Smoking initiation and schizophrenia: a replication study in a Chinese Han population

Polygenic risk scores for late smoking initiation associated with the risk of schizophrenia

Patients with schizophrenia display characteristic smoking-related behaviors and genetic correlations between smoking behaviors and schizophrenia have been identified in European individuals. However, the genetic etiology of the association remains to be clarified. The present study investigated transethnic genetic overlaps between European-based smoking behaviors and the risk of Japanese schizophrenia by conducting polygenic risk score (PRS) analyses. Large-scale European genome-wide association study (GWAS) datasets (n = 24,114-74,035) related to four smoking-related intermediate phenotypes [(i) smoking initiation, (ii) age at smoking initiation, (iii) smoking quantity, and (iv) smoking cessation] were utilized as discovery samples. PRSs derived from these discovery GWASs were calculated for 332 Japanese subjects [schizophrenia patients, their unaffected first-degree relatives (FRs), and healthy controls (HCs)] as a target sample. Based on GWASs of European smoking phenotypes, we investigated the effects of PRSs on smoking phenotypes and the risk of schizophrenia in the Japanese population. Of the four smoking-related behaviors, the PRSs for age at smoking initiation in Europeans significantly predicted the age at smoking initiation (R² = 0.049, p = 0.026) and the PRSs for smoking cessation significantly predicted the smoking cessation (R² = 0.092, p = 0.027) in Japanese ever-smokers. Furthermore, the PRSs related to age at smoking initiation in Europeans were higher in Japanese schizophrenia patients than in the HCs and those of the FRs were intermediate between those of patients with schizophrenia and those of the HCs (R² = 0.015, p = 0.015). In our target subjects, patients with schizophrenia had a higher mean age at smoking initiation (p = 0.018) and rate of daily smoking initiation after age 20 years (p = 0.023) compared with the HCs. A total of 60.6% of the patients started to smoke before the onset of schizophrenia. These findings suggest that genetic factors affecting late smoking initiation are associated with the risk of schizophrenia.

One-day tropisetron treatment improves cognitive deficits and P50 inhibition deficits in schizophrenia

The core features of schizophrenia (SCZ) include cognitive deficits and impaired sensory gating represented by P50 inhibition deficits, which appear to be related to the α7 nicotinic acetylcholine receptor (nAChR). An agonist of nAChR receptor may improve these defects. This study aimed to investigate how administering multiple doses of tropisetron, a partial agonist of nAChR, for 1 day would affect cognitive deficits and P50 inhibition deficits in SCZ patients. We randomized 40 SCZ non-smokers into a double-blind clinical trial with four groups: placebo, 5 mg/d, 10 mg/d, and 20 mg/d of oral tropisetron. Their P50 ratios were all more than 0.5 and they took risperidone at 3-6 mg/day for at least a month before participating in the experiment. We measured the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and P50 inhibition before and one day after treatment. After one day of treatment, the total RBANS scores of the 20 mg and 5 mg tropisetron groups, and the immediate memory of the 10 mg group were significantly higher than placebo group. The P50 ratio was smaller in the 5 mg and 10 mg groups than in the placebo group (both p < 0.05) after treatment. Furthermore, the improvement in RBANS total score was correlated with increased S1 latency (p < 0.05), and the increase in immediate memory score was correlated with decreased S2 amplitude. One day of treatment with tropisetron improved both cognitive and P50 inhibition deficits, suggesting that longer term treatment with α7 nAChR agonists for these deficits in SCZ may be promising.

Association of the manganese superoxide dismutase gene Ala-9Val polymorphism with age of smoking initiation in male schizophrenia smokers

Schizophrenia patients exhibit higher smoking rates than the general population. A growing body of evidence suggests that cigarette smoke impairs the antioxidant defense mechanisms, leading to oxidative damage. Manganese superoxide dismutase (MnSOD) is the major antioxidant in the mitochondria, catalyzing the metabolism of superoxide radicals to form hydrogen peroxide. Since the identification of a well-characterized functional polymorphism, Ala-9Val of MnSOD, a number of studies have evaluated the association between Val-9Ala and schizophrenia or cancer. In this study, we hypothesized that the functional polymorphism of MnSOD Ala-9Val was associated with smoking in patients with schizophrenia. This polymorphism was genotyped in 666 chronic male schizophrenia patients (smoker/never-smoker = 507/159) and 660 male controls (smoker/never-smoker = 360/300) using a case-control design. The cigarettes smoked per day (CPD) and smoking behaviors were evaluated by clinician-administered questionnaires and the Fagerstrom Test for Nicotine Dependence (FTND). The results showed no significant differences in MnSOD Ala-9Val genotype and allele distributions between the patients and healthy controls or between smokers and never-smokers in either patients or healthy controls alone. The smokers with the Ala allele started smoking significantly earlier (19.9 ± 5.8 vs. 21.7 ± 6.5 years, P = 0.005) only in patients. These results suggest that the MnSOD Ala-9Val polymorphism may not influence smoking status in a Chinese male schizophrenia population, but may influence the age at which smoking is started among schizophrenia smokers.

Does tobacco use cause psychosis? Systematic review and meta-analysis

BACKGROUND

Although the association between psychotic illness and cigarette smoking is well known, the reasons are unclear why people with psychosis are more likely to smoke than are the general population. We aimed to test several hypotheses. First, that daily tobacco use is associated with an increased risk of psychotic illness in both case-control and prospective studies. Second, that smoking is associated with an earlier age at onset of psychotic illness. Finally, that an earlier age at initiation of smoking is associated with an increased risk of psychosis. We also aimed to derive an estimate of the prevalence of smoking in patients presenting with their first episode of psychosis.

METHODS

We searched Embase, Medline, and PsycINFO and selected observational studies in which rates of smoking were reported in people with psychotic disorders, compared with controls. We calculated the weighted mean difference for age at onset of psychosis and age at initiation of smoking. For categorical outcomes, we calculated odds ratios from cross-sectional studies and risk ratios from prospective studies.

FINDINGS

Of 3717 citations retrieved, 61 studies comprising 72 samples met inclusion criteria. The overall sample included 14 555 tobacco users and 273 162 non-users. The prevalence of smoking in patients presenting with their first episode of psychosis was 0·57 (95% CI 0·52-0·62; p<0·0001). In case-control studies, the overall odds ratio for the first episode of psychosis in smokers versus non-smokers was 3·22 (95% CI 1·63-6·33), with some evidence of publication bias (Egger's test p=0·018, Begg's test p=0·007). For prospective studies, we calculated an overall relative risk of new psychotic disorders in daily smokers versus non-smokers of 2·18 (95% CI 1·23-3·85). Daily smokers developed psychotic illness at an earlier age than did non-smokers (weighted mean difference -1·04 years, 95% CI -1·82 to -0·26). Those with psychosis started smoking at a non-significantly earlier age than did healthy controls (-0·44 years, 95% CI -1·21 to 0·34).

INTERPRETATION

Daily tobacco use is associated with increased risk of psychosis and an earlier age at onset of psychotic illness. The possibility of a causal link between tobacco use and psychosis merits further examination.

FUNDING

NIHR Maudsley Biomedical Research Centre.

The effect of nicotine dependence on psychopathology in patients with schizophrenia

Introduction. Our study aims to determine the prevalence of nicotine dependence and investigate the effect of nicotine dependence on psychopathology among schizophrenia patients. Methods. A cross-sectional study was carried out in an outpatient psychiatric clinic at a general hospital in Malaysia. 180 recruited subjects were administered the Malay version of Mini International Neuropsychiatric Interview (MINI), the Positive and Negative Symptom Scale (PANSS), and the Malay version of Fagerstrom Test for Nicotine Dependence (FTND-M) questionnaires. Results. The prevalence of nicotine dependence among the subjects was 38.1% (n = 69) and they were mainly composed of male gender, Malay ethnicity, being treated with atypical antipsychotics, and taking other illicit drugs or alcohol. Subjects with severe nicotine dependence scored less in the negative subscale of PANSS compared with the nonsmokers (P = 0.011). On performing the hierarchy multiple regressions, dependence status still significantly predicted negative scores after adjusting the confounders (t = −2.87, P = 0.005). Conclusion. The rate of nicotine use disorder among schizophrenia patients in this study is higher than that of the general population in Malaysia. The significant association between nicotine dependence and negative psychopathology symptoms will help the healthcare practitioners in their management of nicotine dependence among schizophrenia patients.

Prevalence and correlates of cigarette smoking among Chinese schizophrenia inpatients receiving antipsychotic mono-therapy

Objective

To investigate the prevalence rate of cigarette smoking and its socio-demographic and clinical correlates in Chinese schizophrenia inpatients receiving antipsychotic mono-therapy.

Methods

This study was a cross-sectional, two-site, hospital-based survey. Four hundred and twenty-nine schizophrenia patients (male/female: 66.9% vs. 33.1%) were consecutively recruited from psychosis inpatient wards of two large specialty psychiatric hospitals in mainland China. Patients were assessed using a cigarette smoking questionnaire, the Positive and Negative Symptom Scale, the Simpson Angus Scale, the Barnes Akathisia Rating Scale, and the Abnormal Involuntary Movement Scale. Socio-demographic and other clinical data were also collected. We calculated the prevalence of current smoking in our sample as well as its indirectly standardized prevalence ratio (ISPR) using data from the 2010 Global Adult Tobacco Survey in China.

Results

The prevalence rate of current smoking was 40.6% in our sample, and 57.5% in males and 6.3% in females. The ISPRs of all patients, men and women were 1.11(95%CI: 0.95∼1.29), 1.07(95%CI = 0.91∼1.24) and 4.64(95%CI = 2.12∼8.82), respectively. The overall and male-specific prevalence of current smoking did not differ significantly between patients and the general population. In multiple logistic regression analysis, male sex, older age, poor marital status, alcohol use, use of first-generation antipsychotics, longer duration of illness, more frequent hospitalizations, and more severe negative symptoms were independently associated with current smoking.

Conclusion

Male Chinese inpatients with schizophrenia who received a mono-therapy of antipsychotics were not more likely to smoke than the general population. Cigarette smoking is more common in schizophrenia patients with more severe illness.

Cigarette smoking, psychopathology and cognitive function in first-episode drug-naive patients with schizophrenia: a case-control study

BACKGROUND

Although patients with chronic schizophrenia have substantially higher smoking rates than either the general population or patients with other mental illnesses, drug-naive patients with a first episode of schizophrenia have received little systemic study. This study examined smoking rates, the association between smoking and symptom severity and cognitive function in Chinese first-episode schizophrenia (FES) patients using cross-sectional and case-control designs.

METHOD

Two hundred and forty-four drug-naive FES patients and 256 healthy controls matched for gender, age and education completed the Fagerström Test for Nicotine Dependence (FTND) and the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). Patients were also rated on the Positive and Negative Symptom Scale (PANSS).

RESULTS

The rate and quantity of smoking were not significantly higher among FES patients compared to the general population. Among patients, smokers scored higher than non-smokers on the total PANSS and the positive symptom subscale scores. There were no significant associations between cognitive function and smoking in either FES patients or healthy controls.

CONCLUSIONS

In contrast to studies in patients with chronic schizophrenia, drug-naive FES patients did not smoke more frequently than the general population. Furthermore, patients with psychotic disorders who smoked did not exhibit significant cognitive differences compared with those who did not smoke. However, smoking may have other detrimental effects on physical and mental health, for example on positive symptoms.

Clinical characteristics of heavy and non-heavy smokers with schizophrenia

Up to 50-90% of persons with schizophrenia smoke cigarettes. Limited data and theories suggest persons with schizophrenia may smoke for different reasons than persons without schizophrenia, making smoking cessation interventions particularly challenging in this population. Although health consequences of smoking are widely known, less information is available regarding characteristics of different amounts of smoking exposure in this population. This study was performed to investigate differences between heavy (≥ 1 pack per day) and non-heavy (<1 pack per day) smoking in patients with schizophrenia. Data from 745 patients, mean age 41.3+/-12.6 years, were drawn from a population of smokers admitted to State of Maryland inpatient mental health facilities (1994-2000). Records were reviewed to obtain demographic information, diagnosis, medication, smoking and substance use. 43% of patients were characterized as heavy smokers. Heavy and non-heavy groups did not differ in age, GAF, weight, or BMI. No differences were found in race, gender or antipsychotic treatments. However, patients smoking ≥ 1 packs per day were more likely to use other substances such as alcohol (χ(2)=6.67, df=1, p=0.01), cocaine (χ(2)=6.66, df=1, p=0.01), and other substances (χ(2)=9.95, df=1, p=0.003) compared to non-heavy smokers. No differences in cannabis or heroin use were found by smoking category. Controlling for age, race, sex and BMI, heavy smokers had higher total cholesterol (190.7(51.6)mg/dL) compared to non-heavy smokers (178.2 (43.0)mg/dL, p=0.03), but no differences were found in glucose or blood pressure. Heavy smoking may be a particular health risk in schizophrenia and significant efforts for smoking cessation or reduction are needed.

Genetics of schizophrenia and smoking: an approach to studying their comorbidity based on epidemiological findings

The association between schizophrenia and tobacco smoking has been described in more than 1,000 articles, many with inadequate methodology. The studies on this association can focus on: (1) current smoking, ever smoking or smoking cessation; (2) non-psychiatric controls or controls with severe mental illness (e.g., bipolar disorder); and (3) higher smoking frequency or greater usage in smokers. The association with the most potential for genetic studies is that between ever daily smoking and schizophrenia; it may reflect a shared genetic vulnerability. To reduce the number of false-positive genes, we propose a three-stage approach derived from epidemiological knowledge. In the first stage, only genetic variations associated with ever daily smoking that are simultaneously significant within the non-psychiatric controls, the bipolar disorder controls and the schizophrenia cases will be selected. Only those genetic variations that are simultaneously significant in the three hypothesis tests will be tested in the second stage, where the prevalence of the genes must be significantly higher in schizophrenia than in bipolar disorder, and significantly higher in bipolar disorder than in controls. The genes simultaneously significant in the second stage will be included in a third stage where the gene variations must be significantly more frequent in schizophrenia patients who did not start smoking daily until their 20s (late start) versus those who had an early start. Any genetic approach to psychiatric disorders may fail if attention is not given to comorbidity and epidemiological studies that suggest which comorbidities are likely to be explained by genetics and which are not. Our approach, which examines the results of epidemiological studies on comorbidities and then looks for genes that simultaneously satisfy epidemiologically suggested sets of hypotheses, may also apply to the study of other major illnesses.

Differential sensory gating functions between smokers and non-smokers among drug-naive first episode schizophrenic patients

Although an acute effect of cigarette smoking and nicotine on sensory gating of schizophrenias has been investigated in published papers, the chronic effect of cigarette smoking on this phenomenon has not yet been reported. We report the effects of chronic cigarette smoking, without new acute exposure before testing, on sensory gating using the P50 auditory evoked potential in a group of drug-naive first episode schizophrenic smokers and healthy smokers. Sensory gating was evaluated using auditory P50 suppression elicited using the conditioning (S1)-testing (S2) paradigm. Fifty six male drug-naive first episode schizophrenic patients were compared to 41 healthy male controls. Patients were classified into subgroups of current smokers (n=18) and non-smokers (n=38) to explore the effects of smoking on sensory gating. All subjects did not smoke a cigarette for at least 1h prior to testing. Schizophrenic patients showed an increased S2 amplitude and a poorer sensory gating as measured by both S2/S1 ratio and S1-S2 difference of P50 amplitude, as compared to healthy controls. However, smokers showed an increased S1 amplitude and better sensory gating than did non-smokers both in schizophrenia patients and healthy controls. Our findings support a sensory gating deficit among first episode schizophrenic patients. However, it was less pronounced among schizophrenic patients who were current cigarette smokers, suggesting a positive effect of chronic cigarette smoking on ameliorating this sensory gating deficit in schizophrenia. Our findings of the present study present new evidence supporting the self-medication hypothesis of self-medication by cigarette smoking in schizophrenia to possibly ameliorate pre-existing functional deficits.