European Neuropsychopharmacology (v.11, #6)

Genetics of affective disorders by Carolina Johansson; Mårten Jansson; Love Linnér; Qiu-Ping Yuan; Nancy L Pedersen; Douglas Blackwood; Nicholas Barden; John Kelsoe; Martin Schalling (385-394).
Despite substantial evidence for heritability in affective disorders the contributing genes have proven elusive. Here we discuss the genetic epidemiology of depression, as well as methodological issues and results from molecular genetic studies. There has been rapid advances in genetics, genomics and statistical modelling, facilitating the search for molecular mechanisms underlying affective disorders and several strategies reviewed in this paper hold promise to provide progress in the field. Considering the poorly understood biological basis of vulnerability to affective disorders, the identification of genes involved in the pathophysiology will unravel mechanisms and pathways that could permit more personalized therapeutic strategies and result in new targets for pharmacological intervention.
Keywords: Depression; Bipolar; Linkage analysis; Association study; Polymorphism;

Searching for susceptibility genes in schizophrenia by I Jurewicz; R.J Owen; M.C O’Donovan; M.J Owen (395-398).
The existence of an important genetic contribution to the aetiology of schizophrenia is well established from genetic epidemiological studies. However, the mode of transmission is complex and non-Mendelian. The main approaches used to identify susceptibility genes are linkage and association studies and the study of cytogenetic abnormalities associated with or linked to schizophrenia. Many linkage studies have been reported but have failed as yet to produce unequivocal, replicated demonstrations of linkage. However, modest evidence for several regions has been reported in more than one data set. Areas implicated include chromosome 22q11-12, 6p24-22, 6q, 8p22-21, 13q14.1-q32 and 1q21-q22, but in every case there are positive as well as negative findings. Most candidate gene studies have been based upon neuropharmacological studies suggesting that abnormalities in monoamine neurotransmission play a role in the aetiology of schizophrenia. Overall, the results have been disappointing, but it should be noted that the sample sizes in many of the older studies would now generally be regarded as inadequate. Finally, recent work has suggested that velo-cardio-facial syndrome (VCFS) is associated with rates of psychosis possibly as high as 30%. VCFS is caused by small interstitial deletions of chromosome 22q11 in 80–85% of individuals. Work is now under way to try and identify whether a gene or genes within the deleted region are of more general relevance to schizophrenia. Future directions in schizophrenia research include collecting larger samples to increase power of findings and applying novel methods for large-scale genotyping of single-nucleotide polymorphisms.
Keywords: Schizophrenia; Genetics; Linkage; Association;

Microarray technologies for measuring mRNA abundances in cells allow monitoring of gene expression levels for tens of thousands of genes in parallel. By measuring expression responses across hundreds of different conditions or timepoints a relatively detailed gene expression map starts to emerge. Using cluster analysis techniques, it is possible to identify genes that are consistently coexpressed under several different conditions or treatments. These sets of coexpressed genes can then be compared to existing knowledge about biochemical or signalling pathways, the function of unknown genes can be hypothesised by comparing them to other genes with characterised function, or from trends in expression profiles in general — why cell needs to transcribe or silence the genes during particular treatment. The regulation of genes on the DNA level is largely guided by particular sequence features, the transcription factor binding sites, and other signals encaptured in DNA. By analyzing the regulatory regions of the DNA of the genes consistently coexpressed, we can discover the potential signals hidden in DNA by computational analysis methods. The prerequisite for this kind of analysis is the existence of genomic DNA sequence, knowledge about gene locations, and experimental gene expression measurements for a variety of conditions. This article surveys some of the analysis methods and studies for such a computational discovery approach for yeast Saccharomyces cerevisiae.
Keywords: Gene expression analysis; Pattern discovery; Promoter analysis;

Combining genetic and genomic approaches to study mood disorders by Etienne Sibille; René Hen (413-421).
Recent technological advances in genetic manipulations and DNA microarrays are profoundly altering the landscape of biological research, offering opportunities to investigate biological questions that were only dreamed of a few years ago. With this revolution comes the hope of being able to tackle some of the more arduous challenges that the central nervous system has presented to the research community. Specifically, a major goal in the study of neuropsychiatric disorders has been to identify underlying mechanisms of brain dysfunction with the expectation that these insights may allow a better diagnosis, prevention and effective treatments for these disorders. For the most part, treatments of these disorders have relied on serendipitous discovery of pharmacological entities with therapeutic efficacy, while the causes of the disorders have remained unknown. The serotonin system, and the serotonin1A (5-HT1A) receptor in particular, have been under intense investigation, mostly due to the fact that serotonergic drugs that directly or indirectly affect the 5-HT1A receptor, are effective therapeutic agents in treating patients with various neuropsychiatric disorders, including anxiety and depression. Genetic deletion of the receptor in mouse results in increased anxiety, thus supporting an active role for this receptor in mood regulation. However, the analysis of genetic deletion experiments can be confounded by hidden developmental roles of the missing receptor, by adaptive compensatory mechanisms, as well by the fact that the genes or gene products that are responsible for the cellular and molecular aspects of the phenotype may be several steps removed from the genetic intervention. Here, we present a combined methodological approach of tissue specific and conditional genetic manipulations, with large-scale search for altered gene expression, as an experimental framework to investigate the role of genes with complex functions and/or complex expression patterns. The 5-HT1A receptor is used as a model of gene product with complex functions and distributions, and as a prototypical system to which these new genetic approaches are currently being applied.
Keywords: Serotonin receptor; Genetic; Genomic; Depression; Anxiety; Knockout; Microarray;

Genetic dissection of corticosterone receptor function in the rat hippocampus by Erno Vreugdenhil; E.Ronald de Kloet; Marcel Schaaf; Nicole A Datson (423-430).
The hippocampus, a brain structure with a crucial role in learning and memory and an involvement in stress-related neurological or psychiatric disorders, is extremely sensitive to aberrant levels of corticosteroid stress hormones (CORT). We hypothesized that CORT-affected brain disorders are the result of aberrant expression of specific CORT-responsive genes. In order to identify such genes, we have applied several gene expression profiling techniques such as differential display, DNA micro-arrays and in particular the highly sensitive serial analysis of gene expression (SAGE). Using SAGE, a total of 76,790 hippocampal tags were generated which together represent 28,748 unique mRNAs of which 4626 gave a hit with rat sequences in Genbank. By comparing SAGE profiles derived from rat hippocampi treated with different concentrations of corticosteroids, we have identified over 200 CORT-responsive genes with significant differential expression in hippocampus. The identified products include genes that are important for the plasticity of hippocampal neurones such as neural cell adhesion molecules, growth-promoting proteins, genes involved in axogenesis, synaptogenesis and signal-transduction. One novel corticosteroid-responsive gene, classified as Ca2+/calmodulin-dependent protein kinase (CaMK)-VI, exhibited structural resemblance with the family of CaMKs, in particular with that of CaMK-IV. We also identified an alternatively spliced mRNA of this gene encoding a peptide (CaMK-kinase related peptide or CARP) which may function in an autoregulatory feedback loop. These findings suggest a novel mode of operation of the CaMK pathway in control of Ca2+ homeostasis relevant for CORT-related brain disorders.
Keywords: Corticosterone; Hippocampus; Mineralocorticoid receptor; Glucocorticoid receptor; Expression profiling; Differential display; SAGE; Corticosterone-responsive genes; Neuronal plasticity; CaMK;

In clinical psychopharmacology, the existence of marked inter-individual differences in both outcome and side effects is a common observation. Consequently, pharmacogenetics has also gained an increasing interest in psychiatry. Recent exciting findings seem to suggest that the growing interest in regulatory regions of candidate genes and neurotransmitters metabolism, together with the application of sophisticated molecular approaches, may offer new opportunities in neuropsychopharmacology. Indeed, quantitative variation of gene expression and/or of neurotransmitters metabolism could better explain both psychopathology and clinical response to psychotropic drugs. Three functional polymorphisms, and their possible relationship with clinical variables, are discussed. The first is the 44-bp insertion/deletion reported in the promoter region of the serotonin transporter gene. A functional repeat polymorphism in the promoter region of the gene encoding for the enzyme monoamine oxidase A represents the second example. The last is a functional polymorphism within the coding region of the gene encoding for the enzyme catechol-O-methyltransferase
Keywords: Pharmacogenetics; Mood disorders; Panic disorder; Neurotransmitters;

Application of genomics to drug design: the example of the histamine H3 receptor by Jean-Charles Schwartz; Séverine Morisset; Agnès Rouleau; Joël Tardivel-Lacombe; Florence Gbahou; Xavier Ligneau; Anne Héron; Astrid Sasse; Holger Stark; Walter Schunack; Robin C Ganellin; Jean-Michel Arrang (441-448).
The histamine H3 receptor was characterized in the 1980s as an autoreceptor regulating histamine release in brain. Since then, selective drugs have been designed, many of them displaying a high potency in vivo, and used in many studies to delineate the implications of cerebral histaminergic systems in physiological functions such as arousal or cognitive functions. The recent cloning of the H3 receptor, more than 15 years later, has allowed to start molecular studies that led to important findings for optimization of drug design. In agreement some ligands display distinct affinities for the recombinant rat and human H3 receptors, a difference that we assign to two amino acids in the third transmembrane domain. In addition, H3 autoreceptors present in the brain display high constitutive activity including in vivo. As a consequence, inverse agonists enhance histamine neuron activity and constitute a novel potential therapeutic approach to schizophrenia and Alzheimer’s disease.
Keywords: Histaminergic systems; H3 autoreceptor; Constitutive activity; Inverse agonists;

The dopamine transporter is a plasma membrane protein that controls the spatial and temporal domains of dopamine neurotransmission through the accumulation of extracellular dopamine. The dopamine transporter may play a role in numerous dopamine-linked neuropsychiatric disorders. We review the cloning and organization of the human dopamine transporter gene, polymorphisms in its coding and noncoding sequence, and emerging data on its transcriptional regulation.
Keywords: Gene expression; Transcriptional regulation; Gene polymorphisms; Neuron-restrictive silencer; nurr1; Variable number tandem repeat;

Individual differences in drug effects and treatment response are relatively enduring, continuously distributed, as well as substantially heritable, and are therefore likely to result from an interplay of multiple genomic variations with environmental influences. As the etiology and pathogenesis of behavioral and psychiatric disorders is genetically complex, so is the response to drug treatment. Psychopharmacologic drug response depends on the structure and functional expression of gene products, which may be direct drug targets or may indirectly modify the development and synaptic plasticity of neural networks critically involved in drug response. While formation and integration of these neural networks is dependent on the action of manifold proteins, converging lines of evidence indicate that genetically controlled variability in the expression of genes critical to the development and plasticity of distinct neurocircuits influences a wide spectrum of quantitative traits including treatment response. During brain development, neurotransmitter systems (e.g. serotonergic system), which are frequently targeted by psychotropic drugs, control neuronal specification, differentiation, and phenotype maintenance. The formation and maturation of these neurotransmitter systems, in turn, is directed by an intrinsic genetic program. Based on the notion that complex gene–gene and gene environment interactions in the regulation of brain plasticity are presumed to contribute to interindividual differences in drug response, the concept of developmental psychopharmacogenetics is emerging. This review appraises prototypical genomic variation with impact on gene expression and complementary studies of genetic and environmental effects on brain development and synaptic plasticity in the mouse model. Although special emphasis is given to molecular mechanisms of neurodevelopmental genetics, relevant conceptual and methodological issues pertinent to the dissection of the psychopharmacogenetic–neurodevelopmental interface are also considered.
Keywords: Neuropsychopharmacology; Pharmacogenetics; Serotonin; Brain development; Synaptic plasticity; Candidate genes; Knockout mice;

Over just the past few years, tremendous progress has been made in unraveling the molecular basis of the circadian clock in mammals. This success has been primarily due to an approach whereby mutations are induced randomly in the germ line and the offspring of the mutagenized animals are tested for abnormal circadian phenotype. Circadian clock genes have been discovered this way in both fruit flies and mice and it is now clear that most, if not all clock genes show homology between flies and mammals, including humans. This ‘forward genetics’ approach is a powerful tool for uncovering genes which underline complex behaviors and brain disorders. Even when a complex neural function involves many, many genes, mutating just one of these genes can have pronounced effects on the expressed behavior and can lead to the discovery of other genes, and their protein products, that interact directly or indirectly with the mutated gene.
Keywords: Circadian; Sleep rhythms; Mutagenesis; Phenotype screening; Forward genetics;

The identification of the genetic defect underlying the obese phenotype of the viable yellow mouse, ectopic overexpression of the agouti protein which acts as antagonist at the melanocortin-4 receptor, together with the demonstration that the brain melanocortin system was one major downstream effector pathway of leptin signaling has put forward melanocortin receptors as drug targets for obesity. The lack of compounds acting as melanocortin receptor antagonists was the reason why pharmacological studies had not recognized melanocortin receptors as important drug targets earlier. Blockade of brain melanocortin receptors results in increased food intake and body weight, whereas stimulation of the brain melanocortin system results in decreased food intake and activation of the hypothalamo–pituitary–adrenal axis. Anorexia nervosa is characterized by decreased body weight and food intake accompanied by changes in neuroendocrine systems such as strong activation of the hypothalamo–pituitary–adrenal axis. Since agouti-related protein suppresses the activity of the melanocortin system, the AgRP gene was investigated as candidate gene in anorexia nervosa. One variant of the AgRP gene was associated with anorexia nervosa, thus putting forward melanocortin receptor blockade as putative pharmacotherapy. Investigating variations in candidate genes in disease populations appears to be a fruitful approach towards the identification of drug targets.
Keywords: Melanocyte-stimulating hormone; Agouti-related protein; Anorexia Nervosa; Obesity; Single nucleotide polymorphism;

Genomics, the complete tabulation of all the genes in an organism, has made a major impact on the organisation of fully-integrated pharmaceutical companies. Drug discovery begins with bioinformatic elucidation of a human sequence encoding a potential drug target, followed by cloning and expression of the gene in a format for high throughput screening. Target validation is aided by reference to homologous genes in subhuman species as well as production of transgenic animals. In contrast, the impact of genetics on neuropsychopharmacology has been modest. It is interesting to compare the experience of genetics in the two major clinical disciplines dealing with disorders of the nervous system. Neurology has been at the forefront of human genetics with over 600 disorders mapped, of which causative mutations have been assigned to about 200 Mendelian disorders, each individually rare. Psychiatric genetics has been based on two log fewer diagnoses use of which has only yielded complex segregation patterns, a plethora of weak associations and no gene assignments. In neither case has genetics resulted in the development of a novel therapeutic agent. However, by refinements in diagnosis and genetic technology the promise for the future is great, not only for drug discovery, but also for subsequent preclinical and clinical development.
Keywords: Genetics; Genomics; Drug discovery; Target validation; Clinical trials; Pharmacogenetics;