Mechanisms underlying negative symptoms in the 22q11 .2 deletion syndrome: behavioral and brain substrates

Thesis

Reference

Mechanisms underlying negative symptoms in the 22q11 .2 deletion syndrome: behavioral and brain substrates

DUBOURG, Lydia

Abstract

La microdélétion 22q1 1 .2 (del22qll) est un syndrome neurogénétique considéré comme un modèle génétique de la schizophrénie. Comme dans la schizophrénie, le syndrome est caractérisé par la présence de symptômes positifs (ex. hallucinations, délires) et négatifs (anhédonie, retrait social) distincts. Dans ce projet, nous proposons d'examiner les facteurs de risques en lien avec les symptômes négatifs ainsi que leurs réseaux cérébraux sous jacents selon deux axes principaux : les processus liés aux récompense et la cognition sociale. Au travers de ce projet nous avons montré des altérations spécifiques aux traitements des informations sociales dans la del22q11. Au niveau cérébraL les différentes études pointent le rôle du cortex cingulaire postérieur dans les déficits à la fois des processus liés aux récompenses et de perception sociale. Basé sur ces résultats, nous avons proposé un modèle théorique permettant de rendre compte des déficits de motivation sociale dans la del22qll.

DUBOURG, Lydia. Mechanisms underlying negative symptoms in the 22q11 .2

deletion syndrome: behavioral and brain substrates. Thèse de doctorat : Univ. Genève et Lausanne, 2019, no. Neur. 257

DOI : 10.13097/archive-ouverte/unige:138136 URN : urn:nbn:ch:unige-1381361

Available at:

http://archive-ouverte.unige.ch/unige:138136

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Université de Médecine

DOCTORAT EN NEUROSCIENCES

Des Universités de Genève Et de Lausanne

UNIVERSITÉ DE GENÈVE FACULTÉ DE MEDECINE Professeur Stephan Eliez, directeur de thèse

PhD Maude Schneider, co-directeur de thèse

TITRE DE LA THÈSE

Mechanisms underlying negative symptoms in the 22q11.2 deletion syndrome:

behavioral outputs and brain substrates THÈSE

Présentée à la Faculté de médecine De l’Université de Genève

pour obtenir le grade de Docteur(e) en Neurosciences

par Lydia DUBOURG

de

Argentan (61), France Thèse N°

Genève

Editeur ou imprimeur : Université de Genève 2019

This work has been funded by he Swiss National Science Foundation, grant number FNS324730₁21996,324730₁44260and The National Centre of Competence in Research (NCCR)

“Synapsy - The Synaptic Bases of Mental Diseases” (grant number 51NF40-158776) to pro- fessor Stephan Eliez.

This thesis includes the following articles:

Research Articles:

1.Lydia Dubourg, Maude Schneider, Maria Carmela Padula, L´ea Chambaz, Marie Schaer, Stephan Eliez.

Implication of reward alterations in the expression of negative symptoms in 22q11.2 deletion syndrome: a behavioural and DTI study. Psychological Medicine (2017).

2. Lydia Dubourg, Pascal Vrticka, Virginie Pouillard, Stephan Eliez, Maude Schneider.

Deficits of reward processing specific to social stimuli in the 22q11.2 deletion syndrome: an fMRI study (In prep.)

3. Lydia Dubourg, Johanna Maeder, Virginie Pouillard, Stephan Eliez, Maude Schneider.

Goal-directed-behavior in 22q11.2 deletion syndrome: role in social dysfunction and negative symptoms emergence. Frontiers Psychiatry (under review)

4.Dubourg Lydia1, Kojovic Nada , Virginie Pouillard, Marie Schaer, Stephan Eliez,Maude Schneider. Visual processing of complex social scenes in 22q11DS: relevance for social impairments? (In prep)

5. Lydia Dubourg, Maude Schneider, Pascal Vrticka, Martin Debban´e, L´ea Chambaz, Stephan Eliez, Maude Schneider. Neural correlates of socio-emotional perception in 22q11.2 deletion syndrome. Journal of Neurodevelopmental Disorders (2018).

6. Lydia Dubourg, Pascal Vrticka, Virginie Pouillard , Stephan Eliez, Maude Schneider.

Default mode network disconnectivity during social perception in the 22q11.2 deletion syndrome. Psychiatry Research: Neuroimaging (under review).

Acknowledgements

First, I would like to thank my thesis directors Stephan Eliez and Maude Schneider for giv- ing me the opportunity to integrate the DIP lab team. In particular, I would like to thank Maude for her supervision, her advices and the time that she dedicated in revising my work during the four last years. Conducting this PhD was really a great experience. It was very rich in term of personal development.

Thanks to the jury members, Prof. Camilla Bellone, Prof. Therese van Amelsvoort and Prof. Stefan Kaiser for accepting to be part of my thesis committee, for revising this work and for their advices.

A special thank to Johanna, Alexandra Z, L´ea and Virginie, who were on my side since the begining of my PhD. Thank for your support and all the great moments that we have inside and outside the lab!

Thanks to Claire and Cyril, for all the great weekends pasted in Lyon, for giving me some fresh air when needed and to be in my life since so many years now.

Thanks to all the colleagues of the DIP lab for all the moments, aperitif that we shared together, for all the advices that I received inside and outside the 22q11 team.

Thanks to the Lausanne team: L´ea, Johanna, Jo¨elle, Sondes, Cl´emence for all the brunches and the time spent together.

Finally, I would like to thanks my family, mum, dad, Elodie and Dorian for their support.

Version abr´ eg´ ee

Au cours des derni`eres d´ecennies, les travaux r´ealis´es dans le champ de la schizophr´enie se sont majoritairement focalis´es sur les facteurs de risque en lien avec l’´emergence de la psychose. Comme cons´equence, d’autres aspects de la psychopathologie et en particulier la symptomatologie n´egative a ´et´e n´eglig´ee. Or, les symptˆomes n´egatifs ont ´et´e d´emontr´es comme persistants au cours du temps et particuli`erement r´esistants aux diff´erents type de m´edications et d’interventions. De plus, au vu de leurs impacts d´el´et`eres sur la qualit´e de vie des patients ainsi que les r´ecents travaux d´emontrant leur rˆole dans le taux de transition de psychose, un regain d’int´erˆet envers les symptˆomes n´egatifs dans le champ de la psychose a ´et´e observ´e.

Ce projet se focalise sur la microd´el´etion 22q11.2 (del22q11), un syndrome neurog´en´etique repr´esentant la microd´el´etion chromosomale la plus fr´equemment rencontr´ee chez l’homme.

Le syndrome est caract´eris´e par un tableau clinique complexe incluant des manifestations somatiques, cognitives mais ´egalement psychiatriques. Le syndrome est consid´er´e comme un mod`ele g´en´etique de la schizophr´enie et mˆeme s’il apparaˆıt que de nombreux patients ne rem- plissent pas l’ensemble des crit`eres pour un trouble du spectre de la schizophr´enie, la pr´esence de symptˆomes psychotiques att´enu´es est g´en´eralement observ´ee (Baker and Skuse 2005, Deb- ban´e et al., 2006, Schneider, Debban´e, Bassett, Chow, et al. 2014). De plus, il apparaˆıt que les symptˆomes psychotiques observ´es dans la del22q11 sont similaires `a ceux retrouv´es dans d’autres formes de schizophr´enies. En effet, comme dans la schizophr´enie, les patients ayant la del22q11 pr´esentent des symptˆomes positifs et n´egatifs distincts. Alors que les symptˆomes positifs sont retrouv´es chez 23 % `a 45% des adolescents, les symptˆomes n´egatifs apparais- sent plus pr´edominants car touchant approximativement 60 `a 80% des adolescents et jeunes adultes avec la del22q11. Au vu de l’importante pr´evalence des symptˆomes n´egatifs dans la del22q11, ceux-ci sont consid´er´es comme une caract´eristique clinique du ph´enotype de ce syndrome. Pour cette raison, la del22q11 repr´esente un model int´eressant pour examiner les m´ecanismes sous-jacents des symptˆomes n´egatifs. Bien que de nombreuses ´etudes ont mis en

´

evidence l’impact des symptˆomes n´egatifs sur fonctionnement dans la vie quotidienne et la sph`ere professionnelle dans la del22q11, les m´ecanismes sous-jacents `a leur expression restent largement ind´etermin´es dans ce syndrome. Dans ce projet, nous proposons d’examiner les facteurs de risques en lien avec les symptˆomes n´egatifs ainsi que leurs r´eseaux c´er´ebraux sous- jacents selon deux axes principaux : les processus li´es aux r´ecompenses et la cognition sociale.

Les processus de r´ecompense ont ´et´e sugg´er´es comme impliqu´es dans l’´emergence des symptˆomes n´egatifs, en particulier pour le domaine apathie-avolition. Nous avons donc r´ealis´e trois

´

etudes afin d’examiner les corr´elats comportementaux et c´er´ebraux des processus de r´ecompense dans la del22q11. Dans l’´etude 1, nous avons examin´e les capacit´es h´edoniques, la connec-

tivit´e structurelle du syst`eme de r´ecompense et leurs liens avec les symptˆomes n´egatifs dans la del22q11. Dans l’´etude 2, nous avons ´etudi´e les r´eseaux c´er´ebraux sous-tendant le traite- ment des r´ecompenses sociales et non-sociales (plaisir anticip´e et consomm´e) tandis que dans l’´etude 3 nous avons examin´e l’impact de l’initiation verbale et non-verbale (‘com- portement dirig´e vers un but’) dans l’expression des symptˆomes n´egatifs dans la del22q11.

Nos r´esultats ont mis en ´evidence des alt´erations dans plusieurs composantes du traitement de la r´ecompense dans la del22q11. En effet, des d´eficits de plaisir anticip´e et consomm´e ainsi que d’initiation verbale et non-verbale ont ´et´e observ´es. De plus, nous avons montr´e que seuls certains processus du traitement de la r´ecompense semblent li´es `a la s´ev´erit´e des symptˆomes n´egatifs. En effet, seul l’anticipation du plaisir et l’initiation verbale ´etaient as- soci´es `a la s´ev´erit´e des symptˆomes n´egatifs. Grˆace aux ´etudes 1 et 2, nous avons ´egalement montr´e des alt´erations de l’int´egrit´e de la mati`ere blanche du tract accumbofrontal ainsi que l’hypoactivation du cortex cingulaire post´erieur durant la r´eception de r´ecompense sociale chez les individus porteurs de la del22q11 en comparaison aux individus contrˆoles.

En plus du rˆole des processus de r´ecompense, les symptˆomes n´egatifs ont ´egalement ´et´e associ´es aux d´eficits de cognition sociale (Kirkpatrick et al. 2006). En effet, la cognition sociale soutenant les comp´etences sociales ainsi que le fonctionnement social, des difficult´es de ces processus pourraient contribuer `a l’´emergence de certains symptˆomes n´egatifs tels que le retrait social. Pour cette raison, le second objectif de ce projet vise `a examiner les substrats comportementaux et c´er´ebraux d’un processus cl´e de la cognition sociale, la perception sociale, ainsi que son association avec les symptˆomes n´egatifs dans la del22q11.

Dans notre ´etude 4, nous avons quantifi´e l’exploration visuelle de sc`enes sociales complexes en utilisant une m´ethodologie bas´ee sur les donn´ees tandis que dans les ´etudes 5 et 6 nous avons examin´e respectivement, l’activation c´er´ebrale et la connectivit´e fonctionnelle durant la perception sociale. Nos r´esultats ont d´emontr´e une alt´eration de la perception sociale dans la del22q11. En quantifiant l’exploration visuelle de stimuli sociaux nous avons mis en

´

evidence un pattern atypique d’exploration visuelle ainsi qu’une association entre ce pattern d’exploration divergent et les symptˆomes n´egatifs chez les individus porteurs de la del22q11 (´etude 6). De plus, au travers des ´etudes 4 et 5, nous avons montr´e des alt´erations du r´eseau par d´efaut durant la perception sociale, premi`erement en terme activation c´er´ebrale (signal BOLD) et deuxi`emement en terme de connectivit´e fonctionnelle. De plus, l’´etude 5 a mis en ´evidence une association significative entre la disconnectivit´e du r´eseau par d´efaut (IPL- PCC/ precuneus) et la s´ev´erit´e des symptˆomes n´egatifs dans la del22q11.

Ensemble, nos r´esultats indiquent que le cortex cingulaire post´erieur serait un marqueur com- mun pour les d´eficits de perception sociale et des processus de r´ecompense dans la del22q11.

Nous avons ´egalement montr´e l’´evidence de difficult´es sp´ecifiques au traitement des infor- mations de nature sociale dans la del22q11. Enfin, nos ´etudes montrent que les symptˆomes n´egatifs r´esultent plus probablement d’une alt´eration concomitante de m´ecanismes incluant `a la fois une alt´eration des processus de r´ecompenses et de ceux de la cognition sociale, en par- ticulier la perception sociale. Bas´e sur nos r´esultats, nous avons propos´e un mod`ele th´eorique

et explicatif des difficult´es de motivation sociale dans la del22q11. Selon ce mod`ele, la per- ception sociale pourrait repr´esenter un bon candidat pour la mise en place d’intervention th´erapeutique dans la del22q11.

Abstract

Over the last decades, research conducted in the field of schizophrenia predominantly focused on risk factors for the onset of psychosis. As a consequence, others aspects of the psychopathology and particularly the negative symptomatology has been neglected. How- ever, negative symptoms have been demonstrated as persistent over time and particularly resistant to medication and interventions. Moreover, given their deleterious impact on pa- tient’s quality of life as the recent findings demonstrating their implication on psychosis transition rate, there has been a renewed interest toward negative symptoms in the field of psychosis.

This project focuses on the 22q11.2 deletion syndrome (22q11DS), a neurogenetic disor- der representing the most common chromosomal microdeletion syndrome in humans. The syndrome is marked by a complex clinical picture including somatic, cognitive as well as psychiatric manifestations. The syndrome is considered as a genetic model for schizophrenia and even if many patients with 22q11DS do not fill the criteria for a schizophrenia spec- trum disorders, high rates of attenuated psychotic symptoms are generally observed (Baker and Skuse 2005, Debban´e et al., 2006, Schneider, Debban´e, Bassett, Chow, et al. 2014).

Moreover, psychotic symptoms in 22q11DS appear similar to other types of schizophre- nias (McDonald-McGinn et al., 2015). Indeed, as in schizophrenia, patients with 22q11DS present distinct positive and negative symptoms. While positive symptoms are experienced by 23% to 45% of adolescents (Stoddard et al., 2010, Schneider et al., 2012), negative symp- toms appear more predominant as present in approximately 60 to 80% of adolescents and young adults with 22q11DS (Stoddard et al., 2010, Schneider et al., 2012). Given the high prevalence of negative symptoms in 22q11DS, prominent negative symptoms represent a clinical feature of the 22q11DS phenotype. For this reason, the 22q11DS represent an inter- esting model for examining mechanisms underlying negative symptoms. Although several studies have highlighted the importance of negative symptoms on daily-life functioning and vocational outcome (Schneider et al. 2014) in the 22q11DS population, the mechanisms underlying their expression remain largely unknown in this syndrome. In this project, we propose to investigate risk factors for negative symptoms in association with their under- lying cerebral networks along two main axes: reward-related-processing and social cognition.

Reward-related-processes are thought to be involved in the emergence of negative symp- toms, particularly in the apathy-avolition domain. We thus conducted three studies aiming to examine behavioral and neural correlates of reward-related processes in 22q11DS. In Study 1, we examined hedonic capacity, structural connectivity of the reward system and their links

with negative symptoms in 22q11DS. In Study 2, we investigated brain networks underlying social and non-social reward processing (anticipatory and consummatory) in the 22q11DS population while in our Study 3, we investigated the impact of verbal and non-verbal ini- tiation (‘goal-directed behavior’) in the expression of negative symptoms in the 22q11DS population. Our results highlighted deficits in several reward related components in the 22q11DS population. Indeed, we reported deficits in anticipatory and consummatory plea- sure (study 1), as well as in verbal and non-verbal initiation (goal-directed-behavior) (study 2) in the 22q11DS population. Moreover, we demonstrated that only some of these compo- nents seem to contribute to negative symptom severity. Indeed, only anticipatory pleasure and verbal initiation were predictive of the negative symptomatology. Thank to study 1 and 2, we also demonstrated alterations of WM integrity of the accumbofrontal tract, a main tract of the reward system as well as decreased activation of the posterior cingulate cortex during social reward receipt in 22q11DS compared to healthy controls.

In addition to the role of reward processes, negative symptoms have also been associated with social cognition deficits (Kirkpatrick et al. 2006). Indeed, as social cognition sustains social competences and social functioning, difficulties in such processes might contribute to the emergence of some negative symptoms, such as social withdrawal. For this reason, our second aim was to examine the behavioral and neural substrates of a core aspect of social cognition, namely social perception, and its association with negative symptom severity in patients with 22q11DS. In our study 4, we quantified visual processing of complex social scenes based on an eye-tracking data-driven methodology while in our study 5 and 6 we investigated respectively, neural activity and functional connectivity during social percep- tion. Our results demonstrated an alteration of social perception, a lower order process of social cognition, in the 22q11DS population. By quantifying the visual exploration of social stimuli in an unbiased manner, we highlighted an atypical pattern of exploration as well as an association between this divergent pattern of exploration and negative symptom severity in 22q11DS individuals (study 6). Moreover, through studies 4 and 5, we highlighted deficits of the DMN during social perception, first in term of activation (BOLD signal) and secondly in term of connectivity. Moreover, in study 5, we highlighted a significant association be- tween DMN connectivity (IPL-PCC/precuneus connectivity) and negative symptom severity in individuals with 22q11DS.

Taken together, our studies point to the PCC as a common marker for both reward process- ing and social perception impairments in the 22q11DS. We also showed evidence of deficits specific to social information in 22q11DS individuals. Finally, our studies demonstrated that negative symptoms more likely result in a concomitant alteration of mechanisms en- compassing on one hand reward-related components and on the other hand social cognition processes and particularly social perception. Based on our results, we proposed a theoretical and explanatory model of social motivation deficits in the 22q11DS. According to this model, social perception might represent a valuable candidate for therapeutic intervention in the 22q11DS.

Contents

Acknowledgements . . . ii

Version abr´eg´ee . . . iii

Abstract . . . vi

I Introduction 1

1.2 The 22q11DS phenotype . . . 4

1.2.1 Somatic manifestations . . . 5

1.2.2 Cognitive manifestations . . . 7

1.2.3 Psychiatric manifestations . . . 8

1.3 Brain structure and function in 22q11.DS . . . 10

1.3.1 Development of brain structure in 22q11DS compared to healthy controls 10 1.3.2 Brain connectivity alterations in 22q11DS . . . 11

1.4 Deleted genes associated with the 22q11DS . . . 12

2 Negative symptoms 16 2.1 History of the concept . . . 16

2.2 Structure and evaluation of negative symptoms . . . 18

2.2.1 Scales frequently used to measure negative symptoms . . . 18

2.2.2 New conceptualization of negative symptoms . . . 19

2.2.3 Development of new scales to assess negative symptoms . . . 20

2.3 Negative symptoms as a key component in psychosis . . . 20

2.3.1 Prevalence and persistence of negative symptoms . . . 20

2.3.2 Importance of negative symptoms . . . 22

2.3.2.1 Impact on functional outcome . . . 23

2.3.2.2 Implication in psychosis transition rate . . . 23

2.3.2.3 Therapeutic interventions of negative symptoms . . . 24

2.4 Neuroimaging findings associated with negative symptoms . . . 24

3 Current models of negative symptoms 27 3.1 Negative symptoms mechanisms: an overview . . . 27

3.2 Towards new explanatory models of negative symptoms . . . 29

3.2.1 Implication of reward-related processes in the expression of negative symptoms . . . 30

3.2.1.1 The reward processes . . . 33

3.2.1.2 The motivational approach . . . 37

3.2.2 Implication of social cognition in the expression of negative symptoms 40 4 Neuroimaging and behavioral tools to assess mechanisms underlying neg- ative symptoms 47 4.1 Assessing structural connectivity with Diffusion Tensor Imaging . . . 47

4.2 Assessing brain activity with fMRI . . . 50

4.3 Assessing functional connectivity with fMRI . . . 52

4.4 Assessing visual exploration with eye-tracking technique . . . 53

5 Aims and hypotheses 56

II Results 59

2.1.1 Methods . . . 62

2.1.2 Results . . . 62

2.2 Study 2: Monetary and social reward processing in the 22q11.2 deletion syn- drome: an fMRI study . . . 64

2.2.1 Methods . . . 64

2.2.2 Results . . . 65

2.3 Study 3: Goal-directed-behavior in 22q11.2 deletion syndrome: role in social dysfunction and negative symptoms emergence . . . 67

2.3.1 Methods . . . 67

2.3.2 Results . . . 67

2.4 Study 4: Visual processing of complex social scenes in the 22q11.2 deletion syndrome: relevance for negative symptoms . . . 69

2.4.1 Methods . . . 69

2.4.2 Results . . . 69

2.5 Study 5: Neural correlates of socio-emotional perception in 22q11.2 deletion syndrome . . . 73

2.5.1 Methods . . . 73

2.5.2 Results . . . 73

2.6 Study 6: Default mode network dysconnectivity during social perception in the 22q11.2 deletion syndrome . . . 75

2.6.1 Methods . . . 75

2.6.2 Results . . . 75

III Discussion 78

3.1.1 Reward-related processes impairments at the behavioral level . . . . 80

3.1.2 Reward-related processes: neuroimaging findings . . . 82

3.1.3 Reward-related processes impairments and psychotic symptoms . . . 84

3.1.4 COMT polymorphism and reward processes . . . 85

3.2 Social perception alterations in 22q11DS . . . 86

3.2.1 Social perception alterations: behavioral findings . . . 86

3.2.2 Social perception alterations: brain correlates . . . 88

3.2.3 Social perception impairment and negative symptoms . . . 89

3.2.4 Social perception impairment and additional clinical features . . . 90

3.3 Key findings: integration of the two axes . . . 90

3.3.1 The DMN as a common marker for reward and social perception im- pairments in 22q11DS . . . 90

3.3.2 Deficits specific to social information in 22q11DS: relation to the social motivation hypothesis . . . 91

3.3.3 Toward a theoretical model of social motivation deficits in the 22q11DS 92 3.4 Limitations . . . 94

3.4.1 Limitations associated with the DTI sequence and analysis . . . 94

3.4.2 Limitations associated with the fMRI paradigm and analysis . . . 94

3.4.3 Limitations associated with the negative symptoms evaluation . . . . 95

3.5 Future perspective . . . 95

3.5.1 Investigate additional reward-related-components . . . 96

3.5.2 Disentangle the mechanisms of negative symptoms through the classi- fication subgroups of patients . . . 96

3.6 Conclusions . . . 97

A Articles 98

Bibliography 259

changer de regard.

Marcel Proust

Part I

Introduction

The 22q11.2 deletion syndrome (22q11DS), also known as velo-cardio-facial syndrome, is the most common chromosomal microdeletion syndrome in humans. The syndrome is considered as a genetic model for schizophrenia (Bassett and Chow, 2008) and is charac- terized by high rates of distinct positive (e.g. delusions, hallucinations, disorganization) and negative symptoms (e.g. anhedonia, social withdrawal). So far, studies in the field of schizophrenia mainly focused on putative risk factors for psychosis. As a consequence, others aspects of the psychopathology and particularly the negative symptomatology has not been efficiently investigated. Although several studies have highlighted the importance of nega- tive symptoms on daily-life functioning and vocational outcome in the 22q11DS (Schneider et al., 2014b), the mechanisms underlying their expression remain largely unknown in this syndrome. For this reason, we propose to investigate risk factors for negative symptoms in association with their underlying cerebral networks along two main axes: reward-related- processing and social cognition. In the first part of the manuscript, we will first define what is 22q11DS and describe its complex clinical picture including somatic, cognitive and psy- chiatric manifestations. We will continue with a description of negative symptoms, their construct and importance in patients with psychosis. We will then introduce the putative contributors of negative symptoms emergence (reward-related-processing and core aspects of social cognition) along with the cerebral alterations that have been described in patients with schizophrenia and 22q11DS. We will then detail the neuroimaging and behavioral tech- niques that have been used in this project to examine the mechanisms underlying negative symptoms. We will end this chapter describing the aims and hypothesis of this project.

CHAPTER

1

THE 22Q11DS PHENOTYPE

1.1 History of the syndrome

First mentions of the syndrome date back to 1978, in that time under the name of velo- cardio-facial syndrome (VCFS). Given the variable phenotype associated with the deletion - more than 180 features - numerous name have been used to designate the syndrome includ- ing VCFS, Shprintzen syndrome, Sedlackov´a syndrome, DiGeorge syndrome, conotruncal anomaly face syndrome or Cayler syndrome. It was only in 1992, when the specific genetic cause of the syndrome was discovered that the name of 22q11.2 deletion syndrome emerged.

Thereafter, it was established that all of the syndromes previously mentioned share the same genetic etiology. Therefore, the syndrome is now recognized under the name of 22q11.2 dele- tion syndrome (22q11DS).

The 22q11DS has been described as the most frequent copy number variant encounter in human being (Squarcione et al., 2013). Its occurrence is estimated at approximately 1 in 2000-4000 births, and 1 in 1000 fetuses (Grati et al., 2015; McDonald-McGinn et al., 2015; Oskarsdottir et al., 2004; Shprintzen, 2008). The syndrome is caused by an autosomal dominant microdeletion on the long arm of the chromosome 22, the q arm, on the 11.2 band (Figure 1.1).

The majority of patients with 22q11DS identified exhibit a de novo mutation (90-95%), meaning that none of the parents have the deletion (McDonald-McGinn et al., 2001; Scam-

Figure 1.1: Representation of the 22 chromosome showing the short (p) and long (q) arms and the 22q11.2 band depicted by dashed lines. The position of the two low copies repeats (LCRs)

leading to the 3Mb deletion are indicated.

bler, 2000). Nevertheless, in less than 10%, the microdeletion is inherited from an affected parents (Scambler, 2000). The 22q11 region appears to be a complex area of the genome due to the presence of repeated elements known as low copy repeats. Those short elements share 95% identity, making this 22q11 region particularly vulnerable to aberrant recombination during meiosis. Different types of deletion have been described (Figure 1.2). A large study from the International 22q11.2 Brain and Behavior Consortium (IBBC) has recently been conducted on this topic in 1680 participants with 22q11DS (Guo et al., 2018). The authors reported that the most typical deletion of 3MB, which results from a non-allelic homologous recombination between the largest repeats called LCR22A and LCR22D, appears in approx- imately 90% of cases. The proximal nested deletion of 1.5Mb (LCR22A-LCR22B) and 2Mb (LCR22A-LCR22C) occurs respectively in 5.2% and 2.3% of cases, which appear similar to findings reported in smaller samples (Edelmann et al., 1999; Karayiorgou et al., 2010; Shaikh et al., 2000). Guo et al. (2018) also identified new types of recurrent deletion from analysis of microarrays in 2.3% (LCRA+-B and LCRA+-D). In few cases, distal nested deletions (LCR22B-LCR22D and LCR22C-LCR22D) are also observed.

1.2 The 22q11DS phenotype

The 22q11DS is associated with a highly variable clinical phenotype with more than 180 described features (Robin and Shprintzen, 2005) (Figure 1.3). The 22q11DS phenotype

Figure 1.2: Schematic illustration of the 3Mb 22q11.2 region including the low copy repeats present in this region. Main types of deletions and genes associated are indicated.

encompasses clinical features ranging from somatic, cognitive to psychiatric manifestations that we will describe in the following sections.

1.2.1 Somatic manifestations

The 22q11DS is associated with various somatic disorders mainly, immunodeficiency (in 75%), cardiac anomalies (in 75%) and palatal abnormalities (in 50%) (See for a review McDonald-McGinn et al., 2015).

Cardiovascular abnormalities are generally visible in the prenatal or neonatal period and are the first signs leading to diagnosis. They also represent the main cause of mortality in children with 22q11DS (87%). Main abnormalities include: tetralogy of Fallot, truncus arteriosus, interrupted aortic arch type B and ventricular septal defect.

Immunodeficienciesare induced by thymic hypoplasia and impaired T cell production, both leading to various chronic infections.

Palatal abnormalitiesmainly include cleft palate. In most cases submucous cleft palate and bifid uvula are observed, while overt cleft palate are scarcely reported (Bassett et al., 2011). Palatal abnormalities lead to velopharyngeal dysfunction, abnormal nasal resonance

or articulation errors.

Others somatic manifestations include endocrine anomalies (hypocalcemia in 50- 65%), gastrointestinal abnormalities (30%) and many others such as facial malformations or growth retardation.

Figure 1.3: Organs and systems affected in individuals with 22q11DS (from NcDonald-McGinn et al., 2015).

1.2.2 Cognitive manifestations

A wide range of cognitive impairments is observed in the 22q11DS population. Cognitive deficits in children with 22q11DS represent a main concern of parents in view of their impact on educational and vocational trajectories. Global intellectual functioning has been largely studied in the context of the syndrome. Whereas the level of intellectual functioning appears to follow a normal distribution, there is an approximately 30-point shift to the left in indi- viduals with 22q11DS compared to the general population. Patients with 22q11DS hence have a mean full scale IQ around 70-75, with an intellectual level ranging from borderline (55%, ¿70) to mild intellectual disability (45%, IQ 55-70). A discrepancy between verbal abilities (VIQ) and perceptual reasoning abilities is found during early childhood whereas this divergence seems less evident with age, due to a decline in the verbal domain. Recently, a multisite study from the International Consortium on Brain and Behavior in 22q11.2 Dele- tion Syndrome (IBBC), showed a decline in IQ over time, particularly in the verbal domain.

A steeper decline for patients with 22q11DS diagnosed with a psychotic disorder was found, suggesting that IQ decline - and VIQ decline in particular - is predictive of psychosis in this syndrome. Beyond a global decrease of intellectual efficiency, specific deficits in some cognitive domains are also observed in 22q11DS individuals. For instance, visuospatial diffi- culties are also commonly found in 22q11DS. Previous studies showed impaired visuospatial perception and memory in patients with 22q11DS (Azuma et al., 2009; Bearden et al., 2001;

Bostelmann et al., 2016; Henry et al., 2002; Simon et al., 2005, 2008; Wong et al., 2014), which seems related to alterations in frontal and parietal regions (Azuma et al., 2009; Si- mon et al., 2008). Another domain of relative weakness in the 22q11DS profile is executive function. Executive functions are higher order skills including: initiation, inhibition, set shifting, working memory, planning used for the execution and regulation of cognitive and behavioral actions (Gioia et al., 2010). To date, impairment in cognitive flexibility and working memory have been described in patients with 22q11DS (Azuma et al., 2009), while more controversial findings for inhibition have been reported (McCabe et al., 2014; Shapiro et al., 2013). Furthermore, a longitudinal study from our group highlighted that working memory and verbal fluency do not gradually increase with age in patients with 22q11DS compared to what is observed in healthy controls (Maeder et al., 2016). Social cognitive deficits represent an additional feature of the 22q11DS cognitive profile (for a review, seee Norkett et al., 2017). Social cognition encompasses the various processes that underlie social interaction. In patients with 22q11DS, a clear impairment in emotion processing and high order theory of mind (TOM) has been reported. Indeed, several studies have demonstrated difficulties of face recognition and emotion identification in patients with 22q11DS. These deficits seem related to atypical face processing, characterized by shorter scanpath lengths, fewer fixations and less time spent on relevant facial features (eyes, nose, mouth) that has been well established in the 22q11DS (Campbell et al., 2010; Franchini et al., 2016; McCabe et al., 2011; Zaharia et al., 2018). A few studies have also reported difficulties of TOM com- petences in patients with 22q11DS (Badoud et al., 2017; Campbell et al., 2015; Ho et al., 2012; Jalbrzikowski et al., 2012, 2014). In schizophrenia, social cognition processes have been

hypothesized as putative contributors in the expression of negative symptoms (Kirkpatrick et al., 2006). The role of social cognition processes in negative symptoms emergence thus progressively became a focus of interest in the field of psychosis. For this reason, a part of this project will focus on social cognition, a summary of the socio-cognitive deficits observed in schizophrenia and the 22q11DS and their link with negative symptoms will therefore be presented in details in the chapter 3 section 2.2.

1.2.3 Psychiatric manifestations

The psychiatric phenotype of 22q11DS has been extensively described in the literature.

From a general point of view, a higher rate of psychiatric disorders in patients with 22q11DS compared to the general population has been consistently reported. Recently, a large study conducted in collaboration with the IBBC, which included 1400 participants allowed to char- acterize the prevalence of major psychiatric diagnoses over time in 22q11DS (Schneider et al., 2014a). By investigating trajectories of major psychiatric disorders across four time points, the authors found that attention deficit hyperactivity disorder (ADHD) was the most com- mon diagnosis in children with 22q11DS (37%). Anxiety and mood disorders were present at all ages. While anxiety disorders were more frequent in children and adolescents, major de- pressive disorders and schizophrenia spectrum disorders were more prevalent in adults with 22q11DS.

Schizophrenia spectrum disorders and psychotic symptoms

Schizophrenia spectrum disorders appear highly prevalent in patients with 22q11DS af- fecting approximately 10% of adolescents and 40% of individuals over 25 years of age (Schnei- der et al., 2014a) (Figure 1.4). Literature demonstrated that patients with 22q11DS have a 30-fold increased risk to develop schizophrenia compared to the general population (Gothelf et al., 1999; Green et al., 2009; Murphy et al., 1999; Schneider et al., 2014a). Additionally, psychotic disorders such as schizoaffective disorder, schizophreniform disorder, delusional disorder, brief psychotic disorder have also been reported in patients with 22q11DS but are less common (Schneider et al., 2014a). Others studies demonstrated that many patients with 22q11DS do not fill the criteria for a schizophrenia spectrum disorders but still present high rates of attenuated psychotic symptoms (Baker and Skuse, 2005; Debban´e et al., 2006;

Schneider et al., 2014a). Moreover, psychotic symptoms in 22q11DS appear similar to other types of schizophrenias (McDonald-McGinn et al., 2015). Indeed, as in schizophrenia, pa- tients with 22q11DS present distinct positive and negative symptoms, which will be described in more details in the next chapter. While positive symptoms are experienced by 23% to 45% of adolescents (Schneider et al., 2012; Stoddard et al., 2010), negative symptoms appear more predominant as present in approximately 60 to 80% of adolescents and young adults with 22q11DS (Schneider et al., 2012; Stoddard et al., 2010).

Figure 1.4: Prevalence of schizophrenia spectrum disorders over age in individuals with 22q11DS (from Schneider et al., 2014)

The 22q11DS as a model of schizophrenia

In light of the high prevalence of schizophrenia spectrum disorders reported in patients with 22q11DS, the syndrome is considered as a valuable model of schizophrenia. Indeed, studies indicate that the risk for schizophrenia in patients with 22q11DS is about 20 to 25 times higher than in the general population (See for a review Bassett et al., 2000). In addition, one study found that the prevalence of 22q11DS among schizophrenia patients is about 0.5% to 1.2% (See for an overview Hoogendoorn et al., 2008) , which is much higher than the prevalence estimated in the general population. Furthermore, there are neurode- velopmental and genetic evidences supporting the 22q11DS as a model of schizophrenia. On one hand, neurodevelopmental studies demonstrated common features between patients with 22q11DS and those with schizophrenia including developmental delays, speech difficulties, coordination deficits, blunted affect and social withdrawal (See for a review Bassett et al., 2000). Similar brain anomalies are also reported in both disorders such as ventricular en- largement, decreased brain volume (Amelsvoort et al., 2004), midline defects (Chow et al., 1999) and white matter alterations (Amelsvoort et al., 2004; Chow et al., 1999). In addi- tion, the pathogenesis of the two disorders seems to involve the same mechanism, namely abnormal neuronal migration (Bassett and Chow, 2008). On another hand, genetic studies

found that both schizophrenia and 22q11DS results from de novo mutations (Dallapiccola et al., 1996). Moreover, several genes located with the 22q11.2 locus have been related to risk of schizophrenia (Karayiorgou and Gogos, 2004). All these findings have led to the proposal that 22q11DS is a genetic model of neurodevelopmental mechanisms involved in the pathogenesis of schizophrenia.

1.3 Brain structure and function in 22q11.DS

A large number of neuroimaging studies have been conducted to identify brain alterations in individuals with 22q11DS compared to healthy controls. In the next sections, we will provide an overview of the studies examining brain morphology as well as structural and functional connectivity in 22q11DS. Association between brain alterations and symptoms of interest will be detailed in chapter 2 section 4.

1.3.1 Development of brain structure in 22q11DS compared to healthy controls

In the general population, cortical volume develops with a non-linear trajectory, increasing until pre-adolescence and decreasing after adolescence (Giedd et al., 1999; Gogtay et al., 2004). Nevertheless, brain maturation differs between brain regions. Indeed, cortical devel- opment reflects the functional maturation of the brain, with sensorimotor cortices developing earlier and associative areas such as the temporal and frontal cortices having a later mat- uration (Gogtay et al., 2004). Morphological alterations in patients with 22q11DS have been summarized in a review and a meta-analysis (Gothelf et al., 2008; Tan et al., 2009).

Quantitative studies showed a total brain volume reduction in 22q11DS individuals com- pared to healthy controls characterized by more reduction in white matter than grey matter.

Although widespread reductions are observed, different cortical lobes seems to be differ- ently affected during the course of development. In children and adolescent with 22q11DS, posterior brain regions appear mainly altered, including parietal lobes, hippocampus and cerebellum. From adulthood, drastic reductions in the frontal and temporal lobes are ob- served. Thereafter, more sophisticated investigations of subcomponents of cortical volume have been conducted. Briefly, cortical volume is determined by cortical thickness and surface area. The surface area is measured by a gyrification index reflecting the convex hull area and the degree of sulcation. As cortical volume, cortical thickness increases during childhood until reaching a peak during adolescence and then starts to decrease until it stabilizes during adulthood (Shaw et al., 2008). Contrariwise, cortical gyrification mainly develops in utero and reaches a peak during childhood (Chi et al., 1977; White et al., 2010). In 22q11DS, a longitudinal study conducted by our group showed that patients with 22q11DS have higher cortical thickness before adolescence, in particular in the prefrontal region, and then present

a faster cortical thinning, leading to greater thickness loss in adulthood compared to con- trols (Schaer et al., 2010). Ramanathan et al. (2017) reported smaller cortical thickness in parietal regions and slower cortical thinning with age in patients with 22q11DS compared to controls (Ramanathan et al., 2017). Concerning gyrification, widespread reductions have been observed in patients with 22q11DS mainly in cingulate cortices, orbitofrontal, frontal regions, temporo-parietal junction, supramarginal and superior temporal cortices (Schaer et al., 2009; Schmitt et al., 2015; Srivastava et al., 2012). A longitudinal study has been con- ducted that did not reveal any significant changes in gyrification with age in patients with 22q11DS compared to controls (Kunwar et al., 2012). Finally, one recent study conducted in collaboration with the ENIGMA consortium (Enhancing Neuro Imaging Genetics Through Meta-Analysis) - 22q11DS working group - revealed widespread reductions in gyrification bilaterally in the medial occipital and anterior cingulate cortex, superior parietal cortex and rostral middle frontal gyrus in 22q11DS individuals compared to controls. Moreover, a similar pattern of thicker cortex was observed except in bilateral insula and thinner cortex in bilateral parahippocampal and superior temporal gyri and left caudal anterior cingulate cortex (Sun et al., 2018).

1.3.2 Brain connectivity alterations in 22q11DS

White matter volume, similar to grey matter, changes during the course of development (Giedd et al., 1999). White matter integrity (WM) can be estimated through several dif- fusion parameters: the fractional anisotropy (FA) a global measure of WM integrity, axial diffusivity (AD) reflecting axonal integrity and radial diffusivity (RD), which reflects myeli- nation (see section 4.1 for more details). In the general population, studies revealed that diffusion measures (FA, RD, AD) change with age and that the different tracts reach mat- uration at different ages (Bava et al., 2010; Lebel and Beaulieu, 2011; Lebel et al., 2012).

To date, no longitudinal study has been conducted in 22q11DS. As for cross-sectional stud- ies, they demonstrated heterogeneous results, showing both increases and decreases diffusion measures in various white matter tracts (Kikinis et al., 2016; Roalf et al., 2017; Scariati et al., 2016; Tylee et al., 2017). It is only when examining the association with psychotic symptoms that a common pattern of alterations, mostly involving long-range frontal and limbic connections, was identified. Concerning functional connectivity, various networks ap- pear to be affected in 22q11DS, with the most consistent results pointing to impaired default mode network (DMN) connectivity. Moreover, the implication of the ACC disconnectivity has been repetitively demonstrated and associated with the risk of psychosis in 22q11DS individuals (See for a review Padula et al., 2018).

1.4 Deleted genes associated with the 22q11DS

Numerous genes identified in the 22q11.2 locus are hemizygously deleted. Therefore, re- duced gene-dosage of these genes could account for the complex clinical picture depicted in individuals with this syndrome. To date, some genes have received more attention including TBX1, COMT and PRODH (Figure 2). The TBX1 gene has been particularly associated with somatic aspects of patients with 22q11DS (Calmont and Scambler, 2010; Liao et al., 2004; Yagi et al., 2003) and recently its implication in cortical maturation has been empha- sized (Flore et al., 2017) whereas the COMT and PRODH appear to play a crucial role in neurotransmission (Chen et al., 2004; Paterlini et al., 2005) and have been related to cogni- tive and psychiatric manifestations of patients with 22q11DS (Goldman-Rakic et al., 2000;

Gothelf et al., 2007; Jacquet et al., 2002; Moghaddam and Javitt, 2012; Tunbridge et al., 2006; Vijayraghavan et al., 2007).

TBX1 is a transcription factor, which has a crucial implication in formation of tissue and organs. Loss of activation of this gene has been linked to the physical malformations observed in patients with 22q11DS such as cardiac, thymic, craniofacial malformations (Cal- mont and Scambler, 2010; Yagi et al., 2003), or hearing loss (Liao et al., 2004). In addition, it has been demonstrated that TBX1 mutant mice have impaired prepulse inhibition (Paylor et al., 2006), an abnormality that has also been observed in patients with 22q11DS (de Kon- ing et al., 2012; Sobin et al., 2005), and individuals with schizophrenia (Braff, 2010). TBX1 mutation has been previously linked to the presence of psychiatric disorder in 22q11DS patients and in the wider population (Paylor et al., 2006), nevertheless, its implication in the psychiatric phenotype of patients with 22q11DS remains unclear. It is only recently that TBX1 has been shown to play a role in cortical maturation (Flore et al., 2017). A link between haploinsufficiency of TBX1 and premature differentiation of cortical projection neurons, altered migration of cortical neurons, and cortical thickness has been reported in a 22q11DS mouse model (Flore et al., 2017).

PRODH(proline dehydrogenase oxidase) is a gene involved in the degradation of amino- acid proline and has been associated to glutamatergic and GABA transmission (Paterlini et al., 2005). Glutamate is the main excitatory neurotransmitter in the brain (Nedergaard et al., 2002) and is involved in learning, some aspects of memory (Cotman et al., 1988), as well as in emotion regulation and motivational behavior(Mora and Cobo, 1990). Moreover, excessive concentrations of glutamate appear toxic and lead to cell death (Lau and Tymian- ski, 2010). A few spectroscopy studies showed that individuals with 22q11DS and a diagnosis of schizophrenia have increased concentrations of glutamate in the hippocampus compared to those without schizophrenia and healthy controls (da Silva Alves et al., 2011). An addi- tional study reported higher plasma level of glutamate in patients with 22q11DS with low intellectual functioning compared to those with higher intellectual functioning (Evers et al., 2015). Glutamate transmission alterations have also been identified as a risk factor for psy-

chosis(Moghaddam and Javitt, 2012). In addition to abnormal glutamatergic transmission, an hyperprolineamia (elevated level of proline) is observed in one third of the patients with 22q11DS, which may predispose to schizophrenia disorders (Evers et al., 2015; Goodman et al., 2000; Jacquet et al., 2002; Raux et al., 2007; Vorstman et al., 2009). To date, no association between PRODH haploinsufficiency and psychotic symptoms has been reported.

COMTencodes the cathechol-o-Methyltransferase enzyme, which degrades catecholamines including dopamine. In healthy individuals, a common polymorphism of the COMT gene results in a valine (VAL) to methionine (MET) substitution, leading to a change in enzy- matic activity responsive to the dopamine degradation (Chen et al., 2004). The COMT Val carriers exhibit an approximately 40% higher enzymatic activity than COMT-Met carriers, resulting in higher dopamine level. The COMT gene is particularly expressed in the pre- frontal cortex (PFC), where it accounts for 60% of the dopamine turnover (Karoum et al., 1994). Thus, carrying the MET or Val allele strongly influences PFC cognitive functions (Scheggia et al., 2012). In the general population, it has been shown that the Val polymor- phism is associated with an increased risk to develop schizophrenia. Thus, Val homozygous individuals have a higher risk to develop psychosis compared to people with a Val/Met or Met/Met polymorphism (Tunbridge et al., 2006). In the 22q11DS population, the opposite pattern was observed, as the Met polymorphism has been associated with higher risk for psychosis (Goldman-Rakic et al., 2000). According to the Goldman-Rakic model (2000), the relationship between dopamine and PFC cognitive function relies on an inverted U-shaped curve (Figure 1.5), meaning that a certain level of dopamine is required for typical cognitive functioning, while too low or too high level of dopamine seems have a deleterious impact (Goldman-Rakic et al., 2000; Vijayraghavan et al., 2007). As individuals with 22q11DS only have one copy of the Met allele, this will lead to excessively high levels of dopamine. On this opposite in the general population, having a Val/Val genotype leads to excessively low levels of dopamine, placing them on the left side of the curve (Figure 1.5).

In both cases, non-optimal dopamine level is thought to be associated with prefrontal alterations, cognitive difficulties and increased for psychosis (Gothelf et al., 2008). More- over, one study examined dopamine neurotransmission in 22q11DS using neuro-endocrine and peripheral dopamine markers and found a higher index of dopamine turnover compared to healthy controls (Boot et al., 2008). An additional study investigated striatal dopamine release during reward processing and reported higher caudate dopamine release in Met hem- izygotes in comparison to Val hemizygotes (van Duin et al., 2018). However, in the 22q11DS population the relation between the COMT gene and the psychiatric phenotype remains largely unclear (See for a review Armando et al., 2012b). Indeed, inconsistent results were observed, while a few studies reported higher psychotic symptoms in the COMT-Met group than COMT-Val group (Gothelf et al., 2005, 2007) , additional studies did not find signif- icant differences in term of psychotic symptoms between the Met/Val carriers in 22q11DS individuals (Antshel et al., 2010; Baker and Skuse, 2005; Bassett et al., 2007; Murphy et al., 1999).

Figure 1.5: Illustration of the inverted U-shaped relationship between prefrontal dopamine level and cognitive function in the general population and patients with 22q11DS (Gothelf et al.,

2008)(from Gothelf et al., 2008).

Gene-gene interaction associated with the risk of schizophrenia

Given that approximately 40 genes have been identified in the 22q11.2 locus, it is likely that the 22q11DS psychiatric phenotype is not influenced by a single gene but rather by the interaction of several genes. To date, the gene-gene interaction between COMT and PROH has received more interest in the literature. While COMT deficiency leads to in- crease dopamine level in prefrontal cortex, PRODH deficiency underlies increased proline concentration in the brain. Paterlini et al. (2005) reported an interaction between PRODH and COMT at a transcriptional and behavioral level in a mouse model (Paterlini et al., 2005).

The authors observed that PRODH deficient mice showed upregulation of COMT, leading to increased dopamine concentration in the prefrontal cortex secondary to the gene deficiency (Paterlini et al., 2005). Additionally, the interaction between the PRODH and COMT genes was associated with a schizophrenia-like phenotype (Paterlini et al., 2005). In line with these results, it was found that 22q11DS individuals with both hyperprolineamia and the COMT Met allele exhibited higher risk for psychiatric disorders (Raux et al., 2007). Recently, an association between the COMT-PRODH interaction and negative symptoms was reported in patients with schizophrenia and bipolar disorder (Clelland et al., 2016). However, additional results appear more controversial, thus the implication of COMT-PRODH interaction on the risk of psychosis still remains unclear in 22q11DS (de Koning et al., 2015; Vorstman et al., 2009; Zarchi et al., 2013). An additional gene-gene interaction that received some interest is the one between COMT and DTPNB, a gene located outside the 22q11.2 region. The DTNBP1 (dys; dystrobrevin-binding protein 1) encodes for the dysbinding protein. This

protein plays a role in D2 receptors trafficking, thus downregulation of this protein leads to upregulation of D2 receptors and increased D2 signaling. Reduced expression of dys has been associated to the risk for schizophrenia (Bray et al., 2005). In schizophrenia, the associ- ation between reduced dys expression and the COMT Met/Met genotype leads to impaired working memory in mouse and human model (Papaleo et al., 2014). Thus, the COMT-Dys interaction may represent a risk factor for psychosis in the 22q11DS population.

CHAPTER

2

NEGATIVE SYMPTOMS

Since the early writings on schizophrenia, negative symptoms have been considered as a core feature of the disorder. Besides, the predominance of negative symptoms in the clinical picture has been associated with a less favourable prognostic encompassing poor response to medication and decreased functional outcome. During many years, research on negative symptoms has been neglected in favour of positive symptoms. Recently, due to accumu- lating evidence pointing to their persistence, lack of treatment responsiveness and strong impact on real-life functioning, a resurgence of interest in mechanisms underlying negative symptoms emerged. In this second chapter, we will first present the conceptualization of schizophrenia, progressively distinguishing positive and negative symptoms (Section 1). We will then describe the scales most frequently used to assess negative symptoms that led to a heterogeneity of definitions of negative symptoms. In view of this heterogeneity, we will present recent works that have led to a reconceptualization and unified definition of negative symptoms (Section 2). Finally, we will present the numerous reasons that contributed to a renewed interest towards negative symptoms (Section 3).

2.1 History of the concept

Since the end of the 19th century, symptoms of schizophrenia have been divided in two do- mains. Positive symptoms, reflecting an excess of normal functions, and negative symptoms, defined as a reduction or absence of normal functions. Positive symptoms typically include

symptoms such as hallucinations or delusions, whereas the conceptualization of negative symptoms has greatly evolved over time before reaching its current definition. Nowadays, negative symptoms are defined as including five constructs namely blunted affect, alogia, anhedonia, asociality and avolition. This section will aim to provide a history of the concept of negative symptoms in schizophrenia.

The first mention of negative symptoms in the field of psychiatry dates back to the 19th century by John Hughlings Jackson (Jackson, 1931) cited by (Dollfus and Lyne, 2017).

Jackson proposed a hierarchical model of the nervous system, according to which brain is or- ganized like an onion with different layers. Jackson’s theory suggests that a single mechanism leads to the expression of positive and negative symptoms. He postulated that superior cere- bral centers exert an inhibitory control over the inferior centers. According to him, negative symptoms would derive from the ‘dissolution of the cerebral centers’, whereas positive symp- toms would be due to a release of inhibition on the inferior centers reflecting the expression of primitive layers. At the same time, the first descriptions of schizophrenia-like conditions emerged. Kraepelin (Kraepelin, 1919) cited by (Dollfus and Lyne, 2017) proposed the term of dementia praecox, which he defined as a single entity. Bleuler (1911, cited by Dollfus and Lyne 2017) introduced the term of schizophrenia, which he conceptualized as a set of disor- ders - in opposition to Kraepelin - given the heterogeneity of the symptoms observed among individuals. Both, Kraepelin and Bleuler noted that some symptoms dominated the clini- cal picture. Even if the term of negative symptoms was not introduced yet, Kraepelin and Bleuler described manifestations including lack of volition, emotional flatness and withdrawal as central features of the illness. Besides, Bleuler proposed a distinction between classes of symptoms. He differentiated fundamental symptoms, referring to impairment in thought, af- fectivity and attitude towards the outside world, from accessory symptoms, mainly referring to hallucinations and delusions. Thus, both authors conceptualized the core of schizophre- nia to be negative symptomatology. It was a Russian psychiatrist, Snezhenevsky (1968) who first proposed the distinction between positive and negative symptoms and introduced the term of negative symptoms in the field of psychiatry (Snezhenevsky et al. 1968, cited by (Malaspina et al., 2014). During the 1980s, this dichotomous approach was used by Crow (1980), who described two subtypes of schizophrenia: type I associated with positive symp- toms and Type II associated with negative symptoms (Crow, 1980). According to Crow, type I was associated with a better prognosis, favorable response to medication, potential remission, and no intellectual impairment. Type II was associated with poor response to medication, persistent symptomatology, intellectual impairment and poor long-term out- come. He postulated that the two subtypes were sustained by distinct biological substrates, Type I being associated with changes in the dopamine pathway and Type II being related to intellectual impairment and structural changes. A few years later, Carpenter and colleagues (1988) proposed the distinction between primary and secondary negative symptoms (Car- penter et al., 1988). Primary negative symptoms referring to symptoms that are intrinsic to schizophrenia; secondary negative symptoms being symptoms caused by others factors than the illness as positive symptoms, depression, and side effect of medication. Carpenter et al. (1988) introduced the concept of deficit schizophrenia to describe a subgroup of patients

characterized by the presence of primary and persistent negative symptoms.

Through this section, we demonstrated that since the early 19th, a core place have been attributed to negative symptoms in the conceptualization of schizophrenia. Previous works suggested that negative symptoms are partially sustained by distinct mechanisms from those of positive symptoms. Repeatedly, negative symptoms have been associated with a poor prognosis. In particular, unfavorable response to antipsychotics and poor long-term outcomes, have been reported.

2.2 Structure and evaluation of negative symptoms

Numerous definitions of negative symptoms have been proposed over time, which resulted in the development of various assessment scales. In this section we will first present the scales commonly used to assess negative symptoms in schizophrenia and at-risk populations. We will then describe the work that led to the current definition of negative symptoms. Finally, we will present how this new definition contributed to the development of the new assessment scales of negative symptoms.

2.2.1 Scales frequently used to measure negative symptoms

Three scales are commonly used to evaluate the severity of negative symptoms in individuals with schizophrenia, namely the Brief Psychiatric Rating Scale (BPRS, (Overall and Gorham, 1962), the Positive and Negative Syndrome Scale (PANSS,(Kay et al., 1987) and the Scale for the Assessment of Negative Symptoms (SANS, Andreasen, 1982). While the SANS has been specifically developed to evaluate negative symptoms, the PANSS and BPRS evalu- ate the symptomology in a broader way, including also general symptoms as depression or anxiety. The BPRS was developed in the 60’s in order to describe the variety of symptoms present in psychiatric disorders. The scale encompasses 18 items rated on a seven-point Likert scale ranging from 0 (‘not present’) to 6 (‘extreme severe’). Although this scale was not specifically created for schizophrenia, it is widely used to assess the severity of positive and negative symptoms of schizophrenia. However, according to Nicholson et al., there are inconsistencies in the way symptoms factors are defined (Nicholson et al., 1995). Differ- ent studies have thus employed different combinations of symptoms to measure the same dimension. The authors showed that at least four combinations have been used to define negative symptoms. Given their high internal consistency, the authors recommend to use the following BPRS items combination to assess negative symptoms: emotional withdrawal, motor retardation and blunted affect. The PANSS includes 30-items divided in three di- mensions: positive symptoms, negative symptoms and general psychopathology. The items considered to measure negative symptoms are: blunted affect, emotional withdrawal, poor rapport, passive/apathetic social withdrawal, lack of spontaneity and flow of conversation.

However, factorial analysis studies highlighted that two items (motor retardation and active social avoidance) classified in the general domain tend to load on the negative dimension (van der Gaag et al., 2006). The SANS has been developed by Andreasen in 1982. She defined 20 negative symptoms grouped into five factors: affective flattening, alogia, avoli- tion/apathy, anhedonia/asociality and attentional impairment. Each item is rated from 0 (‘no evidence’) to 5 (‘severe’). Two scales aimed to assess clinical high-risk for psychosis are also frequently used to measure the severity of negative symptoms: the Structure Interview for Psychosis-Risk Syndromes (SIPS) and the Comprehensive Assessment of At-risk Mental States (CAARMS). In the CAARMS, three symptoms rated from 0 to 6 measure negative symptoms: alogia, avolition/apathy and anhedonia. In the SIPS, 6 items rated from 0 to 6 al- low the evaluation of negative symptoms: social anhedonia, avolition, expression of emotion, experience of emotion and self, ideational richness and occupational functioning. Neverthe- less, a recent study conducted in the 22q11DS population assessed the factor structure of negative symptoms based on the SIPS and showed that two items ‘Ideational Richness’ and

‘Occupational Functioning’ did not load on the negative symptom factor and thus do not seem to measure the construct of negative symptoms in this population (Schneider et al., 2018).

2.2.2 New conceptualization of negative symptoms

Given the heterogeneity of definitions of negative symptoms and the variety of scales de- veloped, the National Institute of Mental Health (NIMH) - Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) decided in 2005 to group ex- perts on the topic of negative symptoms. Mainly, this conference aimed to achieve consensus regarding the constructs that should be included in the negative dimension and to initiate the development of new scales to measure negative symptoms. The experts agreed on the inclu- sion of five constructs in the negative symptom dimension: blunted affect, alogia, anhedonia, asociality and avolition. According to factorial analysis conducted on negative symptoms, the five constructs could be divided in two main factors: a motivation dimension referring to anhedonia, avolition and asociality and an expressive dimension including blunted affect and alogia (Liemburg et al., 2013; Strauss et al., 2013). Liemburg et al. (2013) examined the structure of negative symptoms through the PANSS in two large cohorts, one composed of 650 patients and the second of 2000 patients with schizophrenia. Strauss et al. (2013) assessed the structure of negative symptoms first using the SANS in a sample including 199 patients with schizophrenia and secondly using the Schedule for the Deficit Syndrome (SDS), an additional scale aimed to measure negative symptoms, with 169 patients with a deficit syndrome, a form of schizophrenia characterized by primary negative symptoms. In both studies, a structure with two factors was found, one factor including symptoms that assess diminished expression and a second factor including symptoms measuring the motivational dimension. Through these studies the bi-factorial model of negative symptoms in schizophre- nia was thus confirmed. In parallel, an analysis exploring the factorial structure of negative

symptoms in the 22q11DS population was conducted (Schneider et al., 2012)(Schneider et al., 2012). Results were similar to those obtained in schizophrenia, as the authors found that negative symptoms were explained by a two-factor solution including ‘amotivation and social withdrawal’ and ‘emotional withdrawal and expression’ (Schneider et al., 2012).

2.2.3 Development of new scales to assess negative symptoms

Following the NIMH-MATRICS conference, two groups were formed to develop new assess- ment scales of negative symptoms. The Brief Negative Symptoms Scale (BNSS, (Kirkpatrick et al., 2006) was designed to be short enough to be feasible in clinical practice and multi- center studies, whereas the Clinical Assessment Interview for Negative Symptoms (CAINS, (Kring and Barch, 2014a) was designed to assess in details the five negative symptom sub- domains proposed by the consensus. The BNSS includes 13-items rated from 0 (‘absent’) to 6 (‘severe’) and evaluates the 5 domains recommended by the NIMH consensus as well as an additional item, Lack of Normal Distress. Moreover, the distinction between anticipatory and consummatory anhedonia has been added, given preliminary evidence showing that indi- viduals with schizophrenia may have alterations of the anticipatory pleasure dimension only (Chan et al., 2010; Favrod et al., 2009; Gard et al., 2006; Lui et al., 2015; Mote et al., 2014;

Wynn et al., 2010). For each domain, both internal experience and behavior are evaluated.

The CAINS was designed to measure each of the five negative dimensions in more details compared to the BNSS. The original version was composed of 23-items. Its evaluation across 2 large-scale multisite studies resulted in a final version of 13-items defined in two factors:

motivation/pleasure (9 items) and expression (4 items).

At the beginning of the Geneva cohort in 2002, the relevance of negative symptoms in the clinical picture of individuals with 22q11DS was still unknown. The PANSS was thus introduced to obtain a large description of symptoms. As individuals with 22q11DS are at increased risk for schizophrenia, the Structure Interview for Psychosis-Risk Syndromes (SIPS) was chosen to assess the severity of attenuated positive and negative symptoms. The importance of negative symptoms in the 22q11DS having been shown only belatedly, the BNSS, specifically measuring negative symptoms was introduced in the Geneva cohort later in 2017 and could therefore not be used in this project.

2.3 Negative symptoms as a key component in psychosis

2.3.1 Prevalence and persistence of negative symptoms

Prevalence /Persistence in psychosis spectrum disorders

In schizophrenia, the proportion of patients with negative symptoms has been estimated as ranging between 40% and 58% (depending on the definition and assessment of negative symptoms) (Bobes et al., 2009; Cohen et al., 2013; J¨ager et al., 2009). Recently, a large study conducted with over 7000 individuals with schizophrenia used the Clinical Record Interactive Search Negative Symptoms Scale (CRIS-NSS), a novel automated method to acquire data on negative symptoms from electronic health records (Patel et al., 2015). Au- thors reported that almost 41% of individuals present at least two negative symptoms. The most reported symptoms were amotivation (30.5%), blunted affect (27.4%), poor eye con- tact (26%) and emotional withdrawal (23.5%) (Patel et al., 2015). As mentioned in section 3.1, Carpenter and colleagues proposed a dichotomy between primary negative symptoms (i.e. symptoms that are intrinsic to schizophrenia) and secondary negative symptoms (i.e.

symptoms caused by others factors than the illness). Whereas most studies in schizophrenia showed that secondary negative symptoms can be improved in the context of improvement of positive, depressive and/or extrapyramidal symptoms, primary negative symptoms appear to be persistent over time. Several studies showed that negative symptoms persist in about 45% of cases when a short-term follow-up (up to 2.5 years) is considered (Malla et al., 2004, 2002; Pogue-Geile and Harrow, 1985), and in 20-30% of cases in long-term (7.5-10 years) follow-up studies (Herbener and Harrow, 2001). Negative symptoms are also present across a large variety of disorders and therefore can be considered as transdiagnostic manifestations.

Indeed, a high prevalence of negative symptoms has also been reported in patients not meet- ing criteria for a schizophrenia spectrum diagnosis (Lyne et al., 2012). A study conducted in 330 first-episode-psychosis patients using the SANS demonstrated that patients having a score of 3 or higher on any item was respectively, 74% for substance induced psychotic disorder, 68% for Major Depressive Disorder, 64% for Delusional disorder, 29% for Brief psychotic disorder, 29% for Bipolar disorders, 51% for other psychotic diagnoses.

Several studies also suggested that negative symptoms are present during the clinical high-risk stage (Azar et al., 2018; Piskulic et al., 2012; Sauv´e et al., 2019). For instance, Piskulic et al. (2012) used data from the North American Prodrome Longitudinal Study (NAPLS), which represents one of the most extensive longitudinal databases on ultra-high risk (UHR) and reported that 82% of individuals with UHR status have at least one nega- tive symptom (measured with the SIPS) at baseline, whereas 54% met these criteria after 12 months. Moreover, a recent meta-analysis including 1838 individuals meeting criteria for a UHR condition reported that avolition and asociality symptoms was present in approxi- mately 50% of cases, blunted affect in 21% of cases, and alogia 21% of cases (Sauv´e et al., 2019). Anhedonia was not considered in the context of this study.

Prevalence/Persistence in the 22q11DS population

In the 22q11DS population, two cross-sectional studies assessed negative symptoms using the SIPS and reported that approximately 60 to 80% of individuals with 22q11DS present at