Twin study of illness history variables in psychosis

Associations between risk factors for schizophrenia and concordance in four monozygotic twin samples

Concordance for schizophrenia is high in monozygotic twins but the extent to which concordance varies according to the presence of other schizophrenia risk factors is not well established. We aimed to investigate this in systematically ascertained twin samples. DSM-III-R/DSM-IV diagnoses were made from original data or published case histories from four systematically ascertained monozygotic twin samples. Probandwise concordance for schizophrenia was calculated according to the presence of psychotic disorder in first-degree relatives, birth order, gender, and age-at-onset. Logistic regression analysis was also performed to adjust for potential confounders. Psychotic disorder in parents and earlier age-at-onset were significantly associated with higher probandwise concordance for schizophrenia, including after adjustment for potential confounders. For example, when no parents had a psychotic disorder concordance was 34/88 (38.6%) versus 10/16 (62.5%) when one parent was affected; and for age-at-onset <23 years concordance was 25/46 (54.3%), declining to 13/44 (29.5%) for age-at-onset >30 years. These results are consistent with psychotic disorder in parents and age-at-onset being markers of the level of familial liability to schizophrenia and these factors may be useful in genetic counseling of monozygotic twins and in identifying and managing those at particularly high risk, if these findings are further replicated.

High loading of polygenic risk in cases with chronic schizophrenia

Genomic risk profile scores (GRPSs) have been shown to predict case-control status of schizophrenia (SCZ), albeit with varying sensitivity and specificity. The extent to which this variability in prediction accuracy is related to differences in sampling strategies is unknown. Danish population-based registers and Neonatal Biobanks were used to identify two independent incident data sets (denoted target and replication) comprising together 1861 cases with SCZ and 1706 controls. A third data set was a German prevalent sample with diagnoses assigned to 1773 SCZ cases and 2161 controls based on clinical interviews. GRPSs were calculated based on the genome-wide association results from the largest SCZ meta-analysis yet conducted. As measures of genetic risk prediction, Nagelkerke pseudo-R(2) and variance explained on the liability scale were calculated. GRPS for SCZ showed positive correlations with the number of psychiatric admissions across all P-value thresholds in both the incident and prevalent samples. In permutation-based test, Nagelkerke pseudo-R(2) values derived from samples enriched for frequently admitted cases were found to be significantly higher than for the full data sets (Ptarget=0.017, Preplication=0.04). Oversampling of frequently admitted cases further resulted in a higher proportion of variance explained on the liability scale (improvementtarget= 50%; improvementreplication= 162%). GRPSs are significantly correlated with chronicity of SCZ. Oversampling of cases with a high number of admissions significantly increased the amount of variance in liability explained by GRPS. This suggests that at least part of the effect of common single-nucleotide polymorphisms is on the deteriorative course of illness.

Inflammation and the two-hit hypothesis of schizophrenia

The high societal and individual cost of schizophrenia necessitates finding better, more effective treatment, diagnosis, and prevention strategies. One of the obstacles in this endeavor is the diverse set of etiologies that comprises schizophrenia. A substantial body of evidence has grown over the last few decades to suggest that schizophrenia is a heterogeneous syndrome with overlapping symptoms and etiologies. At the same time, an increasing number of clinical, epidemiological, and experimental studies have shown links between schizophrenia and inflammatory conditions. In this review, we analyze the literature on inflammation and schizophrenia, with a particular focus on comorbidity, biomarkers, and environmental insults. We then identify several mechanisms by which inflammation could influence the development of schizophrenia via the two-hit hypothesis. Lastly, we note the relevance of these findings to clinical applications in the diagnosis, prevention, and treatment of schizophrenia.

A review of the reliability and validity of OPCRIT in relation to its use for the routine clinical assessment of mental health patients

The OPCRIT program is a symptom checklist with accompanying algorithms producing operationally defined diagnoses. We undertook a review of studies which had used OPCRIT and had reported statistics concerning its reliability and validity, producing summary measures from 44 studies. The first main measure of interest was inter-rater reliability where mean kappa values indicated that agreement between raters was "substantial" with a marginal improvement at the diagnostic (0.76) versus individual item (0.69) level. The second main measure of interest was convergent validity - the agreement between OPCRIT and clinical diagnoses. Most studies reported these figures as concordance rates suggesting mean agreement, unadjusted for chance, of 69%. Very few studies used the chance-adjusted kappa statistic but where this was used agreement was "fair" (0.39). Agreement between OPCRIT and other research diagnoses was "moderate" (0.60). We also considered differences between the way OPCRIT has traditionally been used in research settings and the naturalistic manner in which it will be employed in the hospital ward. This review provides a summary of the reliability and validity of OPCRIT, which will be considered during the preparation for its use in the routine characterization of mental health patients in clinical settings.

Phenotype evaluation and genomewide linkage study of clinical variables in schizophrenia

Genetic factors are likely to influence clinical variation in schizophrenia, but it is unclear which variables are most suitable as phenotypes and which molecular genetic loci are involved. We evaluated clinical variable phenotypes and applied suitable phenotypes in genome-wide covariate linkage analysis. We ascertained 170 affected relative pairs (168 sibling-pairs and two avuncular pairs) with DSM-IV schizophrenia or schizoaffective disorder from the United Kingdom. We defined psychotic symptom dimensions, age at onset (AAO), and illness course using the OPCRIT checklist. We evaluated phenotypes using within sibling-pair correlations and applied suitable phenotypes in multipoint covariate linkage analysis based on 372 microsatellite markers at ∼10 cM intervals. The statistical significance of linkage results was assessed by simulation. The positive and disorganized symptom dimensions, AAO, and illness course qualified as suitable phenotypes. There were no genome-wide significant linkage results. There was suggestive evidence of linkage for the positive dimension on chromosomes 2q32, 10q26, and 20q12; the disorganized dimension on 8p21 and 17q21; and illness course on 2q33 and 22q11. The linkage peak for disorganization on 17q21 remained suggestive after correction for multiple testing. To our knowledge, this is the first study to integrate phenotype evaluation and genome-wide covariate linkage analysis for symptom dimensions and illness history variables in sibling-pairs with schizophrenia. The significant within-pair correlations strengthen the evidence that some clinical variables within schizophrenia are suitable phenotypes for molecular genetic investigations. At present there are no genome-wide significant linkage results for these phenotypes, but a number of suggestive findings warrant further investigation.

Effects of cannabis use on age at onset in schizophrenia and bipolar disorder

BACKGROUND

Cannabis use may decrease age at onset in both schizophrenia and bipolar disorder, given the evidence for substantial phenotypic and genetic overlap between both disorders.

METHODS

766 patients, aged 16 to 65 years, were assessed with the Composite International Diagnostic Interview (CIDI) for substance abuse/use. 676 subjects were diagnosed with schizophrenia and 90 subjects with bipolar disorder. The influence of cannabis use on age at onset in both schizophrenia and bipolar disorder was examined using regression analysis.

RESULTS

Cannabis and other substance use was more frequent in patients with schizophrenia compared to the bipolar group. Both cannabis use and a schizophrenia diagnosis predicted earlier age at onset. There was a significant interaction between cannabis use and diagnosis, cannabis having a greater effect in bipolar patients. Age at onset in users of cannabis was comparable in both diagnostic groups whereas bipolar non-users were significantly older than schizophrenia non-users at onset.

CONCLUSION

Cannabis use may decrease age at onset in both schizophrenia and bipolar patients and reduce the effect of diagnosis. This is consistent with the view that cannabis use may unmask a pre-existing genetic liability that is partly shared between patients with schizophrenia and bipolar disorder.

Heritability estimates for psychotic symptom dimensions in twins with psychotic disorders

Factor analysis of psychotic symptoms frequently results in positive, negative, and disorganized dimensions, but heritability estimates have not yet been reported. Symptom dimensions are usually only measured in individuals with psychotic disorders. Here, it is valuable to assess influences acting via liability to psychosis and independent modifying effects. We estimated heritability for psychotic symptom dimensions, taking account of these issues. Two-hundred-and-twenty-four probandwise twin pairs (106 monozygotic, 118 same-sex dizygotic), where probands had psychoses, were ascertained from the Maudsley Twin Register in London (1948-1993). Lifetime history of DSM-III-R psychotic disorder and psychotic symptom dimensions was assessed from clinical records and research interviews and rated using the Operational Criteria Checklist. Estimates of heritability and environmental components of variance in liability were made with structural equation modeling using a causal-contingent common pathway model adapted for ascertainment from a clinical register. Significant heritability was found for DSM-III-R psychotic disorder (h² = 90%, 95%CI 68-94%) and the disorganized symptom dimension (h² = 84%, 95%CI 18-93%). The heritability for the disorganized dimension remained significant when influences acting through liability to psychosis were set to zero, suggesting that some influences on disorganization are modifying factors independent of psychosis liability. However, the relative extent of modifying factors versus influences acting through psychosis liability could not be clearly determined. To our knowledge, this study provides the first formal evidence of substantive heritability for the disorganized symptom dimension, and suggests that genetic loci influencing disorganization in individuals with psychoses are in some cases different from loci that influence risk of psychotic disorders themselves.