Genetics of Schizophrenia and Affective Disorders

Transgenerational Interaction of Alzheimer's Disease with Schizophrenia through Amyloid Evolvability

Alzheimer's disease (AD), the most common neurodegenerative dementia, leads to memory dysfunction due to widespread neuronal loss associated with aggregation of amyloidogenic proteins (APs), while schizophrenia (SCZ) represents a major psychiatric disorder characterized by delusions, hallucinations, and other cognitive abnormalities, the underlying mechanisms of which remain obscure. Although AD and SCZ partially overlap in terms of psychiatric symptoms and some aspects of cognitive impairment, the causal relationship between AD and SCZ is unclear. Based on the similarity of APs with yeast prion in terms of stress-induced protein aggregation, we recently proposed that evolvability of APs might be an epigenetic phenomenon to transmit stress information of parental brain to cope with the stressors in offspring. Although amyloid evolvability may be beneficial in evolution, AD might be manifested during parental aging as the mechanism of antagonistic pleiotropy phenomenon. Provided that accumulating evidence implicates stress as an important factor in SCZ, the main objective of this paper is to better understand the possible connection of AD and SCZ through amyloid evolvability. Hypothetically, the delivery of information of stress by APs may be less efficient under the decreased evolvability conditions such as disease-modifying treatment, leading to SCZ in offspring. Conversely, the increased evolvability conditions including gene mutations of APs are supposed to be beneficial for offspring, but might lead to AD in parents. Collectively, AD and SCZ might transgenerationally interfere with each other through amyloid evolvability, and this could explain why both AD and SCZ have not been selected out through evolution.

Reduced Hippocampal Volume and Its Relationship With Verbal Memory and Negative Symptoms in Treatment-Naive First-Episode Adolescent-Onset Schizophrenia

Accumulating neuroimaging evidence has shown remarkable volume reductions in the hippocampi of patients with schizophrenia. However, the relationship among hippocampal morphometry, clinical symptoms, and cognitive impairments in schizophrenia is still unclear. In this study, high-resolution structural magnetic resonance imaging data were acquired in 36 patients with adolescent-onset schizophrenia (AOS, age range: 13-18 years) and 30 age-, gender-, and education-matched typically developing controls (TDCs). Hippocampal volume was assessed automatically through volumetric segmentation and measurement. After adjusting for total intracranial volume, we found reduced hippocampal volume in individuals with AOS compared with TDCs, and the hippocampal volume was positively correlated with verbal memory and negatively correlated with negative symptoms in AOS. In addition, mediation analysis revealed the indirect effect of hippocampal volume on negative symptoms via verbal memory impairment. When the negative symptoms were represented by 2 dimensions of deficits in emotional expression (EXP) and deficits in motivation and pleasure (MAP), the indirect effect was significant for EXP but not for MAP. Our findings provide further evidence of hippocampal volume reduction in AOS and highlight verbal memory impairment as a mediator to influence the relationship between hippocampal morphometry and negative symptoms, especially the EXP dimension of negative symptoms, in individuals with AOS.

Genetic variation in the G72 (DAOA) gene affects temporal lobe and amygdala structure in subjects affected by bipolar disorder

BACKGROUND

Variation in the G72 (DAOA) gene is understood to convey susceptibility for bipolar disorder through an uncertain mechanism. Little is known about the structural brain phenotypes associated with this gene. We hypothesised that reductions in temporal lobe and amygdala gray matter would be associated with variation at two loci in the gene for which evidence of genetic linkage has been repeatedly demonstrated.

METHODS

We examined the temporal lobe and amygdala gray matter associations of the risk variants M23 and M24 at the 5' end of the gene encoding G72 in 81 controls and 38 people with bipolar disorder.

RESULTS

Genetic variation at both the M23 and M24 loci in G72 were associated with decreased gray matter density within the left temporal pole in people with bipolar disorder. M23 was also associated with reductions in right amygdala gray matter density. The genetic imaging associations were found only in patients with bipolar disorder.

CONCLUSIONS

Genetic variation at single nucleotide polymorphisms in the G72 gene previously associated with bipolar disorder is related to reductions in temporal pole and amygdala gray matter structure in people with bipolar disorder.

The forthcoming revision of the diagnostic and classificatory system: perspectives based on the European psychiatric tradition

Europe has a rich tradition in psychopathology and psychiatric classification. This could be helpful developing new classification systems like ICD-11 and DSM-V. Some examples of this are described and further discussed, such as the categorical vs. the syndromatological approach, the relevance of hierarchical rules for the delineation of nosological entities, the antagonistic tradition of unitarian vs. splitting approaches and the relevance of a differentiated psychopathological description. Finally, the conclusion is that a too radical change of the classificatory system, e.g. in the direction of a purely symptomatical/dimensional systematic, or a totally new classification based on modern new biological findings, might be problematic and premature.

Multivariate permutation analysis associates multiple polymorphisms with subphenotypes of major depression

Unipolar major depressive disorder (MDD) is a prevalent, disabling condition with multiple genetic and environmental factors impacting disease risk. The diagnosis of MDD relies on a cumulative measure derived from multiple trait dimensions and alone is limited in elucidating MDD genetic determinants. We and others have proposed that MDD may be better dissected using paradigms that assess how specific genes associate with component features of MDD. This within-disease design requires both a well-phenotyped cohort and a robust statistical approach that retains power with multiple tests of genetic association. In the present study, common polymorphic variants of genes related to central monoaminergic and cholinergic pathways that previous studies align with functional change in vitro or depression associations in vivo were genotyped in 110 individuals with unipolar MDD. Subphenotypic characteristics were examined using responses to individual items assessed with the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders (DSM IV), the 17-item Hamilton Rating Scale for Depression (HAM-D) and the NEO Five Factor Inventory. Multivariate Permutation Testing (MPT) was used to infer genotype-phenotype relationships underlying dimensional findings within clinical categories. MPT analyses show significant associations of the norepinephrine transporter (NET, SLC6A2) -182 T/C (rs2242446) with recurrent depression [odds ratio, OR = 4.15 (1.91-9.02)], NET -3081 A/T (rs28386840) with increase in appetite [OR = 3.58 (1.53-8.39)] and the presynaptic choline transporter (CHT, SLC5A7) Ile89Val (rs1013940) with HAM-D-17 total score {i.e. overall depression severity [OR = 2.74 (1.05-7.18)]}. These relationships illustrate an approach to the elucidation of gene influences on trait components of MDD and with replication, may help identify MDD subpopulations that can benefit from more targeted pharmacotherapy.

Genetic analysis of psychiatric disorders in humans

Psychiatric disorders place a large burden not only on affected individuals and their families but also on societies and health services. Current treatment is only effective in a proportion of the patients, so considerable effort has been put into the development of new medications. The susceptibility to all major psychiatric disorders is, at least in part, genetic. Knowledge of the genes that underlie this susceptibility may lead to the identification of new drug targets and the development of more effective treatments. Therefore, numerous genetic studies in search for the genes involved in psychiatric disorders have been performed. Although results of both linkage and association studies have been inconsistent, several promising gene regions and candidate genes have been identified recently. In this article, we will review the strategies that proved to be successful in detecting genes for psychiatric disorders and we will provide some recommendations to increase the probability of detecting susceptibility genes in genetic studies of different designs.

Genetic liability to schizophrenia or bipolar disorder and its relationship to brain structure

Bipolar disorder and schizophrenia are highly heritable conditions that are associated with structural brain abnormalities. Although brain abnormalities are found in the well relatives of people with schizophrenia, the extent to which genetic liability relates to brain structure in either disorder is still unclear. This study sought to ascertain the effects of genetic liability to schizophrenia and bipolar disorder on white and grey matter volume in patients with these diagnoses and their well relatives. Seventy-one patients and 72 unaffected relatives were recruited for the study. Patients included those with schizophrenia from families affected by schizophrenia alone, those with bipolar disorder from families affected by bipolar disorder alone and those with bipolar disorder from families affected by both bipolar disorder and schizophrenia. Samples of unaffected relatives of each patient group were also recruited. Subjects underwent an MRI scan of the brain, which was analysed using optimised voxel-based morphometry (VBM). Grey and white matter volume was then related to a continuous measure of genetic liability based on a threshold-liability model. Genetic liability to schizophrenia was associated with decreased grey matter volume in dorso- (DLPFC) and ventrolateral prefrontal (VLPFC) cortices. The relationship remained after diagnostic status had been taken into account. Complementary white matter changes were also demonstrated. No relationship was demonstrated between a genetic liability to bipolar disorder and either white or grey matter volume. Genes that raise the likelihood of developing schizophrenia may exert their effects by diminishing grey matter volume in the DLPFC and VLPFC and their associated white matter connections. Genes for bipolar illness might have subtle effects on brain structure, which may need particularly large samples to detect.

Bipolar I disorder and schizophrenia: a 440-single-nucleotide polymorphism screen of 64 candidate genes among Ashkenazi Jewish case-parent trios

Bipolar, schizophrenia, and schizoaffective disorders are common, highly heritable psychiatric disorders, for which familial coaggregation, as well as epidemiological and genetic evidence, suggests overlapping etiologies. No definitive susceptibility genes have yet been identified for any of these disorders. Genetic heterogeneity, combined with phenotypic imprecision and poor marker coverage, has contributed to the difficulty in defining risk variants. We focused on families of Ashkenazi Jewish descent, to reduce genetic heterogeneity, and, as a precursor to genomewide association studies, we undertook a single-nucleotide polymorphism (SNP) genotyping screen of 64 candidate genes (440 SNPs) chosen on the basis of previous linkage or of association and/or biological relevance. We genotyped an average of 6.9 SNPs per gene, with an average density of 1 SNP per 11.9 kb in 323 bipolar I disorder and 274 schizophrenia or schizoaffective Ashkenazi case-parent trios. Using single-SNP and haplotype-based transmission/disequilibrium tests, we ranked genes on the basis of strength of association (P<.01). Six genes (DAO, GRM3, GRM4, GRIN2B, IL2RB, and TUBA8) met this criterion for bipolar I disorder; only DAO has been previously associated with bipolar disorder. Six genes (RGS4, SCA1, GRM4, DPYSL2, NOS1, and GRID1) met this criterion for schizophrenia or schizoaffective disorder; five replicate previous associations, and one, GRID1, shows a novel association with schizophrenia. In addition, six genes (DPYSL2, DTNBP1, G30/G72, GRID1, GRM4, and NOS1) showed overlapping suggestive evidence of association in both disorders. These results may help to prioritize candidate genes for future study from among the many suspected/proposed for schizophrenia and bipolar disorders. They provide further support for shared genetic susceptibility between these two disorders that involve glutamate-signaling pathways.

Problems associated with the classification and diagnosis of psychiatric disorders

Several methodological issues of classification of psychiatric disorders are addressed. Beside some historical aspects and basic characteristics of the classification of mental disorders, the advantages and disadvantages of the syndromatological and nosological classifications are broadly described. Finally the current situation of the international standardisation of psychiatric classification and particuarly the improvement of reliability by using operationalised procedures is discussed.

Burden of relatives and predictors of burden. Baseline results from the Munich 5-year-follow-up study on relatives of first hospitalized patients with schizophrenia or depression

In the present study, part of the Munich 5-year follow-up study on key relatives of first-hospitalized schizophrenic and depressive patients, baseline results with respect to relatives' burden and predictors of burden are presented. Basing on a transactional stress model the following hypothesis was tested: the impact of the patients' illness on their relatives' stress outcome is moderated by the psychosocial resources of the relatives. Stress outcome was measured in terms of objective and subjective burden, well-being, self-rated symptoms and global satisfaction with life. Potential moderating variables included age and gender, generalized stress response and illness-related coping strategies, beliefs of control,perceived social support,personality factors, expressed emotion and life stressors. A total of 83 relatives, whose ill family members had been hospitalized in the Department of Psychiatry of the Ludwig-Maximilians-University of Munich for the first time, participated in the study. Findings did not entirely support the hypothesis. On the one hand, relatives' stress outcome was independent of the objective stressors (severity of the illness, kind of symptoms, level of psychosocial functioning at admission). On the other hand, burden was significantly associated with several psychosocial resources and dispositions of the relatives. Multivariate linear regression analyses indicated that expressed emotion, emotion-focused coping strategies and generalized negative stress response are the most relevant predictors of burden. It is argued that a multidimensional approach in burden assessment is necessary and has relevant implications for improving family intervention strategies.

Gene expression microarray studies in polygenic psychiatric disorders: applications and data analysis

Gene expression microarrays have become a mainstream technology that can provide valuable insight into psychiatric disorders. Gene expression studies in post mortem brain samples of schizophrenia and bipolar disorder have the potential to yield novel clues about the pathophysiology of these complex trait disorders. In the present review, a short introduction of the genetic and molecular background of schizophrenia and bipolar disorder is followed by a discussion of the basic concept and limits of gene expression microarray technology, and the complexities surrounding the analysis of thousands of gene transcripts. Although this review is intended for use in most platforms, it has a particular focus on the commercially available Affymetrix system. Various computer programs and their principal features are discussed, and it is shown how these programs can be applied to reveal a biological context of microarray findings. I will demonstrate how the programs can help to judge the results rather than focus on their statistical principles. The strength of gene array experiments is their emphasis on broad, biological themes, rather than on specific genes, and proper biostatistical approaches are important to ensure reproducibility of the findings. All results should be verified by independent means. This review is intended to help brain researchers who want to apply gene expression microarray technology to conceptualize research strategies and sample analysis.

Influenza A virus infection causes alterations in expression of synaptic regulatory genes combined with changes in cognitive and emotional behaviors in mice

Epidemiological studies have indicated a link between certain neuropsychiatric diseases and exposure to viral infections. In order to examine long-term effects on behavior and gene expression in the brain of one candidate virus, we have used a model involving olfactory bulb injection of the neuro-adapted influenza A virus strain, WSN/33, in C57Bl/6 mice. Following this olfactory route of invasion, the virus targets neurons in the medial habenular, midline thalamic and hypothalamic nuclei as well as monoaminergic neurons in the brainstem. The mice survive and the viral infection is cleared from the brain within 12 days. When tested 14-20 weeks after infection, the mice displayed decreased anxiety in the elevated plus-maze and impaired spatial learning in the Morris water maze test. Elevated transcriptional activity of two genes encoding synaptic regulatory proteins, regulator of G-protein signaling 4 and calcium/calmodulin-dependent protein kinase IIalpha, was found in the amygdala, hypothalamus and cerebellum. It is of particular interest that the gene encoding RGS4, which has been related to schizophrenia, showed the most pronounced alteration. This study indicates that a transient influenza virus infection can cause persistent changes in emotional and cognitive functions as well as alterations in the expression of genes involved in the regulation of synaptic activities.

Dysbindin-1 is reduced in intrinsic, glutamatergic terminals of the hippocampal formation in schizophrenia

Eleven studies now report significant associations between schizophrenia and certain haplotypes of single-nucleotide polymorphisms in the gene encoding dysbindin-1 at 6p22.3. Dysbindin-1 is best known as dystrobrevin-binding protein 1 (DTNBP1) and may thus be associated with the dystrophin glycoprotein complex found at certain postsynaptic sites in the brain. Contrary to expectations, however, we found that when compared to matched, nonpsychiatric controls, 73-93% of cases in two schizophrenia populations displayed presynaptic dysbindin-1 reductions averaging 18-42% (P = 0.027-0.0001) at hippocampal formation sites lacking neuronal dystrobrevin (i.e., beta-dystrobrevin). The reductions, which were not observed in the anterior cingulate of the same schizophrenia cases, occurred specifically in terminal fields of intrinsic, glutamatergic afferents of the subiculum, the hippocampus proper, and especially the inner molecular layer of the dentate gyrus (DGiml). An inversely correlated increase in vesicular glutamate transporter-1 (VGluT-1) occurred in DGiml of the same schizophrenia cases. Those changes occurred without evidence of axon terminal loss or neuroleptic effects on dysbindin-1 or VGluT-1. Our findings indicate that presynaptic dysbindin-1 reductions independent of the dystrophin glycoprotein complex are frequent in schizophrenia and are related to glutamatergic alterations in intrinsic hippocampal formation connections. Such changes may contribute to the cognitive deficits common in schizophrenia.