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Functional Neuregulin Variant Linked to Psychosis, Abnormal Brain Activation and IQ

30 October 2006. A high-risk haplotype of the candidate schizophrenia susceptibility gene neuregulin 1 (NRG1), and in particular a single nucleotide polymorphism associated with altered expression, has now been linked with increased psychotic symptoms, abnormal frontal and temporal lobe activation, and lower adult intelligence quotient (IQ) in young adults already at high risk of the disease. The study, by Jeremy Hall and colleagues from the University of Edinburgh, was published online in Nature Neuroscience on October 29.

As a candidate susceptibility gene for schizophrenia, NRG1 is supported by a strong body of evidence (Li et al., 2006). A risk-associated haplotype of NRG1, called the deCODE (or Icelandic) haplotype, has been identified at the 5’ end of the gene (Stefansson et al., 2002) and has been confirmed in the Scottish population (Stefansson et al., 2003). Work published earlier this year by Amanda Law and colleagues from Oxford University, England, and the National Institutes of Health, Bethesda, Maryland, found that the risk allele SNP8NRG243177, which is part of the original deCODE haplotype, is associated with increased expression of the type IV NRG1 transcript in postmortem brain tissue (Law et al., 2006; also see SRF related news story). This effect appears to be due to changes in three transcription factor binding sites in NRG1, those for serum response factor, myelin transcription factor-1, and High Mobility Group Box Protein-1.

In this study, a collaboration between the groups led by Eve Johnstone and David Porteous, Hall and colleagues examined the effects of the SNP8NRG243177 risk allele on the development of psychotic symptoms, brain function, and adult IQ in participants from the Edinburgh High Risk Study (Johnstone et al., 2000). The 79 subjects were aged 16-25, were from families with at least two individuals affected by schizophrenia, and were followed up regularly for up to 10 years. DNA samples were collected from study participants and were genotyped for single nucleotide polymorphisms (SNPs) from the deCODE haplotype (SNP8NRG221132, SNP8NRG221533, SNP8NRG241930, and SNP8NRG243177 and the microsatellites 478B14-848 and 420M9-1395).

The authors found that the SNP8NRG243177 genotype was strongly associated with the development of psychotic symptoms in this sample (Fisher’s exact test 13.5, P = 0.001), and the effect remained significant when related subjects were removed from the analysis. Although each of the other markers was analyzed, no association with the development of psychotic symptoms was found. When all four SNPs of the deCODE haplotype were analyzed together, an association with psychotic symptoms was found, albeit at a lower level of significance than that seen with SNP8NRG243177 alone (Fisher’s exact test 8.4, P <0.05).

Hall and colleagues next conducted an analysis of brain activation in their cohort using functional magnetic resonance imaging (fMRI). Participants performed the Hayling sentence completion task, known to activate frontal and temporal brain regions, while undergoing fMRI. A failure to properly integrate these brain regions has been theorized to underlie psychosis (Friston and Frith, 1995). The authors found that subjects with the risk genotype showed significantly less activation of medial prefrontal cortex (Brodmann area 9) and right temporo-occipital junction (Brodmann areas 39 and 19) than did those without this genotype; the effect was still significant after the removal of related individuals from the groups. In addition, no differences in grey matter density were found between groups in these brain regions by voxel-based morphometry.

Lastly, the researchers found that the risk genotype was significantly associated with a lower adult IQ. Those with the highest risk phenotype (T/T) had a mean score of 94.3 on the National Adult Reading Test (NART), compared with scores of 100.4 and 101.9 in the C/T (moderate risk) and C/C (lowest risk) groups, respectively (P <0.05).

“The abnormalities in cortical function seen in individuals with the risk genotype are in agreement with previous studies of subjects with psychotic symptoms showing abnormal medial prefrontal and posterior temporal lobe function and support the view that abnormal integration of frontal and temporal lobe function underlies the development of psychotic symptoms,” the authors write. They note that NRG1 has been found to be associated with the development of psychotic symptoms in other disorders, which they suggest raises the possibility that NRG1 may contribute to the development of psychotic features across traditional diagnostic boundaries.—Jillian Lokere.

Reference:
Hall J, Whalley HC, Job DE, Baig BJ, McIntosh AM, Evans KL, Thomson PA, Porteous DJ, Cunningham-Owens DG, Johnstone EC, Lawrie SM. A neuregulin 1 variant associated with abnormal cortical function and psychotic symptoms. Advanced online publication 29 October 2006; doi:10.1038/nn1795. Abstract

Comments on News and Primary Papers
Comment by:  Amanda Jayne Law, SRF Advisor
Submitted 8 November 2006
Posted 8 November 2006

Convergent evidence supporting the role of a schizophrenia-associated polymorphic variant in the NRG1 gene (SNP8NRG1243177) with the regulation of cortical function and the development of psychosis
The study of Hall and colleagues describes association of a schizophrenia-related polymorphism in the NRG1 gene promoter (SNP8NRG1243177) with cortical and cognitive dysfunction and the emergence of psychotic symptoms in young individuals at high genetic risk for developing schizophrenia. We have previously demonstrated that the same polymorphism (SNP8NRG1243177) and a 22kb risk haplotype, including this SNP, predicts transcription levels of a novel isoform of the NRG1 gene (Type IV) in the brain of patients with schizophrenia (Law et al., 2006; see SRF related news story). The SNP resides in the NRG1 promoter region for the novel E187 exon (Type IV) and our investigations indicate that the SNP is central to a regulatory transcription factor binding domain. We previously suggested that a potential molecular mechanism behind the clinical association of NRG1 with schizophrenia (at least in the 5’ region of the gene) involves altered transcriptional regulation of the gene, which modifies to a small degree and in an isoform-specific fashion, the efficiency of NRG1 signaling effects on neural development and plasticity. We predicted that such effects may translate into altered adult brain function.

With this in mind, the study of Hall and colleagues provides a remarkable level of functional convergence suggesting a potential link between a molecular phenotype related to genetic risk at this loci (i.e., increased transcriptional regulation of the novel Type IV isoform, Law et al., 2006) and abnormal cortical development, function, and the subsequent manifestation of psychotic symptoms.

The major objective of the study was to determine the relationship between previously identified genetic variants in the 5’ region of NRG1 (Stefansson et al., 2002; see also Harrison and Law, 2006) with aspects of the schizophrenia phenotype (including decreased IQ, altered cortical function, and psychosis) in individuals who are at high risk of developing the disorder. Subjects were followed throughout the course of the study or until they developed schizophrenia. It is noteworthy that the incidence rate of developing schizophrenia was highest in subjects homozygous for the risk (T) allele at NRG1243177 (25 percent). Conversely, the occurrence of schizophrenia in non-risk C/C individuals was lower (15 percent), but still present, demonstrating the complex heterogeneous nature of the disease.

The study was performed on a modest sample of 79 high-risk individuals, 63 of whom fMRI data was available for. Firstly, brain activation patterns were determined by fMRI whilst individuals were performing the Hayling sentence completion task. Subjects who were homozygous for the risk T allele (T/T) at SNP8NRG1243177 exhibited decreased activation of Brodmann area 9 and the right temporo-occipital junction (Brodmann areas 39 and 19) when the activation during the task was compared to the resting state. However, unlike the medial prefrontal cortex, the difference in activation of the right temporal-occipital junction derived from the fact that T/T individuals had a “higher” resting activity compared to C/C individuals (as stated by the authors). Based on this observation, it is difficult to interpret which phenotype, in terms of cortical activation in this region, genetic risk at the allele is associated with—that is, is the risk variant associated with an overactive right temporo-occipital cortex at rest, or with decreased ability to further activate the region during demand?

In the supplementary notes, the authors address this issue, stating that a failure to deactivate the temporal cortex during rest may suggest that frontotemporal activity is disrupted in individuals homozygous for the T allele at SNP8NRG1243177. Furthermore, based on our studies, it would be important to see if genetic risk at SNP8NRG1243177 predicts hippocampal activation during a task that activates this area, allowing one to link the molecular changes in the hippocampus in schizophrenia, related to genetic risk at this SNP, to an outcome measure of brain function. Conversely, it would also be of use to determine whether NRG1 Type IV expression is altered in the brain areas implicated by Hall and colleagues.

Importantly, the study also shows that the genotype effects at SNP8NRG1243177 on cortical function are not related to medication status (all subjects were medication-free). Secondly, Hall and colleagues investigated the effects of the SNP8NRG1243177 risk allele on the development of psychotic symptoms in high-risk individuals. In a remarkable observation, 100 percent of individuals who had the risk T/T genotype developed psychotic symptoms, compared to less than 50 percent of C/C individuals, although the small sample size must be kept in mind. One interesting observation that is not readily apparent in the study is the fact that of the 12 T/T individuals who developed psychotic symptoms, only three of those (25 percent) developed schizophrenia before the end of the study. This may be due to the fact that others later went on to develop the disorder or that they developed other complex mental illnesses which include psychosis, such as bipolar disorder. (This is not clear from the study.) The association of genetic risk in the NRG1 gene and psychotic symptom development is consistent with the fact that genetic risk at NRG1 has been linked to psychosis in other brain diseases such as bipolar disorder and Alzheimer’s disease (see Harrison and Law, 2006). Finally, and perhaps most compelling, there is the observation that genetic risk at SNP8NRG1243177 is related to decreased IQ (measured by NART) in high-risk individuals.

Overall, the study of Hall and colleagues provides novel evidence that genetic variation in the NRG1 promoter, in particular a genetic variant that predicts altered expression of the NRG1 gene in the brain in schizophrenia (Law et al., 2006), is associated with abnormalities in cortical function and cognition and contributes to psychotic symptoms in individuals at high risk of developing the disease.

View all comments by Amanda Jayne LawComment by:  Nicholas Stefanis
Submitted 16 November 2006
Posted 16 November 2006

The readers might find our results (now in press) interesting in the context of the brilliant work by Law and colleaguesLaw et al (2006)and now Hall and colleagues. We examined the potential impact of 18 single nucleotide polymorphisms (SNPs) within the DTNBP1, NRG1, DAOA/G32 and DAAO genes, on cognition and self-rated schizotypy, in a representative population of 2,243 young male military conscripts. Single SNP and haplotype associations were evaluated. The risk allele of functional SNP8NRG243177 was associated with reduced spatial working memory capacity.

This is of particular interest since it has recently been reported that SNP8NRG243177 is a functional polymorphism, the risk allele (T) predicting higher levels of type IV NRG1 mRNA expression (Law et al., 2006), and associated with lower prefrontal (and temporal) activation and development of psychotic symptoms in high risk individuals for schizophrenia (Hall et al., 2006). If not a chance finding, our result constitutes the first independent confirmation that functional SNP8NRG243177 impacts aspects of human prefrontal brain function. Since spatial working deficits constitute an effective endophenotype for schizophrenia, this finding also suggests a mechanism by which this NRG1 variant may confer risk for the disorder at an information processing level. In contrast to Hall and colleagues, no association of SNP8NRG243177 with psychotic-like symptoms or IQ was detected in this study.

References:
Nicholas C. Stefanis, Thomas A. Trikalinos, Dimitrios Avramopoulos, Nikos Smyrnis, Ioannis Evdokimidis, Evangelia E. Ntzani, John P. Ioannidis and Costas N. Stefanis. Impact of schizophrenia candidate genes on schizotypy and cognitive endophenotypes at the population level. Biological Psychiatry (in press).

View all comments by Nicholas Stefanis

Comments on Related News


Related News: Polymorphisms and Schizophrenia—The Ups and Downs of Neuregulin Expression

Comment by:  William Carpenter, SRF Advisor (Disclosure)
Submitted 22 April 2006
Posted 22 April 2006
  I recommend the Primary Papers

Related News: Polymorphisms and Schizophrenia—The Ups and Downs of Neuregulin Expression

Comment by:  Stephan Heckers, SRF Advisor
Submitted 29 April 2006
Posted 29 April 2006
  I recommend the Primary Papers

The gene Neuregulin 1 (NRG1) on chromosome 8p has been identified as one of the risk genes for schizophrenia. It is unclear how the DNA sequence variation linked to schizophrenia leads to abnormalities of mRNA expression. This would be important to know, in order to understand the downstream effects of the neuregulin gene on neuronal functioning in schizophrenia.

Law and colleagues explored this question in post-mortem specimens of the hippocampus of control subjects and patients with schizophrenia. This elegant study of the expression of four types of NRG1 mRNA (types I-IV) is exactly what we need to translate findings from the field of human genetics into the field of schizophrenia neuropathology. The findings are complex and cannot be translated easily into a model of neuregulin dysfunction in schizophrenia. I would like to highlight two findings.

First, the level of NRG1 type I mRNA expression was increased in the hippocampus of schizophrenia patients. This confirms an earlier study of NRG1 mRNA expression in schizophrenia. It remains to be seen how this change in NRG1 type I mRNA expression relates to the finer details of neuregulin dysfunction in schizophrenia.

Second, one single nucleotide polymorphism (SNP8NRG243177) of the risk haplotype linked to schizophrenia in earlier studies predicts NRG1 type IV mRNA expression. The SNP determines a binding site for transcription factors, providing clues for how DNA sequence variation may lead, via modulation of mRNA expression, to neuronal dysfunction in schizophrenia. It is exciting to see that we can now test specific hypotheses of molecular mechanisms in the brains of patients who have suffered from schizophrenia. The study by Law et al. is an encouraging step in the right direction.

View all comments by Stephan Heckers

Related News: Polymorphisms and Schizophrenia—The Ups and Downs of Neuregulin Expression

Comment by:  Bryan Roth, SRF Advisor
Submitted 5 May 2006
Posted 5 May 2006
  I recommend the Primary Papers

I think this is a very interesting and potentially significant paper. It is important to point out, however, that it deals with changes in mRNA abundance rather than alterations in neuregulin protein expression. No measures of isoform protein expression were performed, and it is conceivable that neuregulin isoform protein expression could be increased, decreased, or not changed. A second point is that although statistically significant changes in mRNA were measured, they are modest.

Finally, although multiple comparisons were performed, the authors chose not to perform Bonferroni corrections, noting in the primary paper that, "Correction for random effects, such as Bonferroni correction, would be an excessively conservative approach, particularly given that we have restricted our primary analyses to planned comparisons (based on strong prior clinical association and physical location of the SNPs) of four SNPs and a single haplotype comprised of these SNPs. Because the SNPs are in moderate LD, the degree of independence between markers is low and, therefore, correcting for multiple testing would result in a high type II error rate. The prior probability and the predictable association between the deCODE haplotype and expression of NRG1 isoforms (especially type IV, which is its immediate physical neighbor) combined with the LD between SNPs in this haplotype makes statistical correction for these comparisons inappropriate. Nevertheless, our finding regarding type IV expression and the deCODE haplotype and SNP8NRG243177 requires independent replication."

It will thus be important to determine if these changes in neuregulin mRNA isoform abundance are mirrored by significant changes in neuregulin isoform protein expression and if the findings can be independently replicated with other cohorts.

View all comments by Bryan Roth

Related News: Genetics and Schizophrenia—Calcineurin Connection Grows

Comment by:  Mary Reid
Submitted 26 February 2007
Posted 27 February 2007

Tom Fagan mentions that calcineurin regulates phosphorylations elicited by both glutamatergic and dopaminergic signaling. The activity of D-amino acid oxidase is increased in schizophrenia, and this also affects signaling through both these pathways. Is there any clinical benefit with the use of sodium benzoate which inhibits DAO activity?

He also mentions that EGR3 can be regulated by the activity of neuregulin. Interestingly, Roberts et al. suggest that BDNF, which is decreased in first-episode psychosis (Buckley et al., 2007), induces synthesis of EGR3 to regulate activity of GABRA4. Ma and colleagues (Ma et al., 2005) conclude that GABRA4 is involved in the etiology of autism and it has also has been implicated in nicotine dependence (Saccone et al., 2007).

Glorioso and colleagues (Glorioso et al., 2006) report changes in genes encoding early-immediate genes such as EGR1 and EGR2 and RGS4 which is involved in cellular signaling and has been implicated in schizophrenia following BDNF gene ablation. Several studies report that zinc increases BDNF expression. Does this give support to the zinc deficiency theory of schizophrenia?

View all comments by Mary Reid

Related News: Polymorphisms and Schizophrenia—The Ups and Downs of Neuregulin Expression

Comment by:  Patricia Estani
Submitted 9 June 2007
Posted 10 June 2007
  I recommend the Primary Papers

Related News: Neuregulin and Schizophrenia—Functional Failure Fingers Risk Allele

Comment by:  Ali Mohamad Shariaty
Submitted 14 July 2007
Posted 14 July 2007

It is really a fascinating article which is a step towards understanding the molecular mechanisms underlying phenotypes of schizophrenia. Relating genotypes to phenotypes is really necessary for untangling the puzzle of a complex disorder. However, when a regulatory SNP interferes with normal binding of a transcription factor, is it understood that the transcription factor should play a role in brain and therefore in the molecular pathology of schizophrenia? Is there any direct role for involvement of serum response factor (SRF) in brain development or any neurological process?

View all comments by Ali Mohamad Shariaty

Related News: Neuregulin and Schizophrenia—Functional Failure Fingers Risk Allele

Comment by:  Amanda Jayne Law, SRF Advisor
Submitted 14 July 2007
Posted 15 July 2007

In response to Ali Mohamad Shariaty’s comment: Serum response factor (SRF) plays a key role in regulating the transcription of a number of genes involved in brain development. Genetic manipulation of SRF has revealed a direct role for it as a regulator of cortical and hippocampal function (e.g., Etkin et al., 2006) influencing both learning and memory. At the cellular level SRF has been shown to regulate dendritic morphology and neuronal migration. Therefore, SRF is indeed an important neurodevelopmental molecule, mediated via its regulation of genes, such as NRG1. Genetic variations that are predicted to interfere with SRF binding (such as the SNP characterized in our study) may affect critical aspects of brain development and function that contribute to schizophrenia. Since SRF regulates the expression of a number of genes, beyond that of NRG1, its involvement in schizophrenia is likely mediated “indirectly” via its effects on the regulation of genes associated with the disorder.

References:

Etkin A, Alarcón JM, Weisberg SP, Touzani K, Huang YY, Nordheim A, Kandel ER. A role in learning for SRF: deletion in the adult forebrain disrupts LTD and the formation of an immediate memory of a novel context. Neuron. 2006 Apr 6;50(1):127-43. Abstract

View all comments by Amanda Jayne Law

Related News: Neuregulin and Schizophrenia—Functional Failure Fingers Risk Allele

Comment by:  Robert Hunter
Submitted 17 July 2007
Posted 17 July 2007
  I recommend the Primary Papers