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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

COMT and STH polymorphisms interaction on cognition in schizophrenia

Catechol-O-methyltransferase (COMT) gene, a key regulator of prefrontal cortex (PFC) dopamine (DA) availability, has been extensively studied in relation to cognitive domains, mainly executive functions, that are impaired in schizophrenia, but results are still controversial. Since recent studies in patients affected by neurodegenerative and psychiatric disorders suggested a role of saitohin (STH) gene as a concurring factor in hypofrontality, we hypothesize that STH and COMT polymorphisms could have an additive effect on cognition in schizophrenia. Three forty three clinically stabilized patients with schizophrenia were assessed with a broad neuropsychological battery including the Brief Assessment of Cognition in Schizophrenia, the Wisconsin Card Sorting Test and the Continuous Performance Test and were genotyped for COMT Val108/158Met and STH Q7R polymorphisms. We observed the effects of COMT on speed of processing and executive functions, as well as a significant effect of STH on executive functions performances. Moreover, a significant interaction between COMT and STH polymorphisms was found on executive functions, with COMT Val/Val and STH R carriers performing worse. Our results showed a significant interaction effect of COMT and STH polymorphisms on cognitive performances, strengthening the involvement of STH in cognitive impairments, especially in the domains commonly impaired in schizophrenia.

Factors affecting cognitive remediation response in schizophrenia: the role of COMT gene and antipsychotic treatment

Cognitive remediation is the best available tool to treat cognitive deficits in schizophrenia and has evidence of biological validity; however results are still heterogeneous and significant predictors are lacking. Previous studies showed that cognitive remediation is able to induce changes in PFC function and dopaminergic transmission and thus the study of possible sources of variability at these levels (i.e. antipsychotic treatments and genetic variability) might help to gain a deeper understanding of neurobiological correlates and translate into optimization and personalization of interventions. In the present study, we analyzed the interaction between pharmacological treatment (clozapine vs typical/atypical D2 blockers) and COMT rs4680 polymorphism on cognitive changes after cognitive remediation therapy, in a sample of 98 clinically stabilized patients with schizophrenia. The General Linear Model showed a significant interaction of pharmacological treatment and COMT polymorphism on the improvement in "Symbol Coding" subtest, a global measure of speed of processing. Post-hoc analysis revealed a significant difference between COMT genotypes, when treated with D2 blockers, with worse results among Val/Val patients. These preliminary results suggest that genetic variability, influencing prefrontal dopamine, might affect individual capacity to improve with different patterns, depending on antipsychotic treatment.

COMT and 5-HT1A-receptor genotypes potentially affect executive functions improvement after cognitive remediation in schizophrenia

Cognitive remediation therapy (CRT) has been proved to improve cognitive deficits in schizophrenia and to enhance functional outcomes of classical rehabilitation. However, CRT outcomes are heterogeneous and predictors of response are still unknown. Genetic variability, especially in the dopaminergic system, has been hypothesized to affect CRT. We previously reported that rs4680 of the catechol-O-methyltrasferase (COMT) influences improvements in executive functions in patients treated with CRT, but this result was not confirmed by other studies. Such inconsistent findings may depend, other than on clinical variables, also on other genes involved in cognition. Recent studies proved that serotonin 1A receptor (5-HT1A-R) regulates dopamine in the prefrontal cortex (PFC), and clinical works suggested a 5-HT1A-R role in cognition. We then analysed possible effects of COMT rs4680 and 5-HT1A-R rs6295 on CRT outcomes, taking into account also clinical and demographic factors. Eighty-six clinically stabilized schizophrenia patients treated with three months CRT were assessed with the Wisconsin Card Sorting Test, as a measure of executive functions, at enrolment and after CRT treatment, and underwent COMT and 5-HT1A-R genotyping. We found a significant main effect of COMT genotype and an interaction with 5-HT1A-R on executive function improvement after CRT. The results suggest that these two polymorphisms may have an additive effect on individual capacity to recover from cognitive deficit, probably through their role on PFC dopaminergic transmission modulation, known to be critical for modulating cognitive functions.

Effect of glutamate transporter EAAT2 gene variants and gray matter deficits on working memory in schizophrenia

Glutamate is the major excitatory neurotransmitter in the brain, with up to 40% of all synapses being glutamatergic. An altered glutamatergic transmission could play a critical role in working memory deficts observed in schizophrenia and could underline progressive changes such as grey matter loss throughout the brain. The aim of the study was to investigate if gray matter volume and working memory could be modulated by a genetic polymorphism related to glutamatergic function. Fifty schizophrenia patients underwent magnetic resonance and working memory testing outside of the scanner and were genotyped for rs4354668 EAAT2 polymorphism. Carriers of the G allele had lower gray matter volumes than T/T homozygote and worse working memory performance. Poor working memory performance was associated with gray matter reduction. Differences between the three genotypes are more relevant among patients showing poor performance at the 2-back task. Since glutamate abnormalities are known to be involved in excitotoxic processes, the decrease in cortical thickness observed in schizophrenia patients could be linked to an excess of extracellular glutamate. The differential effect of EAAT2 observed between good and poor performers suggests that the effect of EEAT2 on gray matter might reveal in the presence of a pathological process affecting gray matter.

Criteria for symptom remission revisited: a study of patients affected by schizophrenia and schizoaffective disorders

BACKGROUND

This study aims to compare severity criteria defined by the Remission in Schizophrenia Working Group (RSWGcr) with other criteria in relation to functional and neurocognitive outcome.

METHODS

112 chronic psychotic outpatients were examined. Symptomatic remission according to RSWGcr was compared with the outcome achieved using criteria based on PANSS Positive and Negative Scales (PANSS-PNScr) and the entire PANSS (PANNS-TScr).

RESULTS

Remission rates were 50%, 35% and 23% respectively at RSWGcr, PANSS-PNScr and PANNS-TScr; functional remission rates were 32%, 42% and 54%. Sensitivity, specificity, predictive value and ROC analysis demonstrated the superiority of PANSS-PNScr in identifying patients with higher functional and cognitive outcomes. Regression analysis showed a significant predictive effect of PANSS-TScr on functioning. General linear model analyses demonstrated significantly higher mean scores at PSP and BACS for patients remitted according to PANSS-TScr.

CONCLUSION

The use of more restrictive severity criteria of remission seems to be associated with improved identification of truly remitted patients.

Neurofunctional correlates of theory of mind deficits in schizophrenia

Theory of Mind, the ability to understand the potential mental states and intentions of others, represents a relevant aspect of social cognition, with high impact on the capacity to interact within the social world. This very human ability has been one of the focuses of neuroscience research in the past decades and data from neuroimaging studies allowed to identify a Theory of Mind network and to formulate a neurobiological model. Concurrent neuropsychiatric studies showed that Theory of Mind is differently impaired in several conditions, among these, in schizophrenia, a disease characterized by functional and social disability. This paper addresses the issue of neurofunctional correlates of Theory of Mind deficits in schizophrenia, reviewing functional imaging studies of the past ten years comparing schizophrenia patients to healthy controls. Several differences in hemodynamic response between patients and controls were observed in the areas known to be critically involved in social cognition, such as the medial prefrontal cortex, temporal cortex surrounding superior temporal sulcus and temporo-parietal junction and cingulate cortex. Results are promising, however they are still heterogeneous. The reported variability could depend on factors related to the construct of Theory of Mind itself, technical aspects and psychopathological/physiopathological mechanisms and needs to be further addressed by future studies.

Theory of Mind intervention for outpatients with schizophrenia

Social disability is one of the critical areas known to be a predictor of daily functioning in schizophrenia. Recent studies showed that impairments in Theory of Mind (ToM) contribute to real-world social functioning and are more strongly associated with community outcomes than other neuropsychological domains of cognition. Several experiments revealed an improving potential of social cognition targeted training, particularly through introduction of verbalisation and explicit manipulation of information about others' mental states. Based on these data, we evaluated longitudinally, with a controlled trial, the feasibility and efficacy of ToM training and the possible influences of daily functioning and IQ on the enhancement of ToM abilities. Thirty outpatients with schizophrenia were recruited and randomly allocated to two groups: ToM Intervention (ToMI), based on verbalisation of selected comic strips representing ToM scenarios, or active control group (ACG). Results showed a significant improvement of ToM abilities among subjects allocated to ToMI compared to ACG, confirming the hypothesis of the enhancing potential of training methods targeting ToM functions. Moreover, we observed no influences of neuropsychological and functional variables on ToM improvement. Development of future studies should take into account possible effects of ToM training on functional outcome, according to the strong associations between ToM abilities and real-world social functioning.

Catechol-O-methyltransferase (COMT) genotype biases neural correlates of empathy and perceived personal distress in schizophrenia

BACKGROUND

The catechol-O-methyltransferase (COMT) Val(108/158)Met polymorphism (rs4680) influences enzyme activity with valine (Val) allele associated with higher enzymatic activity. Several studies suggest that factors influencing dopaminergic transmission could control response to stressful situations. Empathy is an essential element of human behavior, requires the ability to adopt another person's perspective, and has been found to be dysfunctional in schizophrenia.

METHODS

Twenty-eight schizophrenic patients underwent functional magnetic resonance imaging performing an empathy task. Perceived empathy has been evaluated with the Interpersonal Reactivity Index.

RESULTS

An effect of COMT on perceived distress subscale has been shown, with methionine (Met)/Met subjects reporting lower rates of stress compared with Val/Val. Moreover, imaging results showed an effect of genotype on empathy processing in the anterior cingulate with Val/Val subjects showing the lowest activation.

DISCUSSION

This is the first study of the effect of rs4680 on interpersonal distress and neural correlates of empathy in schizophrenia. We found a decrease in neural responses in areas that ensure a cognitive control of emotion that is paralleled by perceived distress in interpersonal situation; this functional pattern seems to be influenced by rs4680 COMT polymorphism.

Patterns of evidence integration in schizophrenia and delusion

Previous studies documented a bias against disconfirmatory evidence (BADE) in patients affected by schizophrenia spectrum disorders, with some discrepant findings on its relationship with delusions. In order to further investigate the patterns of evidence integration in schizophrenia and delusion, we recruited 40 deluded and non-deluded patients with schizophrenia and 40 healthy control subjects. Participants were administered the BADE test, which consisted of 30 delusion-neutral scenarios, each one progressively described by three subsequent disambiguating statements and providing four types of interpretation to rate for plausibility; at every additional evidence presentation, participants were asked to adjust their ratings. In contrast to previous works, patients displayed both a BADE and a bias against confirmatory evidence (BACE) relative to healthy subjects, as they reduced plausibility ratings on incorrect interpretations and increased plausibility ratings on correct interpretation significantly less over trial progress. Moreover, BACE and BADE measures showed to discriminate differentially control from schizophrenia participants and delusional from non-delusional patients.

Theory of mind and emotion processing training for patients with schizophrenia: preliminary findings

Impairments in social cognition are critical predictors of social functioning in patients with schizophrenia. Emotion processing (EP) and theory of mind (ToM) are hypothesized to influence real-world behavior more directly than basic cognition and represent important targets of intervention. The use of video scenes depicting human interactions could constitute an appropriate tool to enhance understanding of the characters' behavior and stimulate inferences on mental states. The aim of our pilot study was to evaluate longitudinally, with a controlled trial, the feasibility and the efficacy of a single-paradigm emotion recognition and ToM training designed for outpatients affected by schizophrenia, with the goal to create an ecological treatment, overcoming artificial laboratory biases, by the use of specific videotaped material. Fifty-two outpatients were randomly assigned to an EP and ToM video-based training (n=27) or to a standard social cognitive rehabilitation treatment (n=24). They were assessed before and after 12 weeks of intervention and compared to a time-matched control group (n=24). Our results show a statistically significant improvement in ToM abilities, confirming the hypothesis of the enhancing potential of social cognitive interventions, but no changes with respect to EP; despite the need for a deeper examination, these data support further development of this treatment approach.

Self-awareness of cognitive functioning in schizophrenia: patients and their relatives

Cognitive impairment has been recognized since the earliest descriptions of schizophrenia as a core feature of the illness and different programmes have been developed to remediate these deficits. In all likelihood it is important for compliance and adherence to treatment that not only the patients but also their relatives be aware of the patients; cognitive deficits. Sixty-two patients with a diagnosis of schizophrenia and, for each one of them, one family member and an informant from the medical staff, were recruited and administered the Schizophrenia Cognition Rating Scale (SCoRS) ratings. Patients were tested for cognitive deficits with a neuropsychological battery and their performance was compared to the ratings of cognitive functioning provided by the patient himself, his family member and the informant. Results show no significant association between cognitive performance and SCoRS ratings in patients; only for executive functions the patient's performance was found to be predictive of the respective judgment on the SCoRS that was given by the relative. This is the first study to investigate awareness of the patients' cognitive deficits, both in the patients themselves and in their first degree relatives, through a direct comparison between subjective clinical ratings and objective measures of cognitive performances. When both patients and relatives are unaware of the patients' cognitive deficits, this could affect adherence to remediation treatment and need to be specifically addressed in future rehabilitation strategies.

Cognitive dysfunction and glutamate reuptake: effect of EAAT2 polymorphism in schizophrenia

A disturbance of glutamatergic transmission has been suggested to contribute to the development of schizophrenic pathophysiology, based primarily on the ability of glutamate receptor antagonists to induce schizophrenic-like symptoms. The excitatory amino acid transporter 2 (EAAT2) is responsible for the majority of glutamate uptake. It also contributes to energy metabolism in the brain, by transporting glutamate into astrocytes for conversion into glutamine. A dysregulation of its level of expression has been associated with multiple neurological disorders. Blocking glutamate uptake by EAAT2 in cultured oligodendrocytes leads to cell death, demyelination and axonal damage, suggesting that it is crucial for normal oligodendrocyte function. Different studies focused on EAAT2 alterations among subjects affected by schizophrenia, reporting a decreased expression in the parahippocampal region and in the dorsolateral prefrontal cortex. Moreover, subjects with the high-risk metabotropic glutamate receptor 3 (GRM3) haplotype associated with schizophrenia had lower EAAT2 expression in the prefrontal cortex and also showed impaired cognitive performances for measures of verbal list learning and verbal fluency. EAAT2 protein activity is regulated by a SNP rs4354668 (-181T/G) which falls in the gene promoter region, with the G allele resulting in a lower activity of the transporter. Based on these data, we assessed possible effects of the -181T/G EAAT2 polymorphism on two core prefrontal cognitive performances, known to be impaired in schizophrenia, in a sample of 211 clinically stabilized patients. We observed better executive functions (WCST, no. of categories) and working memory (N-back: 1-back, 2-back) performances in subjects homozygous for the T allele, compared to the G carriers group. These observations suggest that the presence of the G allele is associated, among patients with schizophrenia, with a disadvantageous effect on core cognitive functions that depend on prefrontal cortex activity. These results are preliminary and need to be replicated by future and larger studies, however they suggest that EAAT2 inefficiency may represent a target of interest for development of pharmacological strategies aimed to improve prefrontal performances by compensating the impaired glutamate reuptake.

Effect of 5-HT1A-receptor functional polymorphism on Theory of Mind performances in schizophrenia

Theory of Mind (ToM) abilities are known to be impaired in schizophrenia and data from functional brain imaging studies showed that ToM deficit is correlated to prefrontal cortex (PFC) dysfunction. Moreover, several lines of evidence suggest a critical role for dopaminergic-serotoninergic interactions at the PFC level. In this view, we aimed to analyse the specific effect of the -1019C/G functional polymorphism of the serotonin 1A receptor (5-HT1A-R), involved in both serotonin and dopamine transmission regulation. A total of 118 clinically stabilised schizophrenia patients was assessed with a neuropsychological battery, including evaluation of IQ, verbal memory, attention and executive function and a ToM task; they also underwent 5-HT1A-R genotyping. We observed a significant effect of the 5-HT1A-R genotype on ToM performances, with the CC genotype performing significantly better. The finding suggests an effect of the 5-HT1A-R polymorphism on ToM cognitive performance in schizophrenia patients, probably through complex interactions between dopaminergic and serotoninergic systems, involved in mentalising.

Factors involved in the level of functioning of patients with schizophrenia according to latent variable modeling

PURPOSE

This study aimed at using latent variable modelling to explore the significantly contributing variables to functioning in schizophrenia patients.

METHODS

The study cohort comprised 296 schizophrenia patients evaluated once for demographic characteristics, functioning (FROGS, SWN-K, QLS) and symptomatology (Positive and Negative Syndrome Scale [PANSS]). First exploratory multivariate analyses were conducted and then a model with functioning as a latent variable was proposed and tested with the data.

RESULTS

Symptomatology as negative, cognitive and excitation factor are significant predictors of functioning assessed through FROGS (P<0.0001), SWN-K and QLS (P<0.001). The model was constructed with functioning defined as a latent variable, indicators are subscores on FROGS, SWN-K, QLS and exogenous variable included symptomatology, Duration of Untreated Psychosis (DUP) and educational level.

CONCLUSION

Using the five clinical dimensions of the PANSS, (Positive, Negative, Cognitive, Anxiety/Depression and Excitation) the negative and cognitive dimensions are highly correlated via the latent variable to the three dimensions of functioning evaluated by the FROGS: "daily life", "social functioning" and "treatment" and the QLS subscores (interpersonnal, common object, instrumental role). Educationnal level is positively linked to functioning but not DUP. The model emphasizes the need for treatment strategies that have an effect on cognitive-factors, to improve functioning in schizophrenia.

HTTLPR functional polymorphism in schizophrenia: executive functions vs. sustained attention dissociation

BACKGROUND

Recently attention has been addressed to the role of 5-HT in cognition and several experimental studies revealed that manipulations of the central 5-HT system can produce quite specific changes in cognitive functioning. These results may suggest new treatment strategies to improve cognition in psychiatric conditions characterized by neuropsychological impairments, such as schizophrenia. It is possible to investigate the involvement of 5-HT in cognition by examining the impact of genetic variation in key regulators of serotoninergic neurotransmission. Among these, the serotonin transporter (5-HTT) presents a functional polymorphism in the transcriptional control region of the gene (5-HTTLPR) affecting transcriptional efficiency. In the present study, we aimed to analyze the effect of 5-HTTLPR polymorphism on specific cognitive functions, known to be affected by 5-HT manipulation and altered in schizophrenia.

METHODS

223 schizophrenia patients were tested with Wisconsin Card Sorting Test (WCST), for the evaluation of cognitive flexibility, Continuous Performance Test (CPT), for the evaluation of attention, and genotyped for the 5-HTTLPR.

RESULTS

We found a significant association between HTT polymorphism and executive functions and inversely with sustained attention. The presence of the high-activity long (L) allele in homozygosis was a predictor of better executive performances and poorer performances of attention.

CONCLUSIONS

Our findings suggest that factors affecting serotonin availability may play a specific role in cognitive processes, probably through complex modulation of the different performance components.

'Theory' of mind impairment in patients affected by schizophrenia and in their parents

"Theory of mind" (ToM) is the ability to judge the mental states of the self and others. It is currently considered as a part of the broader concept of social cognition, known to influence the social behaviour of patients affected by schizophrenia. Recently it has been hypothesized that the impairment of ToM is a trait that can be detected both in patients with schizophrenia and in non-psychotic relatives of patients, but it still not clear what the contribution of the familial patterns of cognitive impairment is. The aim of this study is to assess parental impairments of ToM performance considering the effects of the neurocognitive abilities known to be impaired in their first-degree relatives and to influence ToM in schizophrenic patients. Patients, their parents and control trios were assessed with the Wisconsin Card Sorting Test (WCST), the Symbol Coding Task and the ToM Picture Sequencing Task. The ANCOVA analysis on 47 trios including a schizophrenic offspring and 47 healthy trios showed a statistically significant poorer performance of patients and their parents in comparison to control trios at Symbol Coding Task and ToM task. Moreover a regression analysis showed that the neuropsychological abilities tested were significant predictors of ToM performance only in patients. Results confirm a ToM impairment among parents of patients with schizophrenia that is not directly correlated to other aspects of neurocognitive functioning.

Functional and structural brain correlates of theory of mind and empathy deficits in schizophrenia

BACKGROUND

Patients affected by schizophrenia show deficits in social cognition, with abnormal performance on tasks targeting theory of mind (ToM) and empathy (Emp). Brain imaging studies suggested that ToM and Emp depend on the activation of brain networks mainly localized at the superior temporal lobe and temporo-parietal junction.

METHODS

Participants included 24 schizophrenia patients and 20 control subjects. We used brain blood oxygen level dependent fMRI to study the neural responses to tasks targeting ToM and Emp. We then studied voxel-based morphometry of grey matter in areas where diagnosis influenced functional activation to both tasks. Outcomes were analyzed in the context of the general linear model, with global grey matter volume as nuisance covariate for structural MRI.

RESULTS

Patients showed worse performance on both tasks. We found significant effects of diagnosis on neural responses to the tasks in a wide cluster in right posterior superior temporal lobe (encompassing BA 22-42), in smaller clusters in left temporo-parietal junction and temporal pole (BA 38 and 39), and in a white matter region adjacent to medial prefrontal cortex (BA 10). A pattern of double dissociation of the effects of diagnosis and task on neural responses emerged. Among these areas, grey matter volume was found to be reduced in right superior temporal lobe regions of patients.

CONCLUSIONS

Functional and structural abnormalities were observed in areas affected by the schizophrenic process early in the illness course, and known to be crucial for social cognition, suggesting a biological basis for social cognition deficits in schizophrenia.

Influence of catechol-O-methyltransferase Val158Met polymorphism on neuropsychological and functional outcomes of classical rehabilitation and cognitive remediation in schizophrenia

Neurocognitive deficits are recognized as core features of schizophrenia and have a great impact on functional outcome. Recent reports have suggested that a functional polymorphism, Val158Met, of the catechol-O-methyltransferase (COMT) gene, partially influences cognitive performances (mainly cognitive flexibility and working memory) both in schizophrenic patients and in healthy controls, probably by modulating prefrontal dopamine function. While previous studies focused on single evaluation of cognitive functioning, we aimed to analyse the additive effect of COMT genotype and cognitive exercise on dynamic modulation of cognitive performances. We analysed the COMT Val158Met polymorphism in 50 patients with chronic schizophrenia randomly allocated to two treatment conditions for 3 months: standard rehabilitation treatment (SRT) alone and SRT plus specific cognitive exercise of impaired functions. We then divided our sample in four subgroups on the basis of genotype (Val/Val versus Met carriers) and treatment (placebo versus active). We assessed patients with a neuropsychological battery, the Positive and Negative Symptoms Scale (PANSS) and the Quality of Life Scale (QLS) at enrolment, after 3 months of therapy and after further 3 months of follow-up. We found significantly greater improvement of cognitive flexibility performance and QLS total score for Met carriers on active treatment in comparison to Val/Val on placebo. The findings support the hypothesis that COMT polymorphism influences individual capacity to recover from cognitive deficit through rehabilitation therapy after a wider intervention also including deficit-specific cognitive exercise as a potentiating tool.