Genetic variation in the DAOA (G72) gene modulates hippocampal function in subjects at high risk of schizophrenia

d-Amino Acids and pLG72 in Alzheimer's Disease and Schizophrenia

Numerous studies over the last several years have shown that d-amino acids, especially d-serine, have been related to brain and neurological disorders. Acknowledged neurological functions of d-amino acids include neurotransmission and learning and memory functions through modulating N-methyl-d-aspartate type glutamate receptors (NMDARs). Aberrant d-amino acids level and polymorphisms of genes related to d-amino acids metabolism are associated with neurodegenerative brain conditions. This review summarizes the roles of d-amino acids and pLG72, also known as d-amino acid oxidase activator, on two neurodegenerative disorders, schizophrenia and Alzheimer’s disease (AD). The scope includes the changes in d-amino acids levels, gene polymorphisms of G72 genomics, and the role of pLG72 on NMDARs and mitochondria in schizophrenia and AD. The clinical diagnostic value of d-amino acids and pLG72 and the therapeutic importance are also reviewed.

Directly and Indirectly Targeting the Glycine Modulatory Site to Modulate NMDA Receptor Function to Address Unmet Medical Needs of Patients With Schizophrenia

Schizophrenia is a severe mental illness that affects ~1% of the world's population. It is clinically characterized by positive, negative, and cognitive symptoms. Currently available antipsychotic medications are relatively ineffective in improving negative and cognitive deficits, which are related to a patient's functional outcomes and quality of life. Negative symptoms and cognitive deficits are unmet by the antipsychotic medications developed to date. In recent decades, compelling animal and clinical studies have supported the NMDA receptor (NMDAR) hypofunction hypothesis of schizophrenia and have suggested some promising therapeutic agents. Notably, several NMDAR-enhancing agents, especially those that function through the glycine modulatory site (GMS) of NMDAR, cause significant reduction in psychotic and cognitive symptoms in patients with schizophrenia. Given that the NMDAR-mediated signaling pathway has been implicated in cognitive/social functions and that GMS is a potential therapeutic target for enhancing the activation of NMDARs, there is great interest in investigating the effects of direct and indirect GMS modulators and their therapeutic potential. In this review, we focus on describing preclinical and clinical studies of direct and indirect GMS modulators in the treatment of schizophrenia, including glycine, D-cycloserine, D-serine, glycine transporter 1 (GlyT1) inhibitors, and D-amino acid oxidase (DAO or DAAO) inhibitors. We highlight some of the most promising recently developed pharmacological compounds designed to either directly or indirectly target GMS and thus augment NMDAR function to treat the cognitive and negative symptoms of schizophrenia. Overall, the current findings suggest that indirectly targeting of GMS appears to be more beneficial and leads to less adverse effects than direct targeting of GMS to modulate NMDAR functions. Indirect GMS modulators, especially GlyT1 inhibitors and DAO inhibitors, open new avenues for the treatment of unmet medical needs for patients with schizophrenia.

Effect of DAOA genetic variation on white matter alteration in corpus callosum in patients with first-episode schizophrenia

D-amino acid oxidase activator (DAOA) gene, which plays a crucial role in the process of glutamatergic transmission and mitochondrial function, is frequently linked with the liability for schizophrenia. We aimed to investigate whether the variation of DAOA rs2391191 is associated with alterations in white matter integrity of first-episode schizophrenia (FES) patients; and whether it influences the association between white matter integrity, cognitive function and clinical symptoms of schizophrenia. Forty-six patients with FES and forty-nine healthy controls underwent DTI and were genotyped for DAOA rs2391191. Psychopathological assessments were performed by Brief Psychiatric Rating Scale (BPRS) and Scale for Assessment of Negative Symptoms (SANS). Cognitive function was assessed by MATRICS Consensus Cognitive Battery (MCCB). Schizophrenia patients presented lower fractional anisotropy (FA) and higher radial diffusivity (RD), mainly spreading over the corpus callosum and corona radiata compared with healthy controls. Compared with patients carrying G allele, patients with AA showed lower FA in the body of corpus callosum, and higher RD in the genu of corpus callosum, right superior and anterior corona radiata, and left posterior corona radiata. In patients carrying G allele, FA in body of corpus callosum was positively correlated with working memory, RD in genu of corpus callosum was negatively associated with the speed of processing, working memory, and the composite score of MCCB, while no significant correlations were found in AA homozygotes. In our study, patients with FES presented abnormal white matter integrity in corpus callosum and corona radiata. Furthermore, this abnormality was associated with the genetic variation of DAOA rs2391191, with AA homozygotes showing less white matter integrity in the corpus callosum. Our findings possibly provide further support to the evidence that DAOA regulates the process of glutamatergic neurotransmission and mitochondrial function in the pathophysiological mechanism of schizophrenia.

Genetic Effects of DISC1 and G72 (DAOA) on Visual Learning of Patients with Schizophrenia

BACKGROUND

Visual learning plays an important role in general populations and patients with schizophrenia. Genetic influences on visual learning remain unknown. Two functional single nucleotide polymorphisms (SNPs), Ser704Cys of the DISC1 gene and M24 (rs1421292) of the G72 gene, are strongly associated with pathogenesis and pathophysiology of schizophrenia. This study examined these two SNPs' effects on visual learning in schizophrenia patients.

METHODS

Two hundred seventy-one patients (mean age, 37.0 years [SD = 9.3]; 159 men) with chronic schizophrenia were genotyped for the DISC1 Ser704Cys and G72 M24 SNPs and assessed for visual learning with Visual Reproduction II (delayed reproduction) of Wechsler Memory Scale - III (WMS-III). For comparison, verbal learning (using Word list II of WMS-III) and attention (by Continuous Performance Test) were also measured.

RESULTS

The DISC1 Ser carriers excelled DISC1 Cys/Cys homozygotes in visual learning (p=0.004, effect size: 0.43), but not in other cognitive functions. G72 M24 A-allele carriers and G72 M24 T/T homozygotes performed similarly (effect size: 0.07). In SNP-SNP interaction analysis, the patients with Ser carrier_T/T had better visual learning than those with Cys/Cys_T/T (p=0.004, effect size: 0.70) and those with Cys/Cys_A-allele carrier (p=0.003, effect size: 0.65). Education had a positive effect (p=0.007), while negative symptoms had a negative effect (p<0.001) on visual learning.

CONCLUSION

The findings suggest that genetic variations in DISC1 Ser704Cys and G72 M24 affect visual learning in schizophrenia patients. The effect sizes of SNP-SNP interaction surpassed the sum (0.50) of effect sizes from two individual genes, suggesting synergistic DISC1-G72 interaction.

The DAOA gene is associated with schizophrenia in the Taiwanese population

The gene D-amino acid oxidase activator (DAOA), which has a former name of G72, and the D-amino acid oxidase (DAO) gene have been suggested as candidate genes of schizophrenia. However, association studies have so far yielded equivocal results. We analyzed one single nucleotide polymorphism (SNP) for DAO (rs3741775) and seven SNPs for G72 (rs3916956, rs2391191, rs9558562, rs947267, rs778292, rs3918342, and rs1421292) in this study enrolling 248 schizophrenia cases and 267 controls in the Taiwanese samples. In SNP-based single locus association analyses, the rs778292 in the DAOA gene showed significant association with schizophrenia. The rs3741775 in the DAO gene could not withstand statistically significant after multiple corrections. Additionally, a three-SNP haplotype (rs778292-rs3918342-rs1421292) in the DAOA gene were observed to be significantly associated with schizophrenia. Among them, the TCT haplotype presented higher prevalence in controls than in cases whereas the TTT and CTT haplotype were significantly more frequent in cases than in controls. The study also provides significant evidence for epistatic interactions among DAOA and DAO gene in the development of schizophrenia. These results provide additional evidence and indicate that the DAOA gene and DAOA-DAO gene-gene interactions might play a role for schizophrenia in a Taiwanese sample.

G72 primate-specific gene: a still enigmatic element in psychiatric disorders

Numerous studies have demonstrated a link between genetic markers on chromosome 13 and schizophrenia, bipolar affective disorder, and other psychiatric phenotypes. The G72/G30 genes (transcribed in opposite directions) are located on chromosome 13q33, a region demonstrating strong evidence for linkage with various neuropsychiatric disorders. G72/G30 was identified in 2002 as a schizophrenia susceptibility locus; however, subsequent association studies did not reach consensus on single SNPs within the locus. Simultaneously, a new vision for the genetic architecture of psychiatric disorders suggested that schizophrenia was a quantitative trait, therefore ascribable to potentially hundreds of genes and subjected to the vagaries of the environment. The main protein product of G72 gene is named pLG72 or D-amino acid oxidase activator DAOA (153 amino acids) and its function is still debated. Functional analyses, also showing controversial results, indicate that pLG72 contributes to N-methyl-D-aspartate receptor modulation by affecting activity of the flavoprotein D-amino acid oxidase, the enzyme responsible for degrading the neuromodulator D-serine. In this review we, for the first time, summarize findings from molecular genetic linkage and association studies concerning G72 gene, cellular and molecular studies on pLG72, and investigations performed on G72/G30 transgenic mice. This will help elucidate the role of psychosis susceptibility genes, which will have a major impact on our understanding of disease pathophysiology and thus change classification and treatment.

A genome-wide sib-pair scan for quantitative language traits reveals linkage to chromosomes 10 and 13

Although there is considerable evidence that individual differences in language development are highly heritable, there have been few genome-wide scans to locate genes associated with the trait. Previous analyses of language impairment have yielded replicable evidence for linkage to regions on chromosomes 16q, 19q, 13q (within lab) and at 13q (between labs). Here we report the first linkage study to screen the continuum of language ability, from normal to disordered, as found in the general population. 383 children from 147 sib-ships (214 sib-pairs) were genotyped on the Illumina(®) Linkage IVb Marker Panel using three composite language-related phenotypes and a measure of phonological memory (PM). Two regions (10q23.33; 13q33.3) yielded genome-wide significant peaks for linkage with PM. A peak suggestive of linkage was also found at 17q12 for the overall language composite. This study presents two novel genetic loci for the study of language development and disorders, but fails to replicate findings by previous groups. Possible reasons for this are discussed.

Cerebrospinal fluid monoamine metabolite concentrations as intermediate phenotypes between glutamate-related genes and psychosis

Glutamate-related genes have been associated with schizophrenia, but the results have been ambiguous and difficult to replicate. Homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) are the major degradation products of the monoamines dopamine, serotonin and noradrenaline, respectively, and their concentrations in the cerebrospinal fluid (CSF), mainly HVA, have been associated with schizophrenia. In the present study, we hypothesized that CSF HVA, 5-HIAA and MHPG concentrations represent intermediate phenotypes in the association between glutamate-related genes and psychosis. To test this hypothesis, we searched for association between 238 single nucleotide polymorphisms (SNPs) in ten genes shown to be directly or indirectly implicated in glutamate transmission and CSF HVA, 5-HIAA and MHPG concentrations in 74 patients with psychotic disease. Thirty-eight nominally significant associations were found. Further analyses in 111 healthy controls showed that 87% of the nominal associations were restricted to the patients with psychosis. Some of the psychosis-only-associated SNPs found in the d-amino acid oxidase activator (DAOA) and the kynurenine 3-monooxygenase (KMO) genes have previously been reported to be associated with schizophrenia. The present results suggest that CSF monoamine metabolite concentrations may represent intermediate phenotypes in the association between glutamate-related genes and psychosis.

Medial temporal lobe default mode functioning and hippocampal structure as vulnerability indicators for schizophrenia: a MRI study of non-psychotic adolescent first-degree relatives

BACKGROUND

Clues to the etiology and pathophysiology of schizophrenia can be examined in their first-degree relatives because they are genetically related to an ill family member, and have few confounds like medications. Brain abnormalities observed in young relatives are neurobiological indicators of vulnerability to illness. We examined the hypothesis that the hippocampus and parahippocampus are structurally abnormal and are related to default mode network (DMN) function and cognitive abnormalities in relatives of probands.

METHODS

Subjects were 27 non-psychotic, first-degree relatives of individuals diagnosed with schizophrenia, and 48 normal controls, ages 13 to 28, undergoing high-resolution magnetic resonance imaging (MRI) at 1.5 T. After structural scan acquisition a subset of subjects performed 2-back working memory (WM) and 0-back tasks during functional MRI (fMRI) alternating with rest. fMRI data were analyzed using SPM-8. Volumes of total cerebrum, hippocampus, and parahippocampal gyrus were measured using semi-automated morphometry.

RESULTS

Compared to controls, relatives had significantly smaller left hippocampi, without volumetric reduction in the parahippocampus. Relatives showed significantly less suppression of DMN activity in the left parahippocampal gyrus. Left hippocampal and posterior parahippocampal volumes were inversely and significantly associated with DMN processing (smaller volumes, less suppression) in relatives. Task suppression in parahippocampal gyrus significantly correlated with WM performance within the relatives.

CONCLUSION

Results support the hypothesis that the vulnerability to schizophrenia includes smaller hippocampi and DMN suppression deficits, and these are associated with poorer WM. Findings suggest a primary structural, neurodevelopmental, medial temporal lobe abnormality associated with altered DMN function independent of psychosis.

Genomics and epigenomics in novel schizophrenia drug discovery: translating animal models to clinical research and back

INTRODUCTION

Schizophrenia is a major psychiatric disorder that afflicts about 1% of the world's population, falling into the top 10 medical disorders causing disability. Existing therapeutic strategies have had limited success; they have poor effects on core cognitive impairment and long-term disability. They are also burdened by relevant side effects. Although new antipsychotic medications have been launched in the past decades, there has been a general lack of significant innovation over the past 60 years. This lack of significant progress in the pharmacotherapy of schizophrenia is a reflection of the complexity and heterogeneity of its etiopathogenetic mechanisms.

AREAS COVERED

In this article, the authors briefly review genetic models of schizophrenia, focusing on examples of how new therapeutic strategies have been developed from them. They report on the evidence of epigenetic alterations in schizophrenia and their relevance to pharmacological studies. Further, they describe the implications of epigenetic mechanisms in the etiopathogenesis of the disease and the effects of current antipsychotic drugs on epigenetic processes. Finally, they provide their perspective of using epigenetic drugs for treating schizophrenia.

EXPERT OPINION

Current genetic and epigenetic studies are finally shedding light on the biomolecular mechanisms linked to the core pathogenetic alterations in schizophrenia, rather than just their symptoms. These advancements in the understanding of the physiopathology of schizophrenia provide exciting new perspectives for treatments. Indeed, the possibility of looking directly at the biomolecular level allows us to bypass the age-old issues of animal studies pertaining to their questionable validity as behavioral models.

A proposal for reframing schizophrenia research

The current schizophrenia concept is built on experts' agreement on the matter, and it is basically rooted in the epidemiological and clinical evidence. However, the numerous and intensive attempts to find the biological underpinnings of this syndrome face almost constantly a low degree of replication of the results. We have reviewed previously published work to contribute to identify some reasons underlying that failure. The difficulty in replicating biological findings in schizophrenia may relate to the intrinsic heterogeneity among patient samples, acquired through the current diagnostic criteria. As a result, the necessary replication for any finding to be accepted as characteristic data for schizophrenia would be impeded. Therefore, a new frame based on identification of correlates of the most replicated biological anomalies in schizophrenia to date may contribute to overcome those difficulties.

Interaction between effects of genes coding for dopamine and glutamate transmission on striatal and parahippocampal function

The genes for the dopamine transporter (DAT) and the D-Amino acid oxidase activator (DAOA or G72) have been independently implicated in the risk for schizophrenia and in bipolar disorder and/or their related intermediate phenotypes. DAT and G72 respectively modulate central dopamine and glutamate transmission, the two systems most robustly implicated in these disorders. Contemporary studies have demonstrated that elevated dopamine function is associated with glutamatergic dysfunction in psychotic disorders. Using functional magnetic resonance imaging we examined whether there was an interaction between the effects of genes that influence dopamine and glutamate transmission (DAT and G72) on regional brain activation during verbal fluency, which is known to be abnormal in psychosis, in 80 healthy volunteers. Significant interactions between the effects of G72 and DAT polymorphisms on activation were evident in the striatum, parahippocampal gyrus, and supramarginal/angular gyri bilaterally, the right insula, in the right pre-/postcentral and the left posterior cingulate/retrosplenial gyri (P < 0.05, FDR-corrected across the whole brain). This provides evidence that interactions between the dopamine and the glutamate system, thought to be altered in psychosis, have an impact in executive processing which can be modulated by common genetic variation.

Using the high-risk family design to identify biomarkers for major depression

The familial nature of major depressive disorder (MDD) is now well recognized. We followed children and grandchildren of probands with and without MDD to examine transmission of depression over generations, and to identify early vulnerability markers prior to the onset of disease. The study now includes three generations and five completed assessment waves spanning 25 years, with a sixth wave underway. Beginning with the fourth wave, we collected measures of brain structure (magnetic resonance imaging, MRI) and physiology (electroencephalography, EEG) and DNA in order to examine at a biological level why the offspring of depressed parents were at higher risk. In this paper, we provide an overview of the study design, the main findings, including new data, and the role of the high-risk design in translational research. We demonstrate that offspring of depressed parents ('high-risk'), when compared with those of non-depressed parents ('low-risk'), were at increased risk for depressive and anxiety disorders, with anxiety appearing earlier and being a predisposing factor for MDD. Offspring with two generations previously affected were at greatest risk. Thinning of the cortical mantle (MRI) and reduced resting-state activity (EEG) within the right parieto-temporal hemisphere differentiated high- from low-risk offspring, regardless of whether the offspring had MDD, suggesting that these measures might serve as familial trait markers for depression and related syndromes. The high- and low-risk offspring also differed by serotonin transporter promoter length polymorphism genotypes, even though the same genotypes were not associated with the presence of MDD. The high-risk epidemiological design appears to be a particularly valuable asset in translational research as it allows targeting of biological processes that emerge prior to the onset of disease, and identifies individuals at high risk for the disorder who may carry the trait or marker but not yet be affected.

D-serine and schizophrenia: an update

Considering the lengthy history of pharmacological treatment of schizophrenia, the development of novel antipsychotic agents targeting the glutamatergic system is relatively new. A glutamatergic deficit has been proposed to underlie many of the symptoms typically observed in schizophrenia, particularly the negative and cognitive symptoms (which are less likely to respond to current treatments). D-serine is an important coagonist of the glutamate NMDA receptor, and accumulating evidence suggests that D-serine levels and/or activity may be dysfunctional in schizophrenia and that facilitation of D-serine transmission could provide a significant therapeutic breakthrough, especially where conventional treatments have fallen short. A summary of the relevant animal data, as well as genetic studies and clinical trials examining D-serine as an adjunct to standard antipsychotic therapy, is provided in this article. Together, the evidence suggests that research on the next generation of antipsychotic agents should include studies on increasing brain levels of D-serine or mimicking its action on the NMDA receptor.

A genome-wide search for genetic influences and biological pathways related to the brain's white matter integrity

A genome-wide search for genetic variants influencing the brain's white matter integrity in old age was conducted in the Lothian Birth Cohort 1936 (LBC1936). At ∼73 years of age, members of the LBC1936 underwent diffusion MRI, from which 12 white matter tracts were segmented using quantitative tractography, and tract-averaged water diffusion parameters were determined (n = 668). A global measure of white matter tract integrity, g(FA), derived from principal components analysis of tract-averaged fractional anisotropy measurements, accounted for 38.6% of the individual differences across the 12 white matter tracts. A genome-wide search was performed with g(FA) on 535 individuals with 542,050 single nucleotide polymorphisms (SNPs). No single SNP association was genome-wide significant (all p > 5 × 10(-8)). There was genome-wide suggestive evidence for two SNPs, one in ADAMTS18 (p = 1.65 × 10(-6)), which is related to tumor suppression and hemostasis, and another in LOC388630 (p = 5.08 × 10(-6)), which is of unknown function. Although no gene passed correction for multiple comparisons in single gene-based testing, biological pathways analysis suggested evidence for an over-representation of neuronal transmission and cell adhesion pathways relating to g(FA).

Effect of D-amino acid oxidase activator (DAOA; G72) on brain function during verbal fluency

BACKGROUND

The D-Amino acid oxidase activator (G72 or DAOA) is believed to play a key role in the regulation of central glutamatergic transmission which is seen to be altered in psychosis. It is thought to regulate D-amino acid oxidase (DAO), which metabolizes D-serine, a co-agonist of NMDA-type glutamate receptors and to be involved in dendritic arborization. Linkage, genetic association and expression studies have implicated the G72 gene in both schizophrenia and bipolar disorder.

AIMS

To examine the influence of G72 variation on brain function in the healthy population.

METHOD

Fifty healthy volunteers were assessed using functional magnetic resonance imaging while performing a verbal fluency task. Regional brain activation and task-dependent functional connectivity during word generation was compared between different rs746187 genotypes.

RESULTS

G72 rs746187 genotype had a significant effect on activation in the left postcentral and supramarginal gyri (FWE P < 0.05), and on the task-dependent functional coupling of this region with the retrosplenial cingulate gyrus (FWE P < 0.05).

CONCLUSIONS

Our results may reflect an effect of G72 on glutamatergic transmission, mediated by an influence on D-amino acid oxidase activity, on brain areas particularly relevant to the hypoglutamatergic model of psychosis.

D-amino acid oxidase activator gene (DAOA) variation affects cerebrospinal fluid homovanillic acid concentrations in healthy Caucasians

The D-amino acid oxidase activator (DAOA) protein regulates the function of D-amino oxidase (DAO), an enzyme that catalyzes the oxidative deamination of D-3,4-dihydroxyphenylalanine (D-DOPA) and D-serine. D-DOPA is converted to L-3,4-DOPA, a precursor of dopamine, whereas D-serine participates in glutamatergic transmission. We hypothesized that DAOA polymorphisms are associated with dopamine, serotonin and noradrenaline turnover in the human brain. Four single-nucleotide polymorphisms, previously reported to be associated with schizophrenia, were genotyped. Cerebrospinal fluid (CSF) samples were drawn by lumbar puncture, and the concentrations of the major dopamine metabolite homovanillic acid (HVA), the major serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) and the major noradrenaline metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG) were measured. Two of the investigated polymorphisms, rs3918342 and rs1421292, were significantly associated with CSF HVA concentrations. Rs3918342 was found to be nominally associated with CSF 5-HIAA concentrations. None of the polymorphisms were significantly associated with MHPG concentrations. Our results indicate that DAOA gene variation affects dopamine turnover in healthy individuals, suggesting that disturbed dopamine turnover is a possible mechanism behind the observed associations between genetic variation in DAOA and behavioral phenotypes in humans.

Translational epidemiology in psychiatry: linking population to clinical and basic sciences

Translational research generally refers to the application of knowledge generated by advances in basic sciences research translated into new approaches for diagnosis, prevention, and treatment of disease. This direction is called bench-to-bedside. Psychiatry has similarly emphasized the basic sciences as the starting point of translational research. This article introduces the term translational epidemiology for psychiatry research as a bidirectional concept in which the knowledge generated from the bedside or the population can also be translated to the benches of laboratory science. Epidemiologic studies are primarily observational but can generate representative samples, novel designs, and hypotheses that can be translated into more tractable experimental approaches in the clinical and basic sciences. This bedside-to-bench concept has not been explicated in psychiatry, although there are an increasing number of examples in the research literature. This article describes selected epidemiologic designs, providing examples and opportunities for translational research from community surveys and prospective, birth cohort, and family-based designs. Rapid developments in informatics, emphases on large sample collection for genetic and biomarker studies, and interest in personalized medicine--which requires information on relative and absolute risk factors--make this topic timely. The approach described has implications for providing fresh metaphors to communicate complex issues in interdisciplinary collaborations and for training in epidemiology and other sciences in psychiatry.

Are we studying and treating schizophrenia correctly?

New findings are rapidly revealing an increasingly detailed image of neural- and molecular-level dysfunction in schizophrenia, distributed throughout interconnected cortico-striato-pallido-thalamic circuitry. Some disturbances appear to reflect failures of early brain maturation, that become codified into dysfunctional circuit properties, resulting in a substantial loss of, or failure to develop, both cells and/or appropriate connectivity across widely dispersed brain regions. These circuit disturbances are variable across individuals with schizophrenia, perhaps reflecting the interaction of multiple different risk genes and epigenetic events. Given these complex and variable hard-wired circuit disturbances, it is worth considering how new and emerging findings can be integrated into actionable treatment models. This paper suggests that future efforts towards developing more effective therapeutic approaches for the schizophrenias should diverge from prevailing models in genetics and molecular neuroscience, and focus instead on a more practical three-part treatment strategy: 1) systematic rehabilitative psychotherapies designed to engage healthy neural systems to compensate for and replace dysfunctional higher circuit elements, used in concert with 2) medications that specifically target cognitive mechanisms engaged by these rehabilitative psychotherapies, and 3) antipsychotic medications that target nodal or convergent circuit points within the limbic-motor interface, to constrain the scope and severity of psychotic exacerbations and thereby facilitate engagement in cognitive rehabilitation. The use of targeted cognitive rehabilitative psychotherapy plus synergistic medication has both common sense and time-tested efficacy with numerous other neuropsychiatric disorders.

Intermediate phenotypes in psychiatric disorders

The small effect size of most individual risk factors for psychiatric disorders likely reflects biological heterogeneity and diagnostic imprecision, which has encouraged genetic studies of intermediate biological phenotypes that are closer to the molecular effects of risk genes than are the clinical symptoms. Neuroimaging-based intermediate phenotypes have emerged as particularly promising because they map risk associated gene effects onto physiological processes in brain that are altered in patients and in their healthy relatives. Recent evidence using this approach has elucidated discrete, dissociable biological mechanisms of risk genes at the level of neural circuitries, and their related cognitive functions. This approach may greatly contribute to our understanding of the genetics and pathophysiology of psychiatric disorders.

Integrative circuit models and their implications for the pathophysiologies and treatments of the schizophrenias

A preponderance of evidence indicates that the heterogeneous group of schizophrenias is accompanied by disturbances in neural elements distributed throughout multiple levels of interconnected cortico-striato-pallido-thalamic circuitry. These disturbances include a substantial loss of, or failure to develop, both cells and/or appropriate cellular connections in regions that include at least portions of the hippocampus, parahippocampal gyrus, entorhinal cortex, amygdala, prefrontal and anterior cingulate cortex, superior and transverse temporal gyri, and mediodorsal, anterior, and pulvinar nuclei of the thalamus; they appear to reflect failures of early brain maturation, that become codified into dysfunctional circuit properties, that in the opinion of this author cannot be "undone" or even predictably remediated in any physiological manner by existing pharmacotherapies. These circuit disturbances are variable across individuals with schizophrenia, perhaps reflecting the interaction of multiple different risk genes and multiple different epigenetic events. Evidence for these complex circuit disturbances has significant implications for many areas of schizophrenia research, and for future efforts toward developing more effective therapeutic approaches for this group of disorders. The conclusion of this chapter is that such future efforts should focus on further developing and refining medications that target nodal or convergent circuit points within the limbic-motor interface, with the goal of constraining the scope and severity of psychotic exacerbations, to be used in concert with systematic rehabilitative psychotherapies designed to engage healthy neural systems to compensate for and replace dysfunctional higher circuit elements. This strategy should be applied in both preventative and treatment settings, and disseminated for community delivery via an evidence-based manualized format. In contrast to alternative treatment strategies that range from complex polypharmacy to gene therapies to psychosurgical interventions, the use of combined medication plus targeted cognitive and behavioral psychotherapy has both common sense and time-tested documented efficacy with numerous other neuropsychiatric disorders.

Contributions of the D-serine pathway to schizophrenia

The glutamate neurotransmitter system is one of the major candidate pathways for the pathophysiology of schizophrenia, and increased understanding of the pharmacology, molecular biology and biochemistry of this system may lead to novel treatments. Glutamatergic hypofunction, particularly at the NMDA receptor, has been hypothesized to underlie many of the symptoms of schizophrenia, including psychosis, negative symptoms and cognitive impairment. This review will focus on D-serine, a co-agonist at the NMDA receptor that in combination with glutamate, is required for full activation of this ion channel receptor. Evidence implicating D-serine, NMDA receptors and related molecules, such as D-amino acid oxidase (DAO), G72 and serine racemase (SRR), in the etiology or pathophysiology of schizophrenia is discussed, including knowledge gained from mouse models with altered D-serine pathway genes and from preliminary clinical trials with D-serine itself or compounds modulating the D-serine pathway. Abnormalities in D-serine availability may underlie glutamatergic dysfunction in schizophrenia, and the development of new treatments acting through the D-serine pathway may significantly improve outcomes for many schizophrenia patients.

Genetic variation in G72 correlates with brain activation in the right middle temporal gyrus in a verbal fluency task in healthy individuals

The D-amino acid oxidase activator gene (G72) has been found associated with several psychiatric disorders such as schizophrenia, major depression, and bipolar disorder. Impaired performance in verbal fluency tasks is an often replicated finding in the mentioned disorders. In functional neuroimaging studies, this dysfunction has been linked to signal changes in prefrontal and lateral temporal areas and could possibly constitute an endophenotype. Therefore, it is of interest whether genes associated with the disorders, such as G72, modulate verbal fluency performance and its neural correlates. Ninety-six healthy individuals performed a semantic verbal fluency task while brain activation was measured with functional MRI. All subjects were genotyped for two single nucleotide polymorphisms (SNP) in the G72 gene, M23 (rs3918342) and M24 (rs1421292), that have previously shown association with the above-mentioned disorders. The effect of genotype on brain activation was assessed with fMRI during a semantic verbal fluency task. Although there were no differences in performance, brain activation in the right middle temporal gyrus (BA 39) and the right precuneus (BA 7) was positively correlated with the number of M24 risk alleles in the G72 gene. G72 genotype does modulate brain activation during language production on a semantic level in key language areas. These findings are in line with structural and functional imaging studies in schizophrenia, which showed alterations in the right middle temporal gyrus.

Is the EFNB2 locus associated with schizophrenia? Single nucleotide polymorphisms and haplotypes analysis

Recently, evidence of linkage of schizophrenia to chromosome 13q22-q34 has been demonstrated in multiple studies. Based on structure and function, EFNB2 may be considered as a compelling candidate gene for schizophrenia on chromosome 13q33. We genotyped three single-nucleotide polymorphisms (SNPs: rs9520087, rs11069646, and rs8000078) in this region in 846 Han Chinese subjects (477 cases and 369 controls). Significant association between an allele of marker rs9520087 and schizophrenia was found. Furthermore, since no LD was observed in the three SNPs linkage disequilibrium estimation, all three SNPs were used in multiple SNPs haplotype analysis, and a strongly significant difference was found for the common haplotype TTC. Overall our findings indicate that EFNB2 gene may be a candidate susceptibility gene for schizophrenia in the Han Chinese population, and also provide further support for the potential importance of the NMDA receptor pathway in the etiology of schizophrenia.

Schizophrenia risk genes: Implications for future drug development and discovery

Present-day development of improved treatments for schizophrenia is hindered by uncertain models of disease, inter-individual response variability in clinical trials and a paucity of sensitive measures of treatment effects. Findings from genetic research emphasize the potential for schizophrenia risk genes to help develop focused treatments, discover new drug targets and provide markers of clinical subtypes. Advances in genetic technologies also provide novel modes of drug discovery in schizophrenia such as transcriptomics, epigenetics and transgenic animal models. In this review, we discuss proven and proposed ways risk genes can be used to enhance the development and discovery of treatments for schizophrenia and highlight key studies in these approaches.

Selected summaries from the XVII World Congress of Psychiatric Genetics, San Diego, California, USA, 4-8 November 2009

The XVII World Congress of Psychiatric Genetics, sponsored by The International Society of Psychiatric Genetics (ISPG) took place in San Diego, California from 4 to 8 November 2009. Approximately 550 participants gathered to discuss the latest molecular genetic findings relevant to serious mental illness, including schizophrenia, mood disorders, substance abuse, autism, and attention deficit disorder. Recent advances in the field were discussed, including the genome-wide association studies results, copy number variation (CNV) in the genome, genomic imaging, and large multicenter collaborations. The following report, written by junior travel awardees who were assigned sessions as rapporteurs represents some of the areas covered in oral presentation during the conference, and reports on some of the notable major new findings described at this 2009 World Congress of Psychiatric Genetics.

Influence of DAOA gene variants on antipsychotic response after switch to aripiprazole

We investigated possible influences of 3 single nucleotide polymorphisms in the d-amino acid oxidase activator (rs2391191, rs947267, rs3918342) on clinical outcomes and side effects in 86 Korean schizophrenia patients treated with aripiprazole for 8weeks, finding that individuals carrying rs2391191 A allele had significantly lower brief psychiatric rating scale scores than subjects carrying the G allele at each time point. Further research is needed to determine the role of DAOA on the response to antipsychotics.

Grey matter and cognitive deficits in young relatives of schizophrenia patients

Grey-matter volumetric and cognitive deficits in young, high-risk relatives of schizophrenia patients may be vulnerability markers of the illness. Although these markers may be correlated, it is unclear if their distributions in relatives overlap. We examined convergence of these markers in 94 young first and second-degree relatives (HR) and 81 healthy controls. Subjects were assessed using WCST, CPT-IP and Benton-Hamscher tests and on grey-matter volumes of brain regions related to language, attention and executive function using FreeSurfer to process T1-MR-images. K-means clustering using cognitive performance scores split relatives into sub-samples with better (HR+C, n=35) and worse (HR-C, n=59) cognition after controlling for age and gender. All regional volumes and language related regional laterality-indices were compared between HR-C, HR+C and control subjects, controlling for age, gender and intra-cranial volume. Volumes of caudate nuclei, thalami, hippocampi, inferior frontal gyri, Heschl's gyri, superior parietal cortices, supramarginal gyri, right angular gyrus, right middle frontal gyrus and right superior frontal gyrus, leftward laterality of supramarginal and inferior frontal gyri and rightward laterality of the angular gyrus were reduced in HR-C compared to controls. Volumes of Heschl's gyri, left supramarginal gyrus, inferior frontal gyri, hippocampi and caudate nuclei HR-C were smaller in HR-C compared to HR+C. HR+C showed deficits compared to controls only for the superior parietal and right angular volumes. Premorbid neuroanatomical and laterality alterations in schizophrenia may selectively manifest in cognitively compromised relatives. Overlapping structural and cognitive deficits may define a hyper vulnerable sub-sample among individuals at familial predisposition to schizophrenia.

G72 influences longitudinal change in frontal lobe volume in schizophrenia

Schizophrenia is a neurodevelopmental psychiatric disorder characterized by a variety of structural brain abnormalities that appear to progress across the course of illness. Schizophrenia also is highly heritable, and one gene that has emerged as a possible susceptibility factor is G72. G72 influences brain development and activity by an as-yet unclear mechanism, and multiple studies have reported associations between G72 and schizophrenia. We were interested in linking these domains of investigation by determining whether G72 also influences the rate of longitudinal structural brain changes in individuals with schizophrenia. As part of the Iowa Longitudinal Study of Recent Onset Psychoses, we genotyped four G72 polymorphisms previously associated with schizophrenia in 110 subjects with schizophrenia or schizoaffective disorder from whom we had obtained two brain MRI scans an average of 3 years apart. The four polymorphisms captured three haplotypes, one of which was strongly associated with an increased rate of frontal lobe volume decrement. This same haplotype was also associated with more severe psychotic symptoms at the time of the second scan. These data thus suggest that variation in G72 modulates the progressive brain changes that characterize schizophrenia.

The effect of G72 genotype on neural correlates of memory encoding and retrieval

Polymorphisms in the G72 (also named d-amino acid oxidase activator, DAOA) gene increase the vulnerability for schizophrenia and affective psychosis. Three recent genetic neuroimaging studies showed that variation in G72 influences the brain activity in the medial temporal lobe (MTL), supporting the hypothesis that G72 might play a modulatory role on brain activity in MTL structures. In the present study we therefore investigated the effect of G72 on the neural correlates of long-term memory encoding and retrieval in a large sample of healthy subjects (n=83) using functional magnetic resonance imaging. A face encoding and a face retrieval memory task were chosen because on the one hand they specifically activate MTL structures and on the other hand they tap into memory processes that are compromised in patients with schizophrenia and affective disorder. Despite a strong a-priori hypothesis of genotype group activation differences in the MTL along with a large sample size we did neither find an effect of G72 genotype status on brain activity in the MTL nor in any other brain regions. The present data therefore do not support the view of a general modulatory role of G72 on MTL brain activity, at least not in the domain of long-term memory encoding and retrieval. Our results highlight the importance of replication studies in genetic neuroimaging.

Effect of the G72 (DAOA) putative risk haplotype on cognitive functions in healthy subjects

BACKGROUND

In the last years, several susceptibility genes for psychiatric disorders have been identified, among others G72 (also named D-amino acid oxidase activator, DAOA). Typically, the high-risk variant of a vulnerability gene is associated with decreased cognitive functions already in healthy individuals. In a recent study however, a positive effect of the high-risk variant of G72 on verbal working memory was reported. In the present study, we therefore examined the relationship between G72 genotype status and a broad range of cognitive functions in 423 healthy individuals.

METHODS

The G72 carrier status was assessed by the two single nucleotide polymorphisms (SNPs) M23 and M24. Subjects were divided into three risk groups (low, intermediate and high risk).

RESULTS

G72 status influenced a number of cognitive functions, such as verbal working memory, attention, and, at a trend level, spatial working memory and executive functions. Interestingly, the high-risk allele carriers scored better than one or even both other groups.

CONCLUSION

Our data show that the putative high-risk haplotype (i.e. homozygote C/C-allele carriers in SNP M23 and homozygote T/T-allele carriers in SNP M24) is in healthy individuals not necessarily associated with worse performance in cognitive functions, but even with better performance in some domains. Further work is required to identify the mechanisms of G72 on brain functions.

Genetic variation in the G72 (DAOA) gene affects temporal lobe and amygdala structure in subjects affected by bipolar disorder

BACKGROUND

Variation in the G72 (DAOA) gene is understood to convey susceptibility for bipolar disorder through an uncertain mechanism. Little is known about the structural brain phenotypes associated with this gene. We hypothesised that reductions in temporal lobe and amygdala gray matter would be associated with variation at two loci in the gene for which evidence of genetic linkage has been repeatedly demonstrated.

METHODS

We examined the temporal lobe and amygdala gray matter associations of the risk variants M23 and M24 at the 5' end of the gene encoding G72 in 81 controls and 38 people with bipolar disorder.

RESULTS

Genetic variation at both the M23 and M24 loci in G72 were associated with decreased gray matter density within the left temporal pole in people with bipolar disorder. M23 was also associated with reductions in right amygdala gray matter density. The genetic imaging associations were found only in patients with bipolar disorder.

CONCLUSIONS

Genetic variation at single nucleotide polymorphisms in the G72 gene previously associated with bipolar disorder is related to reductions in temporal pole and amygdala gray matter structure in people with bipolar disorder.

G72 gene is associated with susceptibility to methamphetamine psychosis

Methamphetamine psychosis is considered as one of the pharmacological models of schizophrenia, and a hyperdopaminergic one. However, many lines of experimental evidence indicate that glutamatergic signaling is also involved in development of methamphetamine psychosis. Several genes related to glutamate function, e.g. the DTNBP1, G72, and GRM3 genes, were shown to be associated with schizophrenia susceptibility. Recently, we found significant association of the DTNBP1 gene with methamphetamine psychosis. This finding prompted us to examine the G72 gene encoding the d-amino acid oxidase activator (DAOA), which metabolizes d-serine, an NMDA co-agonist, in methamphetamine psychosis. Six SNPs of the G72 gene, which previously showed significant association with schizophrenia, were analyzed in 209 patients with methamphetamine psychosis and 291 age- and sex-matched normal controls. One SNP of M22 (rs778293) showed a significant association with methamphetamine psychosis (genotype: p=0.00016, allele: p=0.0015). Two haplotypes G-A of M12 (rs3916965)-M15 (rs2391191) (p=0.00024) and T-T of M23 (rs947267)-M24 (rs1421292) (p=0.00085) also showed associations with methamphetamine psychosis. The present findings suggest that the G72 gene may contribute to a predisposition to not only schizophrenia but also to methamphetamine psychosis.

The involvement of the NMDA receptor D-serine/glycine site in the pathophysiology and treatment of schizophrenia

Hypofunction of the N-methyl-D-aspartate receptor (NMDAR) has been implicated in the pathophysiology of schizophrenia. The NMDAR contains a D-serine/glycine site on the NR1 subunit that may be a promising therapeutic target for psychiatric illness. This review outlines the complex regulation of endogenous NMDAR D-serine/glycine site agonists and explores their contribution to schizophrenia pathogenesis and their potential clinical utility. Genetic studies have associated genes influencing NMDAR D-serine/glycine site activation with an increased susceptibility to schizophrenia. Postmortem studies have identified abnormalities in several transcripts affecting D-serine/glycine site activity, consistent with in vivo reports of alterations in levels of endogenous D-serine/glycine site agonists and antagonists. Genetically modified mice with aberrant NMDAR D-serine/glycine site function model certain features of the negative and cognitive symptoms of schizophrenia, and similar behavioral abnormalities have been observed in other candidate genes models. Compounds that directly activate the NMDAR D-serine/glycine site or inhibit glycine transport have demonstrated beneficial effects in preclinical models and clinical trials. Future pharmacological approaches for schizophrenia treatment may involve targeting enzymes that affect D-serine synthesis and metabolism.

A putative high risk diplotype of the G72 gene is in healthy individuals associated with better performance in working memory functions and altered brain activity in the medial temporal lobe

G72 is a vulnerability gene for schizophrenia and affective psychosis, disorders that are characterized by deficits in working memory. In the present study we investigated whether the G72 genotype influences verbal and spatial working memory functions in healthy individuals. Working memory was assessed at the behavioural level in 423 subjects using the spatial span of the Wechsler Memory Scale (spatial working memory) and the letter-number-span test (verbal working memory). In a sub-sample of 83 subjects, we assessed working memory functions also at the neural level using functional magnetic resonance imaging during a classical letter variant of the n-back task. Unexpectedly the high risk allele carriers performed better in the verbal working memory task than the other subjects. These behavioural differences were accompanied by brain activation differences in the right parahippocampus, a brain region that plays a major role in schizophrenia and affective disorders. The high risk variant of a vulnerability gene therefore does not necessarily have to negatively affect cognitive abilities per se, but may even have beneficial effects on cognitive functions in the non-affected population.