1
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Schalbroeck R, van Hooijdonk CFM, Bos DPA, Booij J, Selten JP. Chronic social stressors and striatal dopamine functioning in humans: A systematic review of SPECT and PET studies. Mol Psychiatry 2024:10.1038/s41380-024-02581-x. [PMID: 38760501 DOI: 10.1038/s41380-024-02581-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Revised: 04/18/2024] [Accepted: 04/22/2024] [Indexed: 05/19/2024]
Abstract
The dopamine hypothesis of schizophrenia posits that elevated striatal dopamine functioning underlies the development of psychotic symptoms. Chronic exposure to social stressors increases psychosis risk, possibly by upregulating striatal dopamine functioning. Here we systematically review single photon emission computed tomography (SPECT) and positron emission tomography (PET) studies that examined the relationship between chronic social stress exposure and in vivo striatal dopamine functioning in humans. We searched the scientific databases PubMed and PsycINFO from inception to August 2023. The quality of the included studies was evaluated with the ten-item Observational Study Quality Evaluation (PROSPERO: CRD42022308883). Twenty-eight studies were included, which measured different aspects of striatal dopamine functioning including dopamine synthesis capacity (DSC), vesicular monoamine transporter type 2 binding, dopamine release following a pharmacological or behavioral challenge, D2/3 receptor binding, and dopamine transporter binding. We observed preliminary evidence of an association between childhood trauma and increased striatal DSC and dopamine release. However, exposure to low socioeconomic status, stressful life events, or other social stressors was not consistently associated with altered striatal dopamine functioning. The quality of available studies was generally low. In conclusion, there is insufficient evidence that chronic social stressors upregulate striatal dopamine functioning in humans. We propose avenues for future research, in particular to improve the measurement of chronic social stressors and the methodological quality of study designs.
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Affiliation(s)
- Rik Schalbroeck
- Mental Health and Neuroscience Research Institute, Maastricht University, Maastricht, The Netherlands.
- Department of Radiology and Nuclear Medicine, Amsterdam University Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
| | - Carmen F M van Hooijdonk
- Mental Health and Neuroscience Research Institute, Maastricht University, Maastricht, The Netherlands
| | - Daniëlle P A Bos
- Department of Psychiatry, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Jan Booij
- Department of Radiology and Nuclear Medicine, Amsterdam University Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Jean-Paul Selten
- Mental Health and Neuroscience Research Institute, Maastricht University, Maastricht, The Netherlands
- Rivierduinen Institute for Mental Healthcare, Leiden, The Netherlands
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2
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Namavar Y, Duineveld DJ, Both GIA, Fiksinski AM, Vorstman JAS, Verhoeven-Duif NM, Zinkstok JR. Psychiatric phenotypes associated with hyperprolinemia: A systematic review. Am J Med Genet B Neuropsychiatr Genet 2021; 186:289-317. [PMID: 34302426 DOI: 10.1002/ajmg.b.32869] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Revised: 02/26/2021] [Accepted: 06/30/2021] [Indexed: 12/29/2022]
Abstract
Hyperprolinemia Type I and II are genetic metabolic disorders caused by disrupted proline degradation. It has been suggested that hyperprolinemia is associated with increased risk of developmental and mental disorders but detailed information on the psychiatric phenotype in hyperprolinemic patients is limited. Following PRISMA guidelines, we carried out a systematic review to clarify psychiatric phenotypes in patients with hyperprolinemia. We screened 1753 studies and included 35 for analysis, including 20 case reports and 15 case-control and cohort studies. From these studies, a common psychiatric phenotype is observed with a high prevalence of developmental delay, intellectual disability, autism spectrum disorders, and psychosis spectrum disorders. In most cases, a genetic cause of hyperprolinemia was known, these included mutations in the PRODH and ALDH4A1 genes and deletions of chromosome 22q11.2. No evidence for a biochemical phenotype-clinical phenotype correlation was found; that is, no association between higher proline levels and specific psychiatric phenotypes was observed. This suggests that genomic and environmental factors are likely to contribute to clinical outcomes. More studies are needed to clarify whether hyperprolinemia is a primary causal factor underlying the increased risk of developing psychiatric disorders seen in patients with hyperprolinemia, or whether hyperprolinemia and psychiatric disorders are both consequences of a shared underlying mechanism.
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Affiliation(s)
- Yasmin Namavar
- Department of Psychiatry and Brain Center, University Medical Center Utrecht, Utrecht, The Netherlands.,Department of Psychiatry, Amsterdam UMC Location AMC, Amsterdam, The Netherlands
| | - Denise Joanne Duineveld
- Department of Psychiatry and Brain Center, University Medical Center Utrecht, Utrecht, The Netherlands
| | | | - Ania Maria Fiksinski
- Department of Psychiatry and Brain Center, University Medical Center Utrecht, Utrecht, The Netherlands.,Clinical Genetics Research Program, Centre for Addiction and Mental Health, Toronto, Ontario, Canada.,The Dalglish Family 22q Clinic for 22q11.2 Deletion Syndrome, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada
| | - Jacob Abraham Schrey Vorstman
- Program in Genetics and Genome Biology, Research Institute, Toronto, Ontario, Canada.,Department of Psychiatry, The Hospital for Sick Children, Toronto, Ontario, Canada.,Department of Psychiatry, University of Toronto, Toronto, Ontario, Canada
| | - Nanda Margriet Verhoeven-Duif
- Section of Metabolic Diagnostics, Department of Genetics, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands
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3
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Kim G, Moon E, Park JM, Lee BD, Lee YM, Jeong HJ, Kim SY, Lee K, Suh H. Various Psychiatric Manifestation in DiGeorge Syndrome (22q11.2 Deletion Syndrome): A Case Report. CLINICAL PSYCHOPHARMACOLOGY AND NEUROSCIENCE 2020; 18:458-462. [PMID: 32702226 PMCID: PMC7383002 DOI: 10.9758/cpn.2020.18.3.458] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/20/2019] [Revised: 03/18/2019] [Accepted: 03/19/2019] [Indexed: 11/20/2022]
Abstract
This case report aimed to describe various psychiatric manifestation and treatment course in a patient with DiGeorge syndrome. Psychiatric symptoms and treatment course in a female patient with DiGeorge syndrome were described. This patient showed psychotic symptoms, mood symptoms, and intellectual disability. As well as various psychiatric symptoms, treatment response and sensitivity of side effect by antipsychotics were different from typical characteristics in psychiatric disorders. This case suggests that the genetic defect in DiGeorge syndrome might have a great association with psychiatric problems and response of antipsychotics.
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Affiliation(s)
- Giok Kim
- Department of Psychiatry, Medical Research Institute, Pusan National University Hospital, Busan, Korea
| | - Eunsoo Moon
- Department of Psychiatry, Medical Research Institute, Pusan National University Hospital, Busan, Korea.,Department of Psychiatry, Pusan National University School of Medicine, Yangsan, Korea
| | - Je Min Park
- Department of Psychiatry, Medical Research Institute, Pusan National University Hospital, Busan, Korea.,Department of Psychiatry, Pusan National University School of Medicine, Yangsan, Korea
| | - Byung Dae Lee
- Department of Psychiatry, Medical Research Institute, Pusan National University Hospital, Busan, Korea.,Department of Psychiatry, Pusan National University School of Medicine, Yangsan, Korea
| | - Young Min Lee
- Department of Psychiatry, Medical Research Institute, Pusan National University Hospital, Busan, Korea.,Department of Psychiatry, Pusan National University School of Medicine, Yangsan, Korea
| | - Hee Jeong Jeong
- Department of Psychiatry, Medical Research Institute, Pusan National University Hospital, Busan, Korea
| | - Soo Yeon Kim
- Department of Psychiatry, Medical Research Institute, Pusan National University Hospital, Busan, Korea
| | - Kangyoon Lee
- Department of Psychiatry, Medical Research Institute, Pusan National University Hospital, Busan, Korea
| | - Hwagyu Suh
- Department of Psychiatry, Medical Research Institute, Pusan National University Hospital, Busan, Korea
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4
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van Duin EDA, Ceccarini J, Booij J, Kasanova Z, Vingerhoets C, van Huijstee J, Heinzel A, Mohammadkhani-Shali S, Winz O, Mottaghy F, Myin-Germeys I, van Amelsvoort T. Lower [ 18F]fallypride binding to dopamine D 2/3 receptors in frontal brain areas in adults with 22q11.2 deletion syndrome: a positron emission tomography study. Psychol Med 2020; 50:799-807. [PMID: 30935427 PMCID: PMC7168654 DOI: 10.1017/s003329171900062x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/27/2018] [Revised: 08/06/2018] [Accepted: 03/05/2019] [Indexed: 01/24/2023]
Abstract
BACKGROUND The 22q11.2 deletion syndrome (22q11DS) is caused by a deletion on chromosome 22 locus q11.2. This copy number variant results in haplo-insufficiency of the catechol-O-methyltransferase (COMT) gene, and is associated with a significant increase in the risk for developing cognitive impairments and psychosis. The COMT gene encodes an enzyme that primarily modulates clearance of dopamine (DA) from the synaptic cleft, especially in the prefrontal cortical areas. Consequently, extracellular DA levels may be increased in prefrontal brain areas in 22q11DS, which may underlie the well-documented susceptibility for cognitive impairments and psychosis in affected individuals. This study aims to examine DA D2/3 receptor binding in frontal brain regions in adults with 22q11DS, as a proxy of frontal DA levels. METHODS The study was performed in 14 non-psychotic, relatively high functioning adults with 22q11DS and 16 age- and gender-matched healthy controls (HCs), who underwent DA D2/3 receptor [18F]fallypride PET imaging. Frontal binding potential (BPND) was used as the main outcome measure. RESULTS BPND was significantly lower in adults with 22q11DS compared with HCs in the prefrontal cortex and the anterior cingulate gyrus. After Bonferroni correction significance remained for the anterior cingulate gyrus. There were no between-group differences in BPND in the orbitofrontal cortex and anterior cingulate cortex. CONCLUSIONS This study is the first to demonstrate lower frontal D2/3 receptor binding in adults with 22q11DS. It suggests that a 22q11.2 deletion affects frontal dopaminergic neurotransmission.
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Affiliation(s)
- Esther D. A. van Duin
- Department of Psychiatry & Neuropsychology, Maastricht University, Maastricht, The Netherlands
| | - Jenny Ceccarini
- Department of Nuclear Medicine and Molecular Imaging, Division of Imaging and Pathology, University Hospital Leuven, KU Leuven, Belgium
| | - Jan Booij
- Academic Medical Center, Amsterdam, The Netherlands
| | - Zuzana Kasanova
- Department of Neuroscience, Center for Contextual Psychiatry, KU Leuven – Leuven University, Leuven, Belgium
| | - Claudia Vingerhoets
- Department of Psychiatry & Neuropsychology, Maastricht University, Maastricht, The Netherlands
- Academic Medical Center, Amsterdam, The Netherlands
| | - Jytte van Huijstee
- Department of Psychiatry & Neuropsychology, Maastricht University, Maastricht, The Netherlands
| | - Alexander Heinzel
- Department of Nuclear Medicine, University Hospital RWTH, Aachen University, Aachen, Germany
| | | | - Oliver Winz
- Department of Nuclear Medicine, University Hospital RWTH, Aachen University, Aachen, Germany
| | - Felix Mottaghy
- Department of Nuclear Medicine, University Hospital RWTH, Aachen University, Aachen, Germany
- Department of Radiology and Nuclear Medicine, Maastricht University Medical Center (MUMC+), Maastricht, The Netherland
| | - Inez Myin-Germeys
- Department of Neuroscience, Center for Contextual Psychiatry, KU Leuven – Leuven University, Leuven, Belgium
| | - Thérèse van Amelsvoort
- Department of Psychiatry & Neuropsychology, Maastricht University, Maastricht, The Netherlands
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5
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Zinkstok JR, Boot E, Bassett AS, Hiroi N, Butcher NJ, Vingerhoets C, Vorstman JAS, van Amelsvoort TAMJ. Neurobiological perspective of 22q11.2 deletion syndrome. Lancet Psychiatry 2019; 6:951-960. [PMID: 31395526 PMCID: PMC7008533 DOI: 10.1016/s2215-0366(19)30076-8] [Citation(s) in RCA: 58] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/16/2019] [Revised: 02/26/2019] [Accepted: 02/26/2019] [Indexed: 12/20/2022]
Abstract
22q11.2 deletion syndrome is characterised by a well defined microdeletion that is associated with a high risk of neuropsychiatric disorders, including intellectual disability, schizophrenia, attention-deficit hyperactivity disorder, autism spectrum disorder, anxiety disorders, seizures and epilepsy, and early-onset Parkinson's disease. Preclinical and clinical data reveal substantial variability of the neuropsychiatric phenotype despite the shared underlying deletion in this genetic model. Factors that might explain this variability include genetic background effects, additional rare pathogenic variants, and potential regulatory functions of some genes in the 22q11.2 deletion region. These factors might also be relevant to the pathophysiology of these neuropsychiatric disorders in the general population. We review studies that might provide insight into pathophysiological mechanisms underlying the expression of neuropsychiatric disorders in 22q11.2 deletion syndrome, and potential implications for these common disorders in the general (non-deleted) population. The recurrent hemizygous 22q11.2 deletion, associated with 22q11.2 deletion syndrome, has attracted attention as a genetic model for common neuropsychiatric disorders because of its association with substantially increased risk of such disorders.1 Studying such a model has many advantages. First, 22q11.2 deletion has been genetically well characterised.2 Second, most genes present in the region typically deleted at the 22q11.2 locus are expressed in the brain.3-5 Third, genetic diagnosis might be made early in life, long before recognisable neuropsychiatric disorders have emerged. Thus, this genetic condition offers a unique opportunity for early intervention, and monitoring individuals with 22q11.2 deletion syndrome throughout life could provide important information on factors contributing to disease risk and protection. Despite the commonly deleted region being shared by about 90% of individuals with 22q11.2 deletion syndrome, neuropsychiatric outcomes are highly variable between individuals and across the lifespan. A clear link remains to be established between genotype and phenotype.3,5 In this Review, we summarise preclinical and clinical studies investigating biological mechanisms in 22q11.2 deletion syndrome, with a focus on those that might provide insight into mechanisms underlying neuropsychiatric disorders in 22q11.2 deletion syndrome and in the general population.
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Affiliation(s)
- Janneke R Zinkstok
- Department of Psychiatry and Brain Center, University Medical Center, Utrecht, Netherlands.
| | - Erik Boot
- 's Heeren Loo Zorggroep, Amersfoort, Netherlands; The Dalglish Family 22q Clinic for Adults with 22q11.2 Deletion Syndrome, University Health Network, Toronto, ON, Canada; Department of Psychiatry & Neuropsychology, Maastricht University, Maastricht, Netherlands; Department of Radiology and Nuclear Medicine, Amsterdam University Medical Center, Amsterdam, Netherlands
| | - Anne S Bassett
- The Dalglish Family 22q Clinic for Adults with 22q11.2 Deletion Syndrome, University Health Network, Toronto, ON, Canada; Clinical Genetics Research Program, Centre for Addiction and Mental Health, Toronto, ON, Canada; Department of Psychiatry, University of Toronto, Toronto, ON, Canada; Campbell Family Mental Health Research Institute, Toronto, ON, Canada; Division of Cardiology & Toronto General Hospital Research Institute, University Health Network, Toronto, ON, Canada
| | - Noboru Hiroi
- Department of Pharmacology, Department of Cellular and Integrative Physiology, Department of Cell Systems and Anatomy, and Department of Psychiatry, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
| | - Nancy J Butcher
- Child Health Evaluative Sciences, The Hospital for Sick Children Research Institute, Toronto, ON, Canada
| | - Claudia Vingerhoets
- Department of Psychiatry & Neuropsychology, Maastricht University, Maastricht, Netherlands; Department of Radiology and Nuclear Medicine, Amsterdam University Medical Center, Amsterdam, Netherlands
| | - Jacob A S Vorstman
- Sick Children Research Institute, Genetics & Genome Biology Program, Toronto, ON, Canada
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6
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van Duin EDA, Vaessen T, Kasanova Z, Viechtbauer W, Reininghaus U, Saalbrink P, Vingerhoets C, Hernaus D, Booij J, Swillen A, Vorstman J, van Amelsvoort T, Myin-Germeys I. Lower cortisol levels and attenuated cortisol reactivity to daily-life stressors in adults with 22q11.2 deletion syndrome. Psychoneuroendocrinology 2019; 106:85-94. [PMID: 30959234 DOI: 10.1016/j.psyneuen.2019.03.023] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Revised: 01/25/2019] [Accepted: 03/21/2019] [Indexed: 12/13/2022]
Abstract
BACKGROUND 22q11.2 deletion syndrome (22q11DS) is a genetic disorder associated with neurodevelopmental, anxiety and mood disorders, as well as an increased risk for developing psychosis. Cortisol levels and stress reactivity reflect hypothalamic-pituitary-adrenal (HPA)-axis activity, and are believed to be altered in individuals that often experience daily-life stress, depression, and psychotic symptoms. However, it is unknown whether individuals with 22q11DS display an altered stress reactivity. METHODS We included 27 adults with 22q11DS (mean age: 34.1 years, 67% female) and 24 age and sex-matched healthy controls (HC; mean age: 39.9 years, 71% female) into an experience sampling study. Throughout 6 consecutive days, we measured participants' subjective stress related to current activity and at the same time collected salivary cortisol samples. Multilevel regression models were used to analyze cortisol reactivity to activity-related stress. RESULTS Diurnal cortisol levels were significantly lower in the 22q11DS group compared to HCs (B=-1.03, p < 0.001). 22q11DS adults displayed significantly attenuated cortisol reactivity to activity-related stress compared to HCs (B = -0.04, p = 0.026). Post-hoc exploratory analysis revealed that these results were independent from 22q11DS psychiatric diagnosis or medication use. CONCLUSION These results indicate that adults with 22q11DS have lower cortisol levels and attenuated cortisol response to daily stress, possibly resulting from an increased sensitization of the HPA-axis. This suggests that alterations in HPA-axis functioning, previously reported in several psychiatric disorders including post-traumatic stress disorder (PTSD), psychotic disorder, and mood disorder, also appear to be present in adults with 22q11DS.
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Affiliation(s)
- Esther D A van Duin
- Department of Psychiatry & Neuropsychology, Maastricht University, Maastricht, the Netherlands; Department of Radiology and Nuclear Medicine, Amsterdam University Medical Centers, location Academic Medical Center, Amsterdam, the Netherlands
| | - Thomas Vaessen
- Center for Contextual Psychiatry, Department of Neurosciences, KU Leuven, Leuven, Belgium.
| | - Zuzana Kasanova
- Center for Contextual Psychiatry, Department of Neurosciences, KU Leuven, Leuven, Belgium
| | - Wolfgang Viechtbauer
- Department of Psychiatry & Neuropsychology, Maastricht University, Maastricht, the Netherlands
| | - Ulrich Reininghaus
- Department of Psychiatry & Neuropsychology, Maastricht University, Maastricht, the Netherlands; Centre for Epidemiology and Public Health, Health Service and Population Research Department, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, UK
| | - Peter Saalbrink
- Department of Psychiatry & Neuropsychology, Maastricht University, Maastricht, the Netherlands
| | - Claudia Vingerhoets
- Department of Psychiatry & Neuropsychology, Maastricht University, Maastricht, the Netherlands; Department of Radiology and Nuclear Medicine, Amsterdam University Medical Centers, location Academic Medical Center, Amsterdam, the Netherlands
| | - Dennis Hernaus
- Department of Psychiatry & Neuropsychology, Maastricht University, Maastricht, the Netherlands
| | - Jan Booij
- Department of Radiology and Nuclear Medicine, Amsterdam University Medical Centers, location Academic Medical Center, Amsterdam, the Netherlands
| | - Ann Swillen
- Department of Human Genetics, KU Leuven - Leuven University, Leuven, Belgium; Center for Human Genetics, Hospital Gasthuisberg, Leuven, Belgium
| | - Jacob Vorstman
- Department of Psychiatry, The Hospital for Sick Children and University of Toronto, Toronto, ON, Canada; Program in Genetics and Genome Biology, Research Institute, The Hospital for Sick Children, Toronto, ON, Canada
| | - Thérèse van Amelsvoort
- Department of Psychiatry & Neuropsychology, Maastricht University, Maastricht, the Netherlands
| | - Inez Myin-Germeys
- Center for Contextual Psychiatry, Department of Neurosciences, KU Leuven, Leuven, Belgium
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7
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Sagud M, Tudor L, Uzun S, Perkovic MN, Zivkovic M, Konjevod M, Kozumplik O, Vuksan Cusa B, Svob Strac D, Rados I, Mimica N, Mihaljevic Peles A, Nedic Erjavec G, Pivac N. Haplotypic and Genotypic Association of Catechol- O-Methyltransferase rs4680 and rs4818 Polymorphisms and Treatment Resistance in Schizophrenia. Front Pharmacol 2018; 9:705. [PMID: 30018555 PMCID: PMC6037851 DOI: 10.3389/fphar.2018.00705] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Accepted: 06/11/2018] [Indexed: 12/12/2022] Open
Abstract
Treatment-resistant schizophrenia (TRS) continues to be a challenge. It was related to different factors, including alterations in the activity of brain dopaminergic system, which could be influenced by the dopamine-degrading enzyme, catechol-O-methyltransferase (COMT). Variants of the COMT gene have been extensively studied as risk factors for schizophrenia; however, their association with TRS has been poorly investigated. The aim of the present study was to determine the haplotypic and genotypic association of COMT rs4680 and rs4818 polymorphisms with the presence of TRS. Overall, 931 Caucasian patients diagnosed with schizophrenia (386 females and 545 males) were included, while 270 participants met the criteria for TRS. In males, no significant haplotypic and genotypic associations between COMT rs4680 and rs4818 polymorphisms and TRS were detected. However, genotypic analyses demonstrated higher frequency of COMT rs4680 AA genotype carriers compared to G-allele carriers (p = 0.033) and higher frequency of COMT rs4818 CC genotype carriers than G-allele carriers (p = 0.014) in females with TRS. Haplotype analyses confirmed that the presence of the G allele in females was associated with lower risk of TRS. In women with TRS, the high activity G-G/G-G haplotype was rare, while carriers of other haplotypes were overrepresented (p = 0.009). Such associations of COMT rs4680 and rs4818 high-activity (G variants), as well as G-G/G-G haplotype, with the lower risk of TRS in females, but not in males, suggest significant, but sex-specific influence of COMT variants on the development of treatment-resistance in patients with schizophrenia. However, due to relatively low number of females, those findings require replication in a larger sample.
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Affiliation(s)
- Marina Sagud
- School of Medicine, University of Zagreb, Zagreb, Croatia.,Department of Psychiatry, University Hospital Centre Zagreb, Zagreb, Croatia
| | - Lucija Tudor
- Laboratory for Molecular Neuropsychiatry, Division of Molecular Medicine, Rudjer Boskovic Institute, Zagreb, Croatia
| | - Suzana Uzun
- Department of Biological Psychiatry and Psychogeriatrics, University Psychiatric Hospital Vrapce, Zagreb, Croatia.,School of Medicine, Josip Juraj Strossmayer University of Osijek, Osijek, Croatia
| | - Matea Nikolac Perkovic
- Laboratory for Molecular Neuropsychiatry, Division of Molecular Medicine, Rudjer Boskovic Institute, Zagreb, Croatia
| | - Maja Zivkovic
- Department of Integrative Psychiatry, University Psychiatric Hospital Vrapce, Zagreb, Croatia
| | - Marcela Konjevod
- Laboratory for Molecular Neuropsychiatry, Division of Molecular Medicine, Rudjer Boskovic Institute, Zagreb, Croatia
| | - Oliver Kozumplik
- Department of Biological Psychiatry and Psychogeriatrics, University Psychiatric Hospital Vrapce, Zagreb, Croatia.,School of Medicine, Josip Juraj Strossmayer University of Osijek, Osijek, Croatia
| | - Bjanka Vuksan Cusa
- School of Medicine, University of Zagreb, Zagreb, Croatia.,Department of Psychiatry, University Hospital Centre Zagreb, Zagreb, Croatia
| | - Dubravka Svob Strac
- Laboratory for Molecular Neuropsychiatry, Division of Molecular Medicine, Rudjer Boskovic Institute, Zagreb, Croatia
| | - Iva Rados
- Department of Psychological Medicine, University Hospital Centre Zagreb, Zagreb, Croatia
| | - Ninoslav Mimica
- School of Medicine, University of Zagreb, Zagreb, Croatia.,Department of Biological Psychiatry and Psychogeriatrics, University Psychiatric Hospital Vrapce, Zagreb, Croatia
| | - Alma Mihaljevic Peles
- School of Medicine, University of Zagreb, Zagreb, Croatia.,Department of Psychiatry, University Hospital Centre Zagreb, Zagreb, Croatia
| | - Gordana Nedic Erjavec
- Laboratory for Molecular Neuropsychiatry, Division of Molecular Medicine, Rudjer Boskovic Institute, Zagreb, Croatia
| | - Nela Pivac
- Laboratory for Molecular Neuropsychiatry, Division of Molecular Medicine, Rudjer Boskovic Institute, Zagreb, Croatia
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8
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van Duin EDA, Kasanova Z, Hernaus D, Ceccarini J, Heinzel A, Mottaghy F, Mohammadkhani-Shali S, Winz O, Frank M, Beck MCH, Booij J, Myin-Germeys I, van Amelsvoort T. Striatal dopamine release and impaired reinforcement learning in adults with 22q11.2 deletion syndrome. Eur Neuropsychopharmacol 2018; 28:732-742. [PMID: 29703646 DOI: 10.1016/j.euroneuro.2018.03.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/06/2017] [Revised: 02/16/2018] [Accepted: 03/02/2018] [Indexed: 01/09/2023]
Abstract
22q11.2 deletion syndrome (22q11DS) is a genetic disorder caused by a microdeletion on chromosome 22q11.2 and associated with an increased risk for developing psychosis. The catechol-O-methyltransferase (COMT) gene is located in the deleted region and involved in dopamine (DA) breakdown. Impaired reinforcement learning (RL) is a recurrent feature in psychosis and thought to be related to abnormal striatal DA function. This study aims to examine RL and the potential association with striatal DA-ergic neuromodulation in 22q11DS. Twelve non-psychotic adults with 22q11DS and 16 healthy controls (HC) were included. A dopamine D2/3 receptor [18F]fallypride positron emission tomography (PET) scan was acquired while participants performed a modified version of the probabilistic stimulus selection task. RL-task performance was significantly worse in 22q11DS compared to HC. There were no group difference in striatal nondisplaceable binding potential (BPND) and task-induced DA release. In HC, striatal task-induced DA release was positively associated with task performance, but no such relation was found in 22q11DS subjects. Moreover, higher caudate nucleus task-induced DA release was found in COMT Met hemizygotes relative to Val hemizygotes. This study is the first to show impairments in RL in 22q11DS. It suggests that potentially motivational impairments are not only present in psychosis, but also in this genetic high risk group. These deficits may be underlain by abnormal striatal task-induced DA release, perhaps as a consequence of COMT haplo-insufficiency.
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Affiliation(s)
- Esther D A van Duin
- Department of Psychiatry & Neuropsychology, Maastricht University, Maastricht, The Netherlands.
| | - Zuzana Kasanova
- Center for Contextual Psychiatry, Department of Neuroscience, KU Leuven - Leuven University, Leuven, Belgium
| | - Dennis Hernaus
- University of Maryland School of Medicine, Department of Psychiatry; Maryland Psychiatric Research Center, MD, USA
| | - Jenny Ceccarini
- Department of Nuclear Medicine and Molecular Imaging, Division of Imaging and Pathology, University Hospital Leuven, KU Leuven, Belgium
| | - Alexander Heinzel
- Department of Nuclear Medicine, University Hospital RWTH Aachen University, Germany
| | - Felix Mottaghy
- Department of Nuclear Medicine, University Hospital RWTH Aachen University, Germany; Department of Radiology and Nuclear Medicine, Maastricht University Medical Center (MUMC+), Maastricht, The Netherlands
| | | | - Oliver Winz
- Department of Nuclear Medicine, University Hospital RWTH Aachen University, Germany
| | - Michael Frank
- Department of Cognitive, Linguistic and Psychological Sciences, Brown University, Providence, USA
| | - Merrit C H Beck
- Department of Psychiatry & Neuropsychology, Maastricht University, Maastricht, The Netherlands
| | - Jan Booij
- Department of Radiology and Nuclear Medicine, Academic Medical Center Amsterdam, The Netherlands
| | - Inez Myin-Germeys
- Center for Contextual Psychiatry, Department of Neuroscience, KU Leuven - Leuven University, Leuven, Belgium
| | - Thérèse van Amelsvoort
- Department of Psychiatry & Neuropsychology, Maastricht University, Maastricht, The Netherlands
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9
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Vingerhoets C, Bloemen OJN, Boot E, Bakker G, de Koning MB, da Silva Alves F, Booij J, van Amelsvoort TAMJ. Dopamine in high-risk populations: A comparison of subjects with 22q11.2 deletion syndrome and subjects at ultra high-risk for psychosis. Psychiatry Res Neuroimaging 2018; 272:65-70. [PMID: 29174435 DOI: 10.1016/j.pscychresns.2017.11.014] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/25/2017] [Revised: 10/06/2017] [Accepted: 11/17/2017] [Indexed: 10/18/2022]
Abstract
Striatal dopamine (DA) dysfunction has been consistently reported in psychotic disorders. Differences and similarities in the pathogenesis between populations at clinical and genetic risk for developing psychosis are yet to be established. Here we explored markers of dopamine (DA) function in subjects meeting clinically ultra-high risk criteria for psychosis (UHR) and in subjects with 22q11.2 deletion syndrome (22q11DS), a genetic condition associated with significant risk for developing psychotic disorders. Single Photon Emission Computed Tomography (SPECT) with 123I-labelled iodobenzamide ([123I]IBZM) was used to measure striatal DA D2/3 receptor binding potential (D2R BPND). Also, peripheral DAergic markers were assessed in serum and urine (plasma prolactin (pPRL), plasma homovanillic acid (pHVA) and urine DA(uDA)). No significant difference in striatal D2R BPND was found between UHR and 22q11DS subjects. Compared to UHR subjects, pPRL and pHVA were lower and uDA levels were higher in the 22q11DS subjects. However, after correcting for age and gender, only pPRL as significantly lower in the 22q11DS patients. These results may suggest that there are differences in DAergic markers between subjects with UHR and with 22q11DS that may reflect differences in the pathways to psychosis. However, bigger samples are needed to replicate these findings.
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Affiliation(s)
- Claudia Vingerhoets
- Maastricht University, Department of Psychiatry and Psychology, Maastricht, The Netherlands; Academic Medical Center, Department of Nuclear Medicine, Amsterdam, The Netherlands.
| | - Oswald J N Bloemen
- Maastricht University, Department of Psychiatry and Psychology, Maastricht, The Netherlands; GGZ Centraal, Center for Mental Health Care Innova, Amersfoort, The Netherlands
| | - Erik Boot
- Academic Medical Center, Department of Nuclear Medicine, Amsterdam, The Netherlands; The Dalglish Family 22q Clinic, Toronto, Ontario, Canada
| | - Geor Bakker
- Maastricht University, Department of Psychiatry and Psychology, Maastricht, The Netherlands; Academic Medical Center, Department of Nuclear Medicine, Amsterdam, The Netherlands
| | - Mariken B de Koning
- Academic Medical Center, Department of Psychiatry, Amsterdam, The Netherlands
| | | | - Jan Booij
- Academic Medical Center, Department of Nuclear Medicine, Amsterdam, The Netherlands
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van Duin EDA, Goossens L, Hernaus D, da Silva Alves F, Schmitz N, Schruers K, van Amelsvoort T. Neural correlates of reward processing in adults with 22q11 deletion syndrome. J Neurodev Disord 2016; 8:25. [PMID: 27429661 PMCID: PMC4946156 DOI: 10.1186/s11689-016-9158-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/25/2015] [Accepted: 07/05/2016] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND 22q11.2 deletion syndrome (22q11DS) is caused by a microdeletion on chromosome 22q11.2 and associated with an increased risk to develop psychosis. The gene coding for catechol-O-methyl-transferase (COMT) is located at the deleted region, resulting in disrupted dopaminergic neurotransmission in 22q11DS, which may contribute to the increased vulnerability for psychosis. A dysfunctional motivational reward system is considered one of the salient features in psychosis and thought to be related to abnormal dopaminergic neurotransmission. The functional anatomy of the brain reward circuitry has not yet been investigated in 22q11DS. METHODS This study aims to investigate neural activity during anticipation of reward and loss in adult patients with 22q11DS. We measured blood-oxygen-level dependent (BOLD) activity in 16 patients with 22q11DS and 12 healthy controls during a monetary incentive delay task using a 3T Philips Intera MRI system. Data were analysed using SPM8. RESULTS During anticipation of reward, the 22q11DS group alone displayed significant activation in bilateral middle frontal and temporal brain regions. Compared to healthy controls, significantly less activation in bilateral cingulate gyrus extending to premotor, primary motor and somatosensory areas was found. During anticipation of loss, the 22q11DS group displayed activity in the left middle frontal gyrus and anterior cingulate cortex, and relative to controls, they showed reduced brain activation in bilateral (pre)cuneus and left posterior cingulate. Within the 22q11DS group, COMT Val hemizygotes displayed more activation compared to Met hemizygotes in right posterior cingulate and bilateral parietal regions during anticipation of reward. During anticipation of loss, COMT Met hemizygotes compared to Val hemizygotes showed more activation in bilateral insula, striatum and left anterior cingulate. CONCLUSIONS This is the first study to investigate reward processing in 22q11DS. Our preliminary results suggest that people with 22q11DS engage a fronto-temporal neural network. Compared to healthy controls, people with 22q11DS primarily displayed reduced activity in medial frontal regions during reward anticipation. COMT hemizygosity affects responsivity of the reward system in this condition. Alterations in reward processing partly underlain by the dopamine system may play a role in susceptibility for psychosis in 22q11DS.
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Affiliation(s)
- Esther D. A. van Duin
- />Department of Psychiatry and Psychology, Maastricht University, Maastricht, The Netherlands
| | - Liesbet Goossens
- />Department of Psychiatry and Psychology, Maastricht University, Maastricht, The Netherlands
| | - Dennis Hernaus
- />Department of Psychiatry and Psychology, Maastricht University, Maastricht, The Netherlands
| | - Fabiana da Silva Alves
- />Department of Psychiatry, Academic Medical Centre Amsterdam, Amsterdam, The Netherlands
| | - Nicole Schmitz
- />Department of Psychiatry, Academic Medical Centre Amsterdam, Amsterdam, The Netherlands
| | - Koen Schruers
- />Department of Psychiatry and Psychology, Maastricht University, Maastricht, The Netherlands
| | - Therese van Amelsvoort
- />Department of Psychiatry and Psychology, Maastricht University, Maastricht, The Netherlands
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Genetic variation and dopamine D2 receptor availability: a systematic review and meta-analysis of human in vivo molecular imaging studies. Transl Psychiatry 2016; 6:e747. [PMID: 26926883 PMCID: PMC4872447 DOI: 10.1038/tp.2016.22] [Citation(s) in RCA: 75] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/27/2015] [Revised: 01/22/2015] [Accepted: 01/25/2016] [Indexed: 12/21/2022] Open
Abstract
The D2 dopamine receptor mediates neuropsychiatric symptoms and is a target of pharmacotherapy. Inter-individual variation of D2 receptor density is thought to influence disease risk and pharmacological response. Numerous molecular imaging studies have tested whether common genetic variants influence D2 receptor binding potential (BP) in humans, but demonstration of robust effects has been limited by small sample sizes. We performed a systematic search of published human in vivo molecular imaging studies to estimate effect sizes of common genetic variants on striatal D2 receptor BP. We identified 21 studies examining 19 variants in 11 genes. The most commonly studied variant was a single-nucleotide polymorphism in ANKK1 (rs1800497, Glu713Lys, also called 'Taq1A'). Fixed- and random-effects meta-analyses of this variant (5 studies, 194 subjects total) revealed that striatal BP was significantly and robustly lower among carriers of the minor allele (Lys713) relative to major allele homozygotes. The weighted standardized mean difference was -0.57 under the fixed-effect model (95% confidence interval=(-0.87, -0.27), P=0.0002). The normal relationship between rs1800497 and BP was not apparent among subjects with neuropsychiatric diseases. Significant associations with baseline striatal D2 receptor BP have been reported for four DRD2 variants (rs1079597, rs1076560, rs6277 and rs1799732) and a PER2 repeat polymorphism, but none have yet been tested in more than two independent samples. Our findings resolve apparent discrepancies in the literature and establish that rs1800497 robustly influences striatal D2 receptor availability. This genetic variant is likely to contribute to important individual differences in human striatal function, neuropsychiatric disease risk and pharmacological response.
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12
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de Koning MB, van Duin EDA, Boot E, Bloemen OJN, Bakker JA, Abel KM, van Amelsvoort TAMJ. PRODH rs450046 and proline x COMT Val¹⁵⁸ Met interaction effects on intelligence and startle in adults with 22q11 deletion syndrome. Psychopharmacology (Berl) 2015; 232:3111-22. [PMID: 26068888 DOI: 10.1007/s00213-015-3971-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Accepted: 05/04/2015] [Indexed: 11/29/2022]
Abstract
RATIONALE 22q11 deletion syndrome (22q11DS) is associated with an increased risk for psychotic disorders, suggesting a relationship between genotypes and the pathophysiology of psychotic disorders. Two genes in the deleted region, catechol-O-methyl-transferase (COMT) and proline dehydrogenase (oxidase) 1 (PRODH), contain polymorphisms associated with neuropsychiatric phenotypes. OBJECTIVES Here, we explored the association between polymorphisms and full-scale intelligence (FSIQ), startle reactivity (SR) and prepulse inhibition (PPI) in adults with 22q11DS. METHODS Forty-five adults with 22q11DS were genotyped for PRODH rs450046, rs372055 and COMT Val(158)Met. Plasma proline levels, FSIQ, SR and PPI were measured. RESULTS Thirty-five percent of the subjects were hyperprolinemic with a median proline value of 456 μmol/L. C allele carriers of PRODH rs450046 had a lower FSIQ compared to T allele carriers, indicating the C allele to be a risk allele (C allele: mean FSIQ 60.2 (sd 8.7); T allele: mean FSIQ 73.7 (sd 11.5); F 1,43 = 7.59; p = 0.009; partial η (2) = 0.15). A significant interaction effect of proline levels and COMT Val(158)Met genotype was found for SR (F 1,16 = 7.9; p = 0.01; partial η (2) = 0.33), but not for PPI and FSIQ. In subjects with hyperprolinemia, the COMT Val(158)Met genotype effect on SR was stronger than in subjects with normal proline levels. CONCLUSIONS Overall, these data provide further evidence for the risk effect of elevated proline levels combined with the COMT Met allele and support the possibilities of using 22q11DS as a model to investigate genotype effects on psychiatric disorders.
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Affiliation(s)
- Mariken B de Koning
- Arkin Mental Health Care, Baron G.A. Tindalstraat 27, 1019 TS, Amsterdam, The Netherlands,
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13
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Evers LJM, van Amelsvoort TAMJ, Candel MJJM, Boer H, Engelen JJM, Curfs LMG. Psychopathology in adults with 22q11 deletion syndrome and moderate and severe intellectual disability. JOURNAL OF INTELLECTUAL DISABILITY RESEARCH : JIDR 2014; 58:915-925. [PMID: 24528781 DOI: 10.1111/jir.12117] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 12/12/2013] [Indexed: 06/03/2023]
Abstract
BACKGROUND 22q11 deletion syndrome (22q11DS) is associated with mild or borderline intellectual disability (ID). There are hardly any reports on subjects with 22q11DS with moderate or severe ID, and therefore its behavioural and psychiatric characteristics are unknown. METHOD We describe behavioural and psychiatric characteristics of 33 adults with 22q11DS and a Full-Scale IQ (FSIQ) below 55. Participants were divided into two groups: one group having a FSIQ ≤ 55 caused by intellectual decline (n = 21) and one group with a FSIQ ≤ 55 who had always functioned at this level (n = 12). RESULTS High scores on psychopathology sub-scales were found for both subgroups. 22q11DS patients with intellectual decline showed higher rates of co-morbid psychopathology, particularly psychosis. Furthermore, psychosis and intellectual decline were positive correlated. CONCLUSION This is the first report addressing adult patients with 22q11DS and moderate to severe ID. Overall we found high levels of psychopathology with higher scores of psychopathology in the intellectual decline group. Life time psychosis seems to be related to deterioration.
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Affiliation(s)
- L J M Evers
- MFCG, Koraalgroup, Heel, The Netherlands; Governor Kremers Centre, Maastricht University Medical Centre, Maastricht, The Netherlands
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Schreiner MJ, Lazaro MT, Jalbrzikowski M, Bearden CE. Converging levels of analysis on a genomic hotspot for psychosis: insights from 22q11.2 deletion syndrome. Neuropharmacology 2013; 68:157-73. [PMID: 23098994 PMCID: PMC3677073 DOI: 10.1016/j.neuropharm.2012.09.012] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2012] [Revised: 09/04/2012] [Accepted: 09/17/2012] [Indexed: 10/27/2022]
Abstract
Schizophrenia is a devastating neurodevelopmental disorder that, despite extensive research, still poses a considerable challenge to attempts to unravel its heterogeneity, and the complex biochemical mechanisms by which it arises. While the majority of cases are of unknown etiology, accumulating evidence suggests that rare genetic mutations, such as 22q11.2 Deletion Syndrome (22qDS), can play a significant role in predisposition to the illness. Up to 25% of individuals with 22qDS eventually develop schizophrenia; conversely, this deletion is estimated to account for 1-2% of schizophrenia cases overall. This locus of Chromosome 22q11.2 contains genes that encode for proteins and enzymes involved in regulating neurotransmission, neuronal development, myelination, microRNA processing, and post-translational protein modifications. As a consequence of the deletion, affected individuals exhibit cognitive dysfunction, structural and functional brain abnormalities, and neurodevelopmental anomalies that parallel many of the phenotypic characteristics of schizophrenia. As an illustration of the value of rare, highly penetrant genetic subtypes for elucidating pathological mechanisms of complex neuropsychiatric disorders, we provide here an overview of the cellular, network, and systems-level anomalies found in 22qDS, and review the intriguing evidence for this disorder's association with schizophrenia. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.
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Affiliation(s)
- Matthew J. Schreiner
- Interdepartmental Neuroscience Program, University of California, Los Angeles, USA
| | - Maria T. Lazaro
- Interdepartmental Neuroscience Program, University of California, Los Angeles, USA
| | | | - Carrie E. Bearden
- Department of Psychology, University of California, Los Angeles, USA
- Department of Psychiatry and Biobehavioral Sciences, Semel Institute for Neuroscience and Human Behavior, University of California, Los Angeles, USA
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de Koning MB, Boot E, Bloemen OJN, van Duin EDA, Abel KM, de Haan L, Linszen DH, van Amelsvoort TAMJ. Startle reactivity and prepulse inhibition of the acoustic startle response are modulated by catechol-O-methyl-transferase Val(158) Met polymorphism in adults with 22q11 deletion syndrome. J Psychopharmacol 2012; 26:1548-60. [PMID: 22952320 DOI: 10.1177/0269881112456610] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
22q11 deletion syndrome (22q11DS) is a genetic disorder caused by a microdeletion on chromosome 22, which includes the gene coding for catechol-O-methyl-transferase (COMT). High dopamine (DA) levels due to COMT haplo-insufficiency may be associated with the increased risk of developing schizophrenia in adults with 22q11DS. Reduced prepulse inhibition (PPI) of the acoustic startle response has been associated with schizophrenia and with disrupted DAergic transmission in the prefrontal cortex (PFC). COMT Val(158)Met polymorphism has been shown to influence PPI. We report the first study in adults with 22q11DS to examine PPI of the acoustic startle response and its modulation by COMT Val(158)Met polymorphism. Startle reactivity (SR) and PPI of the acoustic startle response were measured in 23 adults with 22q11DS and 21 healthy controls. 22q11DS subjects were genotyped for the functional COMT Val(158)Met polymorphism. 22q11DS Met hemizygotes showed reduced SR and PPI compared with 22q11DS Val hemizygotes. The effect of COMT Val(158)Met polymorphism on PPI was no longer significant when controlling for baseline SR. Met hemizygosity in 22q11DS is associated with reduced SR and influences PPI indirectly. Decreased PFC functioning following excessive PFC DA levels may be one of the mechanisms by which the Met genotype in 22q11DS disrupts SR.
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Affiliation(s)
- Mariken B de Koning
- Department of Psychiatry, Academic Medical Centre, University of Amsterdam, Amsterdam, the Netherlands.
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Abstract
The results of imaging studies have played an important role in the formulation of hypotheses regarding the etiology of psychosis and schizophrenia, as well as in our understanding of the mechanisms of action of antipsychotics. Since this volume is primarily directed to molecular aspects of psychosis and antipsychotics, only the results of molecular imaging techniques addressing these topics will be discussed here.One of the most consistent findings of molecular imaging studies in schizophrenia is an increased uptake of DOPA in the striatum, which may be interpreted as an increased synthesis of L-DOPA. Also, several studies reported an increased release of dopamine induced by amphetamine in schizophrenia patients. These findings played an important role in reformulating the dopamine hypothesis of schizophrenia. To study the roles of the neurotransmitters γ-aminobutyric acid (GABA) and glutamate in schizophrenia, SPECT as well as MR spectroscopy have been used. The results of preliminary SPECT studies are consistent with the hypothesis of NMDA receptor dysfunction in schizophrenia. Regarding the GABA deficit hypothesis of schizophrenia, imaging results are inconsistent. No changes in serotonin transporters were demonstrated in imaging studies in schizophrenia, but studies of several serotonin receptors showed conflicting results. The lack of selective radiotracers for muscarinic receptors may have hampered examination of this system in schizophrenia as well as its role in the induction of side effects of antipsychotics. Interestingly, preliminary molecular imaging studies on the cannabinoid-1 receptor and on neuroinflammatory processes in schizophrenia have recently been published. Finally, a substantial number of PET/SPECT studies have examined the occupancy of receptors by antipsychotics and an increasing number of studies is now focusing on the effects of these drugs using techniques like spectroscopy and pharmacological MRI.
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