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No association between an allele at the D2 dopamine receptor gene (DRD2) and alcoholism.

OBJECTIVE: --We attempted to replicate a positive allelic association between the A1 allele of DRD2 (the D2 dopamine receptor locus) and alcoholism that has been reported. DESIGN: --We compared allele frequencies at the previously described Taq I restriction fragment length polymorphism system of DRD2 in alcoholics and random population controls. SUBJECTS: --The alcoholic subjects were 44 unrelated white individuals, diagnosed by direct structured interview to have alcohol dependence (by the Diagnostic and Statistical Manual of Mental Disorders, Revised Third Edition, criteria). The subjects in our random population control group (N = 68) were also white. RESULTS: --For the control group, allele frequencies at DRD2 were 0.20 (A1) and 0.80 (A2). For the alcoholic group overall, allele frequencies were 0.23 (A1) and 0.77 (A2). There were no significant differences in allele frequencies at the DRD2 locus between alcoholics and controls. The allele frequencies in both groups agreed closely with those observed in most previously described control populations. Subtyping the alcoholic group according to presence or absence of family history of alcoholism, presence or absence of antisocial personality disorder, age of onset, presence or absence of physical withdrawal symptoms, or recent alcohol consumption (as a measure of severity) did not in any case reveal significant differences in allele frequencies. CONCLUSION: --We were not able to replicate the results previously reported. We conclude that our data do not support an allelic association between the A1 allele at DRD2 and alcoholism.

Adult

The importance of dopamine levels and single-nucleotide polymorphism within COMT, DRD1 and DRD2 genes in obstructive sleep apnoea.

BACKGROUND: Obstructive sleep apnoea (OSA) is a prevalent sleep disorder that contributes to serious cardiovascular comorbidities. While the mechanical aspects of OSA are well-studied, its neurobiological underpinnings remain underexplored. In this study, we investigated the role of dopamine and its genetic modulators in OSA pathophysiology. PATIENTS AND METHODS: Serum dopamine levels were assessed in a cohort of 153 participants (96 OSA patients and 57 controls), and single-nucleotide polymorphisms (SNPs) in dopamine-related genes, including COMT, DRD1 and DRD2, were analysed in a cohort of 286 participants (141 OSA patients and 145 controls). RESULTS: Elevated serum dopamine levels were observed in OSA patients (p = 0.01), with dopamine levels correlating independently with OSA and male gender. Genotypic analysis identified the DRD2 rs1800497 T allele as a potential independent predictor of OSA severity (p = 0.011), hypopnea (p = 0.005) and arousals (p = 0.024). CONCLUSIONS: This study advances the understanding of OSA by identifying elevated dopamine levels and genetic variations in DRD2 rs1800497 as potential modulators of its occurrence and severity. These findings pave the way for personalized diagnostic and therapeutic approaches. By integrating neurobiology, genetics, and clinical practice, this research contributes to the evolving framework for precision medicine in sleep disorders.

Humans

Linkage map of eight human chromosome 11q markers, including DRD2, spanning 60 cM.

We have constructed a linkage map of eight RFLP markers located on chromosome 11q in the region of the dopamine D2 receptor gene (DRD2) recognized by probe hD2G1. Abnormalities in dopaminergic neurotransmission mediated by this receptor have been implicated in several psychiatric disorders. The map was generated using six large reference families (from 294 to 419 individuals per locus), which are largely independent of the CEPH families, primarily using the LINKMAP and ILINK programs of the LINKAGE package of Lathrop and Lalouel. The most likely order and recombination frequencies are: [sequence: see text] The relative order of D11S84-STMY, DRD2-D11S29, and D11S146-INT2 could not be resolved reliably. There were no significant sex differences in recombination frequency. We introduce here a version of LINKMAP adapted to run under distributed parallel processing (LINDA-LINKMAP). Using pairwise analyses, we have also placed D11S421 proximal to this group.

Chromosome Mapping

Direct sequencing of the dopamine D2 receptor (DRD2) in schizophrenics reveals three polymorphisms but no structural change in the receptor.

The dopamine D2 receptor gene (gene symbol DRD2) is a candidate gene for schizophrenia because the potency of certain neuroleptics correlates with their affinity for this receptor. Seven regions of likely functional significance including the coding sequences and the splice junctions were fully sequenced in the dopamine D2 receptor of 14 schizophrenics (and partially in several others) meeting DSM-III-R diagnostic criteria and in four unaffected non-Caucasians (97 kb of total sequence). No structural changes were found, suggesting that alteration in the structure of the dopamine D2 receptor is not commonly involved in the etiology of schizophrenia. However, two common and one uncommon intragenic polymorphisms were found. At least one of the polymorphisms was informative for linkage in 70% of Caucasians and 78% of Koreans.

Base Sequence

Detection and characterization of additional DNA polymorphisms in the dopamine D2 receptor gene.

The gene encoding the dopamine D2 receptor (DRD2) has been suggested as a candidate gene for several mental disorders. We previously described the cloning and chromosomal mapping (to 11q22-q23) of a human DRD2 gene as well as its use for the detection of a two-allele TaqI RFLP with a minor allele frequency of 0.24, corresponding to a PIC of 0.30. Family linkage utilizing DRD2 would be facilitated if the PIC of the DRD2 locus were increased. To this end, we have used additional phage and cosmid clones in the vicinity of DRD2 to identify a new two-allele TaqI RFLP as well as a TG microsatellite polymorphism with a PIC of 0.62. We report localizations of the three polymorphisms on the restriction map of the DRD2 locus. The TaqI RFLPs are in apparent linkage equilibrium with the microsatellite, yielding a highly informative compound marker locus with a PIC of 0.76.

Alleles

Structure and linkage of the D2 dopamine receptor and neural cell adhesion molecule genes on human chromosome 11q23.

The gene encoding the D2 dopamine receptor (DRD2) is located on human chromosome 11q23 and has been circumstantially associated with a number of human disorders including Parkinson's disease, schizophrenia, and susceptibility to alcoholism. To determine the physical structure of the DRD2 gene, we utilized cosmid cloning, isolation of yeast artificial chromosomes (YACs), and pulsed-field gel electrophoresis to construct a long-range physical map of human chromosome 11q23 linking the genes for the DRD2 and neural cell adhesion molecule (NCAM). The D2 dopamine receptor gene extends over 270 kb and includes an intron of approximately 250 kb separating the putative first exon from the exons encoding the receptor protein. The resulting physical map spans more than 1.5 mb of chromosome band 11q23 and links the DRD2 gene with the gene encoding the NCAM located 150 kb 3' of the DRD2 gene and transcribed from the same DNA strand. We additionally located the sites of at least four hypomethylated HTF islands within the physical map, which potentially indicate the sites of additional genes. High-resolution fluorescent in situ suppression hybridization using cosmid and YAC clones localized this gene cluster between the ApoAI and STMY loci at the interface of bands 11q22.3 and 11q23.1.

Base Sequence

Gilles de la Tourette syndrome is not linked to D2-dopamine receptor.

Gilles de la Tourette syndrome has an important genetic component; the pathophysiology of this disorder may involve the dopamine system. We tested a D2-dopamine receptor (locus DRD2, recognized by probe hD2G1) for genetic linkage with Gilles de la Tourette syndrome. Using a genetic linkage map of the region of DRD2 on the long arm of chromosome 11 and restriction fragment length polymorphism data from a total of four markers (DRD2 itself, D11S84, D11S29, and PBGD), we were able to exclude linkage of this candidate gene and Gilles de la Tourette syndrome in two extended kindreds segregating for Gilles de la Tourette syndrome. This rules out causation of Gilles de la Tourette syndrome by mutation in DRD2 in the kindreds studied under the genetic assumptions we employed; use of the map and multipoint linkage analyses also allowed us to exclude a Gilles de la Tourette syndrome susceptibility locus from a larger genetic region.

Chromosome Mapping

No linkage between D2 dopamine receptor gene region and schizophrenia.

The dopamine hypothesis is one of the major etiological hypotheses of schizophrenia. The well-established role of genetic factors in schizophrenia together with reports of increased D2 dopamine receptor densities in untreated schizophrenic patients support the D2 dopamine receptor gene as a strong candidate gene for schizophrenia. The recent cloning of the D2 dopamine receptor gene made it possible to test the involvement of the D2 dopamine receptor locus (DRD2) in a large Swedish and a smaller Californian schizophrenia pedigree. Using multipoint linkage analysis between schizophrenia and a genetic map that includes the DRD2 locus and assuming a dominant mode of inheritance, we were able to exclude the DRD2 locus with a lod score of -4.14 for the penetrance of 0.72 and with a lod score of -3.05 for the lower bound penetrance of 0.56. The area of exclusion (lod score, less than -2.00) extended 27 centimorgans. These results provide strong evidence against linkage of the D2 dopamine receptor gene region to schizophrenia in the two pedigrees investigated. We conclude that the genetic predisposition to schizophrenia in these pedigrees is not due to aberrations in the DRD2 locus or the porphobilinogen deaminase locus. Our results do not support the D2 dopamine receptor hypothesis of schizophrenia. However, they cannot exclude the possibility that other genes regulating aspects of D2 dopamine expression might be involved in the etiology of schizophrenia, such as the expression of two D2 dopamine receptor subtypes by alternative RNA splicing.

California

Exclusion of close linkage of bipolar disorder to dopamine D1 and D2 receptor gene markers.

A potential role of dopamine in bipolar disorder has been suggested by several strands of evidence, namely the ability of dopaminergic agonists to induce mania and the effects of lithium, carbamazepine and the antipsychotics on central dopamine receptors and/or turnover. We therefore aimed to determine if bipolar disorder in two large bipolar pedigrees was linked to the recently cloned dopamine D1 (DRD1) and D2 (DRD2) receptors. (These have been mapped to chromosomal regions 5q35.1 and 11q22.3-q23, respectively). Linkage of bipolar disorder and recurrent depression to DRD1 and DRD2 was tested using a series of genetic models with varying penetrance levels. Additionally, linkage was examined using a series of levels of definitions of affective status (ranging from bipolar I alone to all affective illnesses). Close linkage to these markers was strongly excluded using each model and definition. The findings for DRD1 also persisted when a wide range of rates of 'sporadic' (non-genetic) presentations of illness were incorporated in the analysis, but the DRD2 results did not remain statistically significant at high sporadic rates. The exclusion of linkage to DRD2 is consistent with other recent reports.

Adolescent

Physical mapping of the human chromosome 11q23 region containing the ataxia-telangiectasia locus.

Two breakpoints within chromosome 11q23 were characterized with 29 DNA probes to establish a physical map of the region. This region is notable in that it contains at least 14 functional genes which are also syntenic in the mouse (chromosome 9). Chromosome 11q23 includes these markers: STMY, CLG, NCAM, DRD2, APOA1, APOC3, APOA4, CD3E, CD3D, CD3G, PBGD, THY1, ets-1, and cbl-2. The two breakpoints, herein called "X;11" and "4;11," defined a region of approximately 8 cM containing the APO and CD3 complexes as well as the polymorphic marker D11S29. DRD2 localized centromeric to the X;11 breakpoint despite evidence for close genetic linkage to D11S29, suggesting that DRD2 lies close to the X;11 breakpoint. THY1, PBGD, and cbl-2 localized telomeric to the 4;11 breakpoint and thus to the [D11S29--APO--CD3] grouping as well. The physical map helps to correlate the cytogenetic and linkage maps of this region. It also suggests that the human 11q23 syntenic grouping is inverted with respect to its murine counterpart. Based on this physical map and on our primary linkage map of the 11q23 region, we are able to confirm a preliminary localization of the gene for ataxia-telangiectasia group A (ATA) to a region centromeric to the interval defined by D11S144 (pYNB3.12) and THY1.

Animals

The dopamine D2 receptor locus as a modifying gene in neuropsychiatric disorders.

OBJECTIVE: --The A1 allele of the Taq I polymorphism of the dopamine D2 receptor (DRD2) gene has been earlier reported to occur in 69% of alcoholics, compared with 20% of controls. Other research has reported no significant difference in the prevalence of the A1 allele in alcoholics vs controls and no evidence that the DRD2 gene was linked to alcoholism. We hypothesized that these seemingly conflicting results might be because increases in the prevalence of the A1 allele may not be specific to alcoholism. Thus, we examined other disorders frequently associated with alcoholism or those believed to involve defects in dopaminergic neurotransmission. DESIGN: --Case comparison study. To minimize the effect of racial differences in gene frequencies, the study was restricted to non-Hispanic whites. SETTING: --Ambulatory and hospitalized patients. RESULTS: --Among all known controls (n = 314), 77 (24.5%) carried the A1 allele. Of the 69 controls known not to be alcoholics, 10 (14.5%) carried the A1 allele. The prevalence of the A1 allele was significantly increased in patients with Tourette's syndrome (44.9%, n = 147), attention deficit hyperactivity disorder (46.2%, n = 104), autism (54.5%, n = 33), alcoholism (42.3%, n = 104), and posttraumatic stress disorder (45.7%, n = 35). After correction for multiple comparisons (requiring P less than .0009 for significance), all remained significant except posttraumatic stress disorder. The prevalence of the A1 allele was not significantly increased in patients with depression, panic attacks, Parkinson's disease, or obesity. The prevalence of the A1 allele in drug addiction and schizophrenia was only significant when compared with that of controls who were not alcoholics, and no correction was made for multiple comparisons. CONCLUSION: --These results suggest the A1 allele of the DRD2 gene is associated with a number of behavior disorders in which it may act as a modifying gene rather than as the primary etiological agent.

Alcoholism

Lack of association between an RFLP near the D2 dopamine receptor gene and severe alcoholism.

Blum et al (1990) have recently examined a restriction fragment length polymorphism (RFLP) detected by TaqI RFLP to the dopamine D2 receptor gene (DRD2) in deceased alcoholics and nonalcoholics, and reported an association between alcoholism and the A1 allele. Subsequent studies, however, by other investigators have failed to confirm this. We have examined the DRD2 TaqI RFLP in 47 living Caucasian males with severe alcoholism. All alcoholic subjects were thoroughly characterized by a structured interview, and met DSM-III-R criteria for alcohol dependence. Only 9/47 (19%) (1990) of these alcoholics had the AI allele compared to 14/22 (64%) reported by Blum et al. This rate was not significantly different from the rates reported in control populations by Blum et al (1990), CEPH, or Bolos et al (1990), and differed only slightly from those reported by Grandy et al (1990). Alcoholics selected for severe medical complications also displayed a similar rate. Our data do not support an association between alcoholism and the D2 dopamine receptor gene in this population.

Adult

Ataxia-telangiectasia: linkage analysis of chromosome 11q22-23 markers in Turkish families.

To further pinpoint the location of the genes for ataxia-telangiectasia on the long arm of chromosome 11, we performed linkage analysis and analysis of recombinants of genetic haplotypes on 14 Turkish families with ataxia-telangiectasia, 12 of which were consanguineous. These studies used more than 25 polymorphic genetic markers spanning a region of the long arm of chromosome 11 that is larger than 50 cM. Seven markers gave significant LOD scores to AT: CJ5, DRD2, CJ208, S144, CD3E, PBGD, and S147, as did haplotypes created with pairs of markers DRD2/CJ5 and S144/CJ208, giving recombination fractions (theta) of 0.00, 0.00, 0.05, 0.08, 0.03, 0.09, 0.07, 0.00, and 0.06, respectively. Monte Carlo analysis of these 14 Turkish families indicated the best location for a single AT gene to be within a 6 cM sex-averaged (3 cM male-specific) interval defined by STMY and CJ77; this was three times more likely than the next most likely location (peak III) at the DRD2 locus. The analysis also revealed a peak (peak II) between S147 and S133, which may represent the complementation group D gene. Recombinant analysis of haplotypes also localized an AT locus to the STMY-CJ77 interval. Taken together, these results suggest that at least two distinct AT loci exist (ATA and ATD) at 11q22-23, with perhaps a third locus, ATC, located very near to the ATA gene. This genetic heterogeneity further complicates plans to isolate the major ATA and ATC genes and to begin identifying AT carriers in the general population.

Ataxia Telangiectasia

The human dopamine D2 receptor gene is located on chromosome 11 at q22-q23 and identifies a TaqI RFLP.

Human dopaminergic neurons are involved in the control of hormone secretion, voluntary movement, and emotional behavior. Mediating these effects are the dopamine D1 and D2 receptors. These macromolecules belong to a large family of related sequences known as the G protein-coupled receptors. The D2 receptors have been of special interest because they bind, with high affinity and specificity, many of the commonly prescribed antipsychotic drugs. We previously isolated a full-length cDNA clone of the rat D2 receptor. When a chromosome mapping panel was probed with the rat D2 receptor cDNA a 15-kb EcoRI restriction fragment was identified and localized to human chromosome 11. The rat cDNA was also used to clone a human genomic fragment, lambda hD2G1, which contains the last coding exon of the D2 receptor gene (DRD2) and 16.5 kb of 3' flanking sequence. Hybridization of lambda hD2G1 to a chromosome 11 regional mapping panel localized DRD2 to 11q. In situ hybridization of lambda hD2G1 to metaphase chromosomes refined this assignment to the q22-q23 junction of chromosome 11. A search for RFLPs associated with D2DR identified a frequent two-allele TaqI RFLP.

Chromosome Mapping

Genetic and Epigenetic Approaches to Opioid Use Disorder.

BACKGROUND: Opioid use disorder (OUD) is a major global-scale social issue affecting public health. The high potential for addiction and dependence makes opioid use a significant concern, contributing to substance-related disorders. Both genetic and environmental factors contribute to the predisposition to OUD, with the opioidergic, dopaminergic, and GABAergic systems playing primary roles in itsonset. METHODS: This narrative review documents the association between genes and their variants related to these three systems, along with current evidence on epigenetic interventions in OUD. Relevant studies investigating candidate-gene associations and molecular mechanisms were synthesized to highlight genetic variants and epigenetic processes linked to OUD. RESULTS: Genetic associations play a prominent role in OUD, with several single-nucleotide variants identified in affected populations. Key genes implicated include OPRM1, OPRD1, OPRK1, PDYN, OPRL1, and POMC from the opioidergic system; DRD1, DRD2, DRD3, DRD4, ANKK1, and COMT from the dopaminergic system; and GABRA2, GABRB3, GABRG2, GAD1, and GAD2 from the GABAergic system. Evidence also indicates that chronic opioid use is associated with epigenetic changes through posttranslational histone modifications and DNA methylation. However, limitations in existing studies include small sample sizes, limited replication, and potential stratification biases. CONCLUSIONS: Although many candidate-gene associations have been proposed for OUD, robust evidence remains limited. Large, ancestrally diverse genome-wide association studies (GWAS) and systematic replication studies are urgently needed. A deeper understanding of the genetic, epigenetic, and neurobiological bases of addiction will be essential for the development of precisely targeted medications to improve prevention and treatment outcomes for OUD.

Humans

Lentiviral CRISPRa/i in the adult prairie vole brain: modulating neuronal gene expression without DNA cleavage.

Prairie voles (Microtus ochrogaster) are a powerful model for studying the neurobiology of social bonding, yet tools for region- and cell type-specific gene regulation remain underdeveloped in this species. Here, we present a lentivirus-mediated CRISPR activation and interference (CRISPRa/i) platform for somatic gene modulation in the prairie vole brain. This system enables non-mutagenic, titratable regulation of gene expression in the adult brain without germline modification. Our dual-vector system includes one construct expressing dCas9-VPR (VP64-p65-Rta) referred to as CRISPRa or dCas9-KRAB-MeCP2 (Kruppel-associated box-methyl CpG binding protein 2), referred to as CRISPRi under a neuron-specific promoter, and a second construct delivering a U6-driven sgRNA (single guide RNA) alongside an elongation factor 1 alpha (EF1α)-driven mCherry reporter. We detail the design, production, and stereotaxic delivery of these tools and demonstrate their application by targeting four genes implicated in social behavior (Oxtr, Avpr1a, Drd1, and Drd2) across two mesolimbic brain regions: the nucleus accumbens and ventral pallidum. Gene expression analyses confirmed robust, bidirectional transcriptional modulation for selected targets, establishing a proof of concept for CRISPRa/i in this non-traditional model. The dual-vector design is readily adaptable to other gene targets, cell types, and brain regions, and can be multiplexed to provide a flexible and scalable framework for investigating gene function in behaviorally relevant circuits. These advances represent the first successful implementation of somatic CRISPRa/i in prairie voles and expand the genetic toolkit available for this species.

Avpr1a