A serine to glycine substitution at position 9 in the extracellular N-terminal part of the dopamine D3 receptor protein: no role in the genetic predisposition to bipolar affective disorder

Polymorphisms in genes encoding dopamine signalling pathway and risk of alcohol dependence: a systematic review

BACKGROUND

Alcohol dependence (AD) is one of the major elements that significantly influence drinking pattern that provoke the alcohol-induced organ damage. The structural and neurophysiologic abnormalities in the frontal lobes of chronic alcoholics were revealed by magnetic resonance imaging scans. It is well known that candidate genes involved in dopaminergic pathway are of immense interest to the researchers engaged in a wide range of addictive disorders. Dopaminergic pathway gene polymorphisms are being extensively studied with respect to addictive and behavioral disorders.

METHODS

From the broad literature available, the current review summarizes the specific polymorphisms of dopaminergic genes that play a role in alcohol dependence.

RESULTS

No evidence indicating any strong association between AD and polymorphisms of dopamine pathway genes has emerged from the literature.

DISCUSSION

Further studies are warranted, considering a range of alcohol-related traits to determine the genes that influence alcohol dependence.

Case-control association analysis of dopamine receptor polymorphisms in alcohol dependence: a pilot study in Indian males

Background

Brain imaging studies and knock-out animal models have derived substantial abetment for dopamine receptor (DR) subtypes as potential candidates in susceptibility to addictive disorders, including alcohol dependence (AD). Various association studies that compared the frequencies of alleles of the dopamine D1, D2, D3 and D4 receptor genes between alcohol dependent and control subjects have produced suggestive results, though some of them are discordant in nature. In the absence of genetic data from Indian population, we evaluated genetic association of three polymorphisms namely rs4532 in DRD1, rs6280 in DRD3 and 120 bp duplication in 1.2 kb upstream region of DRD4 with AD.

Methods

A total of 90 cases (alcohol dependent males) and 122 age and ethnicity matched healthy male controls were recruited in the study by following DSM-IV criteria. Three polymorphisms, namely rs4532 in DRD1, rs6280 in DRD3 and 120 bp duplication in 1.2 kb upstream region of DRD4 were selected (based on minor allele frequency and available literature) for genotyping by PCR-RFLP/LP method. Allele and genotype frequencies of these genetic markers were compared using Pearson’s χ² test followed by risk assessment using odds ratio. Statistical analysis of clinical parameters such as AUDIT scores of case subjects was also performed.

Results

Statistically significant associations of polymorphisms in DRD1 and DRD4 with alcoholism were found.

Conclusions

Our results underscore that genetic variations in dopamine receptors D1 and D4 may influence genetic predisposition to alcoholism. Unavailability of comparative data from Indian population and small sample size necessitate replication of results in an independent cohort.

Meta-analysis of genetic association studies on bipolar disorder

Numerous candidate gene association studies of bipolar disorder (BP) have been carried out, but the results have been inconsistent. Individual studies are typically underpowered to detect associations with genes of small effect sizes. We conducted a meta-analysis of published candidate gene studies to evaluate the cumulative evidence. We systematically searched for all published candidate gene association studies of BP. We then carried out a random-effects meta-analysis on all polymorphisms that were reported on by three or more case-control studies. The results from meta-analyses of these genes were compared with the findings from a recent mega-analysis of eleven genome-wide association studies (GWAS) in BP performed by the Psychiatric GWAS Consortium (PGC). A total of 487 articles were included in our review. Among these, 33 polymorphisms in 18 genes were reported on by three or more case-control studies and included in the random-effects meta-analysis. Polymorphisms in BDNF, DRD4, DAOA, and TPH1, were found to be nominally significant with a P-value < 0.05. However, none of the findings were significant after correction for multiple testing. Moreover, none of these polymorphisms were nominally significant in the PGC-BP GWAS. A number of plausible candidate genes have been previously associated with BP. However, the lack of robust findings in our review of these candidate genes highlights the need for more atheoretical approaches to study the genetics of BP afforded by GWAS. The results of this meta-analysis and from other on-going genomic experiments in BP are available online at Metamoodics (http://metamoodics.igm.jhmi.edu).

Pharmacogenomic implications of variants of monoaminergic-related genes in geriatric psychiatry

Response to psychiatric medications in later life is highly heterogeneous and complex. Monoaminergic-related polymorphisms may influence medication response and susceptibility to side effects in elderly individuals. Individuals with the lower function short (S) allele of the serotonin transporter gene (SLC6A4) insertion/deletion (indel) promoter polymorphism (5-HTTLPR) have both increased the likelihood of adverse drug events and increased the need for higher antidepressant concentrations to obtain maximum antidepressant response. By contrast, carriers of the higher expression homozygous long allele (L/L) genotype may respond at lower concentrations. The differential role of these polymorphisms appears at early stages of treatment rather than in the final antidepressant outcome. Research findings suggest that the rs25531 SNP may influence functional expression of the L allele. Similarly, a variable number of tandem repeats in the second intron of the serotonin transporter gene may influence the expression of SLC6A4 and the implications of these variants may be influenced by aging. Two polymorphisms, rs2242466 (-182T/C) and rs5569 (1287G/A), in the norepinephrine transporter gene (SLC6A2 or NET) have been associated with antidepressant response. Studies in dopamine-related polymorphisms have focused on associations with neuroleptic-induced movement disorders. The rs1800497 variant (Taq1A) of the dopamine receptor D2 (DRD2) gene located in a noncoding 3´ region may regulate expression of D2 receptors. The rs6280 variant (Ser9Gly) of the dopamine receptor 3 (DRD3) gene may influence the binding affinity of D3 receptors as a result of serine to glycine substitution of the receptor protein. A multicenter collaborative research effort would be an effective strategy to increase sample sizes to further investigate how gene variants impact the pharmacodynamics and pharmacokinetics of psychotropic drugs in elderly persons.

The role of dopamine in bipolar disorder

OBJECTIVE

Despite effective pharmacological treatments for bipolar disorder, we still lack a comprehensive pathophysiological model of the illness. Recent neurobiological research has implicated a number of key brain regions and neuronal components in the behavioural and cognitive manifestations of bipolar disorder. Dopamine has previously been investigated in some depth in bipolar disorder, but of late has not been a primary focus of attention. This article examines the role of dopamine in bipolar disorder, incorporating recent advances into established models where possible.

METHODS

A critical evaluation of the literature was undertaken, including a review of behavioural, neurochemical, receptor, and imaging studies, as well as genetic studies focusing on dopamine receptors and related metabolic pathways. In addition, pharmacologic manipulation of the central dopaminergic pathways and comparisons with other disease states such as schizophrenia were considered, principally as a means of exploring the hypothesised models.

RESULTS

Multiple lines of evidence, including data from pharmacological interventions and structural and functional magnetic resonance imaging studies, suggest that the dopaminergic system may play a central role in bipolar disorder.

CONCLUSION

Future research into the pathophysiological mechanisms of bipolar disorder and the development of new treatments for bipolar disorder should focus on the dopaminergic system.

Direct analysis of candidate genes in impulsive behaviours

Antisocial behaviour is both heterogeneous and the product of interacting genetic and environmental factors acting at different levels of causation. Heritability studies show that individual differences in predisposition to antisocial behaviour are transmitted vertically in families by genetic mechanisms. Owing to aetiological heterogeneity and complexity, study of a variety of other behavioural phenotypes may shed more light on the antecedents of antisocial behaviour than direct studies on antisocial behaviour. Identification of genetic vulnerability factors would clarify mechanisms of vulnerability and the role of the environment. Direct gene analysis and genetic linkage analysis have identified structural variants in genes involved in neurotransmitter function, and some progress has been made towards relating these genetic variants to antisocial personality and other behaviours. Thyroid hormone receptor variants can cause attention deficit/hyperactivity disorder, and a monoamine oxidase A variant leads to aggressive behaviour in one family. Direct gene analyses have revealed non-conservative amino acid substitutions and structural variants (generally rare) at DRD2, DRD3 and DRD4 dopamine receptors and 5-HT1A, 5-HT2A, 5-HT2C and 5-HT7 serotonin receptors. The stage is set to identify the phenotypic significance of these as well as genetic variants at other loci which may be relevant as candidate genes for antisocial behaviour and related behavioural differences.

Major affective disorders and schizophrenia: a common molecular signature?

Psychiatric disorders, including affective disorders (AD) and schizophrenia (SZ) are among the most common disabling brain diseases in Western populations and result in high costs in terms of morbidity as well as mortality. Although their etiology and pathophysiology is largely unknown, family-, twin-, and adoption studies argue for a strong genetic determination of these disorders. These studies indicate that there is between 40 and 85% heritability for these disorders but point also to the importance of environmental factors. Therefore, any research strategy aiming at the identification of genes involved in the development of AD and SZ should account for the complex nature (multifactorial) of these disorders. During the last decade, molecular genetic studies have contributed a great deal to the identification of genetic factors involved in complex disorders. Here we provide a comprehensive review of the most promising genes for AD and SZ, and the methods and approaches that were used for their identification. Also, we discuss the current knowledge and hypotheses that have been formulated regarding the effect of variations on protein functioning as well as recent observations that point to common molecular mechanisms.

No association between D3 dopamine receptor (DRD3) alleles and cocaine dependence

Cocaine is thought to act in the brain primarily by blocking dopamine re-uptake. The dopamine D3 receptor (genetic locus DRD3) is localized to brain regions that have been implicated in the reinforcing effects of a number of substances of abuse, including cocaine. The DRD3 coding region contains a polymorphism identifiable as a polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP). This polymorphism leads to an amino acid substitution at position 9 in the extracellular N-terminus of the D3 dopamine receptor. We examined alleles of the DRD3 gene in cocaine dependence using a genetic association strategy in samples of 62 white and 62 black cocaine-dependent individuals. Comparisons were made with local (Connecticut) control subjects for both groups, and with a larger sample of literature controls (for the white subjects) and a contrast group of schizophrenic patients (for the black subjects). No association was found between cocaine dependence and DRD3 alleles in either group (Bonferroni corrected). There was a significant difference in allele frequency between whites and blacks. These results are consistent with no role for genetic variation of the D3 dopamine receptor in susceptibility to cocaine dependence.

Characterisation, mutation detection, and association analysis of alternative promoters and 5' UTRs of the human dopamine D3 receptor gene in schizophrenia

The dopamine D(3) receptor gene (DRD3) is a candidate for a number of psychiatric conditions including schizophrenia, bipolar disorder and alcohol and drug abuse. Previous studies have reported associations between polymorphisms in DRD3 and these disorders, but these findings may have reflected linkage disequilibrium with pathogenic variants that are further upstream. We have isolated and sequenced approximately 9 kb of genomic sequence upstream of the human DRD3 translational start site. Using 5' RACE, we have identified within this region three additional exons and two putative promoter regions which show promoter activity in three different cell lines. A 5' UTR identified only in lymphoblasts is spread over three exons and is 353 bp long. A second 5' UTR, found in adult and fetal brain, lymphocytes, kidney and placenta is spread over two exons and is 516 bp long. A 260-bp sequence within this 9 kb corresponds to a previously reported EST, but corresponding mRNA could not be found in the tissues above. The EST, 5' UTRs and putative promoter regions have been analysed for polymorphisms, revealing 10 single nucleotide polymorphisms, seven of which were tested for association in a large sample of unrelated patients with schizophrenia and matched controls. No associations were observed with schizophrenia. In addition we failed to replicate previous findings of association with homozygosity of the Ser9Gly variant. The results from this study imply that neither the coding nor the regulatory region of DRD3 plays a major role in predisposition to schizophrenia.

Dopamine receptor genes and migraine with and without aura: an association study

OBJECTIVE

To investigate the role of the dopamine receptor genes, DRD1, DRD3, and DRD5 in the pathogenesis of migraine.

BACKGROUND

Migraine is a chronic debilitating disorder affecting approximately 12% of the white population. The disease shows strong familial aggregation and presumably has a genetic basis, but at present, the type and number of genes involved is unclear. The study of candidate genes can prove useful in the identification of genes involved in complex diseases such as migraine, especially if the contribution of the gene to phenotypic expression is minor. Genes coding for proteins involved in dopamine metabolism have been implicated in a number of neurologic conditions and may play a contributory role in migraine. Hence, genes that code for enzymes and receptors modulating dopaminergic activity are good candidates for investigation of the molecular genetic basis of migraine.

METHODS

We tested 275 migraineurs and 275 age- and sex-matched individuals free of migraine. Genotypic results were determined by restriction endonuclease digestion of polymerase chain reaction products to detect DRD1 and DRD3 alleles and by Genescan analysis after polymerase chain reaction using fluorescently labelled oligonucleotide primers for the DRD5 marker.

RESULTS

Results of chi-square statistical analyses indicated that the allele distribution for migraine cases compared to controls was not significantly different for any of the three tested gene markers (chi2 = 0.1, P =.74 for DRD1; chi2 = 1.8, P =.18 for DRD3; and chi2 = 20.3, P =.08 for DRD5).

CONCLUSIONS

These findings offer no evidence for allelic association between the tested dopamine receptor gene polymorphisms and the more prevalent forms of migraine and, therefore, do not support a role for these genes in the pathogenesis of the disorder.

Allelic variation of a BalI polymorphism in the DRD3 gene does not influence susceptibility to bipolar disorder: results of analysis and meta-analysis

Bipolar disorder is a major psychiatric illness that has evidence for a significant genetic contribution toward its development. In recent years, the BalI RFLP (restriction fragment length polymorphism) in the dopamine D3 receptor gene has been examined as a possible susceptibility factor for both schizophrenia and bipolar disorder. While analysis in schizophrenia has produced examples of increased homozygosity in patients, less encouraging results have been found for bipolar disorder. Recently, however, a family-based association study has found a significant excess of allele 1 and allele 1-containing genotypes in transmitted alleles to bipolar probands over nontransmitted controls. In a large bipolar case control sample (n = 454), we have been unable to replicate the family-based association study (chi-square = 0.137, P = 0.71, 1 df) or detect an effect similar to the positive homozygosity findings in schizophrenia (chi-square = 0.463, P = 0.50, 1 df). A meta-analysis of previous association studies also revealed no difference in allele distributions between bipolar patients and controls for this polymorphism in ethnically homogeneous samples (odds ratio, OR, = 1.04; P = 0.60; 95% confidence interval, CI, = 0.89-1.20). In view of this evidence, we conclude that variation at the BalI RFLP is not an important factor influencing the susceptibility to bipolar disorder. It remains possible, however, that other sequence variations within the DRD3 gene could play a role.

Polymorphisms in dopamine receptors: what do they tell us?

Many genetic studies have focussed on dopamine receptors and their relationship to neuropsychiatric disease. Schizophrenia, bipolar disorder, and substance abuse have been the most studied, but no conclusive linkage or association has been found. The possible influence of dopamine receptor variants on drug response has not received as much attention. While there is some evidence that polymorphisms and mutations in dopamine receptors can alter functional activity and pharmacological profiles, no conclusive data link these gene variants to drug response or disease. The lack of unequivocal findings may be related, in part, to the subtle changes in receptor pharmacology that these polymorphisms and mutations mediate. These subtle effects may be obscured by the influence of genes controlling drug metabolism and kinetics. Further insight into the pharmacogenetics of dopamine receptors may require not just more studies, but novel approaches to the study of complex genetic traits and diseases.

Linkage of mood disorders with D2, D3 and TH genes: a multicenter study

BACKGROUND

It has been suggested that the dopaminergic system is involved in the pathophysiology of mood disorders. We conducted a multicenter study of families with mood disorders, to investigate a possible linkage with genes coding for dopamine receptor D2, dopamine receptor D3 and tyrosine hydroxylase (TH).

METHODS

Twenty three mood disorder pedigrees collected within the framework of the European Collaborative Project on Affective Disorders were analyzed with parametric and non-parametric linkage methods. Various potential phenotypes were considered, from a narrow (only bipolar as affected) to a broad (bipolar+major depressive+schizoaffective disorders) definition of affection status.

RESULTS

Parametric analyses excluded linkage for all the candidate genes, even though small positive LOD (Limit of Detection) scores were observed for TH in three families. Non-parametric analyses yielded negative results for all markers.

CONCLUSION

The D2 and D3 dopamine receptors were, therefore, not a major liability factor for mood disorders in our sample, whereas TH may play a role in a subgroup of patients.

Searching high and low: a review of the genetics of bipolar disorder

OBJECTIVES

To review the methodologies and findings in the genetics of bipolar disorder (BPD), and to suggest future directions for research.

METHODS

Reports of family, twin, adoption, linkage, association, cytogenetic, and animal model studies, and segregation analyses in English, were identified from multiple MEDLINE searches. Hand searches were carried out in bibliographies from review articles.

RESULTS

Family, twin, and adoption studies have provided strong evidence for a genetic etiology in BPD. Early reports of linkage of BPD to DNA markers at several chromosomal sites have not proven robust, perhaps because of the complex nature of BPD inheritance. However, linkage findings in the 1990s, on chromosomes 18, 21q, 12q, and 4p, have provided leads that are being pursued through both genetic and physical mapping. No gene has yet been definitively implicated in BPD.

CONCLUSIONS

Strategies for increasing the power to detect BPD genes include: (1) dividing the phenotype into genetically meaningful subtypes to decrease heterogeneity: and (2) ascertaining a very large family sample--a multicenter study now in progress will collect 700 bipolar I sibling pairs. BPD may result from several genes acting in concert so that new multilocus statistical methods could enhance the capacity to detect loci involved. Family-based association studies using a very large number of newly identified single nucleotide polymorphisms (SNPs) may allow for more efficient screening of the genome. As the Human Genome Project approaches its goal of isolating all genes by 2003, the data generated is likely to speed identification of candidate BPD genes.

No association between dopamine D1, D2, and D3 receptor genes and manic-depressive illness

BACKGROUND

The dopaminergic receptor genes are candidate genes for manic-depressive illness (MDI). To test this putative involvement we used a case-control study on samples from the native population of the northwest part of France.

METHODS

Fifty patients for D1 and D2, 61 patients for D3, and 86-223 controls were tested.

RESULTS

No significant association was found between allelic frequencies or genotype counts and MDI, even when the data were pooled with those from published studies.

CONCLUSIONS

Single mutations of either of the studied receptor genes are not major determinants of MDI.

Association study of bipolar disorder with candidate genes involved in catecholamine neurotransmission: DRD2, DRD3, DAT1, and TH genes

Despite strong evidence for genetic involvement in the etiology of affective disorders (from twin adoption and family studies), linkage and association methodologies are still exploring the nature of genetic factors in these diseases. Interesting testable hypotheses have been described, including candidate genes involved in catecholamine neurotransmission. We studied 69 bipolar patients and 69 matched controls (for age, sex, and geographical origin) for association and linkage disequilibrium with DNA markers at the following genes: the tyrosine hydroxylase gene, dopamine transporter gene, and dopamine D2 and D3 receptor genes. Association and linkage disequilibrium were excluded between bipolar affective disorder and these four candidate genes in our sample.

Association study of schizophrenia and the dopamine D3 receptor gene locus in two independent samples

Using a case-control design, an association of schizophrenia with the dopamine D3 receptor gene (D3RG) locus was investigated. Initial analysis of pooled results from published studies revealed a significant excess of individuals homozygous for either allele among the patients. The association was next tested in two cohorts ascertained independently at Pittsburgh, Pennsylvania and at Houston, Texas. The Pittsburgh sample was comprised of patients with schizophrenia (DSM-III-R) (n = 130). The controls belonged to two groups: adults screened for the absence of substance abuse or major psychiatric illness (n = 128), and neonates (n = 160). Multivariate analysis suggested an association with allele 1 of the biallelic D3RG polymorphism in comparison with the adult, but not the neonatal, controls. The association was most marked among Caucasian patients with a family history of schizophrenia (odds ratio 13.69, confidence intervals 1.80, 104.30). Survival analysis suggested an earlier age of onset among male patients homozygous for allele 2. The Houston cohort included Caucasian patients with schizophrenia or schizoaffective disorder (DSM-III-R criteria, n = 50), and normal controls matched for gender (n = 51). In this group, no significant associations were noted among all the patients or among subgroups of patients based on family history or age of onset. Possible reasons for the discordant results are discussed.

Dopamine D2, D3 and D4 receptor and transporter gene polymorphisms and mood disorders

Disturbances in dopaminergic systems have been implicated in the etiology of mood disorders. Although genetic factors also play an important role, no major gene has been identified. We conducted an association study using the dopamine D2, D3 and D4 receptor, and transporter gene polymorphisms, comparing 101 mood-disorder patients (52 bipolar and 49 unipolar) and 100 controls. Our results suggest that there is a significant association between the dopamine D4 receptor gene and mood disorders, especially major depression, but no association between the other polymorphisms and mood disorders. Further investigations are needed to clarify the clinical significance of this association in the pathophysiology of mood disorders.

Dopamine D3 receptor Gly9/Ser9 polymorphism and schizophrenia: no increased frequency of homozygosity in German familial cases

Disturbances in the dopaminergic transmission have been implicated in the etiology of schizophrenia. Recently, an association of schizophrenia with increased homozygosity of a Gly9/Ser9 polymorphism in the dopamine D3 receptor gene (DRD3) has been reported (Crocq et al., 1992; Mant et al., 1994). This finding reflected a departure from the Hardy-Weinberg equilibrium in the genotype distribution observed in schizophrenic patients. The effect was found to be at its strongest in patients with a high familial loading. In the present study, we tried to replicate this finding in a sample of 146 German patients with a DSM-III-R diagnosis of schizophrenia. All patients had a positive family history of major psychiatric disorder including 70 patients with a family history of schizophrenia. Given our sample size, we have a power of 99.8% to detect 2. deviation from the Hardy-Weinberg equilibrium of the reported magnitude. However, we found no evidence of an excess of homozygosity in our schizophrenic patients. This seems to indicate that homozygosity for the Gly9/Ser9 polymorphism at the DRD3 locus is unlikely to confer susceptibility to schizophrenia in the German population. This held true whether the psychiatric diagnoses in the affected relatives of the patient samples was established by the family history or family interview method.

Identifying alcoholism vulnerability alleles

Identification of vulnerability alleles is one starting point for elucidating the web of interactions leading to alcoholism so that treatment and prevention can be improved. Heritability studies indicate that vulnerability alleles exist. Two molecular approaches for identifying them, direct analysis of candidate genes and genetic linkage, are highlighted in this review. Methodological problems that have been partially addressed and limitations for the applicability of the genetic findings are discussed.

A dopamine D3 receptor genotype is associated with hyperandrogenic chronic anovulation and resistant to ovulation induction with clomiphene citrate in female Hispanics

OBJECTIVE

To determine if dopamine (D3) receptor genotypes are associated with anovulation and response to ovulation induction with clomiphene citrate.

DESIGN

Clinical and laboratory characteristics of anovulatory patients and ovulatory controls were compared with findings at the DNA level.

SETTING

An outpatient clinic at an university medical center.

PATIENTS

One hundred eighty human Hispanic female volunteers (130 of these with documented ovulatory status) were studied.

INTERVENTIONS

Genomic DNAs were extracted from each patient. Polymerase chain reaction with subsequent restriction digest was performed to analyze the D3 receptor allele status (two possible alleles).

MAIN OUTCOME MEASURES

Menstrual history, serum T, and midluteal serum Ps from spontaneous and clomiphene cycles were correlated with D3 receptor genotype.

RESULTS

Hispanic females with the 22 genotype compared with the other genotypes (11 and 12) were more likely to have irregular menses, an elevated serum T (> or = 70 ng/dL [conversion factor to SI unit, 3.467]), and hyperandrogenic chronic anovulation. These patients tended to be resistant to ovulation induction requiring a significantly higher dose of clomiphene to achieve an ovulatory response (22 genotype [mean +/- SEM] [140.0 +/- 19.0 mg] versus 11 [77.1 +/- 17.5 mg] or 12 [69.2 +/- 13.1 mg]). This effect was independent of patient age, weight, or serum T level.

CONCLUSIONS

Hyperandrogenic chronic anovulation may have a genetic component. Genetic analysis may be useful in predicting resistance to ovulation induction with clomiphene.

No allelic association between Parkinson's disease and dopamine D2, D3, and D4 receptor gene polymorphisms

Parkinson's disease is thought to be caused by a combination of unknown environmental, genetic, and degenerative factors. Evidence from necropsy brain samples and pharmacokinetics suggests involvement of dopamine receptors in the pathogenesis or pathophysiology of Parkinson's disease. Genetic association studies between Parkinson's disease and dopamine D2, D3 and D4 receptor gene polymorphisms were conducted. The polymorphism was examined in 71 patients with Parkinson's disease and 90 controls. There were no significant differences between two groups in allele frequencies at the D2, D3, and D4 dopamine receptor loci. Our findings do not support the hypothesis that susceptibility to Parkinson's disease is associated with the dopamine receptor polymorphisms examined.

No evidence of association between dopamine D4 receptor variants and bipolar affective disorder

Disturbance in the dopamine neurotransmitter system has been implicated in the pathogenesis of affective disorder. In this study, we examine the possibility that functional variants of the recently cloned dopamine D4 receptor gene contribute to the genetic component of manic depression. The polymorphism, a 48 bp tandem repeat coding for part of the third cytoplasmic loop, was detected using a PCR based method. In a first sample of 57 patients and 59 controls, we found allele 7 to be in excess in the patients. In contrast, allele 3 was less frequent in patients. A second, larger sample of 90 patients and 91 controls was utilized to test these hypotheses. Data from the two samples were then pooled together for further analyses. We calculated the power of our samples, and if the frequency of 7 repeat allele obtained from sample 1 is true, i.e., 25% (28/114) for patients and 14% (16/118) for controls, then the power of the combined sample is 62% at 5% (two-tailed) significance level. However, both observations were not replicated; we therefore conclude that variations in this repeat at the DRD4 gene do not contribute to the genetic component of manic depression.

Catecholamine metabolism and psychiatric or behavioral disorders

A wealth of pharmacological data point to the involvement of catecholamine metabolism in a number of psychiatric and behavioral disorders. Furthermore, evidence points to many of these affective disorders having a moderate to large genetic component. These observations have provided the impetus to search for differences between individuals in the structure and regulatory elements of genes involved in catecholaminergic neurotransmission. The recent finding that a mutation in the structural gene for the enzyme monoamine oxidase A is associated, in several males of a large kindred, with borderline mental retardation and abnormal behavior is an important breakthrough in the field. Other promising results concern the tyrosine hydroxylase gene in manic depressive illness and the dopamine D2 receptor in alcoholism. These studies, their potential significance and difficulties in dealing with such complex disorders are discussed.