Season of birth, mixed-handedness, and psychometric schizotypy: preliminary results from a prospective study

Early life factors of schizotypal personality disorder in adolescents: A systematic review

WHAT IS KNOWN ON THE SUBJECT?: The complexity and high prevalence of schizotypal personality disorders (SPD) pose serious challenges for mental health practice in its management, and also bring severe consequences for the patients. The identification of the specific early life factors (ELFs) that confer risk to SPD has become a major focus of clinical research on schizophrenia-spectrum disorders which aligns well with the mental health nursing's responsibility in health promotion, prevention and treatment. WHAT THIS PAPER ADDS TO EXISTING KNOWLEDGE?: Adolescents may experience certain ELFs, which contribute to the occurrence of SPD, but no systematic review has been conducted to identify ELF among them. And nursing literature addressing modifiable ELF is very limited. Two clusters of ELF and SPD in adolescents were identified: prenatal and early postnatal factors; childhood trauma and parental factors. The findings also show that more research is needed to determine the specificity and cumulative effects of ELF on the development of SPD by using rigorous and comprehensive measurements and a longitudinal design. WHAT ARE THE IMPLICATIONS FOR PRACTICE?: Mental health nurses, especially nurses in the primary care, should be aware of potentially modifiable ELFs and incorporate more comprehensive and valid instrument for assessing cumulative ELF and SPD. These findings may serve to inform possible future interventions for SPD, such as parent education and support to mitigate these risk factors.

ABSTRACT

INTRODUCTION: Schizotypal personality disorder (SPD) affects 4% of the general population in the United States. The identification of early life factors (ELFs) that confer risk to SPD in adolescents (ages 10-24 years old) has become a major focus of clinical research on schizophrenia-spectrum disorders.

AIM

This systematic review aims to determine what ELFs contribute to the onset of SPD in the adolescent population.

METHODS

A systematic search of PubMed, PsycINFO, Psychiatry online, Scopus, Web of Science, EMBASE and CINAHL databases was conducted using relevant keywords. Data were extracted using a standardized form following PRISMA guidelines.

RESULTS

Twenty-four studies met the criteria for inclusion. ELFs in the development of SPD were grouped into two important clusters: (a) prenatal and early postnatal factors; (b) childhood trauma and parental factors.

CONCLUSION

Mental health nurses, especially nurses in primary care, should be aware of potentially modifiable ELF. Longitudinal research is needed to determine the causative roles of these ELF play in the occurrence of SPD by using rigorous measurements.

IMPLICATIONS FOR PRACTICE

These findings call for awareness of the modifiable ELF for SPD and also inform possible future interventions to reduce these risks, such as parent-training or environmental enrichment programmes.

Is Handedness at Five Associated with Prenatal Factors?

The goal of the study was to investigate some of the factors suspected to be related to children's handedness: presentation during the last weeks of gestation and at birth (cephalic or breech), side of presentation (right or left), number of weeks of gestation, season of birth, parents' handedness and sex. We analyzed the relationships between these factors and the child's handedness at five years. Children (n = 1897) from the EDEN cohort participated in the study, among which 1129 were tested for handedness at five. The father's handedness, but not the mother's, was significantly related to the child's hand preference. The percentage of left-handed children was significantly larger when the father was non-right-handed compared to right-handed, and tended to be larger among children in non-left-cephalic presentation compared to left-cephalic presentation. Girls, but not boys, were significantly less lateralized when they were born before 37 weeks of pregnancy than after. Finally, children born in winter or spring were slightly but significantly less lateralized than children born in summer or autumn. All six children who were not lateralized at 5 presented one or several of these factors. These results are discussed in light of the mixed model of handedness.

Impact of short-term temperature variability on emergency hospital admissions for schizophrenia stratified by season of birth

Diurnal temperature range (DTR) and temperature change between neighboring days (TCN) are important meteorological indicators closely associated with global climate change. However, up to date, there have been no studies addressing the impacts of both DTR and TCN on emergency hospital admissions for schizophrenia. We conducted a time-series analysis to assess the relationship between temperature variability and daily schizophrenia onset in Hefei, an inland city in southeast China. Daily meteorological data and emergency hospital admissions for schizophrenia from 2005 to 2014 in Hefei were collected. After stratifying by season of birth, Poisson generalized linear regression combined with distributed lag nonlinear model (DLNM) was used to examine the relationship between temperature variability and schizophrenia, adjusting for long-term trend and seasonality, mean temperature, and relative humidity. Our analysis revealed that extreme temperature variability may increase the risk for schizophrenia onset among patients born in spring, while no such association was found in patients born in summer and autumn. In patients born in spring, the relative risks of extremely high DTR comparing the 95th and 99th percentiles with the reference (50th, 10 °C) at 3-day lag were 1.078 (95 % confidence interval (CI) 1.025-1.135) and 1.159 (95 % CI 1.050-1.279), respectively. For TCN effects, only comparing 99th percentile with reference (50th, 0.7 °C) was significantly associated with emergency hospital admissions for schizophrenia (relative risk (RR) 1.111, 95 % CI 1.002-1.231). This study suggested that exposure to extreme temperature variability in short-term may trigger later days of schizophrenia onset for patients born in spring, which may have important implications for developing intervention strategies to prevent large temperature variability exposure.

Preliminary validation of the Portuguese Edinburgh Handedness Inventory in an adult sample

The Edinburgh Handedness Inventory (EHI) is persistently the most used inventory to evaluate handedness, being neuropsychological investigation and clinical practice. Despite this, there is no information on how this instrument functions in a Portuguese population. The objective of this study was therefore to examine the sociodemographic influences on handedness and establish psychometric properties of the EHI in a Portuguese sample. The sample consisted of 342 adults (157 men and 185 women), assessed with a battery of neuropsychological tests. The mean EHI Laterality Quotient was 63.52 (SD = 38.00). A much high percentage of ambiguous-handedness compared to left-handedness was detected. An inconsistency was found between the preference for formal education activities (writing-drawing-using scissors) and the remaining EHI activities. From sociodemographic variables, only age, area, and regions of residence showed significant influence on EHI scores. The reliability and temporal reliability of EHI were adequate. Confirmatory factor analysis indicated a one-factor model (χ²/df = 2.141; TLI = 0.972; CFI = 0.979; RMSEA = 0.058). The inconsistency between formal education and nonformal activities could be an indicator of social pressure. The present data give support for the notion that handedness measured by EHI is potentially sensitive to sociodemographic and cultural influences.

Interaction Effects of Season of Birth and Cytokine Genes on Schizotypal Traits in the General Population

Literature suggests that the effect of winter birth on vulnerability to schizophrenia might be mediated by increased expression of proinflammatory cytokines due to prenatal infection and its inadequate regulation by anti-inflammatory factors. As the response of the immune system depends on genotype, this study assessed the interaction effects of cytokine genes and season of birth (SOB) on schizotypy measured with the Schizotypal Personality Questionnaire (SPQ-74). We searched for associations of IL1B rs16944, IL4 rs2243250, and IL-1RN VNTR polymorphisms, SOB, and their interactions with the SPQ-74 total score in a sample of 278 healthy individuals. A significant effect of the IL4 X SOB interaction was found, p = 0.007 and η² = 0.028. We confirmed this effect using an extended sample of 373 individuals. Homozygotes CC born in winter showed the highest SPQ total score and differed significantly from winter-born T allele carriers, p = 0.049. This difference was demonstrated for cognitive-perceptual and disorganized but not interpersonal dimensions. The findings are consistent with the hypothesis that the cytokine genes by SOB interaction can influence variability of schizotypal traits in the general population. The IL4 T allele appeared to have a protective effect against the development of positive and disorganized schizotypal traits in winter-born individuals.

Season of birth and population schizotypy: Results from a large sample of the adult general population

Although the last years have seen an increasing interest in schizotypy and its pathogenesis, there exist only a handful of studies examining the possible interaction between season of birth (SOB) and schizotypic personality structure. Available research used differing screening instruments, rendering comparisons between studies difficult, and sample sizes in adult populations may have been too small to detect a mild effect. The current study examined the association between SOB and psychometric schizotypy in the so far single-largest sample from the adult general population (N=8114), balanced for men and women, and utilizing a valid and reliable instrument for the assessment of schizotypy. Using the 12 most informative items of the Schizotypal Personality Questionnaire Brief, we obtained evidence of a small, but significant, effect of late winter and early spring births (February/March) on psychometric schizotypy. The effect was not constrained to women, but affected men and women alike. The observed association between SOB and schizotypy appears compatible with seasonal variations of temperature and influenza prevalence, and with recent evidence on seasonal variability in the activity of the human immune system. Our findings lend support to the continuum hypothesis of schizotypy and schizophrenia, for which SOB effects have been previously established.

Handedness and schizotypy: The potential effect of changing the writing-hand

Mixed-handedness, which has been associated with schizotypy in recent studies, might exist for at least two different reasons: it is innate or it has been forced. We examined whether the association between mixed-handedness and schizotypy differs depending on its source. We enrolled 3485 college students in Taiwan. We used both the Perceptual Aberration Scale and Schizotypal Personality Questionnaire to assess schizotypy, and the Annett Hand Preference Questionnaire to assess handedness. Two ways of classifying handedness were examined: the three-way classification based on Annett's categories and mixed- vs. non-mixed-handedness based on Degree of Handedness. Both mixed-handedness groups showed higher positive schizotypy scores. Among mixed handers, those who had been required to change their writing hand from left to right had higher positive schizotypy scores. Being forced to change writing hand seemed to be related to a higher level of schizotypy. The potential effect of the social pressure against using the left hand for writing is discussed.

Motor behavior reflects reduced hemispheric asymmetry in the psychosis risk period

BACKGROUND

A body of work focusing on brain connectivity, language dominance, and motor laterality research suggests that reduced hemispheric asymmetry is a core feature in schizophrenia. However, there is little consensus about whether reduced dominance is present in those at ultrahigh risk (UHR) for psychosis.

METHODS

A total of 94 demonstrated right-handed neuroleptic free participants (38 UHR and 56 matched healthy controls) were assessed with structured clinical interviews and completed an innovative handwriting task using a digital tablet computer. A laterality quotient (LQ) was calculated using kinematic variables from the participant's left and right hands. A subset of the sample (26 UHR and 29 controls) returned after 12-months to complete clinical interviews in order to examine relationships between handwriting laterality and progression of psychosis risk symptoms.

RESULTS

The UHR group showed decreased dextrality compared to healthy controls. At the 12-month follow-up, decreased dextrality accounted for 8% of the variance in worsened positive symptoms within the UHR group.

CONCLUSION

The current results suggest that disrupted cerebral dominance is also present in the ultrahigh risk period and that decreased dextrality may serve as a novel biomarker for the progression of psychosis risk.

Association of adoptive child's thought disorders and schizophrenia spectrum disorders with their genetic liability for schizophrenia spectrum disorders, season of birth and parental Communication Deviance

Joint effects of genotype and the environment have turned out to be significant in the development of psychotic disorders. The purpose of the present study was to assess the association of an adoptive child׳s thought and schizophrenia spectrum disorders with genetic and environmental risk indicators and their interactions. A subgroup of the total sample used in the Finnish Adoptive Family Study was considered in the present study. The subjects were 125 adoptees at a high (n=53) or low (n=72) genetic risk of schizophrenia spectrum disorders and their adoptive parents. The risk factors evaluated were the adoptive child's genetic risk for schizophrenia spectrum disorders, winter or spring birth and parental Communication Deviance (CD). Thought disorders in the adoptees were assessed using the Thought Disorder Index and diagnoses were made according to DSM-III-R criteria. The adoptive child׳s Thought Disorder Index was only associated with parental Communication Deviance. The adoptive child's heightened genetic risk or winter or spring birth or parental CD or their interactions did not predict the adoptee's schizophrenia spectrum disorder. The results suggest that studies taking several risk indicators and their interactions into account may change views on the mutual significance of well-known risk factors.

Season of birth and subclinical psychosis: systematic review and meta-analysis of new and existing data

Season of birth (SOB) has been shown to modify the risk of several health outcomes, including a number of neuropsychiatric disorders. Empirical evidence indicates that subclinical forms of psychosis in the general population share some risk factors with categorical diagnoses of psychosis. Hence, by systematically reviewing and meta-analyzing new and existing data, the current work aimed to determine whether there is evidence of an association between winter SOB and subclinical psychosis in the general population. Our meta-analytic results do not indicate an association between winter SOB and schizotypy in adult populations, although they indicate winter SOB may be a risk factor for psychotic experiences or symptoms in children around 12-15 years (OR=1.12, 95%CI:1.03-1.21). In the whole new dataset for adults (n=481, mean age=22.8 years) no association was detected in either an unadjusted model or adjusting for gender and age. Overall, our results indicate that the association between winter SOB and increased subclinical psychosis may hold in children, but does not in the broad general adult population. Nevertheless, the epidemiological and clinicopathological significance of winter SOB as a risk factor for subclinical psychosis would probably be slight due to the small effect sizes indicated by the reports available to date.

Genetics, cognition, and neurobiology of schizotypal personality: a review of the overlap with schizophrenia

Schizotypy refers to a set of temporally stable traits that are observed in the general population and that resemble the signs and symptoms of schizophrenia. Here, we review evidence from studies on genetics, cognition, perception, motor and oculomotor control, brain structure, brain function, and psychopharmacology in schizotypy. We specifically focused on identifying areas of overlap between schizotypy and schizophrenia. Evidence was corroborated that significant overlap exists between the two, covering the behavioral brain structural and functional as well molecular levels. In particular, several studies showed that individuals with high levels of schizotypal traits exhibit alterations in neurocognitive task performance and underlying brain function similar to the deficits seen in patients with schizophrenia. Studies of brain structure have shown both volume reductions and increase in schizotypy, pointing to schizophrenia-like deficits as well as possible protective or compensatory mechanisms. Experimental pharmacological studies have shown that high levels of schizotypy are associated with (i) enhanced dopaminergic response in striatum following administration of amphetamine and (ii) improvement of cognitive performance following administration of antipsychotic compounds. Together, this body of work suggests that schizotypy shows overlap with schizophrenia across multiple behavioral and neurobiological domains, suggesting that the study of schizotypal traits may be useful in improving our understanding of the etiology of schizophrenia.