Birth order and risk for schizophrenia: a 31-year follow-up of the Northern Finland 1966 Birth Cohort

Effectiveness of Psycho-Religious Sexuality Education upon Anger and Depression of Iranian Female Adolescents: The Relationship of Quality Family Relationships and Birth Order

Sexually active adolescents tend to have a wider range of psychosocial problems, including depression, anger, poor academic achievement, low self-esteem, and substance use. Developing a high-quality and curriculum-based comprehensive sexuality education (CSE) program is of great importance for adolescents following Iranian culture. Due to the lack of such an educational program, the purpose of this study was to investigate the effectiveness of psycho-religious CSE upon anger and depression of Iranian female adolescents, as well as the relationship of quality family relationships and birth order. The research design is quasi-experimental with pre-test and post-test with experimental and control groups. The statistical population of this study comprised all Iranian female adolescents aged 15 to 18 years in Mashhad who participated in this workshop voluntarily. For data collection, the Child and Adolescent Depression Inventory and Spielberger's State-Trait Anger Expression Inventory (STAXI) were used. SPSS 21 software and analysis of variance (ANOVA) and covariance (ANCOVA) were used for data analysis. The results showed that there was a significant difference in the mean difference between depression and anger in the control and experimental groups (p-Value < 0.05). The results also showed a significant relationship between birth order and the quality of family relationships on depression and anger. Psycho-religious-based SE can reduce depression and anger in female students. These findings can be used in planning educational interventions with a psycho-religious-based approach to reducing anger, depressive symptoms and dangerous sexual behaviors among adolescents.

Reprint of: Advanced paternal age and risk of schizophrenia in offspring - Review of epidemiological findings and potential mechanisms

A large number of studies have examined the association between advanced paternal age (APA) and risk of schizophrenia in offspring. Here we present an overview of epidemiological studies on this subject published since 2000, and systematically summarize their methodologies and results. Next, we discuss evidence to elucidate the potential mechanisms contributing to the association between APA and offspring schizophrenia, considering paternal psychiatric morbidity and genetic liability, maternal factors, and findings from family design studies. We propose that multiple mechanisms, including causal and non-causal pathways, contribute to the observed relationship between APA and schizophrenia in offspring, and conclude by highlighting the need for multi-disciplinary studies in disentangling these complex, non-mutually exclusive mechanisms.

Advanced paternal age and risk of schizophrenia in offspring - Review of epidemiological findings and potential mechanisms

A large number of studies have examined the association between advanced paternal age (APA) and risk of schizophrenia in offspring. Here we present an overview of epidemiological studies on this subject published since 2000, and systematically summarize their methodologies and results. Next, we discuss evidence to elucidate the potential mechanisms contributing to the association between APA and offspring schizophrenia, considering paternal psychiatric morbidity and genetic liability, maternal factors, and findings from family design studies. We propose that multiple mechanisms, including causal and non-causal pathways, contribute to the observed relationship between APA and schizophrenia in offspring, and conclude by highlighting the need for multi-disciplinary studies in disentangling these complex, non-mutually exclusive mechanisms.

Robust data-driven identification of risk factors and their interactions: A simulation and a study of parental and demographic risk factors for schizophrenia

OBJECTIVES

Few interactions between risk factors for schizophrenia have been replicated, but fitting all such interactions is difficult due to high-dimensionality. Our aims are to examine significant main and interaction effects for schizophrenia and the performance of our approach using simulated data.

METHODS

We apply the machine learning technique elastic net to a high-dimensional logistic regression model to produce a sparse set of predictors, and then assess the significance of odds ratios (OR) with Bonferroni-corrected p-values and confidence intervals (CI). We introduce a simulation model that resembles a Finnish nested case-control study of schizophrenia which uses national registers to identify cases (n = 1,468) and controls (n = 2,975). The predictors include nine sociodemographic factors and all interactions (31 predictors).

RESULTS

In the simulation, interactions with OR = 3 and prevalence = 4% were identified with <5% false positive rate and ≥80% power. None of the studied interactions were significantly associated with schizophrenia, but main effects of parental psychosis (OR = 5.2, CI 2.9-9.7; p < .001), urbanicity (1.3, 1.1-1.7; p = .001), and paternal age ≥35 (1.3, 1.004-1.6; p = .04) were significant.

CONCLUSIONS

We have provided an analytic pipeline for data-driven identification of main and interaction effects in case-control data. We identified highly replicated main effects for schizophrenia, but no interactions.

Associations between birth order with mental wellbeing and psychological distress in midlife: Findings from the 1970 British Cohort Study (BCS70)

BACKGROUND

Previous research indicated that birth order was associated with physical health outcomes in adulthood. However, evidence on its association with mental health was lacking. The aim of this study was to investigate if birth order was associated with mental wellbeing and psychological distress at mid-life, stratified by gender, and taking into account confounding factors in childhood and adulthood.

METHOD

The sample consisted of 9,354 participants of the 1970 British Cohort Study (BCS70). The Warwick Edinburgh Mental Wellbeing Scale (WEMWBS), the Malaise Index and attending a doctor's consultation in the past year for a mental health issue at age forty-two were used to assess mental wellbeing and psychological distress in midlife. Birth order was ascertained via a parental questionnaire and referred to the numerical birth position of the participants. The associations between birth order, mental wellbeing and psychological distress were tested using linear and logistic regression adjusting for birth characteristics: smoking during pregnancy, maternal age, mother's marital status, father's employment, region of birth, parental years of education and parental social class, and factors at age 42: years of education, employment status and partnership status. Potential mediating variables including breastfeeding and birthweight at birth and parental separation and conduct disorder measured at age ten were also taken into account.

RESULTS

We find no evidence to support an association between birth order and midlife psychological distress or attending a doctor's consultation in both men and women. In unadjusted analysis, there was an association between birth order four and above and a reduced WEMWBS score of -0.79 (95% CI -1.57, -0.02) in men only. This association was attenuated after adjusting for birth characteristics and mediators at birth (0.86, 95% -1.78, 0.07) but was maintained once conduct disorder at age 10 was accounted for (-1.19, 95% CI -2.28, -0.09). However, this association was attenuated once again after adjusting for employment status, years in education and partnership status in adulthood (-1.04, 95% CI -2.11, 0.03).

CONCLUSIONS

In this study, birth order was not associated with psychological distress or having a mental health issue at midlife. Accounting for employment status, years of education and partnership status in adulthood attenuated the relationship between birth order and mental wellbeing.

Short duration of marriage at conception as an independent risk factor for schizophrenia

Short duration of marriage (DoM) is a risk factor for preeclampsia that is also related to the risk for schizophrenia. This analysis examined the risk for schizophrenia associated with DoM and its independence from parental psychiatric disorders, parental ages and fathers' age at marriage.

METHOD

Relative Risks (RR) for schizophrenia were estimated using continuous and stratified Cox proportional hazards models in the 90,079 offspring from the prospective population-based Jerusalem birth cohort study (1964-1976). Schizophrenia diagnos in offspring and parental diagnoses of schizophrenia or other psychiatric conditions were identified by cross-linkage to Israel's psychiatric case registry. DoM and paternal age at marriage were abstracted from birth certificates.

RESULTS

In the full model, RR for schizophrenia decreased for each 5 years DoM: 0.83 (0.75-0.95), p_trend = 0.0015. Stratified analyses showed the greatest RR risk for DoM <2 years: 1.53 (1.11-1.66) with lesser risk for 2-4 years DoM: 1.38 (1.05-1.81) compared to more DOM of 10+ years. DoM effects were independent from parental psychiatric diagnoses (RRs = 2-6, p~0.00001), paternal age (1.34: p = 0.0001 /5 years- including fathers of 25-34 years). The apparent risk related to later fathers' age at marriage (1.27: p < 0.0001) was eliminated in after accounting for DoM and later paternal age.

CONCLUSIONS

Offspring born to couples married for less than 3 years, across all paternal ages, harbored a small increased risk for schizophrenia, which was independent of parental psychiatric disorders and paternal age. Fathers who married late had particularly short DoM, which, along with paternal age, completely explained the risks related to later paternal age at marriage. Further studies are needed to replicate these results and examine if pathogenic pathways include prenatal immune activation.

Schizophrenia risk factors in exceptional achievers: a re-analysis of a 60-year-old database

Current medical research has focused on diseases and their associated risk factors. As such, these factors are assumed to have a deleterious effect. An alternative hypothesis is that some of these risk factors would also increase the chance for an opposite, positive outcome. To test this hypothesis, we considered exceptional social achievement and schizophrenia as opposite outcomes. Sixty years ago, researchers in France collected data on socio-demographic factors associated with exceptional social achievement. As the number of female subjects in the original database was very limited, we restricted our analyses to men. We tested the odds of achieving prominence in the presence of factors known to be associated with an increased risk of schizophrenia, namely migration, urbanicity, seasonality of birth, birth order, and paternal age. Three of the five factors tested significantly increased the odds for exceptional social achievement (urban birth, being the first-born and father’s age over 35). Our findings suggest that some of the factors that are currently considered as risk factors for schizophrenia could diversifying factors. Widening the focus of research to include all potential effects of factors associated with disease could have important consequences on our understanding of causal mechanisms and for designing public health interventions.

Sibship size, birth order and psychotic experiences: Evidence from 43 low- and middle-income countries

BACKGROUND

Sibship size and birth order may be contributing factors to the multifactorial etiology of psychosis. Specifically, several studies have shown that sibship size and birth order are associated with schizophrenia. However, there are no studies on their association with psychotic experiences (PE).

METHODS

Cross-sectional, community-based data from 43 low- and middle-income countries which participated in the World Health Survey were analyzed. The Composite International Diagnostic Interview was used to identify four types of past 12-month PE. The association of sibship size and birth order with PE was assessed with multivariable logistic regression.

RESULTS

The final sample consisted of 212,920 adults [mean (SD) age 38.1 (16.0) years; 50.7% females]. In the multivariable analysis, compared to individuals with no siblings, the OR increased linearly from 1.26 (95%CI = 1.01-1.56) to 1.72 (95%CI = 1.41-2.09) among those with 1 and ≥ 9 siblings, respectively. Compared to the first-born, middle-born individuals were more likely to have PE when having a very high number of siblings (i.e. ≥9).

CONCLUSIONS

Future studies should examine the environmental and biological factors underlying the association between sibship size/birth order and PE. Specifically, it may be important to examine the unmeasured factors, such as childhood infections and adversities that may be related to both family structure and PE.

Parental Age and Offspring Psychopathology in the Philadelphia Neurodevelopmental Cohort

OBJECTIVE

Increasing evidence implicates advanced paternal age at offspring birth in neuropsychiatric disorders. Advanced maternal age has also been associated with schizophrenia and other neurodevelopmental disorders, whereas younger maternal age has been linked with behavioral disorders. Few studies have considered the specificity of the associations with respect to comorbidity. In addition, most prior studies have been conducted in clinical samples or registries that may reflect more severe forms of psychopathology. The aim of this research is to examine the independent and joint associations of maternal and paternal age with specific subtypes of psychopathology in offspring in a pediatric sample of adolescents with emergent psychiatric syndromes.

METHOD

A total of 8,725 youths (aged 8-21 years) from the Philadelphia Neurodevelopmental Cohort were included in the analyses. Logistic regression models with parental age predicting offspring psychopathology were adjusted for sociodemographic factors and comorbid disorders.

RESULTS

We found that younger parental ages were generally associated with increased rates of offspring psychopathology. After controlling for sociodemographic characteristics and comorbidity, both younger maternal and paternal ages were associated with behavior syndromes and psychosis in youth, whereas advanced paternal age was associated with pervasive developmental disorders/autism spectrum disorder (PDD/ASD).

CONCLUSION

These findings suggest that both younger and older parental age at birth are associated with specific forms of psychopathology in offspring. The persistence of the influence of parental age after control for demographic factors and an index of social environment suggests that additional explanations for these findings should be examined in future studies.

Sibling characteristics and early onset psychoses among the young adolescent patient population

We investigated the relationship between sibling characteristics (birth order, number of siblings and birth interval) and early onset psychosis among adolescent psychiatric inpatients and their mentally healthy controls. A short birth interval of 1-2 years to the nearest sibling was more common among adolescents with schizophrenia and schizophrenia spectrum psychoses and differed significantly from healthy controls (p = 0.037). A large family (at least 6 children in family) was more common among adolescents with psychosis NOS than among healthy controls (p = 0.035). The birth order among young adolescents with any subtype of psychosis did not differ from healthy controls. Sibling characteristics may be contributing factors in the multifactorial aetiology of schizophrenia and other psychotic disorders. Further studies are required to determine whether sibling characteristics reflect other unknown environmental factors.

Analysis of risk factors for schizophrenia with two different case definitions: a nationwide register-based external validation study

Different case definitions of schizophrenia have been used in register based research. However, no previous study has externally validated two different case definitions of schizophrenia against a wide range of risk factors for schizophrenia. We investigated hazard ratios (HRs) for a wide range of risk factors for ICD-10 DCR schizophrenia using a nationwide Danish sample of 2,772,144 residents born in 1955-1997. We compared one contact only (OCO) (the case definition of schizophrenia used in Danish register based studies) with two or more contacts (TMC) (a case definition of at least 2 inpatient contacts with schizophrenia). During the follow-up, the OCO definition included 15,074 and the TMC 7562 cases; i.e. half as many. The TMC case definition appeared to select for a worse illness course. A wide range of risk factors were uniformly associated with both case definitions and only slightly higher risk estimates were found for the TMC definition. Choosing at least 2 inpatient contacts with schizophrenia (TMC) instead of the currently used case definition would result in almost similar risk estimates for many well-established risk factors. However, this would also introduce selection and include considerably fewer cases and reduce power of e.g. genetic studies based on register-diagnosed cases only.

Twenty Years of Schizophrenia Research in the Northern Finland Birth Cohort 1966: A Systematic Review

Birth cohort designs are useful in studying adult disease trajectories and outcomes, such as schizophrenia. We review the schizophrenia research performed in the Northern Finland Birth Cohort 1966 (NFBC 1966), which includes 10,934 individuals living in Finland at 16 years of age who have been monitored since each mother's mid-pregnancy. By the age of 44, 150 (1.4%) had developed schizophrenia. There are 77 original papers on schizophrenia published from the NFBC 1966. The early studies have found various risk factors for schizophrenia, especially related to pregnancy and perinatal phase. Psychiatric and somatic outcomes were heterogeneous, but relatively poor. Mortality in schizophrenia is high, especially due to suicides. Several early predictors of outcomes have also been found. Individuals with schizophrenia have alterations in brain morphometry and neurocognition, and our latest studies have found that the use of high lifetime doses of antipsychotics associated with these changes. The schizophrenia research in the NFBC 1966 has been especially active for 20 years, the prospective study design and long follow-up enabling several clinically and epidemiologically important findings. When compared to other birth cohorts, the research in the NFBC 1966 has offered also unique findings on course and outcome of schizophrenia.

Birth order and psychopathology

Context:

Ordinal position the child holds within the sibling ranking of a family is related to intellectual functioning, personality, behavior, and development of psychopathology.

Aim:

To study the association between birth order and development of psychopathology in patients attending psychiatry services in a teaching hospital.

Settings and Design:

Hospital-based cross-sectional study.

Materials and Methods:

Retrospective file review of three groups of patients was carried out. Patient-related variables like age of onset, birth order, family type, and family history of mental illness were compared with psychiatry diagnosis (ICD-10) generated.

Statistical Analysis:

SPSS 13; descriptive statistics and one-way analysis of variance (ANOVA) were used.

Results:

Mean age of onset of mental illness among the adult general psychiatry patients (group I, n = 527) was found to be 33.01 ± 15.073, while it was 11.68 ± 4.764 among the child cases (group II, n = 47) and 26.74 ± 7.529 among substance abuse cases (group III, n = 110). Among group I patients, commonest diagnosis was depression followed by anxiety and somatoform disorders irrespective of birth order. Dissociative disorders were most prevalent in the first born child (36.7%) among group II patients. Among group III patients, alcohol dependence was maximum diagnosis in all birth orders.

Conclusions:

Depression and alcohol dependence was the commonest diagnosis in adult group irrespective of birth order.

Gender identity disorder and schizophrenia: neurodevelopmental disorders with common causal mechanisms?

Gender identity disorder (GID), recently renamed gender dysphoria (GD), is a rare condition characterized by an incongruity between gender identity and biological sex. Clinical evidence suggests that schizophrenia occurs in patients with GID at rates higher than in the general population and that patients with GID may have schizophrenia-like personality traits. Conversely, patients with schizophrenia may experience alterations in gender identity and gender role perception. Neurobiological research, including brain imaging and studies of finger length ratio and handedness, suggests that both these disorders are associated with altered cerebral sexual dimorphism and changes in cerebral lateralization. Various mechanisms, such as Toxoplasma infection, reduced levels of brain-derived neurotrophic factor (BDNF), early childhood adversity, and links with autism spectrum disorders, may account for some of this overlap. The implications of this association for further research are discussed.

Birth order and myopia

PURPOSE

An association between birth order and reduced unaided vision (a surrogate for myopia) has been observed previously. We examined the association between birth order and myopia directly in four subject groups.

METHODS

Subject groups were participants in (1) the Avon Longitudinal Study of Parents and Children (ALSPAC; UK; age 15 years; N = 4401), (2) the Singapore Cohort Study of Risk Factors for Myopia (SCORM; Singapore; age 13 years; N = 1959), (3) the Raine Eye Health Study (REHS; Australia; age 20 years; N = 1344), and (4) Israeli Defense Force Pre-recruitment Candidates (IDFC; Israel; age 16-22 years; N = 888,277). The main outcome was odds ratios (OR) for myopia in first-born versus non-first-born individuals after adjusting for potential risk factors.

RESULTS

The prevalence of myopia was numerically higher in first-born versus non-first-born individuals in all study groups, but the strength of evidence varied widely. Adjusted ORs (95% confidence intervals, CIs) were: ALSPAC, 1.31 (1.05-1.64); SCORM, 1.25 (0.89-1.77); REHS, 1.18 (0.90-1.55); and IDFC, 1.04 (1.03-1.06). In the large IDFC sample, the effect size was greater (a) for the first-born versus fourth- or higher-born comparison than for the first-born versus second/third-born comparison (p < 0.001) and (b) with increasing myopia severity (p < 0.001).

CONCLUSIONS

Across all studies, the increased risk of myopia in first-born individuals was low (OR < 1.3). Indeed, only the studies with >4000 participants provided strong statistical support for the association. The available evidence suggested the relationship was independent of established risk factors such as time outdoors/reading, and thus may arise through a different causal mechanism.

Ante- and perinatal circumstances and risk of attempted suicides and suicides in offspring: the Northern Finland birth cohort 1966 study

PURPOSE

To investigate those ante- and perinatal circumstances preceding suicide attempts and suicides, which have so far not been studied intensively.

METHODS

Examination of the Northern Finland Birth Cohort 1966 (n = 10,742), originally based on antenatal questionnaire data and now followed up from mid-pregnancy to age 39, to ascertain psychiatric disorders in the parents and offspring and suicides or attempted suicides in the offspring using nationwide registers.

RESULTS

A total of 121 suicide attempts (57 males) and 69 suicides (56 males) had occurred. Previously unstudied antenatal factors (maternal depressed mood and smoking, unwanted pregnancy) were not related to these after adjustment. Psychiatric disorders in the parents and offspring were the risk factors in both genders. When adjusted for these, the statistically significant risk factors among males were a single-parent family for suicide attempts (OR 3.71, 95% CI 1.62-8.50) and grand multiparity for suicides (OR 2.67, 95% CI 1.15-6.18). When a psychiatric disorder in females was included among possible risk factors for suicide attempts, it alone remained significant (OR 15.55, 8.78-27.53).

CONCLUSIONS

A single-parent family was a risk factor for attempted suicides and grand multiparity for suicides in male offspring even after adjusting for other ante- and perinatal circumstances and mental disorders in the parents and offspring. Mothers' antenatal depressed mood and smoking and unwanted pregnancy did not increase the risk of suicide, which is a novel finding.

Cancer and schizophrenia: is there a paradox?

People with schizophrenia are more likely to die prematurely than the general population from both suicide and physical ill health. Published studies examining the incidence of cancer in schizophrenia patients report increased, reduced or similar incidence compared with the general population. Older studies tended to report lower incidence rates which fuelled speculation as to the biological and other mechanisms for this protective effect. Furthermore, mortality rates in patients with schizophrenia appear higher than expected. We undertook a non-systematic review of published data to give an overview for these variable findings and illustrate methodological confounders by highlighting a systematic review of breast cancer studies.

The antecedents of schizophrenia: a review of birth cohort studies

BACKGROUND

Birth cohort (BC) studies demonstrate that individuals who develop schizophrenia differ from the general population on a range of developmental indices. The aims of this article were to summarize key findings from BC studies in order to identify areas of convergence and to outline areas requiring further research.

METHOD

We define BC studies as studies based on general population BCs where data are collected prospectively from birth or childhood and which identify schizophrenia or related disorders as an outcome. To identify such studies, we searched various electronic databases using the search parameters (schizo* OR psych*) AND (birth cohort). We also checked the references of relevant articles and previous reviews.

RESULTS

We identified 11 BCs from 7 countries that have examined schizophrenia as an outcome in adulthood. There is relatively consistent evidence that, as a group, children who later develop schizophrenia have behavioral disturbances and psychopathology, intellectual and language deficits, and early motor delays. Evidence with respect to alterations in language, educational performance, and physical growth has also been identified in some studies. BC studies have also contributed evidence about a wide range of putative risk factors for schizophrenia.

CONCLUSIONS

BC studies have provided important, convergent insights into how the developmental trajectory of individuals who develop schizophrenia differs from their peers. The combination of new paradigms and larger cohorts, with the tools of modern epidemiology and biomedical science, is advancing our understanding of the developmental pathways to schizophrenia.

Covariance component models for multivariate binary traits in family data analysis

For family studies, there is now an established analytical framework for binary-trait outcomes within the generalized linear mixed models (GLMMs). However, the corresponding analysis of multivariate binary-trait (MBT) outcomes is still limited. Certain diseases, such as schizophrenia and bipolar disorder, have similarities in epidemiological features, risk factor patterns and intermediate phenotypes. To have a better etiological understanding, it is important to investigate the common genetic and environmental factors driving the comorbidity of the diseases. In this paper, we develop a suitable GLMM for MBT outcomes from extended families, such as nuclear, paternal- and maternal-halfsib families. We motivate our problem with real questions from psychiatric epidemiology and demonstrate how different substantive issues of comorbidity between two diseases can be put into the analytical framework.

Foetal brain development in offspring of women with psychosis

Cerebral ventricular enlargement and reduced cortical volume are correlates of chronic schizophrenia. We investigated whether genetic risk for psychosis related to differences in foetal brain development as measured by prenatal ultrasonography. Routine foetal cerebral measures at 19-23 weeks of gestation were compared between the offspring of 35 women with a history of psychosis and 105 control women matched for gestational age. Overall, no significant differences were found between the high-risk and control groups. There was a non-significant trend in the adjusted analysis towards increased lateral ventricular width in the offspring of mothers with psychosis.

Birth order and the severity of illness in schizophrenia

A proposed risk factor for schizophrenia is materno-foetal incompatibility. We tested the hypothesis that, in multiply affected families, later born children would exhibit a more severe form of schizophrenia than their older siblings. The effect of birth order on (1) severity of the worst ever episode of illness; (2) deterioration from premorbid level of functioning; (3) age of onset; (4) response to medication; and (5) illness course, was assessed in 150 sibling pairs with schizophrenia and schizoaffective disorder. We found that later birth order reduced the likelihood of regaining the premorbid level of functioning after an acute episode and was also associated with an earlier age of presentation. This study lends some support to the hypothesis that later birth order results in a more severe form of the disorder, although there are other possible explanations for our findings. Further work is needed to explore the possibility of maternal-foetal genotype incompatibility as a risk factor for schizophrenia.

Predictors of schizophrenia: evidence from the Northern Finland 1966 Birth Cohort and other sources

BACKGROUND

Subtle motor, emotional, cognitive and behavioural abnormalities are often present in apparently healthy individuals who later develop schizophrenia, suggesting that some aspects of causation are established before overt psychosis.

AIMS

To outline the development of schizophrenia.

METHOD

We drew on evidence from The Northern Finland 1966 Birth Cohort supplemented by selected findings from other relevant literature.

RESULTS

The main known risk factors in development of schizophrenia are genetic causes, pregnancy and delivery complications, slow neuromotor development, and deviant cognitive and academic performance. However, their effect size and predictive power are small.

CONCLUSIONS

No powerful risk factor, premorbid sign or risk indicator has been identified that is useful for the prediction of schizophrenia in the general population.

Family structure and risk factors for schizophrenia: case-sibling study

BACKGROUND

Several family structure-related factors, such as birth order, family size, parental age, and age differences to siblings, have been suggested as risk factors for schizophrenia. We examined how family-structure-related variables modified the risk of schizophrenia in Finnish families with at least one child with schizophrenia born from 1950 to 1976.

METHODS

We used case-sibling design, a variant of the matched case-control design in the analysis. Patients hospitalized for schizophrenia between 1969 and 1996 were identified from the Finnish Hospital Discharge Register, and their families from the Population Register Center. Only families with at least two children (7914 sibships and 21059 individuals) were included in the analysis. Conditional logistic regression with sex, birth cohort, maternal schizophrenia status, and several family-related variables as explanatory variables was used in the case-sibling design. The effect of variables with the same value in each sibship was analyzed using ordinary logistic regression.

RESULTS

Having a sibling who was less than five years older (OR 1.46, 95% CI 1.29-1.66), or being the firstborn (first born vs. second born 1.62, 1.87-1.4) predicted an elevated risk, but having siblings who were more than ten years older predicted a lower risk (0.66, 0.56-0.79).

CONCLUSIONS

Several family-structure-related variables were identified as risk factors for schizophrenia. The underlying causative mechanisms are likely to be variable.

Association between short birth intervals and schizophrenia in the offspring

Pregnancy burdens maternal folate reserves. Postpartum restoration to normal folate values may take up to 1 year. Maternal folate deficiency during early pregnancy has been hypothesized as a cause of schizophrenia in the offspring. We investigated whether the risk of schizophrenia is increased in persons conceived shortly after another birth. A population-based cohort was established of 1.43 million persons born in Denmark between 1950 and 1983, yielding 17.6 million person-years of follow-up. Schizophrenia in cohort members (5095 cases) and their siblings and parents was identified by linkage with the Danish Psychiatric Case Register. Relative risks of schizophrenia were estimated by use of log-linear Poisson regression. As compared to intervals of 45 months and longer, the schizophrenia risk ratio was 1.14 (95% confidence interval [CI], 0.97 to 1.35) for interbirth intervals of up to 15 months, 1.32 (95% CI, 1.12 to 1.56) for intervals of 15 to 17 months, 1.38 (95% CI, 1.18 to 1.61), for intervals of 18 to 20 months and 1.13 (95% CI, 1.00 to 1.29) for intervals of 21 to 26 months. Relative risks did not essentially change after adjustment for age, sex, calendar year of diagnosis, maternal and paternal age, history of mental illness in a parent or sibling, sibship size, place of birth, and distance to younger sibling. These results show an association between short birth intervals and schizophrenia in the offspring. Although maternal folate depletion may play a role in this association, we cannot rule out other explanations such as maternal stress during pregnancy and childhood infections.

Developmental precursors of psychosis

Subtle developmental (motor, emotional, cognitive, and behavioral) abnormalities are often present in apparently healthy individuals who later develop psychosis, suggesting that some aspects of causation are established before overt psychosis. These impairments may restrict information processing and social achievements years before manifesting psychosis. The main known risk factors in the development of schizophrenic psychosis are genetic factors, pregnancy and delivery complications, slow neuromotor development, and deviant cognitive and academic performance. However, their effect size and predictive power are small. Developmental precursors are not necessarily specific to schizophrenia, but also common to other psychotic disorders. No powerful risk factor, premorbid sign, or risk indicator has been identified that is useful for prediction of psychoses in the general population.

Paternal and maternal age as risk factors for psychosis: findings from Denmark, Sweden and Australia

BACKGROUND

While the association between increased maternal age and congenital disorders has long been recognized, the offspring of older fathers are also at increased risk of congenital disorders related to DNA errors during spermatogenesis. Recent studies have drawn attention to an association between increased paternal age and increased risk of schizophrenia. The aim of the current study was to examine both paternal and maternal age as risk factors for the broader category of psychosis.

METHOD

We used data from three sources examining psychosis: a population-based cohort study (Denmark), and two case-control studies (Sweden and Australia).

RESULTS

When controlling for the effect of maternal age, increased paternal age was significantly associated with increased risk of psychosis in the Danish and Swedish studies. The Australian study found no association between adjusted paternal age and risk of psychosis. When controlling for the effect of paternal age, younger maternal age was associated with an increased risk of psychoses in the Danish study alone.

CONCLUSIONS

The offspring of older fathers are at increased risk of developing psychosis. The role of paternally derived mutations and/or psychosocial factors associated with older paternal age warrants further research.

Birth order and neural tube defects: a reappraisal

There is evidence that late birth order is associated with some complex disorders. For neural tube defects (NTDs) there is no consensus as to whether first or increased birth order is associated or not. A meta-analysis of published data on NTDs was carried out to ascertain whether there is an increased risk for children first born or of high birth order to have NTDs. All data available with information regarding the frequency of live births and NTDs cases by birth order (1, 2, 3, and 4 or more) were included in the analysis. Effect sizes calculations were performed. Children with higher birth order are more likely to have spina bifida but not anencephaly. This same effect was also seen for all NTDs combined, which probably reflects the association with spina bifida. These results suggest the compilation of anencephaly and spina bifida data can be the explanation for the controversies seen in the literature.

Birth order and oral clefts: a meta analysis

BACKGROUND

There is evidence that late birth order is associated with some complex disorders. For orofacial clefts there is no consensus as to whether increased birth order is associated or not. A meta-analysis of published data on cleft lip or cleft palate (CL/P and CP) was carried out to ascertain whether there is an increased risk for children of high birth order to have an oral cleft.

METHODS

All data available with information regarding the frequency of live births and CL/P and CP cases by birth order (1, 2, 3, and 4 or more) were included in the analysis, and the birth order category "1" was considered to be with no risk (OR = 1.0).

RESULTS

Children with higher birth order are more likely to have CL/P and CP with odds ratios increasing with birth order to a peak of 3.0 in children birth order "4 or more." Results are not different when isolated and syndromic cases are combined.

CONCLUSIONS

CL/P and CP occurrence is correlated with increasing birth order. Further studies, taking into consideration sample size and factors such as income status, race, paternal age, vitamin intake, and social habits, should be done to determine conclusively the association between birth order and oral clefts.