Neuregulin 1 ICE-single nucleotide polymorphism in first episode schizophrenia correlates with cerebral activation in fronto-temporal areas

COMT and Neuregulin 1 Markers for Personalized Treatment of Schizophrenia Spectrum Disorders Treated with Risperidone Monotherapy

Pharmacogenetic markers are current targets for the personalized treatment of psychosis. Limited data exist on COMT and NRG1 polymorphisms in relation to risperidone treatment. This study focuses on the impact of COMT rs4680 and NRG1 (rs35753505, rs3924999) polymorphisms on risperidone treatment in schizophrenia spectrum disorders (SSDs). This study included 103 subjects with SSD treated with risperidone monotherapy. COMT rs4680, NRG1 rs35753505, and rs3924999 were analyzed by RT-PCR. Participants were evaluated via the Positive and Negative Syndrome Scale (PANSS) after six weeks. Socio-demographic and clinical characteristics were collected. COMT rs4680 genotypes significantly differed in PANSS N scores at admission: AG>AA genotypes (p = 0.03). After six weeks of risperidone, PANSS G improvement was AA>GG (p = 0.05). The PANSS total score was as follows: AA>AG (p = 0.04), AA>GG (p = 0.02). NRG1 rs35753504 genotypes significantly differed across educational levels, with CC>CT (p = 0.02), and regarding the number of episodes, TT>CC, CT>CC (p = 0.01). The PANSS total score after six weeks of treatment showed a better improvement for TT Collapse

Key Words

• COMT
• neuregulin 1
• risperidone monotherapy
• schizophrenia spectrum disorders

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MESH Headings

• Humans
• Neuregulin-1/genetics
• Catechol O-Methyltransferase/genetics
• Risperidone/therapeutic use
• Schizophrenia/drug therapy
• Schizophrenia/genetics
• Male
• Female
• Adult
• Polymorphism, Single Nucleotide
• Antipsychotic Agents/therapeutic use
• Middle Aged
• Precision Medicine/methods
• Genotype

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Affiliation(s)

Mariana Bondrescu Department of Neurosciences-Psychiatry, “Victor Babes” University of Medicine and Pharmacy, Eftimie Murgu Square 2, 300041 Timisoara, Romania; (M.B.); (I.P.) Timis County Emergency Clinical Hospital “Pius Brinzeu”, Liviu Rebreanu 156, 300723 Timisoara, Romania; (V.N.); (D.V.M.); (A.E.G.) Doctoral School, “Victor Babes” University of Medicine and Pharmacy, Eftimie Murgu Square 2, 300041 Timisoara, Romania
Liana Dehelean Department of Neurosciences-Psychiatry, “Victor Babes” University of Medicine and Pharmacy, Eftimie Murgu Square 2, 300041 Timisoara, Romania; (M.B.); (I.P.) Timis County Emergency Clinical Hospital “Pius Brinzeu”, Liviu Rebreanu 156, 300723 Timisoara, Romania; (V.N.); (D.V.M.); (A.E.G.)
Simona Sorina Farcas Discipline of Medical Genetics, Department of Microscopic Morphology, Center of Genomic Medicine “Victor Babes” University of Medicine and Pharmacy, Eftimie Murgu Square 2, 300041 Timisoara, Romania; (S.S.F.); (N.I.A.)
Ion Papava Department of Neurosciences-Psychiatry, “Victor Babes” University of Medicine and Pharmacy, Eftimie Murgu Square 2, 300041 Timisoara, Romania; (M.B.); (I.P.) Timis County Emergency Clinical Hospital “Pius Brinzeu”, Liviu Rebreanu 156, 300723 Timisoara, Romania; (V.N.); (D.V.M.); (A.E.G.)
Vlad Nicoras Timis County Emergency Clinical Hospital “Pius Brinzeu”, Liviu Rebreanu 156, 300723 Timisoara, Romania; (V.N.); (D.V.M.); (A.E.G.)
Dana Violeta Mager Timis County Emergency Clinical Hospital “Pius Brinzeu”, Liviu Rebreanu 156, 300723 Timisoara, Romania; (V.N.); (D.V.M.); (A.E.G.)
Anca Eliza Grecescu Timis County Emergency Clinical Hospital “Pius Brinzeu”, Liviu Rebreanu 156, 300723 Timisoara, Romania; (V.N.); (D.V.M.); (A.E.G.)
Petre Adrian Podaru Faculty of Mathematics and Informatics, West University of Timisoara, Vasile Parvan 4, 300223 Timisoara, Romania;
Nicoleta Ioana Andreescu Discipline of Medical Genetics, Department of Microscopic Morphology, Center of Genomic Medicine “Victor Babes” University of Medicine and Pharmacy, Eftimie Murgu Square 2, 300041 Timisoara, Romania; (S.S.F.); (N.I.A.)

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Building better brains: the pleiotropic function of neurotrophic factors in postnatal cerebellar development

The cerebellum is a multifunctional brain region that controls diverse motor and non-motor behaviors. As a result, impairments in the cerebellar architecture and circuitry lead to a vast array of neuropsychiatric and neurodevelopmental disorders. Neurotrophins and neurotrophic growth factors play essential roles in the development as well as maintenance of the central and peripheral nervous system which is crucial for normal brain function. Their timely expression throughout embryonic and postnatal stages is important for promoting growth and survival of both neurons and glial cells. During postnatal development, the cerebellum undergoes changes in its cellular organization, which is regulated by a variety of molecular factors, including neurotrophic factors. Studies have shown that these factors and their receptors promote proper formation of the cerebellar cytoarchitecture as well as maintenance of the cerebellar circuits. In this review, we will summarize what is known on the neurotrophic factors' role in cerebellar postnatal development and how their dysregulation assists in developing various neurological disorders. Understanding the expression patterns and signaling mechanisms of these factors and their receptors is crucial for elucidating their function within the cerebellum and for developing therapeutic strategies for cerebellar-related disorders.

Correlation of rs35753505 polymorphism in Neuregulin 1 gene with psychopathology and intelligence of people with schizophrenia

BACKGROUND AND AIM

Schizophrenia is one of the most severe psychiatric disorders. About 0.5 to 1% of the world's population suffers from this non-Mendelian disorder. Environmental and genetic factors seem to be involved in this disorder. In this article, we investigate the alleles and genotypic correlation of mononucleotide rs35753505 polymorphism of Neuregulin 1 (NRG1), one of the selected genes of schizophrenia, with psychopathology and intelligence.

MATERIALS AND METHODS

102 independent and 98 healthy patients participated in this study. DNA was extracted by the salting out method and the polymorphism (rs35753505) were amplified by polymerase chain reaction (PCR). Sanger sequencing was performed on PCR products. Allele frequency analysis was performed using COCAPHASE software, and genotype analysis was performed using Clump22 software.

RESULTS

According to our study's statistical findings, all case samples from the three categories of men, women, and overall participants significantly differed from the control group in terms of the prevalence of allele C and the CC risk genotype. The rs35753505 polymorphism significantly raised Positive and Negative Syndrome Scale (PANSS) test results, according to a correlation analysis between the two variables. However, this polymorphism led to a significant decrease in overall intelligence in case samples compared to control samples.

CONCLUSION

In this study, it seems that the rs35753505 polymorphism of NRG1 gene has a significant role in the sample of patients with schizophrenia in Iran and also in psychopathology and intelligence disorders.

Gene polymorphisms and response to transcranial direct current stimulation for auditory verbal hallucinations in schizophrenia

OBJECTIVE

Recent observations demonstrate a significant ameliorative effect of add-on transcranial direct current stimulation (tDCS) on auditory verbal hallucinations (AVHs) in schizophrenia. Of the many SNPs, NRG1 rs35753505 and catechol-o-methyl transferase (COMT) rs4680 polymorphisms have shown to have a strong association with neuroplasticity effect in schizophrenia.

METHODS

Schizophrenia patients (n=32) with treatment resistant auditory hallucinations were administered with an add-on tDCS. The COMT (rs4680) and NRG1 (rs35753505) genotypes were determined. The COMT genotypes were categorised into Val group (GG; n=15) and Met group (GG/AG; n=17) and NRG1 genotypes were categorised into AA group (n=12) and AG/GG group (n=20).

RESULTS

The reduction in auditory hallucination sub-scale score was significantly affected by COMT-GG genotype [Time×COMT interaction: F(1,28)=10.55, p=0.003, ɳ2=0.27]. Further, COMT-GG effect was epistatically influenced by the co-occurrence of NRG1-AA genotype [Time×COMT×NRG1 interaction: F(1,28)=8.09, p=0.008, ɳ2=0.22]. Irrespective of genotype, females showed better tDCS response than males [Time×Sex interaction: F(1,21)=4.67, p=0.04, ɳ2=0.18].

CONCLUSION

COMT-GG and NRG1-AA genotypes aid the tDCS-induced improvement in AVHs in schizophrenia patients. Our preliminary observations need replication and further systematic research to understand the neuroplastic gene determinants that modulate the effect of tDCS.

Patients with schizophrenia show aberrant patterns of basal ganglia activation: Evidence from ALE meta-analysis

The diverse circuits and functional contributions of the basal ganglia, coupled with known differences in dopaminergic function in patients with schizophrenia, suggest they may be an important contributor to the etiology of the hallmark symptoms and cognitive dysfunction experienced by these patients. Using activation-likelihood-estimation meta-analysis of functional imaging research, we investigated differences in activation patterns in the basal ganglia in patients with schizophrenia, relative to healthy controls across task domains. This analysis included 42 functional neuroimaging studies, representing a variety of behavioral domains that have been linked to basal ganglia function in prior work. We provide important new information about the functional activation patterns and functional topography of the basal ganglia for different task domains in healthy controls. Crucially however, we demonstrate that across task domains, patients with schizophrenia show markedly decreased activation in the basal ganglia relative to healthy controls. Our results provide further support for basal ganglia dysfunction in patients with schizophrenia, and the broad dysfunction across task domains may contribute to the symptoms and cognitive deficits associated with schizophrenia.

Association study of neuregulin-1 gene polymorphisms in a North Indian schizophrenia sample

BACKGROUND

Neuregulin-1 (NRG1) gene polymorphisms have been proposed as risk factors for several common disorders. Associations with cognitive variation have also been tested. With regard to schizophrenia (SZ) risk, studies of Caucasian ancestry samples indicate associations more consistently than East Asian samples, suggesting heterogeneity. To exploit the differences in linkage disequilibrium (LD) structure across ethnic groups, we conducted a SZ case-control study (that included cognitive evaluations) in a sample from the north Indian population.

METHODS

NRG1 variants (n=35 SNPs, three microsatellite markers) were initially analyzed among cases (DSM IV criteria, n=1007) and controls (n=1019, drawn from two groups) who were drawn from the same geographical region in North India. Nominally significant associations with SZ were next analyzed in relation to neurocognitive measures estimated with a computerized neurocognitive battery in a subset of the sample (n=116 cases, n=170 controls).

RESULTS

Three variants and one microsatellite showed allelic association with SZ (rs35753505, rs4733263, rs6994992, and microsatellite 420M9-1395, p≤0.05 uncorrected for multiple comparisons). A six marker haplotype 221121 (rs35753505-rs6994992-rs1354336-rs10093107-rs3924999-rs11780123) showed (p=0.0004) association after Bonferroni corrections. Regression analyses with the neurocognitive measures showed nominal (uncorrected) associations with emotion processing and attention at rs35753505 and rs6994992, respectively.

CONCLUSIONS

Suggestive associations with SZ and SZ-related neurocognitive measures were detected with two SNPs from the NRG1 promoter region in a north Indian cohort. The functional role of the alleles merits further investigation.

The possible role of the Akt signaling pathway in schizophrenia

Serine/threonine protein kinase v-akt murine thymoma viral oncogene homolog (Akt) is one of the survival kinases with multiple biological functions in the brain and throughout the body. Schizophrenia is one of the most devastating psychiatric disorders. Accumulating evidence has indicated the involvement of the Akt signaling pathway in the pathogenesis of this disorder. Genetic linkage and association studies have identified Akt-1 as a candidate susceptibility gene related for schizophrenia. The level of Akt-1 protein and its kinase activity decreased significantly both in white blood cells from schizophrenic patients and in postmortem brain tissue of schizophrenic patients. Consistent with these findings, alterations in the upstream and downstream pathways of Akt have also been found in many psychiatric disorders. Furthermore, both typical and atypical antipsychotic drugs modify the Akt signaling pathway in a variety of conditions relative to schizophrenia. In addition as a survival kinase, Akt participates in neurodevelopment, synaptic plasticity, protein synthesis and neurotransmission in the central nervous system. It is thought that reduced activity of phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway could at least partially explain the cognitive impairment, synaptic morphologic abnormality, neuronal atrophy and dysfunction of neurotransmitter signaling in schizophrenia. In addition, reduced levels of Akt may increase the effects of risk factors on neurodevelopment, attenuate the effects of growth factors on neurodevelopment and reduce the response of patients to antipsychotic agents. More recently, the role of Akt signaling in the functions of schizophrenia susceptibility genes such as disrupted-in-schizophrenia 1 (DISC-1), neuregulin-1 (NRG-1) and dysbindin-1 has been reported. Thus, Akt deficiency may create a context permissive for the expression of risk-gene effects in neuronal morphology and function. This paper reviews the role of Akt in the pathophysiology of schizophrenia and as a potential therapeutic strategy targeting Akt.

Genetic associations between neuregulin-1 SNPs and neurocognitive function in multigenerational, multiplex schizophrenia families

OBJECTIVES

Recent work shows promising associations between schizophrenia and polymorphisms in neuregulin-1 (NRG1) and a large literature also finds strong familial relationships between schizophrenia and cognitive deficits. Given the role of NRG1 in glutamate regulation and glutamate's effect on cognition, we hypothesized that cognitive deficits may be related to variation within NRG1, providing a possible mechanism to increase risk for schizophrenia.

METHODS

This study examined the associations between NRG1, cognition, and schizophrenia using a multigenerational multiplex family sample (total N=419, 40 families), including 58 affected participants (schizophrenia or schizoaffective disorder-depressed type) and their 361 unaffected relatives. Participants were genotyped for 40 NRG1 single nucleotide polymorphisms (SNPs), chosen largely based on previous associations with schizophrenia. All participants completed structured diagnostic interviews and a computerized neurocognitive battery assessing eight cognitive domains. Variance component quantitative trait analyses tested for associations between individual NRG1 SNPs and cognitive performance in the total sample, a subsample of healthy participants with no Diagnostic and Statistical Manual of Mental Disorders diagnosis, and using general intelligence as a covariate.

RESULTS

Effect sizes (within-family β coefficients) ranged from 0.08 to 0.73, and 61 of these associations were nominally significant (P≤0.05), with 12 associations at P≤0.01, although none achieved the modified Bonferroni significance threshold of P<0.0003. Attention was the most frequently nominally associated domain and rs10503929, a nonsynonymous SNP, was the most frequently nominally associated SNP.

CONCLUSION

Although not significant experiment-wise, these findings suggest that further study of the associations between variation in NRG1 and cognition may be productive.

Cholinergic blockade under working memory demands encountered by increased rehearsal strategies: evidence from fMRI in healthy subjects

The connection between cholinergic transmission and cognitive performance has been established in behavioural studies. The specific contribution of the muscarinic receptor system on cognitive performance and brain activation, however, has not been evaluated satisfyingly. To investigate the specific contribution of the muscarinic transmission on neural correlates of working memory, we examined the effects of scopolamine, an antagonist of the muscarinic receptors, using functional magnetic resonance imaging (fMRI). Fifteen healthy male, non-smoking subjects performed a fMRI scanning session following the application of scopolamine (0.4 mg, i.v.) or saline in a placebo-controlled, repeated measure, pseudo-randomized, single-blind design. Working memory was probed using an n-back task. Compared to placebo, challenging the cholinergic transmission with scopolamine resulted in hypoactivations in parietal, occipital and cerebellar areas and hyperactivations in frontal and prefrontal areas. These alterations are interpreted as compensatory strategies used to account for downregulation due to muscarinic acetylcholine blockade in parietal and cerebral storage systems by increased activation in frontal and prefrontal areas related to working memory rehearsal. Our results further underline the importance of cholinergic transmission to working memory performance and determine the specific contribution of muscarinic transmission on cerebral activation associated with executive functioning.

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.

The role of the cerebellum in schizophrenia: from cognition to molecular pathways

Beside its role in motor coordination, the cerebellum is involved in cognitive function such as attention, working memory, verbal learning, and sensory discrimination. In schizophrenia, a disturbed prefronto-thalamo-cerebellar circuit has been proposed to play a role in the pathophysiology. In addition, a deficit in the glutamatergic N-methyl-D-aspartate (NMDAf) receptor has been hypothesized. The risk gene neuregulin 1 may play a major role in this process. We demonstrated a higher expression of the NMDA receptor subunit 2D in the right cerebellar regions of schizophrenia patients, which may be a secondary upregulation due to a dysfunctional receptor. In contrast, the neuregulin 1 risk variant containing at least one C-allele was associated with decreased expression of NMDA receptor subunit 2C, leading to a dysfunction of the NMDA receptor, which in turn may lead to a dysfunction of the gamma amino butyric acid (GABA) system. Accordingly, from post-mortem studies, there is accumulating evidence that GABAergic signaling is decreased in the cerebellum of schizophrenia patients. As patients in these studies are treated with antipsychotics long term, we evaluated the effect of long-term haloperidol and clozapine treatment in an animal model. We showed that clozapine may be superior to haloperidol in restoring a deficit in NMDA receptor subunit 2C expression in the cerebellum. We discuss the molecular findings in the light of the role of the cerebellum in attention and cognitive deficits in schizophrenia.

Decreased Neuregulin 1 C-terminal fragment in Brodmann's area 6 of patients with schizophrenia

Neuregulin 1 (NRG1) is a susceptibility gene for schizophrenia. A decrease in NRG1-ErbB4 signalling has also been associated with the disease. β-amyloid precursor protein-cleaving enzyme (BACE1) processes type III NRG1 precursor, a major neuregulin variant expressed in the brain, to release NRG1 fragments that trigger signalling events and activation of neurotransmitter receptors. Experimental evidence suggests that muscarinic acetylcholine receptors (CHRM) regulate BACE1 expression. Having recently shown that CHRM1 levels are decreased selectively in frontal cortex regions of a subpopulation of schizophrenic patients (muscarinic receptor deficit schizophrenia, MRDS) we aimed to compare the protein expression of BACE1 and NRG1 in the agranular frontal cortex Brodmann's area 6 of SCZ subjects with normal levels of CHRM1 (N = 19), MRDS (N = 20), and age/gender-matched non-psychiatric (healthy) controls (HC; N = 20). Western blot analysis of post-mortem samples showed that the levels of BACE1 and full-length NRG1 precursor (130 kDa) did not differ significantly between the three groups. In contrast, the levels of the NRG1 C-terminal fragment (NRG1-CTF) were decreased by approximately 50% in both schizophrenic groups compared to the HC group (p<0.0027). The ratio of NRG1-CTF versus NRG1 precursor was significantly reduced in the SCZ groups compared to the HC group (p = 0.051). There was no correlation between the levels of either full-length NRG1, NRG1-CTF, or BACE1 and the final recorded doses of antipsychotic drugs for the subjects with schizophrenia. A positive correlation was found between BACE1 and full-length NRG1 precursor in the HC group (r(2) = 0.671, p<0.001) but not in the schizophrenic groups. These data suggest that the proteolytic processing of NRG1 is impaired in schizophrenia.

A follow-up study: acute behavioural effects of Delta(9)-THC in female heterozygous neuregulin 1 transmembrane domain mutant mice

RATIONALE

Heavy cannabis use is linked with an increased risk for schizophrenia. We showed previously that male heterozygous neuregulin 1 transmembrane domain (Nrg1 HET) mice are more sensitive to some effects of the psychotropic cannabis constituent Delta(9)-tetrahydrocannabinol (THC). We report data from a follow-up study in female Nrg1 HET mice, investigating THC effects on behaviours with some relevance to schizophrenia.

METHODS

Mice were injected with THC (0, 5 or 10 mg/kg i.p.) 30 min before a test battery: open field, elevated plus maze, novel object recognition (set 1) or light-dark, social interaction (SI) and prepulse inhibition (PPI 1: variable interstimulus interval (ISI); set 2). Another set (set 3) was injected with the same doses of THC before a fixed interstimulus interval PPI test (PPI 2).

RESULTS

Female Nrg1 HETs displayed the hallmark increased locomotor activity at 5 months and anxiolytic-like behaviour in the open field at 3 and 5 months. THC decreased locomotor activity in both genotypes. THC selectively reduced some SI behaviours in WT mice. Baseline PPI was enhanced in mutants under a variable ISI, while THC had no effect on PPI using either protocol.

CONCLUSIONS

This study reports novel findings on the baseline PPI profile and resistance to THC-induced social withdrawal in female Nrg1 HET mice. This is the first description of THC effects in females of this mouse model and suggests that the transmembrane domain Nrg1 mutation does not appear to have a severe impact on the behavioural sensitivity to THC in female mice.

NRG1 and BDNF genes in schizophrenia: an association study in an Italian case-control sample

We tested for associations between five single nucleotide polymorphisms (SNPs) located in the area containing the Neuregulin 1 gene (NRG1) and three SNPs within the brain-derived neutrophic factor gene (BDNF) in an Italian sample consisting of 171 schizophrenia subjects and 349 controls. No association was found for any of the polymorphisms tested, either in single locus or in haplotype analysis.

The impact of dystrobrevin-binding protein 1 (DTNBP1) on neural correlates of episodic memory encoding and retrieval

Episodic memory impairment is a frequently reported symptom in schizophrenia. It has been shown to be associated with reduced neural activity of the hippocampus and prefrontal cortex. Given the high heritability of schizophrenia the question arises if alterations in brain activity are modulated by susceptibility genes and might be detectable in healthy risk allele carriers. The present study investigated the effect of the single nucleotide polymorphism (SNP) rs1018381 (P1578) of the dystrobrevin-binding protein 1 (DTNBP1) on brain activity in 84 healthy subjects assessed by functional magnetic resonance imaging (fMRI) while they performed an episodic memory task comprising encoding and retrieval of faces. During encoding, the group of risk allele carriers (n = 29) showed enhanced neural activity in the left middle frontal gyrus (BA 11) and bilaterally in the cuneus (BA 17, 7) when compared with the nonrisk carrier group (n = 55). During retrieval, the risk group (compared to the non risk group) showed increased right hemispheric neural activity comprising the medial frontal gyrus (BA 9), inferior frontal gyrus (BA 9), and inferior parietal lobule (BA 40). Since there were no behavioral performance differences, increased neural activity of the risk group might be interpreted as a correlate of higher effort or differing cognitive strategies in order to compensate for a genetically determined slight cognitive deficit. Interestingly, the laterality of increased prefrontal activity is in accordance with the well known hemispheric encoding/retrieval asymmetry (HERA) model of episodic memory.

Impact of schizophrenia-risk gene dysbindin 1 on brain activation in bilateral middle frontal gyrus during a working memory task in healthy individuals

Working memory (WM) dysfunction is a hallmark feature of schizophrenia. Functional imaging studies using WM tasks have documented both prefrontal hypo- and hyperactivation in schizophrenia. Schizophrenia is highly heritable, and it is unclear which susceptibility genes modulate WM and its neural correlates. A strong linkage between genetic variants in the dysbindin 1 gene and schizophrenia has been demonstrated. The aim of this study was to investigate the influence of the DTNBP1 schizophrenia susceptibility gene on WM and its neural correlates in healthy individuals. Fifty-seven right-handed, healthy male volunteers genotyped for DTNBP1 SNP rs1018381 status were divided in heterozygous risk-allele carriers (T/C) and homozygous noncarriers (C/C). WM was assessed by a 2-back vs. 0-back version of the Continuous Performance Test (CPT), while brain activation was measured with fMRI. DTNBP1 SNP rs1018381 carrier status was determined and correlated with WM performance and brain activation. Despite any differences in behavioral performance, risk-allele carriers exhibited significantly increased activation of the bilateral middle frontal gyrus (BA 9), a part of the dorsolateral prefrontal cortex (DLPFC), compared to noncarriers. This difference did not correlate with WM performance. The fMRI data provide evidence for an influence of genetic variation in DTNBP1 gene region tagged by SNP rs1018381 on bilateral middle frontal gyrus activation during a WM task. The increased activation in these brain areas may be a consequence of "inefficient" or compensatory DLPFC cognitive control functions.

Genetic variation in neuregulin1 is associated with differences in prefrontal engagement in children

The majority of psychopathology is rooted early in life and first emerges during childhood and adolescence. However, little is known about how risk genes affect brain function to increase biological vulnerability to psychopathology in childhood, because most imaging genetic studies published so far have been conducted on adult participants. We examined the impact of neuregulin1 (NRG1), a probable susceptibility gene for schizophrenia and bipolar disorder, on brain function in a sample of 102 ten- to twelve-year-old children. Each participant performed a Go/Nogo task, whereas brain responses were measured using functional magnetic resonance imaging. Statistical parametric mapping was used to estimate the impact of genetic variation in NRG1 on brain activation. Response accuracy and reaction times did not differ as a function of NRG1 genotype. However, individuals with the high-risk variant expressed greater brain activation for both Go and Nogo stimuli in the right posterior orbital gyrus, where NRG1 genotype accounted for 11% of interindividual variance. There were no regions showing a significant interaction between NRG1 genotype and stimulus type even at trend level, suggesting that the impact of NRG1 on brain activation was not specific to either response inhibition or motor execution. These results suggest that that genetic variation in NRG1 is associated with different levels of prefrontal engagement in children as young as 10-12 years of age. Our investigation provides support to the idea that genetic factors may affect brain function to moderate vulnerability to psychopathology from childhood.

Patients with schizophrenia show deficits of working memory maintenance components in circuit-specific tasks

Working memory (WM) deficits are a neuropsychological core finding in patients with schizophrenia and also supposed to be a potential endophenotype of schizophrenia. Yet, there is a large heterogeneity between different WM tasks which is partly due to the lack of process specificity of the tasks applied. Therefore, we investigated WM functioning in patients with schizophrenia using process- and circuit-specific tasks. Thirty-one patients with schizophrenia and 47 controls were tested with respect to different aspects of verbal and visuospatial working memory using modified Sternberg paradigms in a computer-based behavioural experiment. Total group analysis revealed significant impairment of patients with schizophrenia in each of the tested WM components. Furthermore, we were able to identify subgroups of patients showing different patterns of selective deficits. Patients with schizophrenia exhibit specific and, in part, selective WM deficits with indirect but conclusive evidence of dysfunctions of the underlying neural networks. These deficits are present in tasks requiring only maintenance of verbal or visuospatial information. In contrast to a seemingly global working memory deficit, individual analysis revealed differential patterns of working memory impairments in patients with schizophrenia.

Gene expression of NMDA receptor subunits in the cerebellum of elderly patients with schizophrenia

To determine if NMDA receptor alterations are present in the cerebellum in schizophrenia, we measured NMDA receptor binding and gene expression of the NMDA receptor subunits in a post-mortem study of elderly patients with schizophrenia and non-affected subjects. Furthermore, we assessed influence of genetic variation in the candidate gene neuregulin-1 (NRG1) on the expression of the NMDA receptor in an exploratory study. Post-mortem samples from the cerebellar cortex of ten schizophrenic patients were compared with nine normal subjects. We investigated NMDA receptor binding by receptor autoradiography and gene expression of the NMDA receptor subunits NR1, NR2A, NR2B, NR2C and NR2D by in situ hybridization. For the genetic study, we genotyped the NRG1 polymorphism rs35753505 (SNP8NRG221533). Additionally, we treated rats with the antipsychotics haloperidol or clozapine and assessed cerebellar NMDA receptor binding and gene expression of subunits to examine the effects of antipsychotic treatment. Gene expression of the NR2D subunit was increased in the right cerebellum of schizophrenic patients compared to controls. Individuals carrying at least one C allele of rs35753505 (SNP8NRG221533) showed decreased expression of the NR2C subunit in the right cerebellum, compared to individuals homozygous for the T allele. Correlation with medication parameters and the animal model revealed no treatment effects. In conclusion, increased NR2D expression results in a hyperexcitable NMDA receptor suggesting an adaptive effect due to receptor hypofunction. The decreased NR2C expression in NRG1 risk variant may cause a deficit in NMDA receptor function. This supports the hypothesis of an abnormal glutamatergic neurotransmission in the right cerebellum in the pathophysiology of schizophrenia.

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.