Association of dopamine D2 receptor molecular variant with schizophrenia

Step-wise analysis of polymorphisms in the human dopamine D2 receptor gene

Evolutionary analysis of neurotransmitter receptor systems has previously focused on interspecies differentiation. Recently, emphasis has shifted to intragenic evolution within a single species and the functional relevance associated with intraspecies variations. For example, multiple polymorphisms have been identified within the human dopamine D2 receptor (DRD2) gene, many of which have been used in clinical association studies. In an attempt to evaluate the intragenic evolution of the DRD2 gene, genotypes from 116 humans were determined using five biallelic markers which reside within a 30 kb span of the DRD2 gene, that are non-polymorphic in other higher order primates. Only seven different haplotypes, out of a theoretical maximum of 32, were present in the study group of 232 chromosomes. Moreover, five of the seven haplotypes accounted for 99% (n = 230/232) of the human haplotypes. A phylogenetic tree was generated from the haplotypic data using a maximum parsimony algorithm. The relationship of the haplotypes within the phylogenetic tree is consistent with a progressive step-wise nucleotide conversion within the human gene. These data indicate that specific haplotypic subtypes of the human DRD2 gene exist within the human population and allow for the possibility that functional differences may exist between the DRD2 subtypes. Therefore, future studies focused on a functional analysis of the entire human DRD2 haplotype, as opposed to individual polymorphisms, may provide important insights into the functional relevance of molecular variations within the human DRD2 gene.

European Multicentre Association Study of Schizophrenia: a study of the DRD2 Ser311Cys and DRD3 Ser9Gly polymorphisms

As part of the European Multicentre Association Study of Schizophrenia (EMASS), we studied polymorphisms in the dopamine DRD2 and DRD3 receptor genes. The EMASS collaboration was established to create a large, statistically powerful sample of schizophrenic patients and controls from different European centres. Previous studies have suggested associations between schizophrenia and the Ser311Cys polymorphism in exon 7 of the dopamine DRD2 receptor gene [Arinami et al., (1994): Lancet 343:703-704] and a polymorphism Ser9gly in exon 1 of the dopamine DRD3 receptor gene [Crocq et al. (1992): J Med Genet 29:858-860]. We tested for these associations in samples of 373 and 413, and 311 and 306 patients and controls, respectively. We found no evidence for allelic association between schizophrenia and the Cys311 variant of the DRD2 receptor gene and no homozygotes for this variant were observed by any group. However, an excess of homozygotes for both alleles of the DRD3 polymorphism was observed in schizophrenic patients (chi2 = 8.54, P = 0.003, odds ratio = 1.64, 95% CI = 1.18-2.29). We also observed a significant excess of the 1-1 (Ser9Ser) genotype (chi2 = 8.13, P = 0.004, odds ratio = 1.7, 95% CI = 1.18-2.4). No evidence of heterogeneity between samples was detected and there was no evidence of an allelic association. These findings suggest that the rare Cys311 variant in exon 7 of the DRD2 receptor gene does not play a role in the pathogenesis of schizophrenia in European populations. Currently, our results do support the previous findings of an association between increased homozygosity of the Ser/Gly variant of the Dopamine D3 receptor gene and schizophrenia.

An association study between the Cys311 variant of dopamine D2 receptor gene and schizophrenia in the Okinawan population

Neuroleptic drugs have a high affinity for the dopamine D2 receptor (DRD2); therefore DRD2 is thought to be a candidate gene for schizophrenia. Arinami et al. have reported a positive association between schizophrenia and the Cys311 variant of the DRD2 gene. We determined the allele frequency of this polymorphism in 78 Okinawan schizophrenic patients and 112 control subjects. The patients and controls did not differ significantly in allele frequencies of Cys311.

Neurochemical studies of schizophrenia in Japan

Neurobiological research in schizophrenia has been hampered by several confounding factors such as the heterogeneity of the illness and the paucity of biological markers. Recent progress in research methods, however, has enabled the improvement in our understanding its pathophysiology. This paper reviews recent neurochemical investigations of schizophrenia and its animal models which were conducted in Japan in the last decade. The research areas reviewed are (i) monoamine and their metabolites in body fluids, (ii) phospholipids and prostaglandins, (iii) neurochemistry in autopsy brains, (iv) immunological measures, (v) magnetic resonance spectroscopy, (vi) regional cerebral blood flows (rCBF), (vii) molecular genetics, and (viii) animal models. It is worth noting that there exist abnormalities of amino acidergic (glutamatergic and GABAergic) neurotransmission as well as monoaminergic (dopaminergic and serotonergic) one in postmortem schizophrenic brains. These abnormalities and also the findings of altered rCBF indicate the existence of disturbed neuronal circuits that contribute to the diverse symptoms of schizophrenia. Also, dysfunction of membrane phospholipids derived from studies on magnetic resonance spectroscopy may underlie negative symptoms in schizophrenia. Given that schizophrenia is considered to comprise a group of disorders with a diverse heterogeneity of etiologies, research in the next decade is expected to identify putative genes that are involved in vulnerability to schizophrenic phenotype.

Linkage and association of a functional DRD2 variant [Ser311Cys] and DRD2 markers to alcoholism, substance abuse and schizophrenia in Southwestern American Indians

Alcoholism is one of a group of common psychiatric diseases which are well-defined clinically and strongly influenced genetically, but which are likely to be highly heterogeneous in causation, genetically and otherwise. Dopamine is a key neurotransmitter in drug-mediated reinforcement. Based on association studies with the Taq1A downstream marker, the D2 dopamine receptor has been proposed to be the "Reward Deficiency Syndrome Gene." Ser311Cys, a naturally occurring variant which largely inactivates transduction after D2 receptor activation, was abundant (0.16) in a Southwestern American Indian population we studied. Therefore, we were able to provide a critical test of the D2 hypothesis of vulnerability to alcoholism by evaluating Ser311Cys and also the intron-2 STR and Taq1A markers at this locus in a total of 459 subjects, including 373 sib pairs, from large families. The result is that neither alcoholism, substance use disorders nor schizophrenia show a relationship to Ser311Cys genotype, even when the 15 Cys311/Cys311 homozygous individuals are compared to others. Furthermore, sib pair analysis incorporating information across all three sib pair categories: concordant affected, discordant and concordant unaffected revealed no effect of DRD2 genotype or haplotype on alcoholism or substance use disorder.

No association of the Ser/Cys311 DRD2 molecular variant with schizophrenia using a classical case control study and the haplotype relative risk

Arinami et al. (1994) reported an association between the Ser311/Cys311 variant of the DRD2 gene and schizophrenia in a Japanese population. We did not find statistically significant differences in the distribution of the allele frequencies between schizophrenics (103) and controls (97) in a case-control sample (chi 2 = 2.07; p = 0.150) or in 64 nuclear families with the haplotype relative risk (HRR) design (chi 2 = 0.13; p = 0.718). Our results seem to exclude a main involvement of this variant of the dopamine D2 receptor gene in the etiopathogenesis of schizophrenia.

Antagonist binding characteristics of the Ser311-->Cys variant of human dopamine D2 receptor in vivo and in vitro

We report in vivo and in vitro antagonist binding characteristics of the naturally occurring Ser311-->Cys variant of the human D2 dopamine receptor. Striatal receptor binding characteristics in vivo were measured with positron emission tomography and the D2 antagonist [11C]raclopride. The in vitro affinity of raclopride for the Ser311-->Cys variant and the wild type receptor was studied in membrane binding assays from stably transfected cell lines. One healthy male carrying the heterozygous Ser311-->Cys (TCC-->TGC) substitution was identified with denaturing gradient gel electrophoresis and DNA sequencing. The striatal D2 receptor binding characteristics in vivo in this subject were normal. This was supported by the in vitro data as the Ki values of raclopride for the Ser311-->Cys variant and the wild type receptor were identical. Our data suggest that the Ser311-->Cys variant of the human D2 receptor does not influence antagonist-receptor recognition in vivo or in vitro.

A critical review of genetic studies of schizophrenia. II. Molecular genetic studies

Recent molecular genetic studies of schizophrenia have, until now, been unable to demonstrate any specific major gene for schizophrenia. On the contrary, linkage and association studies have yielded almost exclusively negative or contradictory results. Such studies have involved certain candidate genes, such as the genes for dopamine receptors and other brain neurotransmitters. Some of these candidate genes have now actually been excluded as specific aetiological factors in schizophrenia. Similarly, studies searching for a major gene for susceptibility to schizophrenia involving the whole human genome or large parts of chromosomes have not yielded unambiguously positive results. However, the most recent empirical evidence suggests that many polygenes, acting together, could constitute a risk factor for schizophrenia. It is thus most probable that genetic susceptibility to schizophrenic psychoses is polygenic, and that their effects are dependent on interaction with physical and psychosocial environmental factors.

Polymorphisms of dopamine D2-like (D2, D3, and D4) receptors in schizophrenia

The result of most association studies and linkage analyses have suggested a negative association between schizophrenia and D2-like (D2, D3, and D4) receptor polymorphisms. Although the polymorphisms of the D2-like receptor in themselves may not account for the etiology of schizophrenia, they can contribute to the severity of the symptoms. Thus, we studied the associations between the polymorphisms and their combinations, and the vulnerability of schizophrenics. Fragments of the D2-like receptor genes were amplified by means of the polymerase chain reaction, and the polymorphisms were identified by the restriction fragment length polymorphism and single-stranded conformation polymorphism methods. There were no statistically significant differences in the polymorphisms and their combinations between schizophrenics and controls. Schizophrenics with D4E1(A1/A2), which contains 2 and 1 tandem repeats of a 12-base-pair sequence in exon 1, had a lower total positive symptom score before medication than schizophrenics with D4E1(A1/A1). There was no association between the polymorphisms and negative symptoms.

Dopamine D2 receptor gene (DRD2) haplotypes in Caucasians

The human dopamine D2 receptor gene (DRD2) is considered a candidate gene for neuro-psychiatric diseases. We typed three new DNA sequence variants in DRD2 intron 4, intron 6 and exon 8, in combination with the known TaqI A restriction fragment length polymorphism (RFLP) and exon 7 311Ser/Cys in 106 unrelated psychiatrically healthy Caucasians. Based on the genotypic data we delineated 10 distinct DRD2 haplotypes and their genetic relationship. Our data provide evidence that the Taq A1 allele and the 311Cys variant are components of different groups of haplotypes though both variants have been speculated to be associated with alcoholism or schizophrenia in recent studies. Therefore we conclude that the prior knowledge of the frequencies and genetic relationships of DRD2 haplotypes will lead to the selection of more suitable intragenic markers for future association studies.

Functional analysis of the human D2 dopamine receptor missense variants

The human dopamine D2 receptor gene (DRD2) has three polymorphic variants that predict the amino acid substitutions Val96 --> Ala, Pro310 --> Ser, and Ser311 --> Cys in the receptor protein. We have investigated the ligand binding and signal transduction properties of these human D2 receptor variants by stably expressing them in cultured mammalian cells. The Cys311 and Ser310 variants of the human D2 receptor, which involve substitutions located in the third cytoplasmic loop, were markedly less effective in inhibiting cAMP synthesis than the most prevalent form (Pro310, Ser311). Despite this difference, the Cys311 and Ser310 variants couple to G proteins in CHO-K1 (Chinese hamster ovary) cells. The impairment of the Cys311 and Ser310 variants to inhibit cAMP levels thus appears to result from a reduced ability of those variant receptors to activate the appropriate Gi-like protein. The demonstration of substantial functional differences between DRD2 gene variants found in the human population might have important pharmacological implications given the widespread use of D2 receptor blocking drugs in the treatment of schizophrenia and other psychiatric disorders.

Dopamine DRD2/Cys311 is not associated with chronic schizophrenia

A mutation in the DRD2 receptor gene has been reported in association with schizophrenia in Japanese and Caucasian populations. The variation, Ser to Cys at codon 311, occurs in the third intracellular loop of the receptor and is therefore putatively functional. We report the results of screening US Caucasian schizophrenic and nonschizophrenic populations. We detected the occurrence of the DRD2 Cys311 variant in both schizophrenics and controls. Our data demonstrates no significant difference between the frequency of Cys311 in Caucasian schizophrenic and non-schizophrenic populations, indicating no association with schizophrenia.

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.

No association of dopamine D2 receptor molecular variant Cys311 and schizophrenia in Chinese patients

A serine-to-cysteine mutation of dopamine D2 receptor at codon 311 (Cys311) was found to have higher frequency in schizophrenic patients than in normal controls in Japanese by Arinami et al. [1994: Lancet 343: 703-704]. The Cys311 allele was found to be associated with patients with younger age-of-onset, positive family history, and more positive symptoms. To investigate the possible involvement of Cys311 in schizophrenia in the Chinese population, 114 unrelated Taiwanese Chinese schizophrenic patients with positive family history and 88 normal controls were genotyped for Cys311. Four patients and 5 normal controls were heterozygotes of Ser311/Cys311; no homozygotes of Cys311 were identified in either group. The allele frequencies of Cys311 in Chinese schizophrenic patients and normal controls were 2% and 3%, respectively. No significant difference was detected between the two groups. Our results do not support the argument that the Cys311 allele of DRD2 poses a genetic risk for certain types of schizophrenia in Chinese populations.

No evidence for association of dopamine D2 receptor variant (Ser311/Cys311) with major psychosis

We investigated a variant of the dopamine D2 receptor gene (Ser311/Cys311 substitution) in Caucasian patients with schizophrenia (n = 273), delusional disorder (n = 62), bipolar I affective disorder (n = 63), and controls (n = 255). No evidence for association between the receptor variant and any of the diseases was found, even when patients with younger age-of-onset (< 25 years) were compared with controls. Furthermore, in a subgroup of schizophrenia patients whom we assessed for negative symptoms, those with the Cys allele did not differ from the remainder of the group. Also, the bipolar affective disorder patients with psychotic features did not show evidence for association with the receptor variant. Thus, our results do not provide evidence for an association between this D2 receptor variant and schizophrenia, or delusional disorder, or bipolar affective disorder.

No association of the structural dopamine D2 receptor (DRD2) variant 311Cys with alcoholism

The human dopamine D2 receptor (DRD2) has been implied in the vulnerability for alcoholism and/or the modification of its severity. This is supported through animal experimental and pharmacological data. We analyzed the DRD2 311Ser/Cys polymorphism in 312 German alcoholics and 131 ethnically matched controls to investigate the association of genetic DRD2 variants with alcoholism or clinical characteristics of homogeneous subgroups of alcoholics. We observed no association between the 311Cys variant and alcoholism, and none of the clinical characteristics evaluated was significantly associated with 311Cys. The allele frequencies of the 311Cys variant were 0.026 and 0.031 in the alcoholics and controls, respectively. These are the highest reported 311Cys frequencies in Caucasians. The DRD2 TaqI A1/A2 restriction fragment length polymorphism was analyzed simultaneously in our samples. In most cases, the 311Cys allele is associated with the TaqI A2-allele. Data do not suggest a clinical relevance of the 311Cys variant in alcoholism. However, the relevance of this variant in other diseases or the existence of other DRD2 variants with altered receptor function or expression cannot be excluded.

Lack of association between dopamine D2 receptor gene Cys311 variant and schizophrenia

Itokawa et al. [1993] reported identifying one missense nucleotide mutation from C to G resulting in a substitution of serine with cysteine at codon 311 in the third intracellular loop of the dopamine D2 receptor in schizophrenics. Arinami et al. [1994] reported finding a positive association between the Cys311 variant and schizophrenia. In response to the report by Arinami et al. [1994] we examined 106 unrelated Japanese schizophrenics and 106 normal controls to determine if there is any association of the Cys311 variant with schizophrenia. However, we found no statistically significant differences in allelic frequencies of Cys311 between schizophrenia and normal controls. The present results as well as those of all previous studies except for that of Arinami et al. [1994] indicated that an association between the dopamine D2 receptor gene and schizophrenia is unlikely to exist.

Further association study on dopamine D2 receptor variant S311C in schizophrenia and affective disorders

The dopamine D2 receptor gene is a candidate gene for schizophrenia because the potency of certain neuroleptics correlates with their affinity for this receptor. Case-control studies in 291 schizophrenics, 78 patients with affective disorders, and 579 controls on an association of a molecular variant of S311C of the dopamine D2 receptor with psychiatric disorders were conducted. The frequency of individuals with S311C was significantly higher in schizophrenics with the absence of negative symptoms (17.1%, P < 0.00001), but similar in schizophrenics with the presence of negative symptoms (5.7%, P = 0.46) when compared with the controls (4.1%). The frequency of S311C was significantly higher in familial schizophrenics from one local area but not in those from other areas. It was significant that S311C was frequently present in patients with mood-incongruent psychotic affective disorders (33.3%, P < 0.0001), but not in those with other affective disorders. These data suggest that S311C might be one of the genetic factors for symptomatic dimensions of delusions and hallucinations and might be involved in underlying clinical heterogeneity in schizophrenia and affective disorders.

No evidence of linkage between schizophrenia and D2 dopamine receptor gene locus in Italian pedigrees

Our purpose was to test the dopamine D2 receptor gene (DRD2), the tyrosine hydroxylase (TH) gene and the monoamino oxydase A (MAO-A) gene for linkage to schizophrenia and bipolar disorders. We have analyzed seven Italian families with schizophrenia and four families with bipolar disorders for a total of 68 individuals; 32 individuals were affected. Diagnoses were made using the structured clinical interview Schedule for Affective Disorders and Schizophrenia, Lifetime version (SADS-L). The results of our study provide no evidence of linkage between alleles at D2 dopamine receptor loci and schizophrenia or bipolar disorders. The markers TH gene and MAO-A gene give slightly positive or negative results suggesting the utility of further analysis on more informative families.

A search for association between schizophrenia and dopamine-related alleles

Dopamine receptor dysfunction and altered tyrosine hydroxylase activity have both been implicated in the pathophysiology of schizophrenia. Schizophrenic patients and control subjects were examined for allele frequencies in the tyrosine hydroxylase and dopamine D2 and D4 receptor genes. No significant differences of allele or genotype frequencies were found between the two groups after adjustment for multiple comparisons. Neither were any significant relationships observed between allele frequencies and a number of clinical variables within the schizophrenic subsample. When no adjustment was made for multiple testing a few significant tendencies were obtained which warrant further research in extended patient and control materials. The results are compatible with the view that the tyrosine hydroxylase, dopamine receptor D2 and D4 gene polymorphisms examined are not of major importance in the aetiology or pathophysiology of schizophrenia.

Occurrence of the Cys311 DRD2 variant in a pedigree multiply affected with panic disorder

Following the detection of the rare DRD2 codon 311 variant (Ser-->Cys) in an affected member from a large, multiply affected panic disorder family, we investigated the occurrence of this variant in other family members. The variant occurred in both affected and unaffected individuals. Further screening in panic disorder sib pairs unrelated to this family failed to detect the Cys311 variant. Our data suggests that this variant has no pathogenic role in panic disorder.

Exclusion of linkage of schizophrenia to the gene for the dopamine D2 receptor (DRD2) and chromosome 11q translocation sites

There have been previous reports of a 1q43;11q21 translocation cosegregating with schizophrenia and a 9p22;11q22.3 translocation cosegregating with manic depression. In addition, the genes for the dopamine D2 receptor and for tyrosinase both map to chromosome 11q. Three 11q DNA markers were used to investigate 23 pedigrees containing multiple cases of schizophrenia. Strongly negative lod scores were obtained, providing evidence against linkage over a 70 cM region which included both translocation sites and both candidate genes.

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.