No evidence of association between dopamine D3 receptor gene and bipolar affective disorder

The Sardinian Puzzle: Concentration of Major Psychoses and Suicide in the Same Sub-Regions Across One Century

BACKGROUND

Sardinia, the second largest Mediterranean island has long been considered a privileged observatory for the study of several medical conditions. The peculiar epidemiology of mood disorders and suicide across Sardinian sub-regions has long intrigued clinicians and researchers.

OBJECTIVE

The principal aim of the present study was to test whether the geographical distribution of suicides committed in Sardinian over the last three decades are comparable with the geographical origin of patients hospitalized up to half a century ago.

METHOD

The distribution of the municipalities of origin of the patients hospitalized in Sardinia between 1901 and 1964 for schizophrenia, bipolar disorder, and depression was reanalyzed and compared with the distribution of municipalities where suicides were committed between 1980 and 2013. Data were also analyzed by the altitude above the sea level and by the population size of the municipalities.

RESULTS

There was a significant variation of hospitalization and suicide rates across Sardinian sub-regions. The sub-regions of origin of the patients hospitalized for schizophrenia and bipolar disorder correlated with each other (P = 0.047). Both hospitalizations and suicides were more incident in municipalities with a higher altitude and a smaller population size. The incidence of hospitalizations and suicides correlated significantly with each other both at the municipality (P = 1.86 x 10-7) and at the sub-region level (P = 1.71 x 10-7).

CONCLUSION

The present study confirms the peculiar geographical distribution of major psychoses and suicide in Sardinia. The two phenomena appear to have been correlated for as long as one century.

Striatal structure and function in mood disorders: a comprehensive review

OBJECTIVES

  A large and diverse literature has implicated abnormalities of striatal structure and function in both unipolar and bipolar disorder. Recent functional imaging studies have greatly expanded this body of research. The aim of this review is to provide a comprehensive and critical appraisal of the relevant literature.

METHODS

  A total of 331 relevant articles were reviewed to develop an integrated overview of striatal function in mood disorders.

RESULTS

  There is compelling evidence from multiple studies that functional abnormalities of the striatum and greater corticostriatal circuitry exist in at least some forms of affective illness. The literature does not yet provide data to determine whether these aberrations represent primary pathology or they contribute directly to symptom expression. Finally, there is considerable evidence that bipolar disorder may be associated with striatal hyperactivity and some suggestion that unipolar illness may be associated with hypoactivation.

CONCLUSIONS

  Additional research investigating striatal function in affective disorders will be critical to the development of comprehensive models of the neurobiology of these conditions.

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.

No allelic association or interaction of three known functional polymorphisms with bipolar disorder in a northern Swedish isolated population

Most genetic association studies in bipolar disorder have focussed on genes involved in major neurotransmitter systems or brain development. Functional polymorphisms in the serotonin transporter (5-HTTLPR), catechol-O-methyltransferase (Val158Met) and dopamine D3 receptor (Ser9Gly) genes have all been associated with bipolar disorder. We aimed at investigating whether these functional variants contribute to the genetic etiology of bipolar disorder in a northern Swedish isolated population. Moreover, we wanted to gain information about the synergistic contribution of these functional variants. Neither of these functional polymorphisms was associated with bipolar disorder in the northern Swedish patient-control sample nor did we find evidence of gene-gene interaction. Together, our data suggest that these functional variants are not involved in the etiology of bipolar disorder in the northern Swedish population nor did gene-gene interaction analysis support a central role of these variants in bipolar disorder.

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.

Manic-depressive illness: an association study with the inositol polyphosphate 1-phosphatase and serotonin transporter genes

Association studies with candidate genes may contribute towards the understanding of the etiopathogenesis of bipolar disorder. Candidate genes in bipolar disorders are those related to aminergic neurotransmission, which is the target of the effects of antipsychotics and antidepressants, as well as genes related to signal transduction pathways, reporting the target for the mood-stabilizing effects of lithium. Association with such candidate genes may provide clues towards the understanding of the biological components of bipolar disorder. An association study was performed between the 5' regulatory region of the serotonin transporter gene (5-HTTLPR), the inositol polyphosphate 1-phosphatase gene (INPP1) and bipolar disorder using our sample of proband/parent trios. A total of 101 bipolar probands were considered eligible for the study. Since both parents had to be available, mean age at onset of bipolar disorder in probands was relatively young. However, the mean duration of illness and the number of episodes were consistent with a stable diagnosis. In our trios sample, the transmission disequilibrium test revealed no preferential transmission of alleles of the 5-HTTLPR and INPP1 from heterozygous parents to probands. Therefore, additional family-based data are warranted, possibly with a more complete subdivision of 5-HTTLPR alleles, since short and long alleles have recently been divided into four and six kinds of allelic variant, respectively, with significant ethnic differences in allele and genotype distributions.

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.

Association analysis between dopamine receptor genes and bipolar affective disorder

We have performed a case-control analysis of dopamine D2-like receptor (DRD2, DRD3 and DRD4) gene polymorphisms in 118 Han Chinese cases with bipolar affective disorder and 196 control subjects, and replication analysis in 157 English cases and 143 control subjects. We found association between a functional DRD2 promoter variant (P = 0.03 by allele) and the DRD2 taq1A polymorphism (P = 0.001 by allele) in Chinese bipolar disorder patients. However, this finding was not replicated in the Caucasian subjects, indicating that the significant association we observed in the Chinese population is a false positive finding. An alternative explanation is that these polymorphisms are risk factors in Chinese but not Caucasian populations, a hypothesis which seems unlikely in view of the similarity of the clinical characteristics of bipolar disorder in the two populations. We also report a novel, rare one-repeat variant of the DRD4 exon 3 VNTR repeat in Chinese populations, which appears to be absent in Caucasians and is not associated with disease.