Molecular genetics of schizophrenia: a review of the recent literature:

Celecoxib and omega-3 fatty acids alone and in combination with risperidone affect the behavior and brain biochemistry in amphetamine-induced model of schizophrenia

The implications of oxidative stress and neuro-inflammation in the pathogenesis of schizophrenia have been elucidated. Despite their effectiveness against positive symptoms of schizophrenia, antipsychotics have limited effectiveness against negative and cognitive symptoms and are associated with remarkable adverse effects. The use of celecoxib or omega-3 in schizophrenia may have beneficial effects. This study aimed to evaluate the possible efficacies of celecoxib, omega-3 or the combination of celecoxib+risperidone and omega-3+ risperidone compared to risperidone on the behavior and brain biochemistry in rats. In the present study, an amphetamine-induced model of schizophrenia in adult male rats was used to evaluate the effects of celecoxib, omega-3, celecoxib+risperidone and omega-3+ risperidone on the behavior of animals and on brain lipid peroxidation or tumor necrosis factor-alpha. In the water maze task, celecoxib, omega-3, celecoxib+risperidone, omega-3+ risperidone significantly decreased the latency time compared to amphetamine-treated group. Celecoxib, omega-3, celecoxib+risperidone, omega-3+risperidone also significantly reversed the decreased spontaneous alternation induced by amphetamine in the Y-maze task. In the social interaction task, groups treated with celecoxib, omega-3, celecoxib+risperidone, omega-3+ risperidone spent less time to recognize foreign animals than animals in the amphetamine-treated group. Increased brain MDA and TNF-α levels due to amphetamine were significantly reduced in groups treated with celecoxib+risperidone or omega-3+ risperidone. The present findings showed that celecoxib or omega-3 can attenuate amphetamine- induced behavioral impairment and these effects may be associated with their ability to decrease lipid peroxidation and cytokine release. Celecoxib or omega-3 may be promising candidates as adjuvant therapy for schizophrenia.

Ethnic disparities in the perception of ethical risks from psychiatric genetic studies

To examine if ethnic differences in concerns about unfavorable consequences from psychiatric genetic studies, existing between non-Hispanic Black and White populations, persist among participants in an actual genetic study of bipolar disorder. Historically, minority subjects have been less willing to participate in such studies. Participants in the US Bipolar Genome Study (BIGS) were assessed on six items of concerns in the Questionnaire on Genetic Risk (QGR). Each item had five response categories, ranging from "not at all" concerned to "very concerned." Responses from Black (N = 188) and White participants (N = 1,065) formed the base for this analysis. Concerns about unfavorable consequences of conducting psychiatric genetic studies were prevalent in the whole sample. Concern for medical insurance was most prevalent (63.4%), followed by job concern (58.8%) and stigma (57.4%). Racial discrimination was less prevalent (28.1%). Blacks endorsed significantly stronger concerns for all consequences except the medical insurance item (P < 0.008). The most significant ethnic disparity in concerns was for racial discrimination (P < 0.0001). Associations between levels of concern and ethnicity remained significant after adjustments for other factors in multivariate models. Ethnic differences (Blacks vs. Whites) in perceived concerns about unfavorable consequences from participation persist among participants in an actual psychiatric genetic study. This suggests that other factors may play a more critical role in the decision not to participate. Future studies should investigate more comprehensive sources of barriers to consenting for ongoing psychiatric genetic studies in representative samples, incorporating assessments from non-participants as well as participants.

Increased Lymphocyte Caspase-3 Activity in Patients with Schizophrenia

A growing body of evidence indicates that cortical brain cells of schizophrenic patients are vulnerable to apoptosis. As apoptosis is an important mechanism in organism modeling during development, active since the early phase of intrauterine life, it could be involved in the pathogenesis of schizophrenia. To test this hypothesis, caspase-3 activity was determined in peripheral blood mono nuclear cells from 30 patients with schizophrenia and from 30 age and gender matched healthy subjects by a colorimetric commercially available kit. Consistent with increased susceptibility to apoptosis, caspase-3 activity in lymphocytes of patients with schizophrenia was significantly increased (0.111±0.055 μmol/mg protein, p<0.05) in comparison with those in the matched control group (0.086±0.030 μmol/mg protein). The highest activity was obtained in the group showing almost equally positive and negative symptoms (0.159±0.096 μmol/mg protein) and it was significantly higher (p<0.05) compared to the group with a relative predomination of positive symptoms (0.100±0.029 μmol/mg protein). Caspase-3 activity in patients receiving typical antipsychotic drugs (0.124± 0.071 μmol/mg protein) was not significantly different from that in patients treated with atypical antipsychotics (0.104±0.039 μmol/mg protein). To our knowledge to date, this has been the first demonstration that there is a significant increase in caspase-3 activity, determined in native cells, in patients with schizophrenia, indicating a dysregulated apoptotic mechanism in this disease.

Racial and ethnic differences in willingness to participate in psychiatric genetic research

OBJECTIVE

The National Institute of Mental Health's effort to rectify the underrepresentation of American Blacks in the genetic studies of psychiatric disorders has met with mixed success. This study was designed to understand some of the barriers to recruitment.

METHODS

Men and women, who were of Black, White or Hispanic race/ethnicity, aged 18-79 years (N= 353), were recruited from clinical and community settings in New York City. Participants responded to a survey that was designed to measure willingness to participate and attitudes toward genetic research. Principal components analyses generated eight factors including perceived benefits, concerns about, and drawbacks of genetic research, and beliefs about genetic or environmental contributions to psychopathology. Analysis of variance assessed within-ethnic group differences on factor scores, as they related to willingness to participate in genetic research.

RESULTS

Ethnic groups did not differ significantly in stated willingness to participate in genetic research; more than 70% in each group were willing to participate. Among Blacks and Hispanics, mistrust and wariness, and stigma were significantly increased in those unwilling to participate; for Whites, perceived benefit to society and perceived importance for knowledge/education were associated with willingness to participate. For Blacks and Hispanics, youth (aged 18-29 years) and college education reduced, but did not eliminate the association between wariness and mistrust and willingness to participate.

CONCLUSION

Findings suggest that recruitment efforts aimed at increasing the representation of Blacks should be aware of the barriers among those who are less educated, and involve interactive community collaborations, to fully address the mistrust in this population.

Linkage analysis of schizophrenia controlling for population substructure

Etiological heterogeneity and complexity has hampered attempts to identify predisposing genes for schizophrenia. We sought to minimize the number of segregating genes involved by focusing on a population isolate with elevated disease prevalence. We exploited the well-established population history, and searched for disease susceptibility loci in families from two alternative founder lineages. We studied 28 schizophrenia pedigrees (123 nuclear families) from an outlying municipality on the eastern border of Finland. We divided the families based on their genealogy and defined two routes of immigration: southern and northern. We examined the kinship coefficients and allele frequency distributions within each group, and performed a linkage analysis based on 497 microsatellite markers across the genome. A high degree of historical relatedness was demonstrated by higher sharing of alleles than predicted by the relationships we identified within the previous four generations alone, as would be expected. Between the two subpopulations, allele frequencies were significantly different, consistent with their isolated genealogies. The southern families showed some evidence of linkage in a schizophrenia locus at 4q23 (Z = 3.3) near our previous finding with quantitative variation in verbal learning and memory [Paunio et al. (2004); Hum Mol Genet 13: 1693-1702], while the northern pedigrees gave most significant evidence on 10q21 (Z = 2.53). Joint analysis of families from both lineages suggested evidence of linkage only at 3p14 (Z = 3.18). Thus the detailed genealogical information led us to identification of distinct linkage signals for schizophrenia susceptibility loci between the three analyses we performed.

Allelic variation in GAD1 (GAD67) is associated with schizophrenia and influences cortical function and gene expression

Cortical GABAergic dysfunction has been implicated as a key component of the pathophysiology of schizophrenia and decreased expression of the gamma-aminobutyric acid (GABA) synthetic enzyme glutamic acid decarboxylase 67 (GAD(67)), encoded by GAD1, is found in schizophrenic post-mortem brain. We report evidence of distorted transmission of single-nucleotide polymorphism (SNP) alleles in two independent schizophrenia family-based samples. In both samples, allelic association was dependent on the gender of the affected offspring, and in the Clinical Brain Disorders Branch/National Institute of Mental Health (CBDB/NIMH) sample it was also dependent on catechol-O-methyltransferase (COMT) Val158Met genotype. Quantitative transmission disequilibrium test analyses revealed that variation in GAD1 influenced multiple domains of cognition, including declarative memory, attention and working memory. A 5' flanking SNP affecting cognition in the families was also associated in unrelated healthy individuals with inefficient BOLD functional magnetic resonance imaging activation of dorsal prefrontal cortex (PFC) during a working memory task, a physiologic phenotype associated with schizophrenia and altered cortical inhibition. In addition, a SNP in the 5' untranslated (and predicted promoter) region that also influenced cognition was associated with decreased expression of GAD1 mRNA in the PFC of schizophrenic brain. Finally, we observed evidence of statistical epistasis between two SNPs in COMT and SNPs in GAD1, suggesting a potential biological synergism leading to increased risk. These coincident results implicate GAD1 in the etiology of schizophrenia and suggest that the mechanism involves altered cortical GABA inhibitory activity, perhaps modulated by dopaminergic function.

Susceptibility genes for schizophrenia: Characterisation of mutant mouse models at the level of phenotypic behaviour

A wealth of evidence indicates that schizophrenia is heritable. However, the genetic mechanisms involved are poorly understood. Furthermore, it may be that genes conferring susceptibility interact with one another and with non-genetic factors to modulate risk status and/or the expression of symptoms. Genome-wide scanning and the mapping of several regions linked with risk for schizophrenia have led to the identification of several putative susceptibility genes including neuregulin-1 (NRG1), dysbindin (DTNBP1), regulator of G-protein signalling 4 (RGS4), catechol-o-methyltransferase (COMT), proline dehydrogenase (PRODH) and disrupted-in-schizophrenia 1 (DISC1). Genetic animal models involving targeted mutation via gene knockout or transgenesis have the potential to inform on the role of a given susceptibility gene on the development and behaviour of the whole organism and on whether disruption of gene function is associated with schizophrenia-related structural and functional deficits. This review focuses on data regarding the behavioural phenotype of mice mutant for schizophrenia susceptibility genes identified by positional candidate analysis and the study of chromosomal abnormalities. We also consider methodological issues that are likely to influence phenotypic effects, as well as the limitations associated with existing molecular techniques.

The genetics of depression: a review

Major depressive disorder (MDD) is common and moderately heritable. Recurrence and early age at onset characterize cases with the greatest familial risk. Major depressive disorder and the neuroticism personality trait have overlapping genetic susceptibilities. Most genetic studies of MDD have considered a small set of functional polymorphisms relevant to monoaminergic neurotransmission. Meta-analyses suggest small positive associations between the polymorphism in the serotonin transporter promoter region (5-HTTLPR) and bipolar disorder, suicidal behavior, and depression-related personality traits but not yet to MDD itself. This polymorphism might also influence traits related to stress vulnerability. Newer hypotheses of depression neurobiology suggest closer study of genes related to neurotoxic and neuroprotective (neurotrophic) processes and to overactivation of the hypothalamic-pituitary axis, with mixed evidence regarding association of MDD with polymorphisms in one such gene (brain-derived neurotrophic factor [BDNF]). Several genome-wide linkage studies of MDD and related traits have been reported or are near completion. There is some evidence for convergence of linkage findings across studies, but more data are needed to permit meta-analysis. Future directions will include more intensive, systematic study of linkage candidate regions and of the whole genome for genetic association; gene expression array studies; and larger-scale studies of gene-environment interactions and of depression-related endophenotypes.

Altered gene expression in the amygdala in schizophrenia: Up-regulation of genes located in the cytomatrix active zone

The amygdala is implicated in the pathophysiology of schizophrenia through its function in the processing of emotions. However, the genes involved in the dysfunction of the amygdala in schizophrenia are yet to be identified. This study examined gene expression in the amygdala in postmortem tissue from seven matched pairs of schizophrenia and non-psychiatric control subjects, using oligonucleotide-microarrays representing 19,000 gene transcripts and real-time PCR confirmation of gene expression changes in eleven matched pairs. Genes involved in presynaptic function, myelination and cellular signalling were identified as being consistently dysregulated in this cohort of subjects with schizophrenia. In particular, the expression of three genes involved in the cytomatrix active zone, Regulating membrane exocytosis 2, Regulating membrane exocytosis 3 and Piccolo, was up-regulated. These results implicate for the first time the dysfunction of the cytomatrix active zone of synapses in the amygdala in the pathophysiology of schizophrenia.

Recognition and optimal management of schizophrenia and related psychoses

Schizophrenia continues to remain one of the major unsolved conditions of our time, contributing significantly to causes of disability worldwide. Advances in neuroimaging have demonstrated that schizophrenia appears to be primarily a neurodevelopmental disorder. The dopamine theory of schizophrenia continues to hold sway but interest is growing in the role of other neurotransmitters. Genetic linkage studies continue to suggest that specific chromosomes have a role in the aetiology of the condition but the findings are, as yet, inconsistent. A new generation of drug therapies and reforms of the mental health system have meant that it is now possible to treat the majority of those with this condition in the community albeit, in some instances, against their will. The medical complications of both the disorder, the lifestyle changes resulting from the disorder and the new and older medications have come to prominence in recent years. The development of guidelines for treatment has the potential to reduce the variability in clinical practice that currently exists in the management of the condition.

Fine mapping of a schizophrenia susceptibility locus at chromosome 6q23: increased evidence for linkage and reduced linkage interval

We previously reported an autosomal scan for schizophrenia susceptibility loci in a systematically recruited sample of Arab Israeli families. The scan detected significant evidence for linkage at chromosome 6q23 with a nonparametric LOD score (NPL) of 4.60 (P=0.000004) and a multipoint parametric LOD score of 4.16. In order to refine this finding we typed 42 additional microsatellite markers on chromosome 6q between D6S1570 (99.01 cM from the pter) and D6S281 (190.14 from the pter) in the same sample (average intermarker distance approximately 1.7 cM). In the 23 cM region between D6S1715 and D6S311, markers were more closely spaced ( approximately 1.1 cM). Multipoint nonparametric and parametric and single point linkage analyses were performed. The peak NPL rose to 4.98 (P=0.00000058) at D6S1626 (136.97 cM), immediately adjacent to D6S292 (NPL 4.98, P=0.00000068), the marker that gave the highest NPL in the original genome scan, under the broad diagnostic category. The putative susceptibility region (NPL-1) was reduced from 12.0 to 4.96 cM. The peak multipoint parametric LOD score was 4.63 at D6S1626 under a dominant genetic model, core diagnostic category and the LOD-1 interval was 2.10 cM. The maximum single point LOD score (3.55, theta=0.01) was also at D6S1626 (dominant model, core diagnostic category). Increased evidence for linkage in the same sample as in the original genome scan and consistent localization of the linkage peak add further support for the presence of a schizophrenia susceptibility locus at chromosome 6q23. Moreover, the markedly reduced linkage interval greatly improves prospects for identifying a schizophrenia susceptibility gene within the implicated region.

Eye movements and psychiatric disease

PURPOSE OF REVIEW

During the past year a number of studies have been published on eye movement dysfunction in patients with psychiatric disease. According to the mainstream of modern neuropsychiatric research, these studies cover either genetic aspects or the results of pharmacological manipulation.

RECENT FINDINGS

A few studies addressed impaired smooth pursuit eye movements (eye tracking dysfunction) in unaffected relatives of psychiatric patients, and were important in excluding non-specific effects (e.g. medication) and isolating genetic predisposition to the disease. This predisposition could be demonstrated in families of schizophrenic patients irrespective of whether the index case was sporadic or familial. One large study demonstrated pathological distributions of various parameters of smooth pursuit eye movement performance in groups of schizophrenic patients and their relatives. However, another study challenged the specificity of eye tracking dysfunction as a trait marker for schizophrenia by showing that its prevalence was identical among relatives of patients with affective disorder and schizophrenia. Eye tracking dysfunction was associated with two gene polymorphisms that interfere with dopamine metabolism and are thus reasonable candidate genes for the predisposition to schizophrenia. The influence of nicotine and neuroleptic drugs on eye movement performance was studied in schizophrenic patients. Nicotine improved smooth pursuit performance in three studies, one of which attributed this finding to enhanced attention. Two groups of schizophrenic patients treated with two different atypical neuroleptic drugs, risperidone and olanzapine, did not differ in a battery of saccadic tasks.

SUMMARY

Eye movements provide an important tool to measure pharmacological effects in patients and unravel genetic traits in psychiatric disease.