Personal View A major genetic cause for psychotic illness: Mechanistic insights from Prader-Willi Syndrome Author information *Lucie C.S. Aman, MSc, Department of Psychiatry, University of Cambridge Katherine E. Manning, PhD, Department of Psychiatry, University of Cambridge Joyce E. Whittington, PhD, Department of Psychiatry, University of Cambridge Anthony J. Holland, FRCPsych, Emeritus Professor, Department of Psychiatry, University of Cambridge; National Institute for Health Research (NIHR) Collaborations for Leadership in Applied Health Research and Care (CLAHRC) East of England, Cambridge, CB2 8AH, UK; Cambridgeshire and Peterborough Mental Health Services (NHS) Foundation Trust, Cambridge, CB21 5EF Corresponding author: Lucie Aman CIDDRG 18b Trumpington Road Cambridge CB2 8AH UK +44122365210 lcsa2@medschl.cam.ac.uk Abstract The major psychotic illnesses of schizophrenia and bipolar disorder are common, severe and disabling disorders and difficult to research. Using Prader-Willi Syndrome (PWS) as an example, we argue that genetically determined neurodevelopmental disorders associated with a high risk of psychotic illness can provide a unique window into genetic mechanisms and associated neural pathways that are etiologically important. Whilst people with PWS, regardless of the genetic sub-type, share a similar profile of non-psychotic psychopathology and problem behaviors, there are markedly different prevalence rates of psychotic illness, with higher rates in those with PWS due to chromosome 15 maternal uniparental disomy (mUPD) compared with those with PWS due to 15q11-13 deletions of paternal origin (delPWS). Based on this observation and differences between genetic sub-types at the neural level, we hypothesize that the combined effects of the absent expression of specific maternally imprinted genes at 15q11-13 and excess expression of paternally imprinted/ maternally expressed genes on chromosome 15 impact on the GABA/glutamatergic pathways and associated neural networks, underpinning mood regulation and sensory processing and resulting in psychotic illness. Given that genome wide association studies have identified loci close to the PWS critical chromosomal region that confers an increased risk for schizophrenia and affective disorder, findings from the study of psychosis in PWS should also be systematically investigated in the typically developing population. Key words: Prader-Willi syndrome; psychosis; chromosome 15; UBE3A; GABA/glutamate balance Abbreviations α7AChR: the α7-N-acetylcholine receptor delPWS: deletion genetic subtype of Prader-Willi Syndrome ERP: Event Related Potentials IC: Imprinting Center Defect mUPD: Maternal Uniparental Disomy (of chromosome 15 in this article) PWS: Prader-Willi Syndrome snoRNA: Small Nucleolar RNA Introduction If new treatments are to be developed for psychotic illness, neural pathways amenable to modification need to be identified. This is a major challenge because of etiological heterogeneity and limitations inherent in undertaking in-vivo studies of cerebral dysfunction and pathology. Genome-wide association studies have identified genetic loci, each conferring a small increase in risk for schizophrenia and/or bipolar disorder1. Furthermore, schizophrenia is now considered developmental in origin with subtle impairments in social functioning being apparent during early development2. Prader-Willi Syndrome (PWS) is a genetically determined neurodevelopmental disorder associated with the risk of specific psychopathology, including psychotic illness. We propose that this close link offers the possibility for studying the influence of a known genotype on atypical developmental trajectories and on the later emergence of psychopathologypsychotic disorder. Specifically, we argue that marked differences in the risk for psychosis between the genetic types of PWS provides a unique window for hypotheses development and testing at genetic and neural levels that in turn may lead to therapeutic insights. Prader-Willi Syndrome (PWS) PWS is a relatively rare and complex multi-system disorder with a birth incidence estimated between 1 in 25,000-29,000 live births3–6. It is characterized by initial hypotonia and failure to thrive, followed by severe hyperphagia in early childhood, and short stature and disrupted sexual development, a consequence of relative growth and sex hormone deficiencies. PWS results from the absence of, or failure of expression of, alleles of paternal origin of maternally imprinted gene(s) located at the chromosomal locus 15q11-13. This arises as a consequence of one the following: q11-13 de novo deletion on the chromosome 15 of paternal origin (delPWS; ca. 70%), chromosome 15 maternal uniparental disomy (mUPD; ca. 25%), an imprinting center defect (IC; ca. 3-5%), or an unbalanced translocation of chromosome 15 (<5%) (See figure 1 for details). Phenotypic differences between the different genetic types of PWS may be accounted for either by hemizygosity of non-imprinted genes at 15q11-13 in those with delPWS or gene dosage differences between mUPD and delPWS of other paternally or maternally imprinted genes on chromosome 15. For a full review of the genetics of PWS see Bittel and Butler, 20057. Psychotic illness in genetic types of PWS An increased propensity to temper outbursts, mood lability, repetitive and ritualistic behaviors, and severe skin picking8–10 are characteristic of both main genetic types of PWS. In contrast, for psychosis and for autism spectrum disorder there is a markedly higher prevalence rate in those with mUPD compared to delPWS11–1411. Descriptions of psychotic illness affecting people with PWS were published shortly after the syndrome was described by Prader et al in 195615. However, Boer et al., 200217 first identified the markedly different rates of psychosis within a specific genetic type of PWS, reporting that 62% of those with mUPD had a history of symptoms indicative of psychotic illness. This increased to 100% in adults over 28 years of age. Only 8% of all adults with delPWS had experienced psychosis (11% over 28 years), a rate only slightly above that in the wider population of adults with intellectual disabilities18. Subsequent studies have confirmed this observation: ~61.8% of those with mUPD/IC and only ~16.4% of those with delPWS/translocation in a further study in the UK12; 54.5% of those with mUPD/IC compared to ~13.2% with delPWS in a Dutch cohort19; and 50% of those with mUPD/IC aged over 13 years compared to 0% with delPWS/translocation in a study in Belgium3,20. The psychosis in PWS is atypical and difficult to classify within existing diagnostic taxonomies21,22. Common symptoms typically include heightened anxiety, motor disorders, confused states, hallucinations, persecutory delusions, altered sleep patterns and mood alterations. The clinical appearance is usually not fully consistent with specific psychotic disorders, but typically has an affective component23. Age of onset of psychosis varies, ranging between 8 and 40 years, but is generally during the teenage years or early adulthood,12,24 with the majority of studies reporting rapid onset18,20,25. On the basis of the observation that affective dysregulation is common regardless of the genetic cause of PWS but psychotic symptoms largely segregate with the mUPD genotype, Soni et al (2008)12 suggested a two-hit model to account for the differential rates of psychosis in PWS. She hypothesized that the genetics of PWS results, regardless of genetic type, in an increased propensity to affective disturbance with the ‘second-hit’, having a chromosome 15 mUPD, resulting in the markedly increased risk for psychosis. This would suggest that the increased propensity of those with mUPD to develop psychosis must be a combination of both the effects of the PWS genotype on neural development and circuits in the brain that serve mood regulation, as well as gene dosage effects from maternally expressed genes on chromosome 15, which result in aberrant functioning of neural circuits and in the emergence of abnormal mental experiences (see Manning and Holland, 2015 for review)26. Neuropsychological functioning in the main genetic types of PWS PWS, irrespective of genetic type, is associated with mild to moderate intellectual disability, with some differences in cognitive profiles between the types, with higher verbal IQ ability and a greater impairment in processing speed in those with mUPD4,27. In a study using Go/No-Go tasks and measurements of ERPs, people with mUPD were reported to have significantly decreased reaction times compared to those with delPWS and healthy controls, with deficits in both the N200 and P300 peaks related to early modality-specific inhibition and late general inhibition, respectively. Those with delPWS showed impairment only for N200 modulation28. A specific deficit in segregating human voices from a noisy background, and a failure to fully process sensory information before initiation of a behavioral response has also been reported in PWS29, again the deficit being greater in those with mUPD compared to delPWS. A recent study in children with PWS has found significantly reduced white matter microstructure in most of the major white matter tracks in people with PWS due to mUPD compared to delPWS, similar to those reported in people with schizophrenia or those at ultra-high risk for psychosis30. As described it is both these populations that also have been found to have impaired processing speed31–33. Freedman et al (1997) observed compromised P50 sensory gating in patients with schizophrenia as well as some of their unaffected relatives, suggesting a role for such impairments in the etiology of psychosis34. Thus, both impairments in auditory processing and processing speed have been found in people with schizophrenia, those at risk for psychosis, and in people with PWS due to mUPD. Candidate loci and genes of interest Chromosome 15 exhibits high variability with numerous polymorphisms and CNVs with pathogenic potential35 and rearrangements of chromosomal regions in or near 15q11-13, in particular those of maternal origin, have been reported. Case studies have described psychotic symptomatology in individuals with partial duplications of the maternal chromosome 1536,37. On a larger scale Ingason et al. (2011) reported maternally derived duplications of the PWS critical region in 0.05% of a large sample of patients (>7,500) with schizophrenia or schizoaffective disorder, but only in 0.007% of the unaffected control group. Isles et al. (2016) similarly observed a prevalence rate of 0.085% for maternally-derived duplications of 15q11-13 in a large sample of patients with schizophrenia (>28,000), also noting that 76% of patients with this duplication often showed additional learning or developmental difficulties38. In studies of PWS, Soni et al (2008) found that, where there were family members on the maternal but not paternal side with an affective disorder, this increased the likelihood that a person with delPWS would have a psychotic disorder. Thus, observations in PWS and in the general population indicate that the differential expression of both paternally and maternally imprinted genes on chromosome 15 may impact directly or indirectly on particular neural pathways and the risk for psychosis. We propose that the genes listed below are of interest, and hypothesize that GABA/glutamate circuits should be studied as potential therapeutic targets. UBE3A UBE3A,located at 15q11.2, encodes the E3-ubiquitine ligase (E6-AP)39 and is paternally imprinted in the brain only, and consequently, is overexpressed in those with PWS due to mUPD and IC defects40(McNamara and Isles, 2013). An antisense transcript (AST) is produced from the paternal chromosome 15 only, and in binding to the UBE3A gene on the paternal chromosome, inhibits its transcription. Thus, because of the absence of this AST, in those with PWS due to mUPD and IC defect UBE3A is overexpressed40. Noor et al., 201541 reported a family with a 125 kb 15q11.2 maternally inherited duplication encompassing only the UBE3A gene, resulting in increased gene expression, and segregating with developmental delay, anxiety, depression, OCD, schizophrenia and autism42. E6-AP is an enzyme that ubiquinates proteins that are degraded within the cell. Notably, E6-AP degrades P53, which itself activates the ring finger protein BERP, involved in GABA receptor trafficking43. Thus E6-AP negatively modulates GABA receptor activity. Altered GABAA receptors have been implicated in the GABAergic-dopaminergic interactions and dopaminergic abnormalities associated with the positive symptoms of schizophrenia44. E6-AP is also thought to interact with the cytoskeleton-associated protein, ARC, resulting in modification of the glutamatergic system45. E6-AP induces the internalization of the AMPA glutamate receptor, and increased expression of this gene in transgenic mice impairs glutamatergic transmission46,47. Such alterations of GABAergic and glutamatergic function have the potential to disrupt inhibitory/excitatory balance in the brain. CHRNA7 CHRNA7, located at 15q13.3, encodes a α7AChR subunit, which binds nicotine and acetylcholine with low affinity, and mediates fast signal transmission at synapses, possibly implicated in the reduced processing speed found in patients with schizophrenia31. It mostly acts at a presynaptic level, increasing permeability to cations affecting various neural networks, including facilitating the release of noradrenaline, serotonin, GABA, glutamate and dopamine48. At a postsynaptic level, α7AChR acts on phosphorylation and regulation of gene expression. Thus, the α7AChR is involved in many cascades and signalling pathways, with dysregulation likely to have widespread consequences. In most individuals, CHRNA7 is partially duplicated and forms a new chimeric gene, called CHRFAM7A, located at 15q13.32, and specific to humans49. CHRFAM7A mRNA and its product, dupα7, have been found both in the periphery and in the brain50, with levels of expression of CHRFAM7A in the brain 10 times lower than for CHRNA748 . However, even this low level of expression is likely to affect the α7 function. Dupα7 may act as a dominant negative modulator of CHRNA7 function; it can be incorporated as one of the 5 sub-units comprising the acetylcholine receptor, but does not result in a functional ion-channel, decreasing the efficiency of the receptor51. Whilst CHRNA7 is not imprinted, one of its transcription factors, P53, is regulated by UBE3A’s gene product E6-AP, with potential dysregulation consequent upon over-expression of UBE3A in mUPD. Many studies have linked polymorphisms of CHRNA7 and its related gene CHRFAM7A to schizophrenia, although this finding is not universal34,35,50,52–58. α7AChR is widely expressed in the brain, particularly in the hippocampus, thalamus and prefrontal cortex, regions known to be involved in the impaired cognitive processing seen in schizophrenia59. In addition to its role in synaptic transmission, α7AChR and dupα7 play an important role in modulating the immune system. Acetylcholine release by the vagus nerve activates α7AChR, encoded by CHRNA7, triggering acetylcholine release by T cells, finally activating α7AChR of macrophages, suppressing TNFα and antibody release from B cells and macrophages60. Dupα7, is particularly expressed in macrophages and may play a role in inflammatory responses51. It has been hypothesised that the immune system could play a major role in psychosis acting at numerous levels: First, the major histocompatibility complex is involved in many aspects of neural connectivity, synaptic plasticity, and excitatory-inhibitory balance61. Second, antibodies activity against NMDA receptors have been found in psychotic symptoms resulting from encephalitis and schizophrenia62. Lastly, there have been consistent reports of increased levels of pro-inflammatory cytokines and microglia inflammation associated with schizophrenia, involving brain inflammatory processes in psychosis63. In addition to its role in synaptic transmission, α7AChR plays an important role in modulating the immune system60, which has been shown to be over-activated in psychosis, with increased levels of pro-inflammatory cytokines and microglia inflammation associated with schizophrenia64. Acetylcholine release by the vagus nerve activates α7AChR, encoded by CHRNA7, triggering acetylcholine release by T cells, finally activating α7AChR of macrophages, suppressing TNFα and antibody release from B cells and macrophages60. GABRB3, GABRG3 and GABRA5 Three GABAA receptor sub-units are located at 15q12. There is some debate about the imprinting status of this cluster of genes, but it would appear they are not usually imprinted in the brain65. However, epigenetic modifications leading to monoallelic, or nearly monoallelic expression have been reported in several neurodevelopmental disorders. Such alterations have the potential to severely affect brain function65. Moreover, while equally expressed in controls a paternal expression bias of GABRB3 has been found in both disorders of partial monosomy of chromosome 15 - PWS and Angelman syndrome (AS)65. In the case of PWS, this results in reduced GABRB3 expression in both mUPD and delPWS, but this is more pronounced in delPWS. AS also shows reduced expression compared to control but sitting between the delPWS and mUPD levels, but does not show an increased risk of psychosis. This appears counterintuitive; however, Webb et al (2008) reported a duplication encompassing the GABRG3 gene on the maternal chromosome of individuals with delPWS who had developed psychosis. These observations suggest that there may be a particular level of GABRG3 expression that puts individuals at risk for psychosis, while more severely reduced GABRG3 may have different effects. Alternatively, it may be that reduced GABRG3 expression in PWS, whether delPWS or mUPD, results only in increased risk of psychosis when combined with the other genetic alterations, with potential effects on GABA and glutamate balance found in the mUPD genotype, thereby consistent with the 2-hit model of psychosis. One possibility is that the first hit in PWS is the absence of expression of SNORD 115, a snoRNA located in the PWS region and regulating the alternative splicing of the serotonin receptor 2c66. Both PWS main genetic types should have different isoforms of this receptor’s mRNA66. Differences in serotonin function could explain the increased propensity to affective disorders in PWS in general, given the large body of research implicating serotonin in mood disorders67. NECDIN NECDIN, encoded in the PWS region and associated with schizophrenia43, is related to both GABA and glutamate function. When present in the nucleus, NECDIN represses P53 transcriptional activity. DYSBINDIN-1, also associated with schizophrenia, segregates with NECDIN in the cytoplasm, preventing the repression of P53’s transcriptional activity. DYSBINDIN-1 is expressed in glutamatergic neurons, and its dysfunction has been associated with impaired glutamatergic transmission and schizophrenia68. The fact that NECDIN also promotes GABAergic neuronal differentiation69 could explain the increased susceptibility of people with PWS to psychiatric disorders. However, NECDIN is expressed in neither delPWS nor in mUPD. Therefore, like the GABAA receptor sub-units, the absence of NECDIN in PWS may lead to dysregulation of these systems ain both genetic types of PWS, which interacts with the abnormalities due to mUPD to greatly increase risk to psychosis. CYFIP1 CYFIP1 is also located at 15q11.2, and polymorphisms of this region have been associated with schizophrenia, although the role of parent of origin is not well explored70–72. CYFIP1 is involved in two major pathways involved in glutamate function73 (figure 2). Thus, as for UB3EA, this gene has a potential impact on inhibitory/excitatory balance. However, CYFIP1 is likely to be less pertinent than UBE3A in explaining the increased mUPD psychosis incidence, given its presumed biallelic expression. Nevertheless, alterations of CYFIP1 expression may exacerbate an already dysregulated system. Discussion Figure 2 seeks to integrate the above genetic, neural, and clinical observations, the model being based around the fundamental observation of the difference in prevalance rates of psychosis according to whether the cause of PWS is a 15q11-13 deletion of paternal origin or a chromosome 15 mUPD. We propose that several genes at or near the PWS region may be implicated in the development of psychosis but as many act on similar receptors or targets and are co-regulated it is difficult to isolate any individual gene. In addition to the direct effects of the GABAA receptor sub-unit genes on the GABAergic system, CYFIP1 has potential influence on glutamatergic signalling, while UBE3A, and its downstream interaction with CHRNA7 and the absence of NECDIN, may alter GABA, glutamate and dopamine. However, UBE3A appears to be the strongest candidate, given its over-expression in mUPD and interaction with multiple systems and genes of interest. Our hypothesis, illustrated in Figure 2, is that duplication of the UBE3A gene in mUPD leads to a cascade of effects via its direct and indirect interactions with other genes of interest and neurotransmitter systems, which alter the inhibitory/excitatory balance in the brain. The over-expression of UBE3A would act as a catalyser and potentiate small variations which, in turn, affect neurotransmitter systems that alone would have had little effect. UBE3A’s gene product, E6-AP, plays an indirect role in GABA receptor trafficking via its ubiquination of P53, and influences glutamatergic function and dopamine receptors via its regulation of dysbindin. E6-AP also acts on the glutamatergic system in decreasing the endocytosis of the AMPAR. Furthermore, P53 is also one of CHRNA7’s transcription factors, meaning that E6-AP may partially regulate CHRNA7’s activity. The α7AChR, encoded by CHRNA7, is known to influence GABAergic, dopaminergic, autonomic nervous system and inflammatory function. CHRNA7 and its duplicated homologue, CHRFAM7A, and linked to schizophrenia and the associated endophenotype of impaired sensory processing. Thus UBE3A over-expression and its interactions have the potential to disrupt inhibitory/excitatory balance in the brain, as well as acetylcholine and dopaminergic functions. Furthermore, genes encoding three GABAA receptor sub-units are also found at 15q12. While biallelically expressed in the general population, expression may differ in mUPD, with paternal expression bias of GABRG3 documented in PWS, meaning that levels of expression are reduced in both delPWS, where haploinsufficency was present, and in mUPD, since both alleles are of maternal origin65. When compounded by the further disruption of the inhibitory/excitatory function in mUPD, which results from over-expression of UBE3A, this predisposes the mUPD group within PWS to the development of psychosis. These imbalances impact on cognitive and sensory processing, causing the altered processing of information and the development of psychosis. Complementary lines of enquiry supporting the above hypothesis include observations on sensory processing and studies of glutamate and GABA balance. Sensory processing impairments, as well as the presence of positive symptoms of schizophrenia, have been linked to the excitatory/inhibitory balance in the brain, which is primarily regulated by glutamate and GABA: glutamate has an excitatory function when binding to the NMDA receptor (NMDAR) and/or the AMPA receptor (AMPAR), while GABA is inhibitory, and decarboxylation of glutamate results in GABA synthesis. Thus, these neurotransmitters are closely intertwined and a carefully maintained balance between the two appears essential. Dysregulation of both GABAergic and glutamatergic systems have been observed in schizophrenia74. Several markers of GABA metabolism have been reported to be altered in patients with schizophrenia, such as reduced levels of GAD 67, an enzyme that decarboxylates glutamate into GABA75 and lower magnetic resonance spectrography ratios of GABA/creatine in the medial prefrontal cortex74. NMDAR antagonists, which disrupt glutamate function, mimic symptoms of schizophrenia, whilst antibodies against the NMDAR have been found in first-episode psychosis patients later diagnosed with schizophrenia62, as well as in patients with autoimmune encephalitis presenting with psychotic symptoms76. NMDAR hypofunction reduces the excitation of inhibitory GABAergic interneurons, with a resultant disinhibition of glutamatergic pyramidal neurons, which may drive a hyperdopaminergic state that results in psychosis. We suggest that a subset of individuals in the general population who develop psychosis do so through similar mechanisms to those involved in the psychosis seen in people with PWS. Such models as proposed provide testable hypotheses and the potential for developing informed treatments that target the relevant disrupted brain pathways. Acknowledgments Recent research into PWS by our group has been supported by the UK Prader-Willi Syndrome Association, Addenbrooke’s Charitable Trust, the Foundation for Prader-Willi Research, and a donation from Sam’s Foundation. We are very grateful for their support. This review is part of a program of research into PWS, and we would like to thank all the people with PWS and their families for their help, without which this research would not be possible. AH is also supported by the Health Foundation and the NIHR CLAHRC for the East of England. We would also like to thank Dr Howard Ring for his feedback on this article. The views expressed are those of the authors and not necessarily those of NIHR, the NIHR CLAHRC or of the other funders. Financial disclosure The authors report no financial interests or other potential conflicts of interest. Authors contribution Conception of the work: AJH, KEM, LCSA Data collection (article database): LCSA Data analysis and interpretation: LCSA, KEM Drafting the article: LCSA, KEM Critical revision of the article: KEM AJH JEW Final approval: AJH KEM LCSA JEW Figure 1: Genetics of Prader-Willi syndrome FIGURE 1. Prader Willi syndrome (PWS) is a disorder of genomic imprinting resulting from absent paternal expression of maternally imprinted genes at chromosomal locus 15q11-13. This is caused by a de novo deletion on the paternal chromosome (delPWS; ca. 70%), maternal uniparental disomy (mUPD; ca. 25%), an imprinting center defect (IC; ca. 3-5%), or an unbalanced translocation of chromosome 15 (<5%). It is the absence of expression of one or more of these maternally imprinted genes that would appear to account for the core features of PWS common across all genetic types. From rare patients with PWS with microdeletions a 91-kb critical chromosomal region has been identified containing three non-coding genes including SNORD109A, SNORD116 and IPW77. However, it is long been argued, primarily on the basis of knockout mouse studies, that the wider PWS phenotype is a consequence of disruption of several maternally imprinted genes at that site and of their downstream pathways78. There are also significant phenotypic differences between the genetic types. These may be accounted for either by hemizygosity of non-imprinted genes at 15q11-13 in those with delPWS or gene dosage differences between mUPD and delPWS of other paternally or maternally imprinted genes on chromosome 15. 11 Figure 2: Proposed mechanisms and pathways affected by mUPD on chromosome 15 Figure 2 E6-AP, the gene product of UBE3A, which is overexpressed in mUPD, is the central and common factor for almost all pathways and symptoms. E6-AP degrades ARC to regulate excitatory signals (A1). ARC when activated by the action of glutamate on NMDA receptors (A2), increases the endocytosis of the AMPAR (A3). E6-AP plays also an indirect role in GABA receptor trafficking, negatively modulating their activity: E6-AP degrades P53 (A4), which itself activates the ring finger protein BERP (A5) involved in GABA receptor trafficking (A6). Thus E6-AP dysregulates both GABA (A7) and the glutamatergic systems (A8), disrupting excitatory/inhibitory balance in the brain (A9) and with downstream effects on dopamine (A10). Alterations in these neurotransmitter systems have been associated with the positive symptoms in schizophrenia (A11; A12), as well as the sensory processing (A13; A14) and cognitive endophenotypes (A15; A16). NECDIN, encoded in the PWS region, when present in the nucleus, represses P53 transcriptional activity (B1). When functional, DYSBINDIN-1 segregate NECDIN in the cytoplasm, preventing the repression of P53’s transcriptional activity (B2). DYSBINDIN-1 is expressed in glutamatergic neurons (B3), and DYSBINDIN-1 dysfunction has been associated with impaired glutamatergic transmission and schizophrenia. NECDIN also promotes GABAergic neurons differentiation. In addition, P53 is also known to be one of CHRNA7’s transcription factors, meaning that E6-AP is likely to regulate in part CHRNA7’s activity (C1). This is of interest because CHRNA7 and its duplicated homologue, CHRFAM7A, have been linked with schizophrenia and some endophenotypes, such as sensory processing deficits and cognitive symptoms. Moreover, activation of the α7ACh receptor is known to act on GABAergic, dopaminergic, and autonomic system and heart rate variability, as well as on inflammation. The product of CHRFAM7, DUPα7, acts as a dominant negative subunit when incorporated to the α7AChR (C2). The subunit α7, product from CHRNA7 is incorporated to the α7AChR (C3). The α7AChR is activated by acetylcholine (C4), and acts on dopamine (C5), GABA and glutamate (C4) functions. Polymorphisms of the α7AChR subunit have been associated with cognitive symptoms (C7), sensory processing symptoms (C8). B2 Additionally impacting on the GABA system in PWS are three GABAA receptor subunits at 15q 12 (D1). The GABA subunits are incorporated to form a GABAA receptor (D2). Whilst not typically imprinted, a paternal expression bias of one of these subunits, GABRB3, has been demonstrated in PWS, with reduced expression in both delPWS and mUPD. This may set a base level of GABAergic impairment in PWS, which is compounded in mUPD by the further dysregulation arising from overexpression of UBE3A. Finally, under the action of glutamate, CYFIP1 binds to elF4 (E1), forming a complex which phosphorylates and activates FMRP. This complex acts on synaptic translation and inhibits translation of several proteins, including ARC (E2). Thus alterations of CYFIP1 expression may exacerbate an already disrupted system 21 L. Aman References 1 Gejman P V, Sanders AR, Kendler KS. Genetics of schizophrenia: new findings and challenges. Annu Rev Genomics Hum Genet 2011; 12: 121–44. 2 Owen MJ, O’Donovan MC, Thapar A, Craddock N. Neurodevelopmental hypothesis of schizophrenia. Br J Psychiatry 2011; 198: 173–5. 3 Vogels A, De Hert M, Descheemaeker MJ, et al. 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Genet Med 2012; 14: 10–26. 32 | Page Microsoft_PowerPoint_Presentation1.pptx BP1 BP2 NIPA1 NIPA2 CYFIP1 GCP5 MKRN3 MKRN3-AS MAGEL2 NDN PWRN2 PWRN1 C15ORF2 Angelman Syndrome imprinting centre PWS imprinting centre SNURF SNRPN SNORD 107 SNORD 64 SNORD 108 SNORD109A SNORD 116 SNORD 115 IPW GABRB3 GABRA5 GABRG3 P(OCA2) ATP10A UBE3A UBE3A-AT BP3 HERC 2 PWS region Angelamn Syndrome region Type 1 deletion Type 2 deletion Centromere image2.emf Gene biallelically expressed Gene paternally expressed Gene maternally expressed Maternal chromosome Paternal chromosome Breakpoint Microsoft_PowerPoint_Presentation2.pptx Gene biallelically expressed Gene paternally expressed Gene maternally expressed Maternal chromosome Paternal chromosome Breakpoint image3.emf CYFP1 GABRB3 GABRA5 GABRG3 CHRFAM7A CHRNA7 Gene UBE3A-AT BP1 Type 1 deletion Type 2 deletion AS region PWS region BP2 BP3 cyfip1 eIF4e FMRP ARC NMDA GABAA receptor subunits E6-AP alpha7 Dup alpha7 Glutamate GABA Dopamine Acetylcholine GABA A GABA/ Glu equilibrium Sensory processing symptoms AMPA P53 nAlpha7 BERP Product/ Function Circuits of interest in psychosis PWS IC Positive symptoms cognitive symptoms Symptoms Dopamine Dysbindin-1 C4 A10 A9 A12 G3 C7 C8 A14 A13 E1 E2 A3 A2 A1 B1 B2 C3 A4 A5 A6 C1 D1 C2 C3 Ncd B3 NDN A7 A8 A11 A15 A16 C5 C4 D2 Microsoft_PowerPoint_Presentation3.pptx CYFP1 GABRB3 GABRA5 GABRG3 CHRFAM7A CHRNA7 Gene UBE3A-AT BP1 Type 1 deletion Type 2 deletion AS region PWS region BP2 BP3 cyfip1 eIF4e FMRP ARC NMDA GABAA receptor subunits E6-AP alpha7 Dup alpha7 Glutamate GABA Dopamine Acetylcholine GABAA GABA/Glu equilibrium Sensory processing symptoms AMPA P53 nAlpha7 BERP Product/ Function Circuits of interest in psychosis PWS IC Positive symptoms cognitive symptoms Symptoms Dopamine Dysbindin-1 C4 A10 A9 A12 G3 C7 C8 A14 A13 E1 E2 A3 A2 A1 B1 B2 C3 A4 A5 A6 C1 D1 C2 C3 Ncd B3 NDN A7 A8 A11 A15 A16 C5 C4 D2 image4.emf Gene biallelically expressed Gene paternally expressed Gene maternally expressed Maternal chromosome Paternal chromosome Breakpoint Biased expression cyfip1 P53 Gene of interest’s product Other gene’s product GABA A AMPA Neurotransmitter receptor Neurotransmitter receptor composed of gene product encoded on chromosome 15 Direct inhibition Direct activation Direct inhibition by a chr 15 gene product Direct activation by a chr 15 gene product Indirect relation Transcription activation Transcription repression Immune system inflammation GABA Positive symptoms Neurotransmitter system Symptoms of psychosis Body systems known to be involved in psychosis Microsoft_PowerPoint_Presentation4.pptx Gene biallelically expressed Gene paternally expressed Gene maternally expressed Maternal chromosome Paternal chromosome Breakpoint Biased expression cyfip1 P53 Gene of interest’s product Other gene’s product GABAA AMPA Neurotransmitter receptor Neurotransmitter receptor composed of gene product encoded on chromosome 15 Direct inhibition Direct activation Direct inhibition by a chr 15 gene product Direct activation by a chr 15 gene product Indirect relation Transcription activation Transcription repression Immune system inflammation GABA Positive symptoms Neurotransmitter system Symptoms of psychosis Body systems known to be involved in psychosis image1.emf BP1 BP2 NIPA1 NIPA2 CYFIP1 GCP5 MKRN3 MKRN3-AS MAGEL2 NDN PWRN2 PWRN1 C15ORF2 Angelman Syndrome imprinting centre PWS imprinting centre SNURF SNRPN SNORD 107 SNORD 64 SNORD 108 SNORD109A SNORD 116 SNORD 115 IPW GABRB3 GABRA5 GABRG3 P(OCA2) ATP10A UBE3A UBE3A-AT BP3 HERC 2 PWS region Angelamn Syndrome region Type 1 deletion Type 2 deletion Centromere