Criblage génétique et caractérisation fonctionnelle des mutations dans les différentes sous-unités du récepteur GABAA associées à l'épilepsie génétique généralisée

Les épilepsies génétiques généralisées (ÉGGs) sont un groupe de syndromes épileptiques hétérogènes qui se manifestent habituellement durant les périodes de l’enfance et de l’adolescence. Les ÉGGs représentent 30% de toutes les épilepsies. Il n’existe présentement aucun remède à l’épilepsie génétique généralisée. Au sein de ce groupe d’épilepsies, les sujets sont le plus souvent dépourvus de lésions cérébrales, ce qui signifie que les facteurs génétiques jouent un rôle important dans l’étiologie de la maladie. Au cours des dernières années, plusieurs gènes impliqués dans des formes familiales d’ÉGG ont été identifiés. La majorité d'entre elles codent pour des canaux ioniques incluant le récepteur-ligand GABAA (RGABAA). De ce groupe, des mutations ont été identifiées dans quatre sous-unités du récepteur GABAA. Dans un premier temps, l’objectif général de cette thèse vise l’évaluation de la composante génétique de notre cohorte d’ÉGG expliquée par les gènes codant pour les sous-unités du récepteur GABAA. Puis, dans un second souffle, le rôle des variants identifiés est défini et analysé afin de mieux cerner leurs impacts dans la pathogénèse de ce phénotype. La première partie du projet consiste en une analyse exhaustive des mutations existantes dans la partie codante des 19 gènes GABRA pour des patients atteints d’ÉGG. En criblant des familles québécoises avec ÉGG, nous avons identifié 22 variants rares incluant 19 faux-sens et 3 non-sens dans 14 sous-unités du RGABAA. En séquençant ces gènes dans une grande cohorte de cas et de contrôles, nous avons établi le profil des variations rares pour ceux-ci. Ces données suggèrent qu’une proportion significative (8%) des patients atteints d’ÉGG ont des variants rares sur les gènes du RGABAA. La deuxième partie porte directement sur certains gènes identifiés lors de la première partie. De ce groupe, cinq nouvelles mutations ont été découvertes dans des gènes déjà associés à l’épilepsie (GABRA1 et GABRG2). Nous avons constaté l’impact de ces mutations dans les mécanismes génétiques de l’épilepsie, en mesurant les effets des variants sur la structure et la fonction du récepteur GABAA. La troisième partie se concentre sur notre hypothèse, voulant que les RGABAA mutants altèrent l’effet du GABA durant le développement du système nerveux central (SNC). L’objectif principal vise à déterminer la contribution relative de chacune des sous-unités mutées dans le développement du SNC. Ainsi, nous avons démontré qu’une telle perte de fonction a un impact significatif sur le développement des synapses GABAergiques et glutamatergiques ainsi que sur la plasticité des circuits corticaux. Nos résultats nous ont permis de préciser comment les mutations dans les gènes GABRA peuvent mener à l’ÉGG. Éventuellement, la caractérisation moléculaire de ces mutations contribuera à l’élaboration de nouveaux outils diagnostiques et facilitera la mise au point de traitements mieux ciblés pour les gens atteints de cette condition neurologique chronique.Genetic generalized epilepsy (GGE) syndrome is a group of epilepsy disorders that occur early in childhood and adolescence. Genetics generalized epilepsies (GGE) account for approximately 30 % of all epilepsy syndromes. There is currently no cure for GGE. Although patients with GGE typically have no anatomical brain abnormalities, the root cause of these conditions is considered to be genetic in origin. An increasing number of genes predisposing to epilepsy have been identified over the past ten years. It has emerged in many cases that the causative genes for inherited epilepsies code for ion-channels such as the GABAA receptor (GABAAR). Among these genes, mutations in four subunits of the GABAA receptor appear to be an important cause of familial epilepsy. The main aim of the present thesis is to better characterize the genetic component of our GGE cohort explain by GABRA genes and evaluated the critical role of these variants in the pathogenesis of this phenotype. The first part of our project was to investigate the impact of rare variants of GABAAR in GGE, we screened the coding regions of 19 genes encoding for all the known subunits of the GABAAR in unrelated GGE patients, including familial cases. Overall, approximately 8% of our GGE individuals have novel GABRA mutations, including 19 missenses and 3 nonsenses including 1 frameshift mutation. By sequencing those genes in a large cohort of cases and controls, we were able to establish the profile of rare variants for these genes. Our data suggest that a significant proportion of GGE patients share rare variants in GABRA genes. The second part of the work builds on the genes bearing mutations identified in the sequencing analysis. Among this group, five novel mutations have been so far associated to this syndrome (GABRA1 and GABRG2). We characterized the gating properties of GABA-evoked currents and the subcellular localization of the mutated subunits by expressing recombinant GABAA receptors in vitro. The third part of the work aimed to characterize the impact of mutated GABAA receptors on synapse formation and development of neuronal networks. By knocking down these genes in cortical organotypic slices, we provided a better understanding of the specific and distinct neural circuit alterations caused by different GABRA1 mutations and help define the pathophysiology of genetic generalized epilepsy syndromes. We believe that these findings will allow a better understanding of the genetic mechanisms underlying the disease and involve mutations in GABAA receptors in critical mechanisms leading to epilepsy. Eventually, our results could lead to a better diagnosis and counteract the devastating effects of some GGEs early on before this complex condition has had the opportunity to be established

Reducing cannabis use in young adults with psychosis using iCanChange, a mobile health app : protocol for a pilot randomized controlled trial (ReCAP-iCC)

Background: Cannabis use is the most prevalent among adolescents and young adults; frequent consumption is associated with cannabis use disorder (CUD) and psychosis, with a high prevalence (up to 50%) of CUD in individuals with first-episode psychosis (FEP). Early Intervention Services (EIS) for psychosis include face-to-face psychosocial interventions for CUD, because reducing or discontinuing cannabis use improves clinical and health care service use outcomes. However, multiple barriers (eg, staff availability and limited access to treatment) can hinder the implementation of these interventions. Mobile health (mHealth) interventions may help circumvent some of these barriers; however, to date, no study has evaluated the effects of mHealth psychological interventions for CUD in individuals with FEP. Objective: This study describes the protocol for a pilot randomized controlled trial using a novel mHealth psychological intervention (iCanChange [iCC]) to address CUD in young adults with FEP. iCC was developed based on clinical evidence showing that in individuals without psychosis, integrating the principles of cognitive behavioral therapy, motivational interviewing, and behavioral self-management approaches are effective in improving cannabis use–related outcomes. Methods: Consenting individuals (n=100) meeting the inclusion criteria (eg, aged 18-35 years with FEP and CUD) will be randomly allocated in a 1:1 ratio to the intervention (iCC+modified EIS) or control (EIS) group. The iCC is fully automatized and contains 21 modules that are completed over a 12-week period and 3 booster modules available during the 3-month follow-up period. Validated self-report measures will be taken via in-person assessments at baseline and at 6, 12 (end point), and 24 weeks (end of trial); iCC use data will be collected directly from the mobile app. Primary outcomes are intervention completion and trial retention rates, and secondary outcomes are cannabis use quantity, participant satisfaction, app use, and trial recruiting parameters. Exploratory outcomes include severity of psychotic symptoms and CUD severity. For primary outcomes, we will use the chi-square test using data collected at week 12. We will consider participation in iCC acceptable if ≥50% of the participants complete at least 11 out of 21 intervention modules and the trial feasible if attrition does not reach 50%. We will use analysis of covariance and mixed-effects models for secondary outcomes and generalized estimating equation multivariable analyses for exploratory outcomes. Results: Recruitment began in July 2022, and data collection is anticipated to be completed in July 2024. The main results are expected to be submitted for publication in 2024. We will engage patient partners and other stakeholders in creating a multifaceted knowledge translation plan to reach a diverse audience. Conclusions: If feasible, this study will provide essential data for a larger-scale efficacy trial of iCC on cannabis use outcomes in individuals with FEP and CUD

Evaluation of a Cannabis Harm Reduction Intervention for People With First-Episode Psychosis: Protocol for a Pilot Multicentric Randomized Trial

BackgroundCannabis use is highly prevalent in young people with first-episode psychosis (FEP). Most report cannabis use and are often diagnosed with a cannabis use disorder upon admission to specialized services for psychosis. Cannabis use in this population is associated with worse clinical and psychosocial outcomes, rendering it an important clinical target. Despite this, few cannabis-specific interventions have been developed for FEP and empirically evaluated through randomized controlled trials. Most evaluated interventions have targeted cannabis abstinence, with limited efficacy, but none have centered on harm reduction outcomes for people with FEP who use cannabis. Early intervention services (EIS), the standard of care for FEP, have not successfully addressed problematic cannabis use in people with FEP either. Clinical trials are needed to explore the potential of harm reduction strategies, although these should be preceded by robust pilot studies to establish optimal design and approaches. ObjectiveRecognizing the need for harm reduction strategies for individuals with FEP who use cannabis and based on research on patients’ preferences supporting harm reduction interventions, we developed a mobile app–based cannabis harm reduction intervention for this population. This intervention is called Cannabis Harm–reducing Application to Manage Practices Safely (CHAMPS). Here, we describe the protocol for a multicenter, 2-arm, parallel group, randomized pilot trial evaluating the acceptability of CHAMPS for people with FEP who use cannabis and the feasibility of conducting a full-scale trial in this population using CHAMPS. The impact on key clinical outcomes will also be explored. MethodsThis pilot trial aims to recruit 100 young people with FEP using cannabis from 6 Canadian EIS clinics. Participants will be randomized in a 1:1 ratio to CHAMPS+EIS or EIS-only. CHAMPS acceptability will be assessed using completion rates for the intervention arm. Trial feasibility will be assessed using a retention rate for randomized participants. Secondary outcomes will explore tendencies of change in the use of protective behavioral strategies and in motivation to change strategies. Exploratory outcomes include cannabis use–related problems, other substance use, the severity of dependence, psychotic symptoms, and health care service use. ResultsRecruitment began in December 2021. Data collection and analysis are expected to be completed in early 2024. Study results describing CHAMPS acceptability and trial feasibility will then be submitted for publication in a peer-reviewed journal. ConclusionsCHAMPS uniquely combines evidence-based approaches, patient perspectives, and mobile health technology to support harm reduction in people with FEP who use cannabis. Attaining adequate acceptability and feasibility through this trial may justify further exploration of harm reduction tools, particularly within the context of conducting a larger-scale randomized controlled trial. This pilot trial has the potential to advance knowledge for researchers and clinicians regarding a feasible and user-acceptable research design in the cannabis and early psychosis fields. Trial RegistrationClinicalTrials.gov NCT04968275, https://clinicaltrials.gov/ct2/show/NCT04968275 International Registered Report Identifier (IRRID)DERR1-10.2196/5309

Mutation Burden of Rare Variants in Schizophrenia Candidate Genes

<div><p>Background</p><p>Schizophrenia (SCZ) is a very heterogeneous disease that affects approximately 1% of the general population. Recently, the genetic complexity thought to underlie this condition was further supported by three independent studies that identified an increased number of damaging <i>de novo</i> mutations DNM in different SCZ probands. While these three reports support the implication of DNM in the pathogenesis of SCZ, the absence of overlap in the genes identified suggests that the number of genes involved in SCZ is likely to be very large; a notion that has been supported by the moderate success of Genome-Wide Association Studies (GWAS).</p><p>Methods</p><p>To further examine the genetic heterogeneity of this disease, we resequenced 62 genes that were found to have a DNM in SCZ patients, and 40 genes that encode for proteins known to interact with the products of the genes with DNM, in a cohort of 235 SCZ cases and 233 controls.</p><p>Results</p><p>We found an enrichment of private nonsense mutations amongst schizophrenia patients. Using a kernel association method, we were able to assess for association for different sets. Although our power of detection was limited, we observed an increased mutation burden in the genes that have DNM.</p></div

SKAT results for the dataset grouped by data source.

<p>* The significance threshold is p-value < 0.01.</p><p>SKAT results for the dataset grouped by data source.</p

Significant association made on a gene and exon basis.

<p>Significant association made on a gene and exon basis.</p

SKAT results for all exons on the assay.

<p>SKAT analysis were performed using only rare variants (< = 1%) and using exons as sets. The data sources are shown by the colors (Girard et al. = red, Xu et al. = Green, S2D project = Blue, Protein:Protein Interaction = Cyan). P-values significance threshold was set to 1.0 * 10⁻⁴ using simpleM method.</p

SKAT results for all genes on the assay.

<p>SKAT analysis were performed using only rare variants (< = 1%) and using genes as sets. The data sources are shown by the colors (Girard et al. = red, Xu et al. = Green, S2D project = Blue, Protein:Protein Interaction = Cyan). The significance threshold was set using a Bonferonni correction to 4.1 * 10⁻⁴.</p