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Deepak Cyril D'Souza, Staff Psychiatrist, VA Connecticut Healthcare System; Professor of Psychiatry, Yale University School of Medicine,David Castle, University of Tasmania, Australia,Sir Robin Murray, Honorary Consultant Psychiatrist, Psychosis Service at the South London and Maudsley NHS Trust; Professor of Psychiatric Research at the Institute of Psychiatry
The fact that not all cannabis users will develop psychosis suggests that cannabis may exert its causal role only in pre-disposed individuals. However, since the number of people who use cannabis worldwide is so high, those who will eventually develop psychosis, whilst still a minority, represent a large number. The evidence indicates that different patterns of cannabis use have a different impact on the risk of developing psychosis, with young age at first use, and a higher frequency of use of high-potency types of cannabis indicated as the most important risk factors. Nonetheless, given the complex nature of the association between cannabis use and psychosis, it is hard to determine which cannabis users will eventually develop psychosis. The link between cannabis use and schizophrenia is unlikely to be just the result of a genetic predisposition, it is more likely the result of Gene x Environment inter-play.
Childhood adversity and cannabis use are considered independent risk factors for psychosis, but whether different patterns of cannabis use may be acting as mediator between adversity and psychotic disorders has not yet been explored. The aim of this study is to examine whether cannabis use mediates the relationship between childhood adversity and psychosis.
Data were utilised on 881 first-episode psychosis patients and 1231 controls from the European network of national schizophrenia networks studying Gene–Environment Interactions (EU-GEI) study. Detailed history of cannabis use was collected with the Cannabis Experience Questionnaire. The Childhood Experience of Care and Abuse Questionnaire was used to assess exposure to household discord, sexual, physical or emotional abuse and bullying in two periods: early (0–11 years), and late (12–17 years). A path decomposition method was used to analyse whether the association between childhood adversity and psychosis was mediated by (1) lifetime cannabis use, (2) cannabis potency and (3) frequency of use.
The association between household discord and psychosis was partially mediated by lifetime use of cannabis (indirect effect coef. 0.078, s.e. 0.022, 17%), its potency (indirect effect coef. 0.059, s.e. 0.018, 14%) and by frequency (indirect effect coef. 0.117, s.e. 0.038, 29%). Similar findings were obtained when analyses were restricted to early exposure to household discord.
Harmful patterns of cannabis use mediated the association between specific childhood adversities, like household discord, with later psychosis. Children exposed to particularly challenging environments in their household could benefit from psychosocial interventions aimed at preventing cannabis misuse.
While cannabis use is a well-established risk factor for psychosis, little is known about any association between reasons for first using cannabis (RFUC) and later patterns of use and risk of psychosis.
We used data from 11 sites of the multicentre European Gene-Environment Interaction (EU-GEI) case–control study. 558 first-episode psychosis patients (FEPp) and 567 population controls who had used cannabis and reported their RFUC.
We ran logistic regressions to examine whether RFUC were associated with first-episode psychosis (FEP) case–control status. Path analysis then examined the relationship between RFUC, subsequent patterns of cannabis use, and case–control status.
Controls (86.1%) and FEPp (75.63%) were most likely to report ‘because of friends’ as their most common RFUC. However, 20.1% of FEPp compared to 5.8% of controls reported: ‘to feel better’ as their RFUC (χ2 = 50.97; p < 0.001). RFUC ‘to feel better’ was associated with being a FEPp (OR 1.74; 95% CI 1.03–2.95) while RFUC ‘with friends’ was associated with being a control (OR 0.56; 95% CI 0.37–0.83). The path model indicated an association between RFUC ‘to feel better’ with heavy cannabis use and with FEPp-control status.
Both FEPp and controls usually started using cannabis with their friends, but more patients than controls had begun to use ‘to feel better’. People who reported their reason for first using cannabis to ‘feel better’ were more likely to progress to heavy use and develop a psychotic disorder than those reporting ‘because of friends’.
Transmission of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has led to a global pandemic. Many studies are underway to ascertain the mental health impact of this seismic event, however no study has investigated its effect on psychosis incidence. We hypothesise that the overall crude incidence rates of first episode psychosis (FEP) will be higher during the pandemic when comparing the same area of South London in defined pre-pandemic and pandemic time periods.
Clinical records for all patients aged 18 to 64 years presenting to early intervention in psychosis services in the London boroughs of Southwark and Lambeth between July 1st 2019 to December 31st 2019 (pre-pandemic period) and July 1st 2020 to December 31st 2020 (pandemic period) were extracted from the Clinical Record Interactive Search (CRiS), an online database containing anonymised patient records. All patients were manually screened using the Screening Schedule for Psychosis to confirm FEP, with 104/235 cases meeting criteria for FEP in the pre-pandemic period compared with 158/376 in the pandemic period. Crude, age-standardised, and sex-standardised incidence rates and ratios were calculated for interpretation.
The crude incidence rate of FEP was significantly higher in the pandemic period (68.3, 95% CI:[57.6 ; 78.9]) than the pre-pandemic period (44.9, 95% CI:[36.3 ; 53.6]). The crude incidence ratio was 1.52 (95% CI:[1.28 ; 1.77]), indicating that the overall crude incidence of FEP in the pandemic period was significantly higher (52%) than in the pre-pandemic period. The directionality and statistical significance of this ratio was unperturbed by standardisation for age (SIR = 1.45, 95% CI[1.23 ; 1.70]) and sex (SIR = 1.56, 95% CI[1.33 ; 1.83]).
Our results suggest that the COVID-19 pandemic has had a significant impact on the incidence of FEP in the South London boroughs of Southwark and Lambeth. Further research is required to elucidate the factors contributing to this increase to inform targeted interventions and prevent deterioration in at-risk patients.
Schizophrenia (SZ), bipolar disorder (BD) and depression (D) run in families. This susceptibility is partly due to hundreds or thousands of common genetic variants, each conferring a fractional risk. The cumulative effects of the associated variants can be summarised as a polygenic risk score (PRS). Using data from the EUropean Network of national schizophrenia networks studying Gene-Environment Interactions (EU-GEI) first episode case–control study, we aimed to test whether PRSs for three major psychiatric disorders (SZ, BD, D) and for intelligent quotient (IQ) as a neurodevelopmental proxy, can discriminate affective psychosis (AP) from schizophrenia-spectrum disorder (SSD).
Participants (842 cases, 1284 controls) from 16 European EU-GEI sites were successfully genotyped following standard quality control procedures. The sample was stratified based on genomic ancestry and analyses were done only on the subsample representing the European population (573 cases, 1005 controls). Using PRS for SZ, BD, D, and IQ built from the latest available summary statistics, we performed simple or multinomial logistic regression models adjusted for 10 principal components for the different clinical comparisons.
In case–control comparisons PRS-SZ, PRS-BD and PRS-D distributed differentially across psychotic subcategories. In case–case comparisons, both PRS-SZ [odds ratio (OR) = 0.7, 95% confidence interval (CI) 0.54–0.92] and PRS-D (OR = 1.31, 95% CI 1.06–1.61) differentiated AP from SSD; and within AP categories, only PRS-SZ differentiated BD from psychotic depression (OR = 2.14, 95% CI 1.23–3.74).
Combining PRS for severe psychiatric disorders in prediction models for psychosis phenotypes can increase discriminative ability and improve our understanding of these phenotypes. Our results point towards the potential usefulness of PRSs in specific populations such as high-risk or early psychosis phases.
Various psychological and biological pathways have been proposed as mediators between childhood adversity (CA) and psychosis. A systematic review of the evidence in this domain is needed. Our aim is to systematically review the evidence on psychological and biological mediators between CA and psychosis across the psychosis spectrum. This review followed PRISMA guidelines. Articles published between 1979 and July 2019 were identified through a literature search in OVID (PsychINFO, Medline and Embase) and Cochrane Libraries. The evidence by each analysis and each study is presented by group of mediator categories found. The percentage of total effect mediated was calculated. Forty-eight studies were included, 21 in clinical samples and 27 in the general population (GP) with a total of 82 352 subjects from GP and 3189 from clinical studies. The quality of studies was judged as ‘fair’. Our results showed (i) solid evidence of mediation between CA and psychosis by negative cognitive schemas about the self, the world and others (NS); by dissociation and other post-traumatic stress disorder symptoms; and through an affective pathway in GP but not in subjects with disorder; (iii) lack of studies exploring biological mediators. We found evidence suggesting that various overlapping and not competing pathways involving post-traumatic and mood symptoms, as well as negative cognitions contribute partially to the link between CA and psychosis. Experiences of CA, along with relevant mediators should be routinely assessed in patients with psychosis. Evidence testing efficacy of interventions targeting such mediators through cognitive behavioural approaches and/or pharmacological means is needed in future.
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