The G72/G30 gene locus in psychiatric disorders: a challenge to diagnostic boundaries?

Structure models of G72, the product of a susceptibility gene to schizophrenia

The G72 gene is one of the most susceptible genes to schizophrenia and is contained exclusively in the genomes of primates. The product of the G72 gene modulates the activity of D-amino acid oxidase (DAO) and is a small protein prone to aggregate, which hampers its structural studies. In addition, lack of a known structure of a homologue makes it difficult to use the homology modelling method for the prediction of the structure. Thus, we first developed a hybrid ab initio approach for small proteins prior to the prediction of the structure of G72. The approach uses three known ab initio algorithms. To evaluate the hybrid approach, we tested our prediction of the structure of the amino acid sequences whose structures were already solved and compared the predicted structures with the experimentally solved structures. Based on these comparisons, the average accuracy of our approach was calculated to be ∼5 Å. We then applied the approach to the sequence of G72 and successfully predicted the structures of the N- and C-terminal domains (ND and CD, respectively) of G72. The predicted structures of ND and CD were similar to membrane-bound proteins and adaptor proteins, respectively.

DISC1-TSNAX and DAOA genes in major depression and citalopram efficacy

BACKGROUND

Major depressive disorder (MDD) is a common disease with high morbidity and still unsatisfying treatment response. Both MDD pathogenesis and antidepressant effect are supposed to be strongly affected by genetic polymorphisms. Among promising candidate genes, distrupted in schizophrenia 1 (DISC1), translin-associated factor X (TSNAX) and D-amino acid oxidase activator (DAOA) were suggested since their regulator role in neurodevelopment, neuroplasticity and neurotransmission, and previous evidence of cross-involvement in major psychiatric diseases.

METHODS

The present paper investigated the role of 13 SNPs within the reported genes in MDD susceptibility through a case-control (n=320 and n=150, respectively) study and in citalopram efficacy (n=157). Measures of citalopram efficacy were response (4th week) and remission (12th week). Pharmacogenetic findings were tested in the STAR(⁎)D genome-wide dataset (n=1892) for replication.

RESULTS

Evidence of association among rs3738401 (DISC1), rs1615409 and rs766288 (TSNAX) and MDD was found (p=0.004, p=0.0019, and p=0.008, respectively). A trend of association between remission and DISC1 rs821616 and DAOA rs778294 was detected, and confirmation was found for rs778294 by repeated-measure ANOVA (p=0.0008). In the STAR(⁎)D a cluster of SNPs from 20 to 40Kbp from DISC1 findings in the original sample was associated with citalopram response, as well as rs778330 (12,325bp from rs778294).

LIMITATIONS

Relatively small size of the original sample and focus on only three candidate genes.

CONCLUSIONS

The present study supported a role of DISC1-TSNAX variants in MDD susceptibility. On the other hand, genetic regions around DAOA rs778294 and DISC1 rs6675281-rs1000731 may influence citalopram efficacy.

Clinical and molecular genetics of psychotic depression

This review provides a comprehensive overview of clinical and molecular genetic as well as pharmacogenetic studies regarding the clinical phenotype of "psychotic depression." Results are discussed with regard to the long-standing debate on categorical vs dimensional disease models of affective and psychotic disorders on a continuum from unipolar depression over bipolar disorder and schizoaffective disorder to schizophrenia. Clinical genetic studies suggest a familial aggregation and a considerable heritability (39%) of psychotic depression partly shared with schizoaffective disorder, schizophrenia, and affective disorders. Molecular genetic studies point to potential risk loci of psychotic depression shared with schizoaffective disorder (1q42, 22q11, 19p13), depression, bipolar disorder, and schizophrenia (6p, 8p22, 10p13-12, 10p14, 13q13-14, 13q32, 18p, 22q11-13) and several vulnerability genes possibly contributing to an increased risk of psychotic symptoms in depression (eg, BDNF, DBH, DTNBP1, DRD2, DRD4, GSK-3beta, MAO-A). Pharmacogenetic studies implicate 5-HTT, TPH1, and DTNBP1 gene variation in the mediation of antidepressant treatment response in psychotic depression. Genetic factors are suggested to contribute to the disease risk of psychotic depression in partial overlap with disorders along the affective-psychotic spectrum. Thus, genetic research focusing on psychotic depression might inspire a more dimensional, neurobiologically and symptom-oriented taxonomy of affective and psychotic disorders challenging the dichotomous Kraepelinian view. Additionally, pharmacogenetic studies might aid in the development of a more personalized treatment of psychotic depression with an individually tailored antidepressive/antipsychotic pharmacotherapy according to genotype.

A combined study of genetic association and brain imaging on the DAOA gene in schizophrenia

While there has been no objective biomarker available for both diagnosis and prognosis of schizophrenia, compelling evidence suggests that the glutamatergic system may influence susceptibility to schizophrenia. To test genetic association of the glutamatergic system with schizophrenia and abnormal brain activities in resting-state patients with schizophrenia, a two-stage association study was performed in 454 patients and 480 controls, followed by regional homogeneity (ReHo) analysis of resting-state functional magnetic resonance imaging in 48 first-episode medication-free patients and 43 well-matched controls. The differences in ReHo between genotypes of interest were initially tested by the Student's t-test and the 2 × 2 (genotypes × disease status) ANOVA was then performed to identify the main effects of genotypes, disease status and their interactions in schizophrenia. The stage-1 study showed association of the DAOA and PSEN2 genes with schizophrenia in a small sample; the stage-2 study with an expanded sample confirmed the disease association for 2-SNP and 3-SNP haplotypes, and the cis-phase interactions between rs2391191 and some other SNPs in the DAOA gene. Four clusters with altered ReHo in the bilateral culmen, left putamen and left cuneus were associated with rs2391191. Main effects of rs2391191 genotypes were found in the left putamen. The left cuneus showed a genotype × disease status interaction. In conclusion, the DAOA gene may confer genetic risk of schizophrenia and associate with the altered ReHo in schizophrenia; genotype effect and its interaction with disease status may contribute to the altered ReHo, leading to specific ReHo in schizophrenic brain due to glutamatergic modulation.

Involvement of the primate specific gene G72 in schizophrenia: From genetic studies to pathomechanisms

Schizophrenia is a human mental disorder that affects an individual's thoughts, perception, affect and behavior, which is caused by a complex interaction of genetic and environmental factors. Genetic studies have implicated the evolutionary novel, anthropoid primate-specific gene locus G72/G30 in the etiology of schizophrenia and other psychiatric disorders. This gene encodes the protein LG72, which has been discussed as a modulator of the peroxisomal enzyme d-amino-acid-oxidase (DAO), or, alternatively as a mitochondrial protein. Recently, G72 transgenic (G72Tg) mice were generated that express the protein throughout the brain. These mice show several behavioral deficits that are related to schizophrenia. Further, G72Tg mice have a reduced activity of mitochondrial complex I, with a concomitantly increased production of reactive oxygen species, as well as deficits in short-term plasticity. Results from these studies demonstrate that expression of the human G72/G30 gene locus in mice produces behavioral phenotypes that are relevant to schizophrenia. They implicate LG72-induced mitochondrial and synaptic defects as a possible pathomechanism of this disease.

Myelination and oxidative stress alterations in the cerebellum of the G72/G30 transgenic schizophrenia mouse model

G72/G30 is a primate-specific locus that has been repeatedly implicated as a risk factor in genetic studies of schizophrenia. The function of the longest G72 splice variant (LG72 protein) encoded by this locus is not fully understood. To investigate the role of the LG72 protein in vivo, we have generated transgenic (G72Tg) mice carrying the G72/G30 locus that exhibit schizophrenia-like symptoms. We investigated protein expression alterations in the cerebella of G72Tg compared to wild type (WT) mice using a proteomics approach based on in vivo(15)N metabolic labeling and quantitative mass spectrometry (MS). Our data revealed expression level differences of proteins involved in myelin-related processes, oxidative stress and mitochondrial function. Furthermore, in silico pathway analyses suggested common regulators and targets for the observed protein alterations. Our work sheds light on the functional role of the LG72 protein and pinpoints molecular correlates of schizophrenia-like behavior.

DAOA Variants on Diagnosis and Response to Treatment in Patients with Major Depressive Disorder and Bipolar Disorder

OBJECTIVE: This study investigated whether selected D-amino acid oxidase activator ( DAOA) gene single nucleotide polymorphisms (SNPs; rs3916966, rs3916967, rs2391191, rs3916968, rs7139958, rs9558571, rs778293) are associated with major depressive disorder (MDD) and bipolar disorder (BD), and whether they can predict clinical outcomes in Korean in-patients treated with antidepressants and mood stabilizers, respectively. METHODS: In total, 145 patients with MDD, 132 patients with BD and 170 psychiatrically healthy controls were genotyped for the DAOA SNPs. Baseline and final clinical assessments included the Montgomery—Asberg Depression Rating Scale and Young Mania Rating Scale for patients with MDD and BD, respectively. RESULTS: There was no association between DAOA SNP genotypes or alleles with diagnosis, clinical improvement, response rates or remission rates for MDD and BD. Haplotype analyses found no association with MDD or BD diagnosis or clinical outcomes. CONCLUSIONS: The findings suggest that the DAOA SNPs investigated may not affect MDD or BD phenotype, clinical symptoms or other clinical factors, and are unlikely to be involved in MDD or BD development and treatment outcomes. Given the study's limitations, further investigation should be carried out.

Beyond Depression: Towards a Process-Based Approach to Research, Diagnosis, and Treatment

Despite decades of research on the etiology and treatment of depression, a significant proportion of the population is affected by the disorder, fails to respond to treatment and is plagued by relapse. Six prominent scientists, Aaron Beck, Richard Davidson, Fritz Henn, Steven Maier, Helen Mayberg, and Martin Seligman, gathered to discuss the current state of scientific knowledge on depression, and in particular on the basic neurobiological and psychopathological processes at play in the disorder. These general themes were addressed: 1) the relevance of learned helplessness as a basic process involved in the development of depression; 2) the limitations of our current taxonomy of psychological disorders; 3) the need to work towards a psychobiological process-based taxonomy; and 4) the clinical implications of implementing such a process-based taxonomy.

DAOA variants and schizophrenia: influence on diagnosis and treatment outcomes

OBJECTIVE

The present study explored whether d-amino acid oxidase activator (DAOA) variants were associated with schizophrenia and whether they could predict the clinical outcomes of patients treated with various antipsychotics.

METHODS

Two hundred and twenty-one (221) patients with schizophrenia and 170 psychiatrically healthy controls were genotyped for seven DAOA single-nucleotide polymorphisms (SNPs) (rs3916966, rs3916967, rs2391191, rs3916968, rs7139958, rs9558571 and rs778293). We also administered baseline and final clinical measures, including the Positive and Negative Symptoms Scale (PANSS), to patients with schizophrenia.

RESULTS

None of the SNPs under investigation was associated with the development of schizophrenia. However, the rs7139958 AA and rs9558571 TT as well as the rs7139958 A and rs9558571 T genotypes were associated with higher scores on the PANSS positive subscale among patients with schizophrenia, possibly reflecting their greater susceptibility to the development of more severe positive symptoms. No other allele, genotype, or haplotype under investigation was significantly associated with any of the clinical parameters, including clinical improvement, in patients with schizophrenia.

CONCLUSION

Our results suggested that rs7139958 and rs9558571 SNPs may be associated with more severe baseline positive symptoms in patients with schizophrenia. However, further research is needed to draw more definitive conclusions given the limitations of our study.

N-acetyl cysteine treatment rescues cognitive deficits induced by mitochondrial dysfunction in G72/G30 transgenic mice

Genetic studies have implicated the evolutionary novel, anthropoid primate-specific gene locus G72/G30 in psychiatric diseases. This gene encodes the protein LG72 that has been discussed to function as a putative activator of the peroxisomal enzyme D-amino-acid-oxidase (DAO) and as a mitochondrial protein. We recently generated 'humanized' bacterial artificial chromosome transgenic mice (G72Tg) expressing G72 transcripts in cells throughout the brain. These mice exhibit several behavioral phenotypes related to psychiatric diseases. Here we show that G72Tg mice have a reduced activity of mitochondrial complex I, with a concomitantly increased production of reactive oxygen species. Affected neurons display deficits in short-term plasticity and an impaired capability to sustain synaptic activity. These deficits lead to an impairment in spatial memory, which can be rescued by pharmacological treatment with the glutathione precursor N-acetyl cysteine. Our results implicate LG72-induced mitochondrial and synaptic defects as a possible pathomechanism of psychiatric disorders.

Dysbindin (DTNBP1)--a role in psychotic depression?

Previous studies yielded evidence for dysbindin (DTNBP1) to impact the pathogenesis of schizophrenia on the one hand and affective disorders such as bipolar or major depressive disorder (MDD) on the other. Thus, in the present study we investigated whether DTNBP1 variation was associated with psychotic depression as a severe clinical manifestation of MDD possibly constituting an overlapping phenotype between affective disorders and schizophrenia. A sample of 243 Caucasian inpatients with MDD (SCID-I) was genotyped for 12 SNPs spanning 92% of the DTNBP1 gene region. Differences in DTNBP1 genotype distributions across diagnostic subgroups of psychotic (N = 131) vs. non-psychotic depression were estimated by Pearson Chi(2) test and logistic regression analyses adjusted for age, gender, Beck Depression Inventory (BDI) and the Global Assessment of Functioning Scale (GAF). Overall, patients with psychotic depression presented with higher BDI and lower GAF scores expressing a higher severity of the illness as compared to depressed patients without psychotic features. Four DTNBP1 SNPs, particularly rs1997679 and rs9370822, and the corresponding haplotypes, respectively, were found to be significantly associated with the risk of psychotic depression in an allele-dose fashion. In summary, the present results provide preliminary support for dysbindin (DTNBP1) gene variation, particularly SNPs rs1997679 and rs9370822, to be associated with the clinical phenotype of psychotic depression suggesting a possible neurobiological mechanism for an intermediate trait on the continuum between affective disorders and schizophrenia.

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.

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.

Neurodegeneration in schizophrenia

The neurodegenerative aspect of schizophrenia presupposes gene-environmental interactions involving chromosomal abnormalities and obstetric/perinatal complications that culminate in predispositions that impart a particular vulnerability for drastic and unpredictable precipitating factors, such as stress or chemical agents. The notion of a neurodevelopmental progression to the disease state implies that early developmental insults, with neurodegenerative proclivities, evolve into structural brain abnormalities involving specific regional circuits and neurohumoral agents. This neurophysiological orchestration is expressed in the dysfunctionality observed in premorbid signs and symptoms arising in the eventual diagnosis, as well as the neurobehavioral deficits reported from animal models of the disorder. The relative contributions of perinatal insults, neonatal ventral hippocampus lesion, prenatal methylazoxymethanol acetate and early traumatic experience, as well as epigenetic contributions, are discussed from a neurodegenerative view of the essential neuropathology. It is implied that these considerations of factors that exert disruptive influences upon brain development, or normal aging, operationalize the central hub of developmental neuropathology around which the disease process may gain momentum. Nonetheless, the status of neurodegeneration in schizophrenia is somewhat tenuous and it is possible that brain imaging studies on animal models of the disorder, which may describe progressive alterations to cortical, limbic and ventricular structures similar to those of schizophrenic patients, are necessary to resolve the issue.

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.

The DAOA/G30 locus and affective disorders: haplotype based association study in a polydiagnostic approach

BACKGROUND

The DAOA/G30 (D-amino acid oxidase activator) gene complex at chromosomal region 13q32-33 is one of the most intriguing susceptibility loci for the major psychiatric disorders, although there is no consensus about the specific risk alleles or haplotypes across studies.

METHODS

In a case-control sample of German descent (affective psychosis: n = 248; controls: n = 188) we examined seven single nucleotide polymorphisms (SNPs) around DAOA/G30 (rs3916966, rs1935058, rs2391191, rs1935062, rs947267, rs3918342, and rs9558575) for genetic association in a polydiagnostic approach (ICD 10; Leonhard's classification).

RESULTS

No single marker showed evidence of overall association with affective disorder neither in ICD10 nor Leonhard's classification. Haplotype analysis revealed no association with recurrent unipolar depression or bipolar disorder according to ICD10, within Leonhard's classification manic-depression was associated with a 3-locus haplotype (rs2391191, rs1935062, and rs3916966; P = 0.022) and monopolar depression with a 5-locus combination at the DAOA/G30 core region (P = 0.036).

CONCLUSION

Our data revealed potential evidence for partially overlapping risk haplotypes at the DAOA/G30 locus in Leonhard's affective psychoses, but do not support a common genetic contribution of the DAOA/G30 gene complex to the pathogenesis of affective disorders.

A systematic association mapping on chromosome 6q in bipolar affective disorder--evidence for the melanin-concentrating-hormone-receptor-2 gene as a risk factor for bipolar affective disorder

Strong evidence of linkage between chromosomal region 6q16-q22 and bipolar affective disorder (BPAD) has previously been reported. We conducted a systematic association mapping of the 6q-linkage interval using 617 SNP markers in a BPAD case-control sample of German descent (cases = 330, controls = 325). In this screening step, 46 SNPs showed nominally significant BPAD-association (P-values between 0.0007 and 0.0484). Although none of the 46 SNPs survived correction for multiple testing, they were genotyped in a second and ethnically matched BPAD sample (cases = 328, controls = 397). At the melanin-concentrating-hormone-receptor-2 (MCHR2) gene, we found nominal association in both the initial and second BPAD samples (combined P = 0.008). This finding was followed up by the genotyping of 17 additional MCHR2-SNPs in the combined sample in order to define our findings more precisely. We found that the MCHR2-locus can be divided into three different haplotype-blocks, and observed that the MCHR2-association was most pronounced in BPAD male patients with psychotic symptoms. In two neighboring blocks, putative risk-haplotypes were found to be 7% more frequent in patients (block II: 23.3% vs. 16.2%, P = 0.005, block III: 39.2% vs. 32.0%, P = 0.024), whereas the putative protective haplotypes were found to be 5-8% less frequent in patients (block II: 11.6% vs. 16.4%, P = 0.041, block III: 30.0% vs. 38.8%, P = 0.007). The corresponding odds ratios (single-marker analysis) ranged between 1.25 and 1.46. Our findings may indicate that MCHR2 is a putative risk factor for BPAD. These findings should be interpreted with caution and replicated in independent BPAD samples.

Searching for valid psychiatric phenotypes: discrete latent variable models

INTRODUCTION

A primary challenge in psychiatric genetics is the lack of a completely validated system of classification for mental disorders. Appropriate statistical methods are needed to empirically derive more homogenous disorder subtypes.

METHODS

Using the framework of Robins and Guze's ('Establishment of diagnostic validity in psychiatric illness: its application to schizophrenia', American Journal of Psychiatry, 1970, 126(7), 983-987) five phases, latent variable models to derive and validate diagnostic groups are described. A process of iterative validation is proposed through which refined phenotypes would facilitate research on genetics, pathogenesis, and treatment, which would in turn aid further refinement of disorder definitions.

CONCLUSIONS

Latent variable methods are useful tools for defining and validating psychiatric phenotypes. Further methodological research should address sample size issues and application to iterative validation.

Possible association of different G72/G30 SNPs with mood episodes and persecutory delusions in bipolar I Romanian patients

The G72/G30 gene is one of the common loci shared both by schizophrenia and bipolar disorder. Studies accumulating since the discovery of this gene complex produced controversial results in both disorders in different populations.

OBJECTIVE

We investigated the association between the G72/G30 gene and bipolar I disorder (BPI) in the Romanian population paying special attention to the association of G72/G30 with lifetime psychosis and in particular with persecutory delusions in BPI patients.

METHOD

Fourteen G72/G30-SNPs were genotyped in a Romanian sample of 198 BPI patients and 180 controls screened for psychiatric disorders. Statistical analysis was performed with FAMHAP and HAPLOVIEW-v3.32. The significance level of the results was corrected through permutations in 100,000 simulations.

RESULTS

None of the fourteen SNPs was associated with the global diagnosis of BPI in our total patient sample or with the psychotic BPI subtype. When confining the psychotic phenotype to persecutory delusions, we observed trends to association for SNPs previously associated with schizophrenia and persecutory delusions in BPI [M21 (P=0.080); M22 (P=0.092; P=0.042 under dominant transmission model); M24 (P=0.092)]. Four SNPs reached nominal significance in the non-psychotic BPI subgroup [rs3916965 (M12) (P=0.044), rs1935057 (P=0.037), rs3916967 (M14) (P=0.043), and rs2391191 (M15, non-synonymous) (P=0.043)]. After correction through permutations, the haploblock GA including M14 and M15 showed a trend to association with BPI (P=0.0524; OR=1.82) in the non-psychotic BPI subgroup.

CONCLUSION

We report a potential association of different G72/G30-SNPs with non-psychotic mood episodes and with persecutory delusions in BPI Romanian patients. The results represent a first partial replication of two studies: Williams et al. (2006) and Schulze et al. (2005). The results have just a suggestive value since the Bonferroni correction for multiple testing was not applied.

New Genetic Findings in Schizophrenia: Is there Still Room for the Dopamine Hypothesis of Schizophrenia?

Schizophrenia is a highly heritable disorder, but the identification of specific genes has proven to be a difficult endeavor. Genes involved in the dopaminergic system are considered to be major candidates since the “dopamine hypothesis” of impairment in dopaminergic neurotransmission is one of the most widely accepted hypotheses of the etiology of schizophrenia. The overall findings from candidate studies do provide some support for the “dopamine hypothesis.” However, results from the first systematic genome-wide association (GWA) studies have implicated variants within ZNF804A, NRGN, TCF4, and variants in the MHC region on chromosome 6p22.1. Although these genes may not immediately impact on dopaminergic neurotransmission, it remains possible that downstream impairments in dopaminergic function are caused. Furthermore, only a very small fraction of all truly associated genetic variants have been detected and many more associated variants will be identified in the future by GWA studies and alternative approaches. The results of these studies may allow a more comprehensive re-evaluation of the dopamine hypothesis.

Prefrontal-temporal gray matter deficits in bipolar disorder patients with persecutory delusions

OBJECTIVES

Although brain structural deficits have been repeatedly associated with bipolar disorder (BD), inconsistency in morphometric results has been a feature of neuroimaging studies. We hypothesize that this discrepancy is related to the heterogeneity of BD, and examine the question of whether or not more homogeneous clinical subgroups display a more coherent pattern of morphometric abnormalities.

METHODS

In a case-control design, we examined differences in gray matter (GM), white matter (WM) and cerebrospinal fluid (CSF) concentration in 42 BD patients and 42 healthy matched controls using optimized voxel-based morphometry (VBM). Subgroup analyses of patients with a lifetime history of psychotic symptoms (BDP, n=30) and patients with mood-incongruent psychotic symptoms in the form of persecutory delusions (BDPD, n=15) were performed to accord with previous genetic findings.

RESULTS

Analysis of the total BD sample was largely inconclusive, but the BDPD patient subgroup displayed a widespread pattern of significant decreases in GM concentration in the dorsolateral prefrontal (DLPFC), temporal and cingulate cortices, and a significant CSF increase in the adjacent outer ventricular sulci. Comparison of BDPD patients versus BD and BDP patients without persecutory delusions revealed a significant GM decrease in the left DLPFC for the former group.

CONCLUSIONS

BDPD show pronounced structural abnormalities of the prefrontal and temporal lobes which are similar to the deficits previously reported for schizophrenia (SCZ). Our findings suggest that stratification based solely on psychotic symptoms is insufficient for the differentiation of BD into biologically meaningful subgroups, but also question the pathophysiological validity of the dichotomy in classification between schizophrenia and BD.

The effect of Neuregulin 1 on neural correlates of episodic memory encoding and retrieval

Neuregulin 1 (NRG1) has been found to be associated with schizophrenia. Impaired performance in episodic memory tasks is an often replicated finding in this disorder. In functional neuroimaging studies, this dysfunction has been linked to signal changes in prefrontal and medial temporal areas. Therefore, it is of interest whether genes associated with the disorder, such as NRG1, modulate episodic memory performance and its neural correlates. Ninety-four healthy individuals performed an episodic memory encoding and a retrieval task while brain activation was measured with functional MRI. All subjects were genotyped for the single nucleotide polymorphism (SNP) rs35753505 in the NRG1 gene. The effect of genotype on brain activation was assessed with fMRI during the two tasks. While there were no differences in performance, brain activation in the cingulate gyrus (BA 24), the left middle frontal gyrus (BA 9), the bilateral fusiform gyrus and the left middle occipital gyrus (BA 19) was positively correlated with the number of risk alleles in NRG1 during encoding. During retrieval brain activation was positively correlated with the number of risk alleles in the left middle occipital gyrus (BA 19). NRG1 genotype does modulate brain activation during episodic memory processing in key areas for memory encoding and retrieval. The results suggest that subjects with risk alleles show hyperactivations in areas associated with elaborate encoding strategies.

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.

G72/G30 (DAOA) and juvenile-onset mood disorders

The chromosome 13q region has been linked to bipolar disorder in a number of genome scans as well as focused linkage studies. Previously we identified linkage to the 13q32 region in a genome scan of 146 affected sibling pair families from Hungary with juvenile-onset mood disorders. Within this region are the overlapping genes G72/G30, with G72 now officially named as D-amino-acid oxidase activator (DAOA). This locus has been associated with panic disorder, schizophrenia, and bipolar disorder. In this study, we tested for association to 11 markers in these genes and mood disorders in a sample of 646 nuclear families identified with a proband with onset of a mood disorder before 14.9 years of age. We identified evidence for association to three markers within the gene (rs2391191, rs3918341, rs1935062), two of which had been associated with bipolar disorder in previous studies. When corrected for the number of markers tested, the results were no longer significant, however the prior evidence for association of this gene in multiple studies points to this gene as a potential contributor to juvenile-onset mood disorders.

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.

Behavioral changes in G72/G30 transgenic mice

Genetic studies have implicated the evolutionary novel, primates-specific gene locus G72/G30 in schizophrenia, bipolar and panic disorders. It encodes for a protein LG72 whose function has been controversially discussed as putative regulator of the peroxisomal enzyme D-amino-acid-oxidase (DAO), or as a mitochondrial protein, which promotes robust mitochondrial fragmentation in mammalian cell lines including human and rat primary neurons. Because of this conserved function we here have generated "humanized" BAC transgenic mice (G72Tg) expressing alternatively spliced G72 and G30 transcripts, and the LG72 protein. G72 expression is prominent in granular cells of the cerebellum, the hippocampus, the cortex and the olfactory bulb. Most strikingly, G72Tg mice displayed deficits in sensorimotor gating which could be reversed with haloperidol, increased sensitivity to PCP, motor-coordination deficits, increased compulsive behaviors and deficits in smell identification. These results demonstrate that expression of the human G72/G30 gene locus in mice produces behavioral phenotypes that are relevant to psychiatric disorders.

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.

Association study between genetic variants at the VAMP2 and VAMP3 loci and bipolar affective disorder

OBJECTIVES

Vesicle-associated membrane proteins 2 and 3 (VAMP2 and VAMP3) are required for the release of D-serine, a competitive agonist of the neurotransmitter glycine at the glutamatergic N-methyl-D-aspartate receptors. Several lines of evidence point to an involvement of altered D-serine levels in the central nervous system in the aetiology of bipolar affective disorder (BPAD). Strong association findings between BPAD and two genes, G72 and DAAO, which are involved in the enzymatic degradation of D-serine, are reported. Based on the functional evidence and on the hypothesis that further genes, which are involved in the regulation of D-serine, could be involved in the disease aetiology, we considered VAMP2 and VAMP3 as candidate genes for BPAD.

METHODS

We analyzed three and four single nucleotide polymorphism (SNP) markers covering VAMP2 and VAMP3, respectively, in an initial BPAD case-control sample of German descent (409 cases, 407 controls). For replication, we analyzed three SNP markers covering VAMP2 in a second sample of the same ethnicity (378 cases, 384 controls).

RESULTS

Although no association was found for VAMP3 markers, we observed evidence of association with SNPs at the VAMP2 locus in the initial sample (P values between 0.005 and 0.033). To validate these findings, we analyzed a second BPAD sample and failed to replicate the initial findings at the single-marker and haplotypic level.

CONCLUSION

In conclusion, our results do not suggest that a common genetic variant at VAMP2 or VAMP3 contributes to the development of BPAD in German patients.

Genetic variation in the DAOA gene complex: impact on susceptibility for schizophrenia and on cognitive performance

INTRODUCTION

The genetic region coding for d-amino acid oxidase activator (DAOA) is considered an intriguing susceptibility locus for schizophrenia. However, association studies have often resulted in conflicting findings, and the risk-conferring variants and their biological impact remain elusive. Our aim in this study was to investigate the relationship between DAOA variation and schizophrenia, and the influence of DAOA on cognitive performance.

METHODS

We analyzed block structure and association patterns of an approximately 173 kb region on chromosome 13q33, applying genotype data of 55 SNPs derived from Caucasian North American sample (178 cases, 144 healthy controls). Haplotypes were assigned using the program PHASE and frequencies compared between cases and controls. We applied MANOVA to investigate the relationship between the identified risk haplotype on cognitive performance.

RESULTS

We identified multiple haplotypes within the region containing the DAOA gene. Of these, one was significantly associated with schizophrenia, being over-represented in schizophrenia versus healthy controls. This haplotype was also associated with one aspect of cognitive performance, semantic fluency. Carriers of the risk haplotype showed better semantic fluency than non-carriers.

CONCLUSIONS

We report a significant effect of DAOA variation on risk for schizophrenia. Moreover, we identified a relationship between DAOA genetic variation and specific aspects of neurocognitive function. As the identified DAOA risk haplotype was associated with better performance on a semantic fluency measure, further work is required to identify the mechanism of DAOA action on CNS function, including the possibility of a role for balanced selection at this locus.

[The genetics of depressive disorders]

Among the most common severe psychiatric disorders worldwide, depressive disorders are a leading cause of morbidity, the onset usually occurring during childhood or adolescence. Symptomatology, prevalence, outcome and treatment differentiate depressive disorder nosologically as being either unipolar depression or bipolar disorder, which is characterized by one or more episodes of mania with or without episodes of depression. Genetic factors decisively influence the susceptibility to depressive disorders. Family studies and twin studies have been essential in defining the magnitude of familial risk and liability to heritability, particularly in the case of bipolar disorder. In recent years, linkage and association studies have made great strides towards identifying candidate genes. Particularly the s-allele of the serotonin transporter has been repeatedly confirmed to be a risk factor. Meta-analyses suggest, however, that the genetic contributions of the ascertained loci are relatively small. Along with genetic factors, environmental factors are heavily involved. Gene-environment action plays a pivotal role, particularly in unipolar depression. The genetic disposition seems to be modulated by a protective or pathogenic environment. Early-onset disorders must be further investigated in future as studies to date are somewhat limited.

Genetic variation of the FAT gene at 4q35 is associated with bipolar affective disorder

A recent study suggested that the cadherin gene FAT exerts an influence on susceptibility to bipolar affective disorder (BPAD). We aimed to replicate this finding in a German sample (425 BPAD I and 419 controls). In addition, we performed a comprehensive linkage disequilibrium mapping of the whole genomic region of FAT and the neighboring circadian gene MTNR1A (48 single nucleotide polymorphisms (SNPs) covering 191 kb). No significant association was observed for SNPs located in the MTNR1A gene. In FAT, however, nine SNPs showed association, eight of them being located in the same haplotype block found to be associated with BPAD by Blair et al. The smallest P-value of 0.00028 (OR 1.71) was seen for non-synonymous SNP rs2637777. A combination of five markers including this marker showed a haplotype distribution with a nominal P-value of 1.8 x 10(-5) that withstands correction for multiple testing. While the control allele frequencies between our sample and the samples of the original study are comparable, tendencies of risk allele frequencies are opposite. Possible explanations for this include potential differences in linkage disequilibrium structure between the German, Australian, UK, and Bulgarian populations sampling variation, multilocus effects and/or the occurrence of independent mutational events. We conclude that our results support an involvement of variation at the FAT gene in the etiology of BPAD, but that further work is needed both to clarify possible reasons for the observed risk allele differences and to ultimately identify the functionally relevant variant(s).

Which perspectives can endophenotypes and biological markers offer in the early recognition of schizophrenia?

The early recognition of schizophrenia seems crucial; various studies relate a longer duration-of-untreated-psychosis to a worse prognosis. We give an overview over common psychopathological early recognition instruments (BSABS, CAARMS, SIPS, IRAOS, ERIraos). However, many clinical symptoms of prodromal schizophrenia stages are not sufficiently specific. Thus we review recent contributions of neuroimaging and electrophysiological as well as genetic studies: which new diagnostic perspectives offer endophenotypes (such as P300, P50 sensory gating, MMN, smooth pursuit eye movements; indicating a specific genetic vulnerability) together with a better understanding of schizophrenic pathophysiology (state-dependent biological markers, e.g. aggravated motor neurological soft signs during psychosis) in prodromal schizophrenia when still ambiguous clinical symptoms are present. Several examples (e.g. from COMT polymorphisms to working memory deficits) illustrate more specific underlying neuronal mechanisms behind behavioural symptoms. This way, a characteristic pattern of disturbed cerebral maturation might be distinguished in order to complement clinical instruments of early schizophrenia detection.