The ecogenetics of schizophrenia: a review

Gene–Environment Correlation in Humans: Lessons from Psychology for Quantitative Genetics

Evolutionary biologists have long been aware that the effects of genes can reach beyond the boundary of the individual, that is, the phenotypic effects of genes can alter the environment. Yet, we rarely apply a quantitative genetics approach to understand the causes and consequences of genetic variation in the ways that individuals choose and manipulate their environments, particularly in wild populations. Here, I aim to stimulate research in this area by reviewing empirical examples of such processes from the psychology literature. Indeed, psychology researchers have been actively investigating genetic variation in the environments that individuals experience—a phenomenon termed “gene–environment correlation” (rGE)—since the 1970s. rGE emerges from genetic variation in individuals’ behavior and personality traits, which in turn affects the environments that they experience. I highlight concepts and examples from this literature, emphasizing the relevance to quantitative geneticists working on wild, nonhuman organisms. I point out fruitful areas of crossover between these disciplines, including how quantitative geneticists can test ideas about rGE in wild populations.

Interactions Between Variation in Candidate Genes and Environmental Factors in the Etiology of Schizophrenia and Bipolar Disorder: a Systematic Review

Schizophrenia and bipolar disorder (BD) are complex and multidimensional disorders with high heritability rates. The contribution of genetic factors to the etiology of these disorders is increasingly being recognized as the action of multiple risk variants with small effect sizes, which might explain only a minor part of susceptibility. On the other site, numerous environmental factors have been found to play an important role in their causality. Therefore, in recent years, several studies focused on gene × environment interactions that are believed to bridge the gap between genetic underpinnings and environmental insults. In this article, we performed a systematic review of studies investigating gene × environment interactions in BD and schizophrenia spectrum phenotypes. In the majority of studies from this field, interacting effects of variation in genes encoding catechol-O-methyltransferase (COMT), brain-derived neurotrophic factor (BDNF), and FK506-binding protein 5 (FKBP5) have been explored. Almost consistently, these studies revealed that polymorphisms in COMT, BDNF, and FKBP5 genes might interact with early life stress and cannabis abuse or dependence, influencing various outcomes of schizophrenia spectrum disorders and BD. Other interactions still require further replication in larger clinical and non-clinical samples. In addition, future studies should address the direction of causality and potential mechanisms of the relationship between gene × environment interactions and various categories of outcomes in schizophrenia and BD.

An experience sampling study on the ecological validity of the SWN-20: Indication that subjective well-being is associated with momentary affective states above and beyond psychosis susceptibility

Subjective well-being (SWB) is associated with treatment adherence and symptom outcome in people with psychotic disorders. Also, it is associated with psychosis susceptibility and it is partly hereditable. The SWN-20 is a widely used tool to assess subjective well-being in patients; it was also found to be suitable for assessing SWB in healthy populations. Yet it is unclear how this retrospectively measured construct may be associated with momentary affective state, which is the proposed underlying mechanism of subjective well-being. This study therefore investigated the ecological validity of the SWN-20 in people at different risk for psychosis. In 63 patients with a psychotic disorder and 61 siblings of patients with a psychotic disorder we assessed whether subjective well-being as measured with the SWN-20, was associated with momentary positive affect, negative affect, reward experience and stress-sensitivity as measured by the experience sample method (ESM). Higher subjective well-being was associated with higher momentary positive affect and lower negative affect, and this association was not conditional on psychosis vulnerability. Subjective well-being was not associated with stress-sensitivity or reward-experience. SWN-20 is an easy-to-use and ecologically valid tool to measure subjective well-being in people with different vulnerability for psychosis.

Schizotypal and affective traits in the offspring of antenatally depressed mothers - Relationship to family history of psychosis in the Northern Finland 1966 Birth Cohort

BACKGROUND

Maternal depression is relatively common during pregnancy. However, follow-ups of the adult offspring of antenatally depressed mothers are scarce. Previously we found the risk of schizophrenia to be higher in the adult offspring with antenatally depressed mothers and parents with psychosis than in subjects with only one or neither of these risk factors. The aim was to study whether the risk of schizotypal or affective traits differ among adult offspring with antenatally depressed mothers with or without a parental history of psychosis when compared with offspring without antenatally depressed mothers and without parental psychosis.

METHODS

In the general population-based Northern Finland 1966 Birth Cohort (NFBC 1966), the mothers of the cohort members were asked at mid-gestation whether they felt depressed. Parental psychosis (Familial Risk, FR) was detected using the Finnish Care Register for Health Care. In the 31-year field study, seven psychometric questionnaires surveyed schizotypal and affective traits in the offspring. The final sample included 4928 individuals (2203 males).

RESULTS

There were no statistically significant differences in mean scores on the schizotypal and affective scales between offspring with and without antenatally depressed mothers, or between subjects with and without parental psychosis. The scores were not highest in the subjects with both maternal antenatal depressed mood and FR.

CONCLUSION

Surprisingly, maternal depressed mood during pregnancy was unlikely to increase the risk of schizotypy or affective traits in adult offspring, and not even with parental psychosis (FR) in this general population-based birth cohort with about 5000 subjects.

Effects of the adverse life events and Disrupted in Schizophrenia-1 (DISC1) gene polymorphisms on acute symptoms of schizophrenia

The aim of this study was to evaluate the effects of traumatic childhood events and recent adverse life events, as well as the Disrupted in Schizophrenia-1 (DISC1) gene polymorphisms on types of last acute symptoms of patients with schizophrenia. Hundred patients with schizophrenia were given the Childhood Trauma Questionnaire, the Social Readjustment Rating Scale, Scale for Assessment of Positive Symptoms (SAPS), Scale for Assessment of Negative Symptoms (SANS), Brief Psychiatric Rating Scale (BPRS), and Calgary Depression Scale for Schizophrenia (CDSS). The patients' and healthy controls' DISC1 gene was evaluated for the -274G>C, c.791G>A, and c.2110A>T polymorphisms. There was no statistically significant difference with regard to the DISC1 gene polymorphisms between patient and healthy control groups. No significant relationship was found between the -274G>C, c.791G>A, and c.2110A>T haplotypes and development of different acute symptoms of schizophrenia. Having a recent stressful life event significantly affected SAPS (95% confidence interval [CI]=-67.547, -21.473; p=0.00) and BPRS-1 scores (95% CI=-51.405, -6.885; p=0.01), whereas emotional abuse at childhood significantly affected SANS scores (95% CI=-37.300, -10.401; p=0.00). This study shows that features of acute symptoms in schizophrenia are not influenced by the polymorphisms on the DISC1 gene, but are influenced by recent adverse life events and emotional abuse at childhood.

Detecting psychotic symptoms in Indigenous populations: a review of available assessment tools

As efforts to shorten the duration of untreated psychosis increase, there is a need for short screening instruments to identify those at-risk. It is feared that remote Indigenous populations, manifesting many of the risk factors associated with schizophrenia and often lacking access to adequate mental health services, may be overlooked as the general population effort shifts towards early detection. This article aimed to review studies investigating psychotic symptoms in Indigenous communities in Australia, New Zealand, Canada and United States of America and aimed to evaluate the usefulness of the instruments. Eleven relevant studies were identified using seven unique instruments. The available instruments assessed psychotic symptoms to varying degrees, although no screener for early detection was found thus supporting concerns that these disadvantaged populations do not have access to suitable support enabling early detection of psychosis. We recommend that a rapid screening tool for detecting at-risk individuals be developed and validated for community use in Indigenous populations living in remote areas.

Natural genetic variation in social niche construction: social effects of aggression drive disruptive sexual selection in Drosophila melanogaster

Social niche construction (SNC) occurs when animals actively shape their social environments. Currently the fitness consequences of SNC are poorly understood, and no study has examined whether variation in SNC has a genetic basis. Here we report the first instance of genetic variation in SNC by showing that Drosophila male aggression shapes the social environment. We allowed flies of different genotypes to interact in complex arenas; we measured the number and sex of individuals in the groups that formed and counted instances of mating. Arenas containing more aggressive male genotypes formed groups with fewer males, demonstrating that aggressive male genotypes experienced different social environments than nonaggressive genotypes. Further, genotypes with highest mating success were those whose SNC behavior generated the social environment in which they were most adept at mating: genotypes who mate most often after winning aggressive encounters benefit from aggressive SNC, while genotypes who mate most often after losing achieve high mating rates by forgoing aggression. The presence of these alternative strategies-which were robust across eight population densities-revealed that selection on aggression and context-dependent mating was disruptive, consistent with the hypothesis that SNC can maintain genetic variation in multiple behaviors.

Cannabis use and age at onset of psychosis: further evidence of interaction with COMT Val158Met polymorphism

OBJECTIVE

To examine, in a sample of young psychiatric patients, (n = 157, mean age 17.01 years (SD = 3.6)) whether i) age at first cannabis use and age at emergence of psychiatric disorders are related and ii) such a relationship is modulated by the Val158Met polymorphism in the COMT gene.

METHOD

Cannabis use profiles and COMT Val158Met genotypes were obtained from 80 inpatients with schizophrenia-spectrum disorders and 77 inpatients with other non-psychotic disorders.

RESULTS

First, age at first cannabis use correlates with age at onset in both schizophrenia-spectrum and other psychiatric disorder groups: those who started using cannabis earlier had an earlier age at onset of psychiatric disorders. Second, the distribution of the Val158Met genotypes was not different either between diagnosis groups or between cannabis users and non-users. Third, an interaction between Val158Met genotypes and cannabis use was observed specifically on age at emergence of psychotic disorders, with Val/Val genotype carriers showing an earlier age at onset than Met carriers.

CONCLUSION

Our results suggest the importance of brain maturation timing in which exposure to cannabis occurs. The COMT Val158Met genotype seems to modulate the association between cannabis and age at onset of psychotic disorders. These results are consistent with previous studies.

Reduced cortical thickness as an outcome of differential sensitivity to environmental risks in schizophrenia

BACKGROUND

The etiology of schizophrenia is thought to involve differential-likely genetically mediated-sensitivity to environmental exposures. However, examination of differential sensitivity in models of psychopathologic constructs is subject to bias because psychopathology itself may distort exposure assessment. The use of neuroimaging phenotypes, conversely, may provide unbiased evidence for differential sensitivity to environmental exposures. This study examined the impact of two environmental exposures associated with both schizophrenia and magnetic resonance imaging (MRI) cerebral alterations in models of cerebral cortical thickness.

METHODS

T1-weighted MRI scans were acquired from 88 patients with schizophrenia, 98 healthy siblings at higher than average genetic risk for schizophrenia, and 87 control subjects. Freesurfer software was used to measure cortical thickness for 68 brain regions. Associations between 1) cortical thickness and 2) cannabis use and developmental trauma were examined.

RESULTS

A significant group × developmental trauma interaction (χ(2) = 9.65, p = .01), as well as a significant group × cannabis interaction (χ(2) = 6.04, p = .05) was apparent, indicating differential sensitivity of the patient group, which displayed stronger reductions of cortical thickness for both exposures. A similar pattern was found in the sibling-control comparison for cannabis. For developmental trauma, siblings did not differ from control subjects, displaying an increase in cortical thickness with higher levels of trauma.

CONCLUSIONS

The findings suggest that schizophrenia and its genetic liability are associated with differential cerebral cortical sensitivity to developmental environmental exposures such as cannabis. Gene-environment interactions may underlie some of the brain alterations observed in patients with schizophrenia and their relatives.

"Attenuated psychotic symptoms syndrome" as a risk syndrome of psychosis, diagnosis in DSM-V: The debate

Schizophrenia is a common disorder, affecting approximately 1 out of every 100 people, with a typical onset during adolescence and early adulthood. The personal and societal costs of schizophrenia are extremely high. Prevention of schizophrenia, would offer substantial benefits to patients, their family members, and the community at large. The prodromal phase of schizophrenia has been recognized since the 19th century. At-risk individuals for psychosis and schizophrenia are the subjects who can provide information for intervention prior to development of frank psychosis. This approach is currently being investigated. The question remains, however, whether it can be a diagnostic category by itself. The proposal for including the risk syndrome is one of the recommendations by the working group on schizophrenia and psychotic disorders for the forthcoming DSM-V. There are differing views in academia regarding this proposal. Prior to becoming fully psychotic, a consistent literature demonstrates that patients generally had suffered from accelerating attenuated symptoms and distress. It is important that the prodromal phase be accurately recognized in order to accomplish the goal of prevention. We can then purposefully engage in early intervention aiming toward prevention. A recent strong resurgent interest in this area stems largely from two developments: First, the identification of the neurobiological deficit processes associated with the severity and chronicity of schizophrenia, and second, the development of reliable criteria for diagnosis. Although the general at-risk construct appears to offer great potential to advance both the treatment and research dealing with psychotic illnesses, it seems premature to many researchers to include the syndrome as an established entity in the text of the new DSM-V. It would be far more appropriate to include this proposed syndrome in the appendix and evaluate the many contemporary issues in future studies. The main issues involved in this discussion are the clinical validity of the syndrome, concern about stigma and unnecessary treatment, and need for responding to patients' distress in addition to the ethical dilemma. In this review we examine the issue of inclusion of the risk syndrome as a diagnosis.

The epidemiology of schizophrenia: replacing dogma with knowledge

Major advances have been made in our understanding of the epidemiology of schizophrenia. We now know that the disorder is more common and severe in young men, and that the incidence varies geographically and temporally. Risk factors have been elucidated; biological risks include a family history of the disorder, advanced paternal age, obstetric complications, and abuse of drugs such as stimulants and cannabis. In addition, recent research has also identified social risk factors such as being born and brought up in a city, migration, and certain types of childhood adversity such as physical abuse and bullying, as well as social isolation and adverse events in adult life. Current research is focussing on the significance of minor psychotic symptoms in the general population, gene-environmental interaction, and how risk factors impact on pathogenesis; perhaps all risk factors ultimately impact on striatal dopamine as the final common pathway.

Neurodevelopmental animal models of schizophrenia: role in novel drug discovery and development

Schizophrenia is a devastating mental illness that is associated with a lifetime of disability. For patients to successfully function in society, the amelioration of disease symptoms is imperative. The recently published results of two large antipsychotic clinical trials (e.g., CATIE, CUtLASS) clearly exemplified the limitations of currently available treatment options for schizophrenia, and further highlighted the critical need for novel drug discovery and development in this field. One of the biggest challenges in schizophrenia-related drug discovery is to find an appropriate animal model of the illness so that novel hypotheses can be tested at the basic science level. A number of pharmacological, genetic, and neurodevelopmental models have been introduced; however, none of these models has been rigorously evaluated for translational relevance or to satisfy requirements of "face," "construct" and "predictive" validity. Given the apparent polygenic nature of schizophrenia and the limited translational significance of pharmacological models, neurodevelopmental models may offer the best chance of success. The purpose of this review is to provide a general overview of the various neurodevelopmental models of schizophrenia that have been introduced to date, and to summarize their behavioral and neurochemical phenotypes that may be useful from a drug discovery and development standpoint. While it may be that, in the final analysis, no single animal model will satisfy all the requirements necessary for drug discovery purposes, several of the models may be useful for modeling various phenomenological and pathophysiological components of schizophrenia that could be targeted independently with separate molecules or multi-target drugs.

Can the role of genetic factors in schizophrenia be enlightened by studies of candidate gene mutant mice behaviour?

Schizophrenia is one of the most severe psychiatric disorders. Despite the knowledge accumulated over years, aetiology and pathophysiology remain uncertain. Research on families and twins suggests that genetic factors are largely responsible for the disease and implies specific genes as risk factors. Genetic epidemiology indicates a complex transmission mode, compatible with a multi-locus model, with single genes accounting for specific traits rather than for the entire phenotype. To better understand every single gene contribution to schizophrenia, the use of intermediate endophenotypes has been proposed. A straight communication between preclinical and clinical researchers could facilitate research on the association between genes and endophenotypes. Many behavioural tasks are available for humans and animals to measure endophenotypes. Here, firstly, we reviewed the most promising mouse behavioural tests modelling human behavioural tasks altered in schizophrenia. Secondly, we systematically reviewed animal models availability for a selection of candidate genes, derived from linkage and association studies. Thirdly, we systematically reviewed the studies which tested mutant mice in the above behavioural tasks. Results indicate a large mutant mice availability for schizophrenia candidate genes but they have been insufficiently tested in behavioural tasks. On the other hand, multivariate and translational approach should be implemented in several behavioural domains.

AKT1 Gene Polymorphisms and Obstetric Complications in the Patients with Schizophrenia

OBJECTIVE

We performed a genetic association study with schizophrenic patients to investigate whether the V-akt murine thymoma viral oncogene homolog 1 (AKT1) gene plays a role in obstetric complications.

METHODS

One-hundred-eighty patients with schizophrenia (male, 113; female, 67) were included. All patients fulfilled DSM-IV criteria for schizophrenia. Obstetric complications were measured by the Lewis scale. Prenatal and perinatal information was retrospectively collected from the patients' mothers. We selected six single nucleotide polymorphisms (SNPs) for the AKT1 gene: SNP1 (rs3803300), SNP2 (rs1130214), SNP3 (rs3730358), SNP4 (rs 1130233), SNP5 (rs2494732), and SNPA (rs2498804). The genotype data were analyzed for an association with the Lewis total score in terms of allele, genotype, and haplotype distribution.

RESULTS

The mean total Lewis scores were 1.30+/-1.61 for males and 1.54+/-1.87 for females. Higher total score tended to be correlated with an earlier age of onset of schizophrenia in females. In the total sample, no SNP was associated with obstetric complications. However, the additional analyses for male and female subgroups found a significant association between SNPA and SNP4 and Lewis score in females (p=0.02 for SNPA, p=0.04 for SNP4). The SNP5-SNPA haplotype showed a positive association with obstetric complications (p=0.03) in the female patient group.

CONCLUSION

We found an association between SNPs in the AKT1 gene and total Lewis score measuring obstetric complications in female patients with schizophrenia. Because these findings did not survive a correction for multiple testing, the significance should be interpreted carefully and replication studies are required.

Gene-environment interactions in schizophrenia: review of epidemiological findings and future directions

Concern is building about high rates of schizophrenia in large cities, and among immigrants, cannabis users, and traumatized individuals, some of which likely reflects the causal influence of environmental exposures. This, in combination with very slow progress in the area of molecular genetics, has generated interest in more complicated models of schizophrenia etiology that explicitly posit gene-environment interactions (EU-GEI. European Network of Schizophrenia Networks for the Study of Gene Environment Interactions. Schizophrenia aetiology: do gene-environment interactions hold the key? [published online ahead of print April 25, 2008] Schizophr Res; S0920-9964(08) 00170-9). Although findings of epidemiological gene-environment interaction (G x E) studies are suggestive of widespread gene-environment interactions in the etiology of schizophrenia, numerous challenges remain. For example, attempts to identify gene-environment interactions cannot be equated with molecular genetic studies with a few putative environmental variables "thrown in": G x E is a multidisciplinary exercise involving epidemiology, psychology, psychiatry, neuroscience, neuroimaging, pharmacology, biostatistics, and genetics. Epidemiological G x E studies using indirect measures of genetic risk in genetically sensitive designs have the advantage that they are able to model the net, albeit nonspecific, genetic load. In studies using direct molecular measures of genetic variation, a hypothesis-driven approach postulating synergistic effects between genes and environment impacting on a final common pathway, such as "sensitization" of mesolimbic dopamine neurotransmission, while simplistic, may provide initial focus and protection against the numerous false-positive and false-negative results that these investigations engender. Experimental ecogenetic approaches with randomized assignment may help to overcome some of the limitations of observational studies and allow for the additional elucidation of underlying mechanisms using a combination of functional enviromics and functional genomics.

Cannabis, cannabinoids and schizophrenia: integration of the evidence

Understanding of the neurophysiological basis of cognitive, behavioural and perceptual disturbances associated with long-term cannabis use has grown dramatically. Exogenous cannabinoids alter the normative functioning of the endogenous cannabinoid system. This system is an important regulator of neurotransmission. Recent research has demonstrated abnormalities of the cannabinoid system in schizophrenia. The purpose of the present paper was to selectively review the links between cannabis use and psychosis, drawing upon recent epidemiological, clinical, cognitive, brain imaging and neurobiological research. The aim is to assist clinicians to probe more deeply into the newly unfolding world of cannabinoid physiology and to critically evaluate the potential role of cannabis in the onset and persistence of cognitive impairments and psychosis in otherwise healthy users and in schizophrenia.

Effects of acute metabolic stress on the dopaminergic and pituitary-adrenal axis activity in patients with schizophrenia, their unaffected siblings and controls

A genetically mediated abnormal sensitivity to stress is thought to play a role in the onset, exacerbation and relapse of schizophrenia. In a double blind, placebo-controlled crossover study, peak increases in plasma ACTH (Delta ACTH) and homovanillic-acid, a dopamine metabolite, (Delta HVA) following exposure to a metabolic stressor(2DG) were studied in unaffected siblings of patients with schizophrenia (n=15), their patient relatives (n=15) and healthy controls (n=14). Siblings showed a stress response (both Delta ACTH and Delta HVA) that was significantly greater compared to controls and significantly less pronounced compared to patients. The results suggest that the genetic risk for schizophrenia may be characterized by an enhanced sensitivity to stress.

Serotonergic response to stress: a protective factor against abnormal dopaminergic reactivity in schizophrenia?

In a double-blind-crossover-study, 10 patients with schizophrenia, 10 of their unaffected siblings and 9 healthy controls randomly received metabolic stressor and placebo. A significant HVA plasma elevation in response to stress was found in siblings whose response was intermediate to that of patients and controls. Only siblings additionally displayed an exaggerated 5HIAA response.

Over-representation of Maori New Zealanders among adolescents in a schizotypy taxon

BACKGROUND

Minority ethnic and migrant groups are often over-represented among those with schizophrenia.

OBJECTIVES

The aim of this study was to determine whether Maori, the aboriginal minority of New Zealand, are over-represented in a schizotypy taxon derived from a general population sample of adolescents.

METHOD

Secondary school students (n = 387) aged 13 to 17 years completed self-report measures of four schizotypy attributes, magical thinking, hallucinatory tendency, self-referential ideation, and perceptual aberration, and indicated ethnic descent and self-identified ethnic belonging.

RESULTS

Taxometric analyses (maximum covariance, maximum eigenvalue, latent modes) yielded consistent evidence of taxonicity of schizotypy. Participants who were of Maori descent were over-represented in the schizotypy group.

CONCLUSIONS

Ethnicity, or the stress and resilience factors for which ethnicity is a proxy measure, has a measurable impact on psychometric risk for schizophrenia.

Data gathering: biased in psychosis?

This study examined whether the probabilistic reasoning bias referred to as a "jumping-to-conclusions" (JTC) style of reasoning, which, according to previous research, is associated with particular psychotic symptoms such as delusions, represents a trait that can also be detected in nonpsychotic relatives of patients with schizophrenia and in nonpsychotic individuals with a high level of psychotic experiences. Participants were, in order of level of psychosis liability, 40 patients with schizophrenia or a schizoaffective disorder, 40 first-degree nonpsychotic relatives, 41 participants from the general population with above average expression of psychotic experiences, and 53 participants from the general population with an average level of psychotic experiences. A "jumping-to-conclusions" bias was assessed using the beads task. A dose-response relationship was found in the association between level of psychosis liability and JTC (defined as needing only a single bead to complete the beads task) (odds ratio [OR] linear trend = 1.59, 95% CI: 1.13-2.24), and, independently, alinear association was apparent between JTC and level of delusional ideation (OR linear trend = 2.59, 95% CI: 1.18-5.69). In addition, the association between psychosis liability and JTC was generally much stronger as the level of delusional ideation was higher. JTC is associated with liability to psychosis (trait), in particular if the psychosis phenotype is characterized by delusional ideation (state).

Evidence for instrument and family-specific variation of subclinical psychosis dimensions in the general population

It is unknown to what degree dimensions of schizotypy (subclinical psychosis) show independent, family-specific variation in the general population. Psychologists administered the Community Assessment of Psychic Experiences, the Structured Interview for Schizotypy-Revised (SIS-R), and the Brief Psychiatric Rating Scale to 257 subjects pertaining to 82 general population families. All 3 instruments showed family-specific variation for positive and negative subclinical psychosis dimensions with between-families proportions of total variance between 10% and 40%. However, only the SIS-R showed family-specific variation of the negative dimension independent of its correlation with the positive dimension. The positive dimension of subclinical psychosis shows familial-specific variation in samples unselected for psychiatric disorder, suggesting dimensional liability in the population. The SIS-R additionally captures family-specific variation in the negative domain.

Childhood trauma, psychosis and schizophrenia: a literature review with theoretical and clinical implications

OBJECTIVE

To review the research addressing the relationship of childhood trauma to psychosis and schizophrenia, and to discuss the theoretical and clinical implications.

METHOD

Relevant studies and previous review papers were identified via computer literature searches.

RESULTS

Symptoms considered indicative of psychosis and schizophrenia, particularly hallucinations, are at least as strongly related to childhood abuse and neglect as many other mental health problems. Recent large-scale general population studies indicate the relationship is a causal one, with a dose-effect.

CONCLUSION

Several psychological and biological mechanisms by which childhood trauma increases risk for psychosis merit attention. Integration of these different levels of analysis may stimulate a more genuinely integrated bio-psycho-social model of psychosis than currently prevails. Clinical implications include the need for staff training in asking about abuse and the need to offer appropriate psychosocial treatments to patients who have been abused or neglected as children. Prevention issues are also identified.

Predictors of schizophrenia: evidence from the Northern Finland 1966 Birth Cohort and other sources

BACKGROUND

Subtle motor, emotional, cognitive and behavioural abnormalities are often present in apparently healthy individuals who later develop schizophrenia, suggesting that some aspects of causation are established before overt psychosis.

AIMS

To outline the development of schizophrenia.

METHOD

We drew on evidence from The Northern Finland 1966 Birth Cohort supplemented by selected findings from other relevant literature.

RESULTS

The main known risk factors in development of schizophrenia are genetic causes, pregnancy and delivery complications, slow neuromotor development, and deviant cognitive and academic performance. However, their effect size and predictive power are small.

CONCLUSIONS

No powerful risk factor, premorbid sign or risk indicator has been identified that is useful for the prediction of schizophrenia in the general population.

Size of burden of schizophrenia and psychotic disorders

Schizophrenia is a severe mental disorder characterised by fundamental disturbances in thinking, perception and emotions. More than 100 years of research have not been able to fully resolve the puzzle that schizophrenia represents. Even if schizophrenia is not a very frequent disease, it is among the most burdensome and costly illnesses worldwide. It usually starts in young adulthood. Life expectancy is reduced by approximately 10 years, mostly as a consequence of suicide. Even if the course of the illness today is considered more favourable than it was originally described, it is still only a minority of those affected, who fully recover. The cumulative lifetime risk for men and women is similar, although it is higher for men in the age group younger than 40 years. According to the Global Burden of Disease Study, schizophrenia causes a high degree of disability, which accounts for 1.1% of the total DALYs (disability-adjusted life years) and 2.8% of YLDs (years lived with disability). In the World Health Report [The WHO World Health Report: new understanding, new hope, 2001. Geneva], schizophrenia is listed as the 8th leading cause of DALYs worldwide in the age group 15-44 years. In addition to the direct burden, there is considerable burden on the relatives who care for the sufferers. The treatment goals for the moment are to identify the illness as early as possible, treat the symptoms, provide skills to patients and their families, maintain the improvement over a period of time, prevent relapses and reintegrate the ill persons into the community so that they can lead as normal a life as possible.

The potential impact of genetic counseling for mental illness

Mental disorders are relatively highly heritable, yet complex with important interactions between genetic risk and environmental factors in determining illness expression. Due to the high prevalence of these complex disorders, steady increase in knowledge about genetic contributions, and increasing public awareness, this area may come to represent a significant proportion of all genetic counseling. The potential impact of genetic counseling in mental illness is broad. As well as the conventional expectations, genetic counseling may have the positive outcomes of reducing the guilt, shame, and stigma associated with mental illness, even within families. However, like many interventions in medicine, genetic counseling for mental disorders could potentially have unintended consequences resulting in increased stigma, guilt, and shame. The potential impacts of genetic education and providing recurrence risks on stigma are reviewed, as well as the role of education about the environment as a way of modifying family members' guilt. The review allows a preliminary formulation of a series of suggestions for genetic counseling in mental illness.

Social context in gene-environment interactions: retrospect and prospect

While many behavioral scientists believe that gene-environment (GE) interactions play an important and perhaps pervasive role in human development and aging, little attention has been devoted to a fundamental conceptual issue: What is it about social context that could alter gene expression? We draw on existing examples of GE interactions to formulate a typology that identifies a set of generic mechanisms by which E moderates G. Empirical studies suggest four ideal types: Social context can trigger a genetic diathesis, compensate for a genetic diathesis, act as a control to prevent behaviors for which there is a genetic predisposition, and enhance adaptation through proximal processes. This typology highlights several problems, however, with prior empirical research, which may explain, in part, why so few GE interactions have actually been observed. These problems include inattention to the dynamic nature of social experience, the manifold, often-intercorrelated dimensions of social context ("EE interactions"), mediators that link social context and the genotype, and analytic models that examine GE interactions as processes that characterize individual development. In turn, these insights call for the integration of life course sociology and behavioral genetics to foster ways of studying genes, context, and aging.

Predictors of schizophrenia--a review

Schizophrenia is an aetiologically heterogeneous syndrome that usually becomes overtly manifest in adolescence and early adulthood, but in many cases subtle impairments in neurointegrative function are present from birth; hence it is considered to be a disorder with a neurodevelopmental component. The strongest risk factor that has been identified is familial risk with genetic loading. Other risk factors include pregnancy and delivery complications, infections during pregnancy, disturbances of early neuromotor and cognitive development and heavy cannabis use in adolescence. Unfortunately, to date it has not been possible to utilize the predictors of the disorder that have been identified in primary preventative interventions in a general population. However, some authors have claimed that in future it might be possible to reduce the risk for developing schizophrenia through general health policy. In clinical settings, it is helpful to map out possible early risk factors, at least familial risk for psychosis, especially in child, adolescent and young adult mental patients. Furthermore, in the future we may have predictive models combining data from genetic factors for schizophrenia, antenatal risk factors, childhood and adolescent development and clinical symptomatology, as well as brain structural and functional abnormalities.

Genotype-environment interaction in schizophrenia-spectrum disorder. Long-term follow-up study of Finnish adoptees

BACKGROUND

Earlier adoption studies have convincingly confirmed the importance of a genetic contribution to schizophrenia. The designs, however, did not incorporate observations of the rearing-family environment.

AIMS

To test the hypothesis that genetic factors moderate susceptibility to environmentally mediated risks associated with rearing-family functioning.

METHOD

A Finnish national sample of adopted-away offspring of mothers with schizophrenia-spectrum disorders was compared blindly with adoptees without this genetic risk. Adoptive rearing was assessed using family rating scales based upon extended family observations at initial assessment. Adoptees were independently re-diagnosed after a median interval of 12 years, with register follow-up after 21 years.

RESULTS

In adoptees at high genetic risk of schizophrenia, but not in those at low genetic risk, adoptive-family ratings were a significant predictor of schizophrenia-spectrum disorders in adoptees at long-term follow-up.

CONCLUSIONS

Adoptees at high genetic risk are significantly more sensitive to adverse v. 'healthy' rearing patterns in adoptive families than are adoptees at low genetic risk.

The genetics of schizophrenia: glutamate not dopamine?

The major targets of current drugs used in mental health, such as neurotransmitter receptors and transporters, are based on serendipitous findings from several decades ago, and there is currently a severe drought of new drug targets. There is a pressing need for novel drugs, and much hope has been placed on the use of molecular genetics to help define them. However, despite evidence for a genetic basis to schizophrenia stretching back for over a century, and a heritability of about 80%, the identification of susceptibility genes has been an uphill struggle. Candidate gene studies, which have generally focussed on obvious candidates from the dopamine and serotonin systems, as well as genes involved in brain development, have not generally been successful, although meta-analysis indicates that the dopamine D3 receptor gene (DRD3) and the serotonin receptor gene type 2A (HTR2A) may have a very small influence on risk. Linkage analysis has provided robust evidence of genetic loci, for example, on chromosomes 8p, 13q and 22q, and also implies shared genetic aetiology with bipolar disorder. The identification of these loci together with advances in genetic technology, especially the characterisation of polymorphisms, the understanding of haplotypes and the development of statistical methods, has lead to the identification of several plausible susceptibility genes, including neuregulin 1, proline dehydrogenase and dysbindin. Interestingly, these genes point more towards a role for the glutamate pathway rather than the dopamine pathway in schizophrenia. We have attempted to replicate some of these findings in schizophrenic patients from SW China, and we find significant association with a novel neuregulin 1 haplotype, with proline dehydrogenase polymorphisms, but not with catechol-O-methyltransferase (COMT). The replication of neuregulin 1 association on chromosome 8p by several investigators is the most convincing to date, and the presence of a syndrome similar to dementia praecox of 8p linked families, and the lack of linkage of bipolar disorder to this region is a testament to the ideas of Kraepelin more than 100 years ago.

The stress-vulnerability hypothesis in psychotic disorders: focus on the stress response systems

The vulnerabilty stress model is an intriguing concept to look into the etiology of psychotic disorders and, in particular, into the "nature nurture" principle. That stress affects a vulnerable nature may be obvious, but its mechanism is not well understood, and many questions remain to be answered, let alone how to define "vulnerability". The present review tries to focus on the core issues of the vulnerability stress concept--identifying vulnerability, the way stress interferes with it, and the possiblilities of modulating their interaction. Attention is drawn to the biologic stress response systems, the autonomic nervous system (ANS), the hypothalamic pituitary adrenal (HPA) system, and the immune system, and highlights the plasticity of the HPA system as the mediator of adaptation.

Similar effect of family history of psychosis on Sylvian fissure size and auditory P200 amplitude in schizophrenic and bipolar subjects

Several cerebral studies point to the non-specificity of structural and functional changes described in schizophrenia and bipolar disorders. Furthermore, the origin of these changes is still unclear. The present study investigated the effect of a family history (FH) of psychotic disorders in first-degree relatives on computed tomographic (CT) measures (ventricular, cerebral and Sylvian fissure size) and auditory event-related potentials (amplitudes and latencies of peak components in oddball paradigms) in 30 schizophrenic patients and 24 bipolar type I patients. We found a significant correlation between FH and the size of the right Sylvian fissure, and between FH and auditory P200 amplitude. More specifically, the schizophrenic and bipolar patients with negative FH (n=36) had larger right Sylvian fissures and smaller P200 amplitude than patients with positive FH (n=18). These findings were independent of the specific diagnosis, gender, and age of subjects. Our results suggest some underlying process common to schizophrenia and bipolar I disorder, and they provide support for the continuum view of the nosologic structure of psychotic illness.

Long-term course in schizophrenia: concepts, methods and research strategies

OBJECTIVE

This paper summarizes current knowledge about course and outcome in schizophrenia by selecting particular information and by drawing conclusions in the light of theoretical and methodological considerations, in order to illustrate future research strategies, as well as to consider novel targets of treatment.

METHOD

Based on examples from the literature the concepts of course and outcome as well as intervening factors of course and outcome are discussed by considering study results within their methodological and theoretical framework restrictions.

RESULTS

The heterogeneity of the disorder, manifest in its variable phenomenology, illness course, treatment response and outcome, complicates research but at the same time offers clues to elucidate the heterogeneity of aetiology and pathogenesis. The search for intervening factors and predictors is of particular interest in order to explore the illness mechanisms.

CONCLUSION

Future research should focus on the biopsychosocial determinants of course and outcome in methodologically improved long-term studies.

What risk factors tell us about the causes of schizophrenia and related psychoses

Genetic, epidemiologic, and molecular studies concur that liability to schizophrenia is transmitted through the inheritance of a number of genes of relatively small effect, some of which are shared with other psychoses. Each of these susceptibility genes causes minor deviations that are relatively innocent in themselves, for example, increased lateral ventricular volume, schizotypal personality, or subtle cognitive difficulties. However, when an individual is unlucky enough to inherit several of these traits, their cumulative effect, often compounded by environmental hazards, propels that person over a threshold for the expression of frank psychosis. Early environmental risk factors for schizophrenia include urban and winter birth, fetal malnutrition and hypoxia, and possibly prenatal viral infections; these early hazards have only a modest risk-increasing effect, and operate in the context of genetic risk. Preschizophrenic children are more likely to have minor psychomotor and cognitive problems; low IQ has a linear relationship with risk for schizophrenia. However, schizophrenia is not simply a neurodevelopmental disorder, because risk factors have been identified that have their effects proximal to the onset of psychosis: drug abuse, immigrant status, and social adversity and isolation. Both genetic and environmental risk factors appear to operate across diagnostic categories and therefore support a dimensional model of psychosis.

Early and late environmental risk factors for schizophrenia

Although a high proportion of liability to schizophrenia is under genetic control, a number of environmental risk factors have been identified. The earliest of these are complications of pregnancy and birth, though whether these cause or reflect disturbed brain development is not absolutely clear. Neurodevelopmental deviance is also indicated by neurological dysfunction, social, behavioural and cognitive deficits during childhood. Immigrant status is a significant risk factor, especially prominent among the African Caribbean population in England, though the mechanism is unknown. Later environmental risk factors include adverse life events and substance abuse. An additive model of multiple genetic and environmental risk factors of small effect may be too simplistic and an interactive model where genetic predisposition is compounded by environmental effects is more in keeping with current evidence. The nature of such interactions can be explored more fully when susceptibility genes for schizophrenia are identified.

Schizophrenia: genes and environment

The historical and genetic foundations of our current understanding of schizophrenia are reviewed, as are the present and future directions for research. Genetic epidemiological investigations, including family, twin, and adoption studies have confirmed the contributions of genetic and environmental determinants of schizophrenia. For example, identical twins show average concordance rates of only 50%; rates of 100% would be expected on the basis of genetic equivalence alone. Genetic factors may cause errors in brain development and synaptic connections. A broad range of environmental components may further damage the brain. Biological components may include pregnancy and delivery complications, such as intrauterine fetal hypoxia, infections, and malnutrition. Primarily nonbiological components may include psychosocial stressors, such as residence in an urban area and dysfunctional family communication. It is likely that the environmental factors interact with the genetic liability in a negative manner to produce disorders in the schizophrenic spectrum. Genetic and environmental components of the disorder are examined, as well as their interactions in producing either neurodevelopmental syndromes or schizophrenia itself. The implication of these findings for prevention and treatment are considered.

Molecular characterization of a MSRV-like sequence identified by RDA from monozygotic twin pairs discordant for schizophrenia

Retroviral-related amplicons were used in modified RDA to identify four sequences from affected members of three pairs of monozygotic twins discordant for schizophrenia. One sequence (schizophrenia associated retrovirus, SZRV-1, GenBank Accession No. AF135487) is characterized here. It is similar to two known sequences of retroviral origin: multiple sclerosis-associated retrovirus, MSRV (GenBank Accession No. AF009668), and ERV-9 (GenBank Accession No. S77575). It is present in multiple copies in the human genome and has been localized to six different chromosomal sites. A zooblot shows that this multicopy sequence is predominant in the primate lineage and present in rhesus monkeys and humans. SZRV-1 is expressed as a 9-kb RNA band in the placenta. This could offer support to the hypothesis that retroviral sequences transposing during fetal growth may alter neurodevelopmental genes and cause diseases, although its direct involvement in the causation of schizophrenia remains to be established.