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Phenotypic Effects of Polygenic Risk for Schizophrenia

Special Issue Information

In recent years, polygenic risk scores that summarize an individual’s polygenic risk for schizophrenia (SZ) have been increasingly researched, both in patient and control populations. This special issue of the Journal of Psychiatry and Brain Science aims to provide a clearer picture of the associations of phenotypes with SZ polygenic risk. Articles that will be published in this special issue are not limited to any specific clinical or non-clinical population or kind of phenotype (e.g. behavioral or biological), as it is our goal to capture the full spectrum of effects of SZ polygenic risk. Importantly, also articles with negative findings (non-associations) of phenotypes theoretically thought to be related to polygenic risk for SZ are explicitly invited.

We are welcoming both original research articles and review articles, and article processing fees for the papers submitted to this Special Issue are totally waived.

Dr. Urs Heilbronner

Guest Editor

Submission Deadline: 31 October 2018

Online Submission

Manuscripts should be submitted online through ScholarOne Manuscripts for Journal of Psychiatry and Brain Science © Clarivate Analytics. Please visit Guide for Authors before submitting a manuscript. Authors are encouraged to submit a paper as soon as it is ready and don’t need to wait until the deadline. Submissions will be sent to peer-review in order of arrival. Accepted papers will be published continuously in Journal of Psychiatry and Brain Science and then gathered together on the special issue webpage. We welcome Research articles, Review papers and Short Communications. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Planned Papers

Type of Paper: Original Research Article

Paper Title: Polygenic Risk for Schizophrenia, Bipolar Disorder and Cannabis Abuse

Authors: Kristina Adorjan 1,2 and Sergi Papiol 1

Author Affiliations:

1 Institute of Psychiatric Phenomics and Genomics (IPPG), University Hospital, Ludwig Maximilian University Munich

2 Department of Psychiatry, University Hospital, Ludwig Maximilian University Munich

Abstract: A mental disorder is a multifactorial phenomenon in which not only environmental influences but also genetic factors play an important role. The basis for this is a complex mode of inheritance with high polygenicity, in which a large number of common genetic variants with small effects are decisive. One way to measure this polygenic risk is the calculation of polygenic risk scores (PRS). These reflect the complex multifactorial interaction of coding and regulatory DNA variants in the development of mental illness.

In addition to the genetic factors, environmental influences also play an important role in the development of mental illnesses. It is known that the use of cannabis in patients with schizophrenia (SCZ) and bipolar disorder (BD) is much higher than in the general population. Studies have shown that a genetic predisposition to schizophrenia is associated with increased cannabis use. Power et al. have used PRS analyses and found that healthy individuals with cannabis use have a higher PRS for schizophrenia than individuals who do not use cannabis (R2 = 0.47%,p = 2.6 × 10−4). Verweij et al. were able to achieve similar results: Individuals with increased PRS for schizophrenia consume more cannabis throughout their lives than individuals with a lower risk score (R2 = 3.3% p < 0.001). In view of this relationship, we also investigated whether PRS for schizophrenia can also predict cannabis use in patients with schizophrenia and bipolar disorder. In addition, we tested whether cannabis-PRS has an influence on cannabis use in these two patient groups.

Although an exact clinical prognosis based on PRS is not possible at the present, the results found by PRS investigations so far are quite promising. Initial results suggest that people with SCZ or BD and an increased polygenic risk of schizophrenia are more likely to use cannabis. The connection between mental illnesses and cannabis use could therefore not simply be seen as an environmental risk, but rather explained as a gene-environment interaction. In the future, larger sample sizes will be necessary to investigate the genetic association between a mental disorder and cannabis use and to identify common genes and biological mechanisms that can explain this genetic association.

Keywords: Schizophrenia, Bipolar Disorder, Genetics, Polygenic Risk Score

Type of Paper: Original Research Article

Paper Title: Phenotypic Traits of Bipolar Disorder Predicted by Polygenic Risk for Schizophrenia in Romanian Bipolar-I Patients. Partial Preliminary Results

Authors: Maria Grigoroiu-Serbanescu 1, Tim Bigdeli 2, Johan Thygesen3, Stefan Herms4, Andreas Forstner5, Markus Noethen5,
Andrew McQuillin3

Author Affiliations:

1 Alexandru Obregia Clinical Psychiatric Hospital, Psychiatric Genetics Research Unit, Medical University, Bucharest, Romania

2 SUNY Downstate Medical Center, Brooklyn, New York, USA

3 University College London, Dept. Psychiatry, London, UK

4 University of Basel, Division of Medical Genetics, Basel, Switzerland

5 Institute of Human Genetics, University of Bonn, Bonn, Germany

Abstract: Genome-wide research suggests that the molecular basis of Bipolar disorder (BP) and Schizophrenia (SCZ) overlaps. The objective of the present work was therefore to investigate whether polygenic risk scores (PRS) based on SCZ-associated SNPs might be associated with phenotypic traits of BP-I in Romanian patients, namely the presence of psychosis and incongruent psychosis, age of onset (AO), family history for major affective disorders (BP, Unipolar Depression, Schizoaffective Disorder) and SCZ, and the number of manic/mixed episodes.

439 BP-I cases and 283 controls were genotyped on Illumina SNP-arrays, PRS profiles for three p-value thresholds of association with SCZ were created using PLINK 1.07 (p ≤ 0.05, p ≤ 0.01 and p ≤ 0.10) and analyzed with logistic and multinomial regression.

The SCZ-PRS significantly discriminated between cases and controls at all investigated p-value thresholds (p < 0.001).

In BP-I patients, SCZ-PRS predicted both the presence of incongruent psychosis and psychosis, the former being also associated with sex. There was a trend towards association with AO when AO was subdivided in three AO groups (early AO ≤ 21 years; intermediate AO = 22–34 years; late AO > 34 years). Family history for major affective disorders and SCZ tended to be associated with SCZ-PRS as did the number of manic/mixed episodes in the early AO group.

While the association with PRS for SCZ varied in our sample according to the chosen P-value thresholds, this study demonstrates distinct effects of SCZ-PRS on phenotypic traits in BP patients and their ability to discriminate between BP patients and controls.

Keywords: Schizophrenia, Bipolar Disorder, Genetics, Polygenic Risk Score

Type of Paper: Review

Paper Title: Bipolar Disorder and Polygenic Risk for Schizophrenia

Authors: Susanne Bengesser, Eva Reininghaus

Author Affiliations:

Department of Psychiatry and Psychotherapeutic Medicine, Medical University of Graz

Abstract: Bipolar disorder is a mood disorder with mood swings between the pole of depression and the pole of mania. The pathomechanism of those mood swings has not been completely elucidated yet. According to current scientific knowledge affective episodes are caused by a concatenation between a genetic predisposition and biopsychosocial triggers. Even though diverse genome wide associated gene variants (e.g. single nucleotide polymorphisms of CACNA1C, ANK3 or NCAN) were associated with Bipolar disorder in the last decade, there is still missing heritability. Thus, innovative approaches and endophenotypes of Bipolar disorder must be used to decipher the underlying pathomechanisms of Bipolar disorder. Recently, the Polygenic Risk Score for Schizophrenia was investigated in the lithium-response endophenotype of Bipolar disorder. The polygenic score for Schizophrenia was inversely associated with the lithium response phenotype in study participants with Bipolar disorder. The latter underlines the genetic overlaps between psychiatric diseases, which also demonstrates the importance of cross-disorder design studies to elucidate the missing heritability of Bipolar disorder.

Keywords: Bipolar Disorder, Polygenic Risk Score, Schizophrenia

Guest Editor

  • Dr. Urs Heilbronner

    Institut für Psychiatrische Phänomik und Genomik (IPPG) Klinikum der Universität München, LMU München

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