes -cognition and tardive dyskinesia.

METHODS

We tested association of functional variants 19bp Ins/Del, rs1989787 and rs1611115 in DBH with i) schizophrenia (1236 cases, 1136 controls), ii) tardive dyskinesia (83 positive, 162 negative) and iii) performance functions of cognition (357 cases, 306 controls) estimated by the Penn Computerized Neurocognitive Battery.

RESULTS

A modest haplotypic (Ins-C; 19bp Ins/Del - rs1989787 C>T; p=0.04) association was observed with schizophrenia. We observed ~39% reduction in activity of 19bp Del allele on luciferase assay. Analysis of covariance revealed interactions of tardive dyskinesia status and: i) 19bp Ins/Del (genotypic, p=0.04) and ii) rs1989787 and rs1611115 (combined genotypic, p=0.004) on Abnormal Involuntary Movement Scale total score. Association of rs1611115 with positive and negative syndrome scale (PANSS) total score (p=0.05) and allelic/genotypic association with lower positive (p=0.03/0.04), general psychopathology (p=0.01/0.01) PANSS scales in tardive dyskinesia-positive; and allelic/genotypic (p=0.02/0.05) with higher score of depressive factors in tardive dyskinesia-negative subgroups were observed. Analysis of covariance with continuous variable of cognition showed interaction of health status with: i) rs1989787 on accuracy and efficiency (p=0.03) of abstraction and mental flexibility; ii) rs1611115 on accuracy of working memory and emotion (p=0.05); iii) 19bp Ins/Del on processing speed of emotion (p=0.03). Allelic/genotypic association of rs1989787 with spatial ability (p=0.02-0.05) among healthy controls; association of rs1611115 with Global Assessment Scale scores in the past month (p=0.05) among schizophrenia subjects of cognition cohort was also observed.

CONCLUSIONS

With modest genotype-phenotype correlations available for DBH variants, personalized treatment regimens based on DBH activity for ameliorating tardive dyskinesia and cognitive symptoms may be plausible.

Lack of zinc finger protein 521 upregulates dopamine β-hydroxylase expression in the mouse brain, leading to abnormal behavior

AIM

Previously, we reported that mice deficient in most of the Zfp521 coding region (Zfp521^Δ/Δ mice) displayed abnormal behaviors, including hyperlocomotion and lower anxiety. In this study, we aimed to elucidate the involvement and mechanisms of monoamine variation.

MAIN METHODS

First, we compared the levels of dopamine (DA), noradrenaline (NA), and serotonin in the brains of Zfp521^Δ/Δ and Zfp521^+/+ mice using enzyme-linked immunosorbent assay. Next, we elucidated the mechanisms using quantitative PCR and Western Blotting. Additionally, we administered inhibitory drug to the mice and performed behavioral tests.

KEY FINDINGS

Our results showed that the DA level decreased and the NA level increased in Zfp521^Δ/Δ mice. We found that ZFP521 suppresses the expression of dopamine β-hydroxylase (DBH), which converts DA into NA. We also demonstrated that paired homeodomain transcription factor 2 and early growth response protein-1, which are the transcription factors for Dbh, were involved in the upregulation of Dbh by ZFP521. The administration of nepicastat, a specific inhibitor of DBH, attenuated the abnormal behaviors of Zfp521^Δ/Δ mice.

SIGNIFICANCE

These results suggest that the lack of ZFP521 upregulates the expression of DBH, which leads to a decrease in the DA level and an increase in the NA level in the brain, resulting in abnormal behaviors.

DNA methylation of dopamine-related gene promoters is associated with line bisection deviation in healthy adults

Handedness and language lateralization are the most investigated phenotypes among functional hemispheric asymmetries, i.e. differences in function between the left and the right half of the human brain. Both phenotypes are left hemisphere-dominant, while investigations of the molecular factors underlying right hemisphere-dominant phenotypes are less prominent. In the classical line bisection task, healthy subjects typically show a leftward attentional bias due to a relative dominance of the right hemisphere for visuospatial attention. Based on findings of variations in dopamine-related genes affecting performance in the line bisection task, we first tested whether DNA methylation in non-neuronal tissue in the promoter regions of DBH, SLC6A3, and DRD2 are associated with line bisection deviation. We replicated the typical behavioral pattern and found an effect of DNA methylation in the DBH promoter region on line bisection deviation in right-aligned trials. A second exploratory analysis indicated that an overall DNA methylation profile of genes involved in dopamine function predicts line bisection performance in right-aligned trials. Genetic variation in dopamine-related genes has been linked to attention deficit hyperactivity disorder (ADHD), a neurodevelopmental trait associated with rightward attentional bias. Overall, our findings point towards epigenetic markers for functional hemispheric asymmetries in non-neuronal tissue not only for left hemisphere-dominant, but also for right hemisphere-dominant phenotypes.

Characterization of SNPs in the dopamine-β-hydroxylase gene providing new insights into its structure-function relationship

Dopamine-β-hydroxylase (DBH, EC 1.14.17.1), an oxido-reductase that catalyses the conversion of dopamine to norepinephrine, is largely expressed in sympathetic neurons and adrenal medulla. Several regulatory and structural variants in DBH associated with various neuropsychiatric, cardiovascular diseases and a few that may determine enzyme activity have also been identified. Due to paucity of studies on functional characterization of DBH variants, its structure-function relationship is poorly understood. The purpose of the study was to characterize five non-synonymous (ns) variants that were prioritized either based on previous association studies or Sorting Tolerant From Intolerant (SIFT) algorithm. The DBH ORF with wild type (WT) and site-directed mutagenized variants were transfected into HEK293 cells to generate transient and stable lines expressing these variant enzymes. Activity was determined by UPLC-PDA and corresponding quantity by MRM^HR on a TripleTOF 5600 MS respectively of spent media from stable cell lines. Homospecific activity computed for the WT and variant proteins showed a marginal decrease in A318S, W544S and R549C variants. In transient cell lines, differential secretion was observed in the case of L317P, W544S and R549C. Secretory defect in L317P was confirmed by localization in ER. R549C exhibited both decreased homospecific activity and differential secretion. Of note, all the variants were seen to be destabilizing based on in silico folding analysis and molecular dynamics (MD) simulation, lending support to our experimental observations. These novel genotype-phenotype correlations in this gene of considerable pharmacological relevance have implications for dopamine-related disorders.

Analysis of dopamine beta hydroxylase gene polymorphisms in migraine

BACKGROUND

Migraine is a complex neurological disorder characterized by severe recurrent headache, nausea, vomiting, photophobia, and phonophobia. The frequency and duration of these symptoms varies among individuals. Dopaminergic systems are believed to be involved in migraine pathophysiology. We aimed to look for association of polymorphisms in dopaminergic genes in genetic susceptibility to migraine in Turkey population.

METHODS

The present study was designed to explore possible association of three polymorphisms, (1021C>T (Rs1611115), +1603C>T (Rs6271; C535R) and +444G>A (rs1108580), of Dopamin Beta Hydroxylase gene in migraine patients. 200 migraine patients and 267 healthy controls were included in the study. Genomic DNA was extracted from blood and genotypes were analyzed using polymerase chain reaction-restriction fragment length polymorphism methods (PCR-RFLP).

RESULTS

Statistical evaluation of data results showed a significant association for allelic and genotypic frequency distribution between the Dopamin Beta Hydroxylase gene +1603C>T polymorphism and migraine (p=0.000, OR: 4.36, 95% CI: 2.73-7.16). There was no association observed between the -1021C>T and +444 G>A polymorphisms of the Dopamin Beta Hydroxylase gene and migraine (p=0.8731 and p=0.7584).

CONCLUSIONS

This study reflects that Dopamin Beta Hydroxylase gene +1603C>T polymorphism may be one of the many genetic factors for migraine susceptibility in the Turkish population.

Neuronal copper homeostasis susceptibility by genetic defects in dysbindin, a schizophrenia susceptibility factor

Environmental factors and susceptible genomes interact to determine the risk of neurodevelopmental disorders. Although few genes and environmental factors have been linked, the intervening cellular and molecular mechanisms connecting a disorder susceptibility gene with environmental factors remain mostly unexplored. Here we focus on the schizophrenia susceptibility gene DTNBP1 and its product dysbindin, a subunit of the BLOC-1 complex, and describe a neuronal pathway modulating copper metabolism via ATP7A. Mutations in ATP7A result in Menkes disease, a disorder of copper metabolism. Dysbindin/BLOC-1 and ATP7A genetically and biochemically interact. Furthermore, disruption of this pathway causes alteration in the transcriptional profile of copper-regulatory and dependent factors in the hippocampus of dysbindin/BLOC-1-null mice. Dysbindin/BLOC-1 loss-of-function alleles do not affect cell and tissue copper content, yet they alter the susceptibility to toxic copper challenges in both mammalian cells and Drosophila. Our results demonstrate that perturbations downstream of the schizophrenia susceptibility gene DTNBP1 confer susceptibility to copper, a metal that in excess is a neurotoxin and whose depletion constitutes a micronutrient deficiency.

Regulatory polymorphisms in human DBH affect peripheral gene expression and sympathetic activity

RATIONALE

Dopamine β-hydroxylase (DBH) catalyzes the conversion of dopamine to norepinephrine in the central nervous system and peripherally. DBH variants are associated with large changes in circulating DBH and implicated in multiple disorders; yet causal relationships and tissue-specific effects remain unresolved.

OBJECTIVE

To characterize regulatory variants in DBH, effect on mRNA expression, and role in modulating sympathetic tone and disease risk.

METHODS AND RESULTS

Analysis of DBH mRNA in human tissues confirmed high expression in the locus coeruleus and adrenal gland, but also in sympathetically innervated organs (liver>lung>heart). Allele-specific mRNA assays revealed pronounced allelic expression differences in the liver (2- to 11-fold) attributable to promoter rs1611115 and exon 2 rs1108580, but only small differences in locus coeruleus and adrenals. These alleles were also associated with significantly reduced mRNA expression in liver and lung. Although DBH protein is expressed in other sympathetically innervated organs, mRNA levels were too low for analysis. In mice, hepatic Dbh mRNA levels correlated with cardiovascular risk phenotypes. The minor alleles of rs1611115 and rs1108580 were associated with sympathetic phenotypes, including angina pectoris. Testing combined effects of these variants suggested protection against myocardial infarction in 3 separate clinical cohorts.

CONCLUSIONS

We demonstrate profound effects of DBH variants on expression in 2 sympathetically innervated organs, liver and lung, but not in adrenals and brain. Preliminary results demonstrate an association of these variants with clinical phenotypes responsive to peripheral sympathetic tone. We hypothesize that in addition to endocrine effects via circulating DBH and norepinephrine, the variants act in sympathetically innervated target organs.

Meta-analyses of 10 polymorphisms associated with the risk of schizophrenia

Schizophrenia (SCZ) is a severe complex psychiatric disorder that generates problems for the associated family and society and causes disability with regards to work for patients. The aim of the present study was to assess the contribution of 10 genetic polymorphisms to SCZ susceptibility. Meta-analyses were conducted using the data without a limitation for time or language. A total of 27 studies with 7 genes and 10 polymorphisms were selected for the meta-analyses. Two polymorphisms were found to be significantly associated with SCZ. SNAP25 rs3746544 was shown to increase the SCZ risk by 18% [P=0.01; odds ratio (OR), 1.18; 95% confidence interval (CI), 1.05-1.34] and GRIK3 rs6691840 was found to increase the risk by 30% (P=0.008; OR, 1.30; 95% CI, 1.07-1.58). Significant results were found under the dominant (P=0.001; OR, 1.36; 95% CI, 1.13-1.65) and additive (P=0.02; OR, 1.45; 95% CI, 1.06-1.98) model for the SNAP25 rs3746544 polymorphism and under the additive model for the GRIK3 rs6691840 polymorphism (P=0.03; OR, 1.73; 95% CI, 1.04-2.85). There were no significant results observed for the other eight polymorphisms, which were CCKAR rs1800857, CHRNA7 rs904952, CHRNA7 rs6494223, CHRNA7 rs2337506, DBH Ins>Del, FEZ1 rs559668, FEZ1 rs597570 and GCLM rs2301022. In conclusion, the present meta-analyses indicated that the SNAP25 rs3746544 and GRIK3 rs6691840 polymorphisms were risk factors of SCZ, which may provide valuable information for the clinical diagnosis of SCZ.

Association of the dopamine β-hydroxylase 19 bp insertion/deletion polymorphism with positive symptoms but not tardive dyskinesia in schizophrenia

OBJECTIVE

Overactivity of dopaminergic neurotransmission is a putative mechanism of tardive dyskinesia (TD). Dopamine beta-hydroxylase (DBH) is a key enzyme in the conversion of dopamine to norepinephrine, and plasma DBH activity is altered in TD patients. This study examined whether the functional DBH 5'-Ins/Del polymorphism was associated with TD severity in Chinese patients with schizophrenia.

METHODS

We compared the rate of this polymorphism in patients with (n = 312) and without TD (n = 435), and healthy controls (n = 625). The severity of TD was assessed using the Abnormal Involuntary Movement Scale (AIMS) and psychopathology using the Positive and Negative Syndrome Scale (PANSS).

RESULTS

There were no significant differences in the distribution of the allele and genotype frequencies between the patients and controls, or between the patients with and without TD. Also, there was no significant difference in the AIMS total score between the three genotype groups. However, the PANSS positive symptom subscore was significantly higher in patients with Del/Del genotype (13.2 ± 5.2) than those with Ins/Del (11.2 ± 4.9) and Ins/Ins (11.1 ± 3.1) genotypes (both p < 0.05).

CONCLUSION

These results suggest that although the DBH 5'-Ins/Del polymorphism was not associated with susceptibility to TD in patients with schizophrenia, it might be related to positive symptoms of schizophrenia.

Association of functional dopamine-beta-hydroxylase (DBH) 19 bp insertion/deletion polymorphism with smoking severity in male schizophrenic smokers

Recent evidence suggests that a dopamine beta-hydroxylase (DBH) polymorphism may play a role in determining an individual's predisposition to developing nicotine dependence. The mechanism for such an association may reflect nicotine's mediation of drug reward in the brain through actions on dopamine, a key mediator of drug reward. Because schizophrenia patients have usually high rates of nicotine use, they are a model group to study such an association. In this study, we hypothesized that the functional polymorphism of DBH (DβH5'-Ins/Del) was associated with smoking in patients with schizophrenia. This polymorphism was genotyped in 636 chronic male schizophrenia (smoker/nonsmoker=490/146) and 396 male controls (smoker/nonsmoker=231/165) using a case-control design. The cigarettes smoked per day (CPD) and smoking behaviors were evaluated by clinician-administered questionnaires and the Fagerstrom Test for Nicotine Dependence (FTND). The results showed no significant differences in DBH 5'-Ins/Del genotype and allele distributions between the patients and healthy controls or between smokers and nonsmokers in either patients or healthy controls alone. However, schizophrenic smokers with the Del allele smoked fewer cigarettes each day and had lower FTND score than those with Ins/Ins genotype. These results suggest that the DBH 5'-Ins/Del polymorphism may influence smoking severity among schizophrenic smokers.

Association between dopamine beta hydroxylase gene polymorphism and age at onset in male schizophrenia

OBJECTIVES

The heterogeneity of schizophrenia mainly results from variations in clinical expressions of the disease, such as age at onset, gender differences in onset of illness, symptoms and response to antipsychotic treatment. Enhanced sensitisation of dopamine pathways in males, having consistently an earlier onset, might be implicated as disease modifiers for schizophrenia in males.

METHODS

In this study, we performed a case (n = 87)-control (n = 100) association study between the DBH5'-ins/del and DBH-444g/a polymorphisms of the DBH gene and also compared the level of psychotic symptoms between patients with different DBH genotypes/haplotypes with respect to antipsychotic therapeutic response and gender difference.

RESULTS

No significant differences between allele and genotype and haplotype frequencies at either groups (p < 0.05). When the age is considered in patient group, a significant difference was observed between patients with ID genotype and with II genotype (p = 0.018). Patients with ID genotype have been diagnosed as schizophrenics in early ages when compared to II genotype carriers. We also found a significant difference between II and ID genotype (p = 0.007) when the gender had taken into account, showing that the ID genotype carriers had an early onset to schizophrenia.

CONCLUSIONS

This association was more significant in male schizophrenia patients than females. Thus, this finding may constitute a novel biological support for the prior finding that onset of schizophrenia varies with gender. The results also showed that critical genetic vulnerability may be associated with the presence or absence of the ID genotype of DBH5'-ins/del.

The dopamine b-hydroxylase 19 bp insertion/deletion polymorphism was associated with first-episode but not medicated chronic schizophrenia

BACKGROUND

Numerous studies report dysfunctional dopaminergic and noradrenergic neurotransmission in the pathogenesis of schizophrenia. Dopamine beta-hydroxylase (DBH) is an intracellular enzyme catalyzing the conversion of dopamine to noradrenaline. Functional polymorphisms have been reported in the promoter region of DBH gene, including a 19 bp insertion/deletion polymorphism. The purpose of this study was to investigate whether there was an association between the functional polymorphism (DBH5'-Ins/Del) and schizophrenia in a Han Chinese population.

METHODS

This polymorphism was genotyped in 221 first-episode schizophrenics, 360 chronic schizophrenics and 318 healthy controls using a case-control design. We assessed their psychopathology using the Positive and Negative Syndrome Scale (PANSS).

RESULTS

We showed that the DBH5'-Ins/Del deletion (Del) allelic and genotypic frequencies were significantly lower in controls than first-episode of schizophrenics (FES) (both p < 0.001), but controls were not different from chronic schizophrenics. Furthermore, the PANSS positive symptom and total scores were significantly higher in FES with the Del/Del genotype than those with Ins/Del and Ins/Ins genotypes (all p < 0.05).

CONCLUSIONS

The DBH5'-Ins/Del polymorphism may play a role in susceptibility to the positive symptoms of FES and to these FES not progressing on to chronic schizophrenia.

Dopamine and the Management of Attentional Resources: Genetic Markers of Striatal D2 Dopamine Predict Individual Differences in the Attentional Blink

The attentional blink (AB)—a deficit in reporting the second of two target stimuli presented in close succession in a rapid sequence of distracters—has been related to processing limitations in working memory. Given that dopamine (DA) plays a crucial role working memory, the present study tested whether individual differences in the size of the AB can be predicted by differences in genetic predisposition related to the efficiency of dopaminergic pathways. Polymorphisms related to mesocortical and nigrostriatal dopaminergic pathways were considered, as well as polymorphisms related to norepinephrine (NE), a transmitter system that has also been suspected to play a role in the AB. In a sample of 157 healthy adults, we studied the dependency of the individual magnitude of the AB and the C957T polymorphism at the DRD2 gene (associated with striatal DA/D2 receptors), the DARPP32 polymorphism (associated with striatal DA/D1), the COMT Val158Met polymorphism (associated with frontal DA), DBH444 g/a and DBH5′-ins/del polymorphisms (polymorphisms strongly correlated with DA beta hydroxylase, the enzyme catalyzing the DA–NE conversion) and NET T-182C (a polymorphism related to the NE transporter). DRD2 C957T T/T homozygotes showed a significantly smaller AB, whereas polymorphisms associated with frontal DA and NE were unrelated to performance. This outcome pattern suggests a crucial role of the nigrostriatal dopaminergic pathway and of nigrostriatal D2 receptors, in particular, in the management of attentional resources.

Linkage analysis of plasma dopamine β-hydroxylase activity in families of patients with schizophrenia

Dopamine β-hydroxylase (DβH) catalyzes the conversion of dopamine to norepinephrine. DβH enters the plasma after vesicular release from sympathetic neurons and the adrenal medulla. Plasma DβH activity (pDβH) varies widely among individuals, and genetic inheritance regulates that variation. Linkage studies suggested strong linkage of pDβH to ABO on 9q34, and positive evidence for linkage to the complement fixation locus on 19p13.2-13.3. Subsequent association studies strongly supported DBH, which maps adjacent to ABO, as the locus regulating a large proportion of the heritable variation in pDβH. Prior studies have suggested that variation in pDβH, or genetic variants at DβH, associate with differences in expression of psychotic symptoms in patients with schizophrenia and other idiopathic or drug-induced brain disorders, suggesting that DBH might be a genetic modifier of psychotic symptoms. As a first step toward investigating that hypothesis, we performed linkage analysis on pDβH in patients with schizophrenia and their relatives. The results strongly confirm linkage of markers at DBH to pDβH under several models (maximum multipoint LOD score, 6.33), but find no evidence to support linkage anywhere on chromosome 19. Accounting for the contributions to the linkage signal of three SNPs at DBH, rs1611115, rs1611122, and rs6271 reduced but did not eliminate the linkage peak, whereas accounting for all SNPs near DBH eliminated the signal entirely. Analysis of markers genome-wide uncovered positive evidence for linkage between markers at chromosome 20p12 (multi-point LOD = 3.1 at 27.2 cM). The present results provide the first direct evidence for linkage between DBH and pDβH, suggest that rs1611115, rs1611122, rs6271 and additional unidentified variants at or near DBH contribute to the genetic regulation of pDβH, and suggest that a locus near 20p12 also influences pDβH.

Methylphenidate-induced psychosis in adult attention-deficit/hyperactivity disorder: report of 3 new cases and review of the literature

OBJECTIVE

We present 3 new cases of psychotic symptoms in patients with adult attention-deficit/hyperactivity disorder while regularly treated with a stimulant therapy with methylphenidate.

METHODS

Existing literature about this theme is reviewed, and potential mechanisms are discussed.

RESULTS AND CONCLUSIONS

Medication with methylphenidate should be avoided in patients with vulnerability to schizophrenia and in drug addiction, but reported cases without these risk factors demonstrate that a careful and regular psychiatric monitoring is essential in all patients treated with methylphenidate.

Association of tagging single nucleotide polymorphisms on 8 candidate genes in dopaminergic pathway with schizophrenia in Croatian population

AIM

To perform a comprehensive evaluation of association of common genetic variants in candidate genes in the dopaminergic pathway with schizophrenia in a sample from Croatian population.

METHODS

A case-control association study was performed on 104 unrelated patients with schizophrenia recruited from a psychiatric hospital in Zagreb and 131 phenotypically normal Croatian subjects. Forty-nine tagging single nucleotide polymorphisms (tagSNPs) in 8 candidate genes in the dopaminergic pathway were identified from the HapMap database and tested for association. Genotyping was performed using the SNPlex platform. Statistical analysis was conducted to assess allelic and genotypic associations between cases and controls using a goodness of fit chi(2) test and trend test, respectively; adjustment for multiple testing was done by permutation based analysis.

RESULTS

Significant allele frequency differences between schizophrenia cases and controls were observed at 4 tagSNPs located in the genes DRD5, HTR1B1, DBH, and TH1 (P<0.005). A trend test also confirmed the genotypic association (P<0.001) of these 4 tagSNPs. Additionally, moderate association (P<0.05) was observed with 8 tagSNPs on SLC6A3, DBH, DRD4, SLC6A4, and COMT.

CONCLUSIONS

Common genetic variants in genes involved in the dopaminergic pathway are associated with schizophrenia in the populations of Caucasian descent.

Association of variants in MANEA with cocaine-related behaviors

CONTEXT

Cocaine dependence (CD) and related behaviors are highly heritable, but no genetic association has been consistently demonstrated. A recent genome-wide study of drug dependence identified an association between cocaine-induced paranoia (CIP) and a single-nucleotide polymorphism (SNP) in the alpha-endomannosidase (MANEA) locus in a family-based sample of European Americans and African Americans.

OBJECTIVE

To conduct a comprehensive genetic association study of the MANEA locus with CD and CIP.

DESIGN

Genome-wide association study.

SETTING

Four university hospitals.

PARTICIPANTS

A total of 3992 individuals from 2 family-based and 2 case-control samples.

INTERVENTION

Participants were classified as having CD or CIP or as a control using the Semi-Structured Assessment for Drug Dependence and Alcoholism. They were genotyped for 11 SNPs spanning MANEA and its surrounding region.

MAIN OUTCOME MEASURE

Association of CD and CIP with individual SNPs and haplotypes.

RESULTS

Cocaine-induced paranoia was associated with 6 SNPs in the European American families and 9 SNPs in the African American families. The strongest evidence in the total sample of families was observed in 3 markers located in the promoter and 3' untranslated regions (P < .001). The association of MANEA SNPs with CD in both family samples was much weaker. In the African American case-control sample, multiple markers were significantly associated with CIP and CD; CIP and CD were also significantly associated with a 2-SNP haplotype in the European American case-control sample. The A allele of the 3' untranslated region SNP rs9387522 was associated with increased risk of CIP in all 4 data sets.

CONCLUSIONS

Our findings suggest that CD and associated behaviors may involve biological pathways not typically thought to be associated with brain metabolism.

Physiogenomic analysis of localized FMRI brain activity in schizophrenia

The search for genetic factors associated with disease is complicated by the complexity of the biological pathways linking genotype and phenotype. This analytical complexity is particularly concerning in diseases historically lacking reliable diagnostic biological markers, such as schizophrenia and other mental disorders. We investigate the use of functional magnetic resonance imaging (fMRI) as an intermediate phenotype (endophenotype) to identify physiogenomic associations to schizophrenia. We screened 99 subjects, 30 subjects diagnosed with schizophrenia, 13 unaffected relatives of schizophrenia patients, and 56 unrelated controls, for gene polymorphisms associated with fMRI activation patterns at two locations in temporal and frontal lobes previously implied in schizophrenia. A total of 22 single nucleotide polymorphisms (SNPs) in 15 genes from the dopamine and serotonin neurotransmission pathways were genotyped in all subjects. We identified three SNPs in genes that are significantly associated with fMRI activity. SNPs of the dopamine beta-hydroxylase (DBH) gene and of the dopamine receptor D4 (DRD4) were associated with activity in the temporal and frontal lobes, respectively. One SNP of serotonin-3A receptor (HTR3A) was associated with temporal lobe activity. The results of this study support the physiogenomic analysis of neuroimaging data to discover associations between genotype and disease-related phenotypes.

Dopamine genes and schizophrenia: case closed or evidence pending?

The dopamine hypothesis of schizophrenia (SZ) has motivated a large number of genetic association studies but few if any dopaminergic (DA) polymorphisms are accepted as credible risk factors at present. To evaluate whether dopamine-related genes have been investigated adequately, we surveyed public genetic databases and published SZ association studies with regard to 14 conventional DA genes and 7 selected dopamine-interacting proteins. We estimate that 325 polymorphisms would be required to evaluate the impact of common variation on SZ risk among Caucasian samples. To date, 98 polymorphisms have been analyzed in published association studies. We estimate that only 19 of these variations have been evaluated in samples with at least 50% power to detect an association of the effect size commonly found in genetically complex disorders. While it is possible that DA genes do not harbor genetic risk factors for SZ, our review suggests that satisfactory conclusions for most genes cannot be drawn at present. Whole-genome association studies have begun to fill this void, but additional analyses are likely to be needed. Recommendations for future association studies include analysis of adequately powered samples, judiciously selected polymorphisms, multiple ethnic groups, and concurrent evaluation of function at associated single-nucleotide polymorphisms.

Specificity of the effect of a nicotinic receptor polymorphism on individual differences in visuospatial attention

Cortical neurotransmitter availability is known to exert domain-specific effects on cognitive performance. Hence, normal variation in genes with a role in neurotransmission may also have specific effects on cognition. We tested this hypothesis by examining associations between polymorphisms in genes affecting cholinergic and noradrenergic neurotransmission and individual differences in visuospatial attention. Healthy individuals were administered a cued visual search task which varied the size of precues to the location of a target letter embedded in a 15-letter array. Cues encompassed 1, 3, 9, or 15 letters. Search speed increased linearly with precue size, indicative of a spatial attentional scaling mechanism. The strength of attentional scaling increased progressively with the number of C alleles (0, 1, or 2) of the alpha-4 nicotinic receptor gene C1545T polymorphism (n = 104). No association was found for the dopamine beta hydroxylase gene G444A polymorphism (n = 135). These findings point to the specificity of genetic neuromodulation. Whereas variation in a gene linked to cholinergic transmission systematically modulated the ability to scale the focus of visuospatial attention, variation in a gene governing dopamine availability did not. The results show that normal variation in a gene controlling a nicotinic receptor makes a selective contribution to individual differences in visuospatial attention.

Familiality in a five-factor model of schizophrenia psychopathology: findings from a 16-month follow-up study

We sought to examine stability associations between family history and variability of schizophrenia symptoms repeatedly examined during a naturalistic follow-up study. The Positive and Negative Syndrome Scale, the Insight and Treatment Attitudes Questionnaire, and the Abnormal Involuntary Movement Scale were administered to 69 patients with familial and 79 patients with sporadic schizophrenia, at hospital admission and at stabilization stage (about 16 months later). Analysis of covariance was applied to identify the association of symptom factors with familiality of schizophrenia. We found that schizophrenia patients with positive family histories had significantly higher dysphoric, activation and negative factors. However, familiality of activation and negative factors were dependent on additional variables such as age of onset (both factors), baseline ratings, insight, and side effects (negative factor). No significant association of family history with intensity of positive and autistic preoccupation factors was found. Familial schizophrenia is characterized by higher severity of dysphoric mood factors that may represent impaired emotional reactivity. It is suggested that dysphoric mood may be a useful phenotype for molecular genetic studies of schizophrenia with positive family history.

Comparison of microarray-based mRNA profiling technologies for identification of psychiatric disease and drug signatures

The gene expression profiles of human postmortem parietal and prefrontal cortex samples of normal controls and patients with bipolar disease, or human neuroblastoma flat (NBFL) cells treated with the mood-stabilizing drug, valproate, were used to compare the performance of Affymetrix oligonucleotide U133A GeneChips and Agilent Human 1 cDNA microarrays. Among those genes represented on both platforms, the oligo array identified 26-53% more differentially expressed genes compared to the cDNA array in the three experiments, when identical fold change and t-test criteria were applied. The increased sensitivity was primarily the result of more robust fold changes measured by the oligonucleotide system. Essentially all gene changes overlapping between the two platforms were co-directional, and ranged from 4 to 19% depending upon the amount of biological variability within and between the comparison groups. Q-PCR validation rates were virtually identical for the two platforms, with 23-24% validation in the prefrontal cortex experiment, and 56% for both platforms in the cell culture experiment. Validated genes included dopa decarboxylase, dopamine beta-hydroxylase, and dihydropyrimidinase-related protein 3, which were decreased in NBFL cells exposed to valproate, and spinocerebellar ataxia 7, which was increased in bipolar disease. The modest overlap but similar validation rates show that each microarray system identifies a unique set of differentially expressed genes, and thus the greatest information is obtained from the use of both platforms.