Investigation of shared genetic effects for psychotic and obsessive symptoms in young adult twins

Exploring the effects of family and life events on genetic and environmental architecture of schizotypal and hypomanic dimensions: Insights from a twin study

BACKGROUND

Strategies of prevention for psychiatric disorders need a deep understanding of the aetiological factors involved in the psychopathological processes. Our twin study aims at disentangling the contributions of genes and environment to schizotypal and hypomanic dimensions, considering the role of stressful life events (LEs) and the quality of family relationships.

METHODS

The Magical Ideation Scale (MIS) and Perceptual Aberration Scale (PAS) were used to assess positive schizotypy, while Hypomanic Personality Scale (HPS) and its sub-scales were used to investigate proneness to affective disorders. 268 twins (54.5 % female; aged 18.0 ± 6.68) were included. Participants filled out a questionnaire on LEs and their parents provided an evaluation of intra-family relationship (Relationship Quality Index, RQI). Classic univariate twin models for quantitative traits were fitted for scales, and the effects of covariates (LEs and RQI) were assessed.

RESULTS

For MIS, HPS and its sub-scales, significant common and unique environmental effects were detected, with genetic factors affecting only HPS Social Vitality sub-scale. Unique environment was the only source of variance of PAS score. The number of recent LEs influenced MIS and PAS models, while RQI score affected MIS model.

LIMITATIONS

The main limitation of the study is the small sample size, which reduces statistical power and may potentially lead to an underestimation of heritability. Additionally, the cross-sectional design limits the possibility to draw causal considerations.

CONCLUSIONS

Findings provide preliminary evidence for a significant environmental role in modulating states of vulnerability. Moreover, the expression of positive schizotypy resulted influenced by recent stressors and intra-family relationships.

The genetic epidemiology of obsessive-compulsive disorder: a systematic review and meta-analysis

The first systematic review and meta-analysis of obsessive-compulsive disorder (OCD) genetic epidemiology was published approximately 20 years ago. Considering the relevance of all the studies published since 2001, the current study aimed to update the state-of-art knowledge on the field. All published data concerning the genetic epidemiology of OCD from the CENTRAL, MEDLINE, EMBASE, BVS, and OpenGrey databases were searched by two independent researchers until September 30, 2021. To be included, the articles had to fulfill the following criteria: OCD diagnosis provided by standardized and validated instruments; or medical records; inclusion of a control group for comparison and case-control, cohort or twin study designs. The analysis units were the first-degree relatives (FDRs) of OCD or control probands and the co-twins in twin pairs. The outcomes of interest were the familial recurrence rates of OCD and the correlations of OCS in monozygotic compared with dizygotic twins. Nineteen family, twenty-nine twin, and six population-based studies were included. The main findings were that OCD is a prevalent and highly familial disorder, especially among the relatives of children and adolescent probands, that OCD has a phenotypic heritability of around 50%; and that the higher OCS correlations between MZ twins were mainly due to additive genetic or to non-shared environmental components.

The Italian Twin Registry: An Update at 18 Years From Its Inception

The Italian Twin Registry (ITR), established in 2001, is a population-based registry of voluntary twins. To date, it consists of approximately 29,000 twins who gave their consent to participate in the studies proposed by the ITR research group. The database comprises 11,500 monozygotic and 16,700 dizygotic twins resident throughout the country and belonging to a wide age range (from 0 to 95 years, mean 36.8 years). This article provides an overview of the recruitment strategies along with the major phenotypes investigated during an 18 years' research period. Over the years, several self-reported questionnaire data were collected, together with saliva/blood samples and measurements taken during in-person interviews or outpatient clinical examinations. Mental and behavioral phenotypes as well as atherosclerotic traits were studied in depth across different age groups. A birth cohort of twins was established and followed up. Novel research hypotheses are also being tested in ongoing projects. The ITR is involved in international studies in collaboration with other twin registries and represents a valuable resource for national and international research initiatives regarding a broad spectrum of health-related characteristics.

The Assertive Brain: Anterior Cingulate Phosphocreatine plus Creatine Levels Correlate With Self-Directedness in Healthy Adolescents

Despite various advances in the study of the neurobiological underpinnings of personality traits, the specific neural correlates associated with character and temperament traits are not yet fully understood. Therefore, this study aims to fill this gap by exploring the biochemical basis of personality, which is explored with the temperament and character inventory (TCI), during brain development in a sample of adolescents. Twenty-six healthy adolescents (aged between 13 and 21 years; 17 males and 9 females) with behavioral and emotional problems underwent a TCI evaluation and a 3T single-voxel proton magnetic resonance spectroscopy (¹H MRS) acquisition of the anterior cingulate cortex (ACC). Absolute metabolite levels were estimated using LCModel: significant correlations between metabolite levels and selective TCI scales were identified. Specifically, phosphocreatine plus creatine (PCr+Cre) significantly correlated with self-directedness, positively, and with a self-transcendence (ST), negatively, while glycerophosphocholine plus phosphocholine (GPC+PC) and myo-inositol negatively correlated with ST. To the best of our knowledge, this is the first study reporting associations of brain metabolites with personality traits in adolescents. Therefore, our results represent a step forward for personality neuroscience within the study of biochemical systems and brain structures.

Suspiciousness in young minds: Convergent evidence from non-clinical, clinical and community twin samples

BACKGROUND

We validated the Social Mistrust Scale (SMS) and utilized it to examine the structure, prevalence, and heritability of social mistrust in a large sample of Chinese children and adolescents.

METHODS

In Study 1, a large sample of healthy twins (N=2094) aged 8 to 14years (M=10.27years, SD=2) completed the SMS. Structural equation modeling (SEM) was conducted to assess the structure of the SMS and to estimate the heritability of social mistrust in a sub-sample of twins (n=756 pairs). In Study 2, 32 adolescents with childhood-onset schizophrenia were compared with 34 healthy controls on levels of suspiciousness and clinical symptoms to examine the associations between the SMS and the Positive and Negative Syndrome Scale (PANSS).

RESULTS

We found a three-factor structure for social mistrust (home, school, and general mistrust). Social mistrust was found to be moderately - heritable (19%-40%), with mistrust at home most strongly influenced by genetic factors. Compared with 11.76% of the healthy controls, 56.25% of the adolescents with early-onset schizophrenia exhibited very high levels of social mistrust on all three subscales of the SMS. The SMS exhibited good discriminant validity in distinguishing adolescents with childhood-onset schizophrenia from healthy controls and showed associations with a broad range of symptoms assessed by the PANSS.

CONCLUSIONS

Social mistrust assessed by the SMS may be heritable. The SMS demonstrates good discriminant validity with clinical diagnoses of schizophrenia. However, it seems to be correlated with multiple aspects of psychopathology in the schizophrenia group, rather than being specific to delusional ideation/paranoia.

Longitudinal associations of temperament and character with paranoid ideation: A population-based study

The aim of this study was to examine (a) the associations of temperament and character dimensions with paranoid ideation over a 15-year follow-up in the general population (b) the associations of explosive temperament and organized character profiles with paranoid ideation. 2137 subjects of the Young Finns Study completed the Temperament and Character Inventory and the Paranoid Ideation Scale of the Symptom Checklist-90 Revised in 1997, 2001, and 2012. Temperament dimensions of high novelty seeking, high harm avoidance, low reward dependence and explosive temperament profile were associated with the development of higher paranoid ideation. Regarding character, high self-directedness, high cooperativeness, and low self-transcendence and organized character profile were associated with lower paranoid ideation. These associations sustained after controlling for age, gender, and socioeconomic factors. However, the associations between temperament and paranoia mostly disappeared after taking character into account. Our study supported the hypothesis that personality dimensions contribute to the development of paranoid ideation. Temperament and character might combine a variety of single previously found risk factors into a more comprehensive framework for the developmental etiology of paranoia. Our findings provide evidence for psychotherapeutic interventions that support the self-regulation of temperamental vulnerabilities by internalizing mature concepts about the self and social relationships.

Normative data of the Magical Ideation Scale from childhood to adulthood in an Italian cohort

The assessment of schizotypy allows to identify people at risk to develop psychosis. For this purpose, psychometric tools have been developed, such as the Magical Ideation Scale (MIS). This scale investigates attenuated forms of thought transmission experiences, thought withdrawal and aberrant beliefs, related to positive schizotypy. This study aims at providing an Italian version of the MIS and its normative data in the general population from childhood to adulthood, being the first study evaluating subjects under 17year-old. The Italian MIS version was translated by three independent operators and administered to 1378 non-clinical participants, stratified into four age groups (i.e., 8-13, 14-17, 18-24 and 25-34). The unidimensionality of the scale was supported, and its internal consistency was satisfactory (i.e., ordinal Cronbach's αs ranging from 0.86 to 0.90 in different age groups), as well as test-retest reliability (i.e., 1-month ICC of 0.82 in a retested sub-sample). Normative data for the age groups were provided. Specific gender and age-related differences in MIS score were found, i.e. females scored higher than males in the 25-34 age group, which in general, as a group, scored lower than all the other age groups. This study provided evidence of reliability for the Italian version of the MIS in childhood and adolescence, for the first time, as well as in adulthood, showing specific gender and age effects in the early adult cohort.

Reliability and normative data of the Perceptual Aberration Scale in an Italian juvenile general population sample

Psychometric tools, such as the Perceptual Aberration Scale (PAS), have been developed to identify people at risk to develop psychosis. This paper aims at providing an Italian version of the Perceptual Aberration Scale and its normative data for the general juvenile Italian population. The Italian version of the PAS was produced using three independent translators. It was administered to 1089 non-clinical participants, stratified into three age-groups, i.e., 8-13, 14-17 and 18-24. The Italian version of the PAS displayed good internal consistency in each age-group evaluated (i.e. Alpha Coefficients: 0.90 for the 8-13 age-group, 0.84 for the 14-17 age-group, and 0.87 for the 18-24 age-group) and the assumption of unidimensionality was corraborate. Furthermore, normative data for the three groups were collected (i.e. cut-offs: 25 for the 8-13 age-group, 21 for the 14-17 age-group and 20 for the 18-24 age-group) and an age-related difference, as the 18-24 group scored lower than the younger groups, was found. The Italian version of the PAS proved to be a reliable psychometric tool to investigate perceptual aberration during childhood, adolescence and young adulthood.

Genetic relationships between schizophrenia, bipolar disorder, and schizoaffective disorder

There is substantial evidence for partial overlap of genetic influences on schizophrenia and bipolar disorder, with family, twin, and adoption studies showing a genetic correlation between the disorders of around 0.6. Results of genome-wide association studies are consistent with commonly occurring genetic risk variants, contributing to both the shared and nonshared aspects, while studies of large, rare chromosomal structural variants, particularly copy number variants, show a stronger influence on schizophrenia than bipolar disorder to date. Schizoaffective disorder has been less investigated but shows substantial familial overlap with both schizophrenia and bipolar disorder. A twin analysis is consistent with genetic influences on schizoaffective episodes being entirely shared with genetic influences on schizophrenic and manic episodes, while association studies suggest the possibility of some relatively specific genetic influences on broadly defined schizoaffective disorder, bipolar subtype. Further insights into genetic relationships between these disorders are expected as studies continue to increase in sample size and in technical and analytical sophistication, information on phenotypes beyond clinical diagnoses are increasingly incorporated, and approaches such as next-generation sequencing identify additional types of genetic risk variant.

Genetic and environmental bases of the interplay between magical ideation and personality

Sub-threshold psychotic symptoms are quite commonly present in general population. Among these, Magical Ideation (MI) has been proved to be a valid predictor of psychosis. However, the genetic and environmental influences on the interplay between MI and personality have not fully been explored. A total of 534 adult twins from the population-based Italian Twin Register were assessed for MI using the MI Scale (MIS) and for personality with the temperament and character inventory (TCI). A Multivariate Cholesky model was applied with Mx statistical program. The best-fitting model showed that additive genetic and unshared environmental factors explain approximately the same proportion of variance in MI, whereas a less strong genetic influence on personality traits emerged. Relevant correlations between MI and specific personality traits (novelty seeking, cooperativeness, self-directedness, self-transcendence) were found, suggesting shared influences for MI and these traits. Both genetic and environmental factors explained these correlations, with genetic factors playing a predominant role. Moderate-to-substantial genetic effects on MI and personality were found. Shared genetic and environmental effects underlie the phenotypic correlation between MI (psychosis-proneness) and personality traits, i.e. self-directedness (negative association) and self-transcendence (positive association), potentially representing predictive markers of psychosis liability related to schizotypy and personality.

An Update on the Italian Twin Register: Advances in Cohort Recruitment, Project Building and Network Development

The Italian Twin Register has been in place for more than 10 years. Since its establishment, it has been focusing, on the one hand, on a continuous update of the existing information, and on the other hand, on new phenotypes and sample collection. Demographic data on about 140,000 twins have been updated using the municipality registries. The Italian Twin Register has been carrying out several new studies during the last few years. A birth cohort of twins, Multiple Births Cohort Study, has been started and the enrolment is ongoing. For this cohort, data on pregnancy and birth are collected, and periodical follow-ups are made. DNA is being collected for the twins and their parents. In the area of behavioral genetics, most efforts have been directed to psychological well being assessed with self-reported tools. Research on age-related traits continues with studies on arteriosclerosis development, early biomarkers in mild cognitive impairment, and the relation between lifestyle habits and mutagen sensitivity. The Italian Twin Register biobanking has grown in its size and in its know-how in terms of both technical issues and ethical procedures implementation. Furthermore, attitudes toward biobank-based research, together with willingness and motivation for donation, are being investigated. A valuable key resource for the Italian Twin Register is the possibility of linking twin data with disease registries. This approach has been yielding several important results, such as the recent study on the heritability of type 1 diabetes.

Etiology of obsessions and compulsions: a meta-analysis and narrative review of twin studies

The relative importance of genetic and environmental factors in the etiology of obsessive-compulsive (OC) symptoms is unclear. Cognitive-behavioral models propose that shared environment (e.g., parenting style) is important. Family segregation studies suggest that nonadditive genetic factors may be involved. To investigate the etiology of OC symptoms, a meta-analysis was conducted of 37 twin samples from 14 studies, supplemented by a narrative review. Results indicated that in terms of mean effect sizes, (a) additive genetic effects and nonshared environment accounted for most of the variance in OC symptoms, (b) shared environment and nonadditive genetic effects made little or no contribution; (c) these findings did not vary with sex or symptom severity; (d) variance due to nonshared environment increased with age; (e) gene-environment interactions play an etiologic role; (f) OC symptoms are shaped by etiologic factors common to all types of OC symptoms but also have symptom-specific etiologies; and (g) OC symptoms are also shaped by very general etiologic factors (e.g., those influencing negative emotionality). Overall, the findings indicate that OC symptoms have a complex etiologic architecture that is not adequately explained by contemporary etiological models.