Exclusion of close linkage of bipolar disorder to the Gs-alpha subunit gene in nine Australian pedigrees

The Genetic Side of the Mood: A Scientometric Review of the Genetic Basis of Mood Disorders

Mood disorders are highly heritable psychiatric disorders. Over the years, many genetic polymorphisms have been identified to pose a higher risk for the development of mood disorders. To overview the literature on the genetics of mood disorders, a scientometric analysis was performed on a sample of 5342 documents downloaded from Scopus. The most active countries and the most impactful documents in the field were identified. Furthermore, a total of 13 main thematic clusters emerged in the literature. From the qualitative inspection of clusters, it emerged that the research interest moved from a monogenic to a polygenic risk framework. Researchers have moved from the study of single genes in the early 1990s to conducting genome-wide association studies around 2015. In this way, genetic overlaps between mood disorders and other psychiatric conditions emerged too. Furthermore, around the 2010s, the interaction between genes and environmental factors emerged as pivotal in understanding the risk for mood disorders. The inspection of thematic clusters provides a valuable insight into the past and recent trends of research in the genetics of mood disorders and sheds light onto future lines of research.

COMPARISON OF THE POLYMORPHISMS OF ANDROGEN RECEPTOR GENE AND ESTROGEN α AND β GENE BETWEEN ADOLESCENT FEMALES WITH FIRST-ONSET MAJOR DEPRESSIVE DISORDER AND CONTROLS

This study was to elucidate the role of genetic variation in androgen receptor (AR) gene, estrogen receptor alpha (ER alpha) and ER beta gene on first-onset major depressive disorder (MDD) in female adolescents. Results showed that AR gene in MDD group have shorter microsatellites' length, and ER beta gene have shorter microsatellites' length and higher rates of S alleles, SS, genotype, and lower rate of LL genotype than control group. The results suggest that shorter length of AR and ER beta gene microsatellites might influence the onset of MDD in female adolescents, a further elucidation of the mechanisms is warranted.

The involvement of G proteins and regulators of receptor-G protein coupling in the pathophysiology, diagnosis and treatment of mood disorders

Biochemical research in mood disorders has focused, along the cascade of events involved in signal transduction, from studies at the level of the monoamine neurotransmitter to the level of the neurotransmitter receptors, and lately to information transduction mechanisms beyond receptors, involving the coupling of receptors with signal transducers. We review findings concerning (a) the involvement of G proteins, in the pathophysiology, diagnosis and treatment of mood disorders; (b) the importance of regulation of receptor-G protein coupling, G protein-coupled receptor kinases (GRKs), beta-arrestins, to the pathophysiology of mood disorders and the mechanism of action of antidepressants. We relate to the special complexity of mental disorders with regards to etiology and pathophysiological diagnosis as well as to the strength and limitations of the 'pharmacological bridge' approach governing studies to unravel the etiology of mental disorders. There are presently no established and reliable, sensitive and specific objective biological diagnostic markers in psychiatry that can serve as 'gold standards'. The future achievement of an objective biochemical differential diagnostic system for major mental disorders that will also enable an objective biological treatment monitoring is expected to be revolutionary for psychiatry with a magnitude similar to the impact of the discovery of psychopharmacological treatments for mental disorders more than 50 years ago.

Complex haplotype structure of the human GNAS gene identifies a recombination hotspot centred on a single nucleotide polymorphism widely used in association studies

The alpha subunit of the heterotrimeric G protein Gs (Gsalpha) is involved in numerous physiological processes and is a primary determinant of cellular responses to extracellular signals. Genetic variations in the Gsalpha gene may play an important role in complex diseases and drug responses. To characterize the genetic diversity in this locus, we resequenced exons and flanking introns of the gene in 44 genomic samples and analysed the haplotype structure of the gene in an additional 50 African-Americans and 50 Caucasians. Significant differences in allele frequency for nearly all the genotyped single nucleotide polymorphism (SNPs) were detected between the two ethnic groups. Linkage disequilibrium (LD) analysis of this locus revealed two haplotype blocks characterized by strong LD and reduced haplotype diversity, especially in Caucasians. Between the two blocks is a narrow (approximately 3 kb) recombination hotspot centred on exons 4 and 5, and a widely used genetic marker in association studies in this region (rs7121) was in linkage equilibrium with the rest of the gene. The haplotype structure of the GNAS locus warrants reevaluation of previous association studies that used marker rs7121 and affects choice of SNP markers to be used in future studies of this locus.

Psychiatric genetics in Australia

Australian research in psychiatric genetics covers molecular genetic studies of depression, anxiety, alcohol dependence, Alzheimer's disease, bipolar disorder, schizophrenia, autism, and attention deficit hyperactivity disorder. For each disorder, a variety of clinical cohorts have been recruited including affected sib pair families, trios, case/controls, and twins from a large population-based twin registry. These studies are taking place both independently and in collaboration with international groups. Microarray studies now complement DNA investigations, while animal models are in development. An Australian government genome facility provides a high throughput genotyping and mutation detection service to the Australian scientific community, enhancing the contribution of Australian psychiatric genetics groups to gene discovery.

Altered CTX-catalyzed and endogenous [32P]ADP-ribosylation of stimulatory G protein alphas isoforms in postmortem bipolar affective disorder temporal cortex

Reports of elevated Gs alpha subunit (alpha(s)) immunolabeling and cAMP-mediated hyper-functionality in autopsied cerebral cortical brain regions from bipolar affective disorder (BD) patients suggest signal transduction abnormalities occur in this disorder. Because covalent modification of alpha(s) can affect its turnover and levels, we determined whether CTX-catalyzed and endogenous [(32)P] adenosine diphosphate (ADP)-ribosylation of alpha(s) isoforms are altered in temporal and occipital cortical regions, which show elevated alpha(s) levels in BD as compared to nonpsychiatric subjects. Reduced CTX-catalyzed [(32)P]ADP-ribosylated alpha(s-S) and endogenous [(32)P]ADP-ribosylation of a 39-kDa alpha(s)-like protein were found in BD temporal cortex compared to controls. These findings suggest that clearance of these alpha(s) isoforms through ADP-ribosylation may be decreased in BD temporal cortex. Although no differences were observed in mean levels of endogenous and CTX-catalyzed [(32)P]ADP-ribosylation of alpha(s-L) in BD temporal cortex, alpha(s-L) immunolabeling was elevated significantly and correlated inversely with the degree of endogenous [(32)P]ADP-ribosylation of this subunit. In addition, endogenous [(32)P]ADP-ribosylation of an exogenous substrate, myelin basic protein, was similar in BD and comparison subject temporal cortex. Taken together, these observations suggest that elevations of alpha(s) in BD brain are more likely related to factors affecting the disposition or availability of alpha(s) to this posttranslational enzymatic modification.

Association analysis of a polymorphism in the G-protein stimulatory alpha subunit in patients with major depression

Growing evidence suggests that G-proteins may be involved in pathogenesis and treatment of affective disorders. Several studies have reported altered levels and/or activities of stimulatory G-proteins in depression. The aim of this study was to investigate whether a polymorphism in the stimulatory alpha subunit of G-proteins (T/C point mutation in exon 5; ATT --> ATC at codon 131) is associated with major depression or response to antidepressant treatment. Therefore, we performed a case-control association study with 212 depressive patients and 137 healthy, unrelated controls. There was no evidence for an association between the investigated polymorphism in the G(alpha)(s) gene and major depression, as well as to treatment response. The results of our study are in concordance with recently published findings which do not support the hypothesis that the gene for the stimulatory alpha subunit of G-proteins is a major susceptibility factor in the pathophysiology of major depression.

The neurobiology of bipolar disorder: focus on signal transduction pathways and the regulation of gene expression

OBJECTIVE

This article presents an overview of signal transduction pathways and reviews the research undertaken to study these systems in clinically relevant samples from patients with bipolar disorder (BD).

METHOD

We reviewed the published findings from studies of postmortem brain tissue and blood samples from patients with BD.

RESULTS

Although the exact biochemical abnormalities have yet to be identified, the presented findings strongly suggest that BD may be due, at least in part, to abnormalities in signal transduction mechanisms. In particular, altered levels or function, or both, of G-protein alpha subunits and effector molecules such as protein kinase A (PKA) and protein kinase C (PKC) have consistently been associated with BD both in peripheral cells and in postmortem brain tissue, while more recent studies implicate disruption in novel second-messenger cascades, such as the ERK/MAPK pathway.

CONCLUSIONS

Despite the difficulties inherent in biochemical studies of clinically relevant tissue samples, numerous investigations have illuminated the signal transduction mechanisms in patients with BD. These studies also suggest that BD may be due to the interaction of many abnormalities. In this context, novel techniques enabling the study of gene expression promise to assist in untangling these complex interactions, through visualizing the end result of these changes at the level of gene transcription.

Is lithium response related to G(s)alpha levels in transformed lymphoblasts from subjects with bipolar disorder?

BACKGROUND

A series of studies from independent laboratories have found increased levels of G(s)alpha in bipolar disorder in postmortem brain and peripheral blood cells. Long-term lithium administration blunts G-protein coupled cAMP signaling and may regulate G(s)alpha levels.

METHODS

We measured G(s)alpha in transformed lymphoblasts obtained from subjects with bipolar disorder and compared the findings with 23 age- and sex-matched controls. To reduce patient heterogeneity, we included only patients with an excellent response to lithium prophylaxis.

RESULTS

We found no differences in G(s)alpha protein levels measured with immunoblotting. G(s)alpha levels did not correlate with age, age of onset or duration of lithium therapy.

LIMITATIONS

This study made use of transformed lymphoblasts, which may not fully represent changes that occur in regionalized brain tissue. Furthermore, the transformed lymphoblasts used in this study were acquired from a select group of bipolar disorder subjects that responded to lithium treatment. Lastly, consideration has to be given to the small sample size of the study.

CONCLUSIONS

These results are consistent with recent observations suggesting that mood state and treatment effects may account at least in part for increased G(s)alpha levels in bipolar disorder.

CLINICAL RELEVANCE

This study suggests a need to further characterize biological phenotypes in subjects with mood disorders to enhance genetic studies.

Implications of the cAMP signaling pathway in psychiatric disorders: a systematic review of the evidence

The last decade has seen a shift in the theoretical framework addressing the pathophysiology of psychiatric disorders. During this period, research endeavors have been directed toward investigating the biochemical mechanisms involved in the transduction of information from the cell surface to the cell interior. The emerging picture, supported by growing evidence, is that in addition to neurotransmitters and their receptors, various signal transduction pathways may be linked to the pathophysiology of major psychiatric disorders. In this review, the role of one such pathway--the cyclic adenosine monophosphate (cAMP) signaling pathway--will be highlighted. We review data suggesting the involvement of the upstream and downstream components of this system in the pathophysiology of psychiatric disorders.

Parental sex effects in bipolar affective disorder pedigrees

A combined linkage analysis was performed on chromosome 18 data and produced modest evidence in three of four data sets for linkage of a susceptibility locus for bipolar disorder to markers on chromosome 18p. All data sets showed a preponderance of females among affected individuals. When this was taken into account, no convincing evidence was obtained for excess transmission from mothers compared to fathers. In addition, there was no evidence for differences in the proportions of affected offspring from affected fathers and mothers. We conclude that these combined data do not support previous suggestions of a maternal effect on transmission of bipolar affective disorder.

The role of G proteins in the psychobiology and treatment of affective disorders and their integration with the neurotransmitter hypothesis

Heterotrimeric G proteins are a crucial point of convergence in the transmission of signals from a variety of primary messengers and their membrane receptors to downstream intracellular second messenger effector enzymes and ionic channels. Thus, these proteins have raised increasing interest in the clinical perspective of altered G protein function. This article addresses the most recent significant findings regarding the role of G proteins in the pathophysiology of mood disorders and in the molecular mechanisms underlying the treatment of these disorders, with emphasis on biochemical and genetic approaches.

Nonparametric simulation-based statistical analyses for bipolar affective disorder locus on chromosome 21q22.3

Straub et al. [1994: Nat Genet 8:291-296] reported a candidate bipolar affective disorder (BAD) locus on chromosome 21q22.3. As a replication study, we analyzed 12 Australian BAD pedigrees for the presence of excess allele sharing and cosegregation with the putative chromosome 21q22.3 BAD locus, using six microsatellite markers. The nonparametric simulation-based statistic SimAPM produced positive results for the marker PFKL (P < 0.001) and D21S198 (P = 0.007). PFKL also demonstrated linkage (P < 0.001) when analyzed using the more conservative statistic, SimIBD. Comparable results were obtained when using the original APM statistic (P = 0.02 for D21S198). However, other nonparametric analyses such as GENEHUNTER and model-free linkage (MFLINK) analysis did not yield significant results. Combined LOD scores for the 12 families were strongly negative for all six markers under six genetic models. Two-point and multipoint analyses of individual families revealed one family, family 17, with maximal LOD scores greater than 1.41 for the 10.5-cM region between PFKL and D21S198. This report provides additional support for the suggestive linkage of a susceptibility locus for BAD on chromosome 21q22.3.

Exclusion of linkage between bipolar affective disorder and chromosome 16 in 12 Australian pedigrees

Several recent reports of possible susceptibility loci for bipolar affective disorder (BAD) have identified sites on a number of chromosomes. Specifically, two Danish studies have suggested the presence of a susceptibility locus for BAD on chromosome 16p13. As the first step of a whole genome scan, we screened 12 Australian families with markers at 16p13 and also a number of markers spanning the entirety of chromosome 16. Linkage analysis was undertaken using both the parametric lod score method (two- and multipoint) with different models and diagnostic thresholds, and the nonparametric affected pedigree member (APM) method. Results of lod score analysis convincingly excluded the 16p13 region from linkage to BAD in these families, while APM provided no support for linkage. Furthermore, using the broad definition of BAD, with individuals affected by bipolar I and II and recurrent unipolar disorders included, the entire chromosome was excluded from linkage to BAD with autosomal-dominant transmission at a maximum age-specific penetrance of 60%, and with autosomal-dominant and recessive modes of transmission at a maximum age-specific penetrance level of 90%. Diagnostic thresholds which did not include unipolar affected individuals were somewhat less informative. However, a majority (between 63-96%, depending upon the model) of the chromosome was clearly excluded using narrow diagnostic thresholds. Moreover, no positive lod scores were obtained at theta = 0.00 for any tested model or diagnostic threshold. Our results indicate that no linkage exists between BAD and chromosome 16 markers in this group of Australian families.

Characterization of the genomic structure, promoter region, and a tetranucleotide repeat polymorphism of the human neurotensin receptor gene

In the present study, we have cloned the human neurotensin receptor (NTR) gene, determined its structure, demonstrated that its promoter is functional in transfection experiments, and identified the start site of transcription and a tetranucleotide repeat polymorphism that locates at less than 3 kilobase pairs from the gene. The gene contains three introns, all in the coding regions. Several differences in genomic clones and previously characterized cDNA sequences are reconciled. The 5' regulatory region, which is rich in presumptive transcription factors, can drive luciferase expression in transfected CHO-K1 cells. Stepwise 5' deletions identify a positive modulator between -782 and -1309 and a negative modulator between -1309 and -1563. Southern blot analyses demonstrate a single copy gene for the NTR. The tetranucleotide repeat polymorphism is highly informative with at least 23 alleles and might serve as a very useful marker for genetic study of the relationship between the NTR and neuropsychiatric disorders.

Stimulatory G-protein alpha-subunit mRNA levels are not increased in autopsied cerebral cortex from patients with bipolar disorder

Increased alpha-subunit (alpha s) levels of both the 45- and 52-kDa isoforms of the stimulatory guanine nucleotide binding protein (G-protein), have been found in postmortem brain and mononuclear leukocytes from patients with bipolar disorder (BD). The pathophysiological mechanism responsible for increased alpha s protein levels is unknown, however, it may involve increased expression of the gene encoding this protein. To assess this possibility, alpha s mRNA levels were determined by RT-PCR in postmortem brain from 10 subjects with an antemortem diagnosis of BD and age- and sex-matched control subjects in whom we had previously reported increased alpha s protein levels. There were no significant differences in alpha s mRNA levels in frontal, temporal, or occipital cortex between BD and control subjects. Cerebral cortex alpha s mRNA levels did not correlate with age or postmortem interval. These findings do not support the notion that higher alpha s levels found in BD postmortem brain are a result of increased gene expression.

Nonlinkage of D6S260, a putative schizophrenia locus, to bipolar affective disorder

To examine whether genes that predispose to schizophrenia also confer a predisposition to other psychiatric disorders such as bipolar affective disorder (BAD), we tested for linkage between the recently identified schizophrenia susceptibility locus D6S260 and the inheritance of BAD in 12 large Australian pedigrees. We found no evidence for linkage over a region of 12-27 cM from the D6S260 locus, depending on the model used. Our results therefore do not provide support for the continuum theory of psychosis.

A systematic evaluation of linkage studies in bipolar disorder

Genetic factors have long been implicated in the aetiology of bipolar disorder (BD). During the past two decades several linkage studies have been carried out with the aim of identifying major genes. However, remarkable discrepancies in results both between and within studies have constituted a major problem. In order to elucidate some of these conflicts, we assessed the published literature on linkage studies of bipolar disorder, focusing on methodological issues. Studies published between January 1980 and December 1994 were identified by computerized literature searches and subsequent scanning of review articles, and the reference lists of the articles primarily identified. A set of defined inclusion and exclusion criteria was used to select studies for assessment. A total of 31 variables were determined, and pre-defined codes were assigned in a structured manner. More than 200 citations were reviewed, and 60 articles were included in this study. Descriptive statistical analyses of the variables, as well as associations between variables, are presented. The findings are discussed with regard to the possibility that, beyond the genetic complexity of the disorder itself, there are several other similarly complicated study design issues which should be more carefully observed. Moreover, the need for standardization of basic criteria to use and report clinical and analytical parameters employed in linkage studies is strongly suggested.