Association between short birth intervals and schizophrenia in the offspring

The association of family size and birth order in adolescence to the likelihood of developing psychotic disorders in young adulthood: A follow-up study of former adolescent inpatients

This is a clinical follow-up study of 508 former adolescent psychiatric inpatients admitted to hospital between 2001 and 2006 in Northern Finland. The participants were interviewed using the K-SADS-PL and the EuropASI instruments. Until 2016, the national Finnish Care Register for Health Care provided data on psychiatric diagnoses. Using logistic regression analysis, we examined how birth order and childhood family size affected the incidence of schizophrenia spectrum disorder (SSD) and other psychotic disorders by young adulthood. Participants were separated into three diagnostic subgroups 1) participants with SSD (n = 76), 2) participants with a psychotic disorder other than SSD (n = 107) and 3) participants with only one nonpsychotic depressive episode (n = 118). The main conclusions were that large family size in adolescence (six or more children), male sex and father having psychiatric problems or being unemployed, were significantly associated with a higher likelihood of SSD among study participants. Large family size also associated to a higher likelihood of developing other psychotic disorders. Being the first born or an only child reduced the likelihood of psychotic disorders other than SSD. When diagnosing and treating children and teenagers with psychotic symptoms, information regarding their family size and sibling position may be relevant.

How Parental Incarceration Shapes the Timing and Structure of Fertility for Children of Incarcerated Parents

The timing and structure of fertility have important implications for individuals and society. Families play a critical role in fertility; however, little is known about how parental incarceration shapes fertility despite it being a common experience in the life course of disadvantaged children. This study examines the consequences of parental incarceration for children's fertility using the National Longitudinal Survey of Youth 1997. I employ multiple-decrement life tables and survival analyses to estimate the relationship between parental incarceration and fertility. Individuals who experience parental incarceration have different timing of fertility, with earlier first births and a quicker pace of subsequent births, as well as more nonmarital fertility, compared with those who do not experience parental incarceration. This analysis finds consistent evidence that parental incarceration is associated with the timing and structure of fertility and suggests that a parent's incarceration carries consequences over the life course of children. This study advances our understanding of how mass incarceration shapes American families, illustrates how the broader consequences of mass incarceration contribute to social inequality, and provides evidence that the enduring implications of incarceration span multiple generations.

The synergistic effects of short inter-pregnancy interval and micronutrients deficiency on third-trimester depression

Objective

To explore the effect of inter-pregnancy interval (IPI) and micronutrients on depression in the third trimester of pregnancy.

Materials and methods

A total of 5,951 eligible pregnant women were included in this single-center retrospective cohort study. Variables with potential effects on third-trimester depression were collected. These variables included: maternal factors [age, pregnancy interval, body mass index (BMI), BMI change, gravidity, native place, education, smoking, and alcohol consumption], previous delivery outcomes [preterm birth, preeclampsia, intrahepatic cholestasis of pregnancy (ICP), gestational diabetes mellitus (GDM), fetal growth restriction (FGR), and delivery mode], and micronutrients in early pregnancy (folic acid, 25-hydroxy vitamin D, vitamin B12, calcium, and ferritin). Univariate and multivariate analyses were used to screen the factors affecting the occurrence of depression. Based on these factors, the nomogram model was established. At the same time, the interaction between IPI and micronutrients was verified.

Results

The incidence of depression in the third trimester of pregnancy was 4.3%. Univariate and multivariate analysis showed that there were five independent risk factors for third-trimester depression: gravidity, previous cesarean section delivery, folic acid, and vitamin D levels in early pregnancy and IPI. According to the multivariate logistic regression analysis, the prediction model and nomogram were established. The prediction cut-offs of the corresponding factors were calculated according to the Youden index. Finally, the synergistic effect of short IPI and micronutrient deficiency was verified.

Conclusion

There is a synergistic effect between short IPI and micronutrient deficiency in early pregnancy, which can aggravate the occurrence of depression in late pregnancy.

Increased Risk of ADHD at Short and Long Interpregnancy Intervals in a National Birth Cohort

BACKGROUND

Short or long interpregnancy interval (IPI) may adversely impact conditions for foetal development. Whether attention deficit hyperactivity disorder (ADHD) is related to IPI has been largely unexplored.

OBJECTIVES

To examine the association between IPI and ADHD in a large, population-based Finnish study.

METHODS

All children born in Finland between 1991 and 2005 and diagnosed with ADHD (ICD-9 314x or ICD-10 F90.x) from 1995 to 2011 were identified using data from linked national registers. Each subject with ADHD was matched to 4 controls based on sex, date of birth, and place of birth. A total of 9564 subjects with ADHD and 34,479 matched controls were included in analyses. IPI was calculated as the time interval between sibling birth dates minus the gestational age of the second sibling. The association between IPI and ADHD was determined using conditional logistic regression and adjusted for potential confounders.

RESULTS

Relative to births with an IPI of 24 to 59 months, those with the shortest IPI (<6 months) had an increased risk of ADHD (odds ratio [OR] 1.30, 95% confidence interval (CI) 1.12, 1.51) and the ORs for the longer IPI births (60-119 months and ≥120 months) were 1.12 (95% CI 1.02, 1.24) and 1.25 (95% CI 1.08, 1.45), respectively. The association of longer IPI with ADHD was attenuated by adjustment for maternal age at the preceding birth, and comorbid autism spectrum disorders did not explain the associations with ADHD.

CONCLUSIONS

The risk of ADHD is higher among children born following short or long IPIs although further studies are needed to explain this association.

Modeling successive birth interval of women in Ethiopia: application of parametric shared frailty and accelerated failure time model

BACKGROUND

Both short and long birth intervals are associated with many risk factors and about 29% of births are short birth intervals in Ethiopia. The purpose of this study is to model the birth intervals of adult women aged 15-49 years using accelerated failure time and shared frailty models in order to analyze the birth intervals of Ethiopian women.

METHODS

The data was obtained from the 2016 Ethiopian Demographic and Health Survey (EDHS). Accelerated failure time with different baseline and shared frailty models are used for the analysis to identify important demographic and socio-economic factors affecting the length of birth intervals and correlates of the birth intervals respectively.

RESULTS

The data consists of 9147 women, of which about 7842 (85.5%) are closed interval and the rest of 1323(14.5%) are open interval. Accelerated failure time (AFT) result revealed that women education level, husbands education level, age at first birth, marital status, religion and family wealth index are significant factors affecting birth interval of women in Ethiopia.

CONCLUSION

Women with closely spaced births tend to have larger family sizes when compared with women with longer inter-birth interval. Longer successive birth interval tends to reduce the total fertility rate of women. Furthermore, improvements in socio-economic status and level of education of women associate with reduced fertility, improved maternal and child wellbeing, and longer birth interval.

Factors associated with short birth interval in low- and middle-income countries: a systematic review

Background

There is ample evidence of associations between short birth interval and adverse maternal and child health outcomes, including infant and maternal mortality. Short birth interval is more common among women in low- and middle-income countries. Identifying actionable aspects of short birth interval is necessary to address the problem. To our knowledge, this is the first systematic review to systematize evidence on risk factors for short birth interval in low- and middle-income countries.

Methods

A systematic mixed studies review searched PubMed, Embase, LILACS, and Popline databases for empirical studies on the topic. We included documents in English, Spanish, French, Italian, and Portuguese, without date restriction. Two independent reviewers screened the articles and extracted the data. We used the Mixed Methods Appraisal Tool to conduct a quality appraisal of the included studies. To accommodate variable definition of factors and outcomes, we present only a narrative synthesis of the findings.

Results

Forty-three of an initial 2802 documents met inclusion criteria, 30 of them observational studies and 14 published after 2010. Twenty-one studies came from Africa, 18 from Asia, and four from Latin America. Thirty-two reported quantitative studies (16 studies reported odds ratio or relative risk, 16 studies reported hazard ratio), 10 qualitative studies, and one a mixed-methods study. Studies most commonly explored education and age of the mother, previous pregnancy outcome, breastfeeding, contraception, socioeconomic level, parity, and sex of the preceding child. For most factors, studies reported both positive and negative associations with short birth interval. Shorter breastfeeding and female sex of the previous child were the only factors consistently associated with short birth interval. The quantitative and qualitative studies reported largely non-overlapping results.

Conclusions

Promotion of breastfeeding could help to reduce short birth interval and has many other benefits. Addressing the preference for a male child is complex and a longer-term challenge. Future quantitative research could examine associations between birth interval and factors reported in qualitative studies, use longitudinal and experimental designs, ensure consistency in outcome and exposure definitions, and include Latin American countries.

Trial registration

Prospectively registered on PROSPERO (International Prospective Register for Systematic Reviews) under registration number CRD42018117654.

Shorter birth intervals between siblings are associated with increased risk of parental divorce

Birth intervals are a crucial component of fertility behaviour and family planning. Short birth intervals are associated—although not necessarily causally—with negative health-related outcomes, but less is known about their associations with family functioning. Here, the associations between birth intervals and marital stability were investigated by Cox regression using a nationally representative, register-based sample of individuals with two (N = 42,481) or three (N = 22,514) children from contemporary Finland (observation period 1972–2009). Shorter interbirth intervals were associated with an increased risk of parental divorce over a ten-year follow-up. Individuals with birth intervals of up to 1.5 years had 24–49 per cent higher divorce risk compared to individuals whose children were born more than 4 years apart. The pattern was similar in all socioeconomic groups and among individuals with earlier and later entry to parenthood. Our results add to the growing body of research showing associations between short birth intervals and negative outcomes in health and family functioning.

Risk factors and child outcomes associated with short and long interpregnancy intervals

Previous research assessing consequences of interpregnancy intervals (IPIs) on child development is mixed. Utilizing a population-based US sample (n=5,339), we first estimated the associations between background characteristics (e.g., sociodemographic and maternal characteristics) and short (≤ 1 year) and long (> 3 years) IPI. Then, we estimated associations between IPI and birth outcomes, infant temperament, cognitive ability, and externalizing symptoms. Several background characteristics, such as maternal age at childbearing and previous pregnancy loss, were associated with IPI, indicating research on the putative effects of IPI must account for background characteristics. After covariate adjustment, short IPI was associated with poorer fetal growth and long IPI was associated with lower infant activity level; however, associations between short and long IPI and the other outcomes were neither large nor statistically significant. These findings indicate that rather than intervening to modify IPI, at-risk families may benefit from interventions aimed at other modifiable risk factors.

Outcome-dependent associations between short interpregnancy interval and offspring psychological and educational problems: a population-based quasi-experimental study

Background

Causal interpretation of associations between short interpregnancy interval (the duration from the preceeding birth to the conception of the next-born index child) and the offspring's psychological and educational problems may be influenced by a failure to account for unmeasured confounding.

Methods

Using population-based Swedish data from 1973-2009, we estimated the association between interpregnancy interval and outcomes [autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), severe mental illness, suicide attempt, criminality, substance-use problem and failing grades] while controlling for measured covariates. We then used cousin comparisons, post-birth intervals (the interval between the second- and third-born siblings to predict second-born outcomes) and sibling comparisons to assess the influence of unmeasured confounding. We included an exploratory analysis of long interpregnancy interval.

Results

Interpregnancy intervals of 0-5 and 6-11 months were associated with higher odds of outcomes in cohort analyses. Magnitudes of association were attenuated following adjustment for measured covariates. Associations were eliminated for ADHD, severe mental illness and failing grades, but maintained magnitude for ASD, suicide attempt, criminality and substance-use problem in cousin comparisons. Post-birth interpregnancy interval and sibling comparisons suggested some familial confounding. Associations did not persist across models of long interpregnancy interval.

Conclusions

Attenuation of the association in cousin comparisons and comparable post-birth interval associations suggests that familial genetic or environmental confounding accounts for a majority of the association for ADHD, severe mental illness and failing grades. Modest associations appear independently of covariates for ASD, suicide attempt, criminality and substance-use problem. Post-birth analyses and sibling comparisons, however, show some confounding in these associations.

Birth Intervals and Health in Adulthood: A Comparison of Siblings Using Swedish Register Data

A growing body of research has examined whether birth intervals influence perinatal outcomes and child health as well as long-term educational and socioeconomic outcomes. To date, however, very little research has examined whether birth spacing influences long-term health. We use contemporary Swedish population register data to examine the relationship between birth-to-birth intervals and a variety of health outcomes in adulthood: for men, height, physical fitness, and the probability of falling into different body mass index categories; and for men and women, mortality. In models that do not adjust carefully for family background, we find that short and long birth intervals are clearly associated with height, physical fitness, being overweight or obese, and mortality. However, after carefully adjusting for family background using a within-family sibling comparison design, we find that birth spacing is generally not associated with long-term health, although we find that men born after very long birth intervals have a higher probability of being overweight or obese in early adulthood. Overall, we conclude that birth intervals have little independent effect on long-term health outcomes.

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.

Inter-Pregnancy Intervals and the Risk of Autism Spectrum Disorder: Results of a Population-Based Study

Recent studies have reported an increased risk of autism among second-born children conceived <12 versus >36 months after the birth of a sibling. Confirmation of this finding would point to inter-pregnancy interval (IPI) as a potentially modifiable risk factor for autism. This study evaluated the relationship between IPI and autism spectrum disorder (ASD) risk in a Wisconsin birth cohort of 31,467 second-born children, of whom 160 resided in the study area and were found to have ASD at age 8 years. In adjusted analyses, both short (<12) and long (>84 month) IPIs were associated with a two-fold risk of ASD relative to IPIs of 24-47 months (p < 0.05). The long IPI association was partially confounded by history of previous pregnancy loss.

Linking databases on perinatal health: a review of the literature and current practices in Europe

Background: International comparisons of perinatal health indicators are complicated by the heterogeneity of data sources on pregnancy, maternal and neonatal outcomes. Record linkage can extend the range of data items available and thus can improve the validity and quality of routine data. We sought to assess the extent to which data are linked routinely for perinatal health research and reporting. Methods: We conducted a systematic review of the literature by searching PubMed for perinatal health studies from 2001 to 2011 based on linkage of routine data (data collected continuously at various time intervals). We also surveyed European health monitoring professionals about use of linkage for national perinatal health surveillance. Results: 516 studies fit our inclusion criteria. Denmark, Finland, Norway and Sweden, the US and the UK contributed 76% of the publications; a further 29 countries contributed at least one publication. Most studies linked vital statistics, hospital records, medical birth registries and cohort data. Other sources were specific registers for: cancer (70), congenital anomalies (56), ART (19), census (19), health professionals (37), insurance (22) prescription (31), and level of education (18). Eighteen of 29 countries (62%) reported linking data for routine perinatal health monitoring. Conclusion: Research using linkage is concentrated in a few countries and is not widely practiced in Europe. Broader adoption of data linkage could yield substantial gains for perinatal health research and surveillance.

Interpregnancy Interval and Risk of Autism Spectrum Disorders

OBJECTIVE

To determine whether subsequent births after short and long interpregnancy intervals (IPIs) are associated with risk of autism spectrum disorder (ASD).

METHOD

We assessed the association between IPI and ASD risk in a cohort of 45 261 children born at Kaiser Permanente Northern California (KPNC) between 2000 and 2009. Children with ASD were identified from International Classification of Diseases, Revision 9 diagnostic codes 299.0, 299.8, and 299.9 recorded in KPNC electronic medical records. IPI was defined as the time from the birth of the first child to the conception of the second child. Survival analysis and logistic regression models were used to evaluate the association between IPI and risk of ASD in second-born children.

RESULTS

Children born after an IPI of <12 months or ≥72 months had a 2- to 3-fold increased ASD risk compared with children born after an interval of 36 to 47 months. Respective adjusted hazard ratios (95% confidence intervals) were as follows: <6 months, 3.0 (1.9-4.7); 6 to 8 months, 2.1 (1.4-3.3); 9 to 11 months, 1.9 (1.3-2.1); 12 to 23 months, 1.5 (1.1-2.1); and ≥72 months, 2.4 (1.5-3.7). The results are not explained by maternal BMI or change in BMI between pregnancies or by parental age, maternal antidepressant medication use, or unfavorable events occurring during the first or second pregnancy.

CONCLUSIONS

Children born after interpregnancy intervals <2 years or >6 years may be at increased risk of ASD. The mechanism explaining this association is unknown, and more research is needed.

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.

Somatic diseases and conditions before the first diagnosis of schizophrenia: a nationwide population-based cohort study in more than 900 000 individuals

OBJECTIVE

Schizophrenia is associated with excess physical comorbidity. Yet, to our knowledge, large studies are lacking on the associations with somatic diseases before the onset of schizophrenia. The authors conducted a nationwide study of the full spectrum of treated somatic diseases before the first diagnosis of schizophrenia.

METHOD

Nationwide sample of the Danish population consisting of singletons (n = 954351) born 1977-1993 and followed from birth to 2009, during which period 4371 developed schizophrenia. Somatic diagnoses at all general hospital contacts (admitted or outpatient care at a somatic hospital) from 1977 to 2009 were used as exposures. The incidence rate ratio (IRR) of schizophrenia was calculated using Poisson regression adjusted for confounders.

RESULTS

Among the 4371 persons who developed schizophrenia from 1992 to 2009, a total of 4180 (95.6%) persons had a previous somatic hospital contact. A history of any somatic hospital contact was associated with an elevated risk of schizophrenia (IRR = 2.04, 95% CI = 1.77-2.37). A wide range of somatic diseases and conditions were associated with an increased risk of schizophrenia, including epilepsy (IRR = 2.26, 95% CI = 1.93-2.62), nutritional or metabolic disorders (IRR = 1.57, 95% CI = 1.39-1.77), circulatory system diseases (IRR = 1.63, 95% CI= 1.38-1.92), and brain injury (IRR = 1.58, 95% CI = 1.45-1.72).

CONCLUSIONS

A wide range of potential etiological factors could have contributed to the observed associations, including genetic or physiological overlaps between conditions, and interacting immunological, behavioral, and neurodevelopmental factors.

An exploratory spatial analysis of geographical inequalities of birth intervals among young women in the Democratic Republic of Congo (DRC): a cross-sectional study

BACKGROUND

The length of time between two successive live births (birth interval), is associated with child survival in the developing world. Short birth intervals (<24 months) contribute to infant and child mortality risks. Contraceptive use contributes to a reduction in short birth intervals, but evidence is lacking in the DRC. We aimed to investigate the proportion of short birth intervals at the provincial level among young women in the DRC.

METHODS

Data from the Demographic and Health Survey undertaken in the DRC in 2007 were analyzed. Logistic regression and Bayesian geo-additive models were used to explain provincial inequalities in short birth intervals among women of reproductive age and young women. Posterior odds ratio (OR) and 95% credible region (CR) were estimated via Markov chain Monte Carlo (MCMC) techniques. Posterior spatial effects and the associated posterior probability maps were produced at the provincial-level to highlight provinces with a significant higher risk of short birth interval.

RESULTS

The overall proportion of short birth intervals among all women of reproductive age (15-49 years) and young women (15-24 years) were 30.2% and 38.7% respectively. In multivariate Bayesian geo-additive regression analyses, among the whole sample of women, living in rural areas [OR = 1.07, 95% CR: (0.97, 1.17)], exclusive breastfeeding [1.08 (1.00, 1.17)] and women with primary education [1.06 (1.00, 1.16)], were consistently associated with a higher risk of short birth intervals. For the young women, none of the factors considered were associated with the risk of short birth interval except a marginal effect from the lack of education. There was a spatial variation in the proportion of women reporting short birth intervals and among all women of reproductive age across provinces, with Nord-Kivu [1.12 (1.02, 1.24)], Sud Kivu [1.17 (1.05, 1.29)] and Kasai Occidental [1.18 (1.06, 1.32)] reporting a higher risk of short birth intervals. For young women, the higher risk provinces were Nord-Kivu [1.22 (1.00, 1.54)] and Sud Kivu [1.34 (1.14, 1.63)].

CONCLUSIONS

This study suggests distinct geographic patterns in the proportion of short birth intervals among Congolese women, as well as the potential role of demographic and geographic location factors driving the ongoing higher youth fertility, higher childhood and maternal mortality in the DRC.

The epigenome and postnatal environmental influences in psychotic disorders

OBJECTIVES

Schizophrenia spectrum disorders and bipolar spectrum disorders are the product of both heritable and non-heritable factors, the impact of which converges at different biological levels. Recent evidence from molecular approaches has provided new insights about how environmental exposures cause persistent alterations in the regulation of gene expression, particularly by so-called epigenetic mechanisms. The aim of this review is to provide an overview of findings of epigenetic studies in psychotic disorders, summarizing findings of human and animal studies on epigenetic alterations due to postnatal environmental exposures associated with psychotic disorders.

METHODS

Electronic and manual literature search of MEDLINE, EMBASE and PSYCHINFO, using a range of search terms around epigenetics, DNA methylation, histone modifications, psychoses, schizophrenia, bipolar disorder and environmental risks associated with psychotic disorders as observed in human and experimental animal studies, complemented by review articles and cross-references.

RESULTS

Despite several promising findings of differential epigenetic profiles in individuals with psychotic disorders in the studies published to date, the knowledge of the role of epigenetic processes in psychotic disorder remains very limited, and should be interpreted cautiously given various challenges in this rapidly evolving field of research.

CONCLUSIONS

Integration of epigenetic findings into biopsychosocial models of the etiology of psychotic disorders eventually may yield important insights into the biological underpinnings of the onset and course of psychotic disorders.

Interpregnancy interval and risk of autistic disorder

BACKGROUND

A recent California study reported increased risk of autistic disorder in children conceived within a year after the birth of a sibling.

METHODS

We assessed the association between interpregnancy interval and risk of autistic disorder using nationwide registry data on pairs of singleton full siblings born in Norway. We defined interpregnancy interval as the time from birth of the first-born child to conception of the second-born child in a sibship. The outcome of interest was autistic disorder in the second-born child. Analyses were restricted to sibships in which the second-born child was born in 1990-2004. Odds ratios (ORs) were estimated by fitting ordinary logistic models and logistic generalized additive models.

RESULTS

The study sample included 223,476 singleton full-sibling pairs. In sibships with interpregnancy intervals <9 months, 0.25% of the second-born children had autistic disorder, compared with 0.13% in the reference category (≥ 36 months). For interpregnancy intervals shorter than 9 months, the adjusted OR of autistic disorder in the second-born child was 2.18 (95% confidence interval 1.42-3.26). The risk of autistic disorder in the second-born child was also increased for interpregnancy intervals of 9-11 months in the adjusted analysis (OR = 1.71 [95% CI = 1.07-2.64]).

CONCLUSIONS

Consistent with a previous report from California, interpregnancy intervals shorter than 1 year were associated with increased risk of autistic disorder in the second-born child. A possible explanation is depletion of micronutrients in mothers with closely spaced pregnancies.

Fetal growth and schizophrenia: a nested case-control and case-sibling study

The association between low birth weight and schizophrenia has been suggested by many studies. Small for gestational age (SGA) is a measure used as a proxy for intrauterine growth restriction. We aim to examine if children who are born SGA are at increased risk of developing schizophrenia and whether an association may be explained by factors shared among siblings. We linked 3 population-based registers: the Danish National Medical Birth Register, the Danish Psychiatric Central Register, and the Danish Civil Registration register to identify all persons born between 1978 and 2000. A nested case-control study and a case-sibling study design were used. There were 4650 cases of schizophrenia. Incidence rate ratios (IRRs) were estimated using conditional logistic regression. SGA was defined as the lowest 10th birth weight percentile for a given sex and gestational age. SGA was associated with an IRR of 1.23 (95% CI: 1.11-1.37) for schizophrenia in the case-control study. An IRR of 1.28 (95% CI: 0.97-1.68) was found in the case-sibling study. There is a modest association between SGA and schizophrenia. Our results indicate that this association is due to an independent effect of factors associated with low birth weight for gestational age per se, rather than other factors shared by siblings.

The evolutionary paradox and the missing heritability of schizophrenia

Schizophrenia is one of the most detrimental common psychiatric disorders, occurring at a prevalence of approximately 1%, and characterized by increased mortality and reduced reproduction, especially in men. The heritability has been estimated around 70% and the genome-wide association meta-analyses conducted by the Psychiatric Genomics Consortium have been successful at identifying an increasing number of risk loci. Various theories have been proposed to explain why genetic variants that predispose to schizophrenia persist in the population, despite the fitness reduction in affected individuals, a question known as the evolutionary paradox. In this review, we consider evolutionary perspectives of schizophrenia and of the empirical evidence that may support these perspectives. Proposed evolutionary explanations include balancing selection, fitness trade-offs, fluctuating environments, sexual selection, mutation-selection balance and genomic conflicts. We address the expectations about the genetic architecture of schizophrenia that are predicted by different evolutionary scenarios and discuss the implications for genetic studies. Several potential sources of "missing" heritability, including gene-environment interactions, epigenetic variation, and rare genetic variation are examined from an evolutionary perspective. A better understanding of evolutionary history may provide valuable clues to the genetic architecture of schizophrenia and other psychiatric disorders, which is highly relevant to genetic studies that aim to detect genetic risk variants.

Interpregnancy interval and obstetrical complications

Obstetricians are often presented with questions regarding the optimal interpregnancy interval (IPI). Short IPI has been associated with adverse perinatal and maternal outcomes, ranging from preterm birth and low birth weight to neonatal and maternal morbidity and mortality. Long IPI has in turn been associated with increased risk for preeclampsia and labor dystocia. In this review, we discuss the data regarding these associations along with recent studies revealing associations of short IPI with birth defects, schizophrenia, and autism. The optimal IPI may vary for different subgroups. We discuss the consequences of short IPI in women with a prior cesarean section, in particular the increased risk for uterine rupture and the considerations regarding a trial of labor in this subgroup. We review studies examining the interaction between short IPI and advanced maternal age and discuss the risk-benefit assessment for these women. Finally, we turn our attention to women after a stillbirth or an abortion, who often desire to conceive again with minimal delay. We discuss studies speaking in favor of a shorter IPI in this group. The accumulated data allow for the reevaluation of current IPI recommendations and management guidelines for women in general and among subpopulations with special circumstances. In particular, we suggest lowering the current minimal IPI recommendation to only 18 months (vs 24 months according to the latest World Health Organization recommendations), with even shorter recommended minimal IPI for women of advanced age and those who conceive after a spontaneous or induced abortion.

The association between interpregnancy interval and birth weight: what is the role of maternal polyunsaturated fatty acid status?

Background

The objective of this study was to evaluate the mediating role of maternal early pregnancy plasma levels of long chain polyunsaturated fatty acids (LCPUFAs) in the association of interpregnancy interval (IPI) with birth weight and smallness for gestational age (SGA) at birth.

Methods

We analysed a subsample of the Amsterdam Born Children and their Development (ABCD) cohort, comprising 1,659 parous pregnant women recruited between January 2003 and March 2004. We used linear and logistic regression to evaluate the associations between fatty acid status, interpregnancy interval and pregnancy outcome.

Results

Low plasma phospholipids concentrations of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and dihomo-gamma-linolenic acid (DGLA), and high concentrations of arachidonic acid (AA) during early pregnancy were associated with reduced birth weight and/or an increased risk of SGA. Short IPIs (< 6 months, with 18–23 months as a reference) were associated with a mean decrease of 207.6 g (SE: ± 73.1) in birth weight (p = 0.005) and a twofold increased risk of SGA (OR: 2.05; CI: 0.93–4.51; p = 0.074). Adjustment for maternal fatty acid concentrations did not affect these results to any meaningful extent.

Conclusions

Despite the observed association of maternal early pregnancy LCPUFA status with birth weight and SGA, our study provides no evidence for the existence of an important role of maternal EPA, DHA, DGLA or AA in the association of short interpregnancy intervals with birth weight and SGA.

Effects of birth spacing on maternal, perinatal, infant, and child health: a systematic review of causal mechanisms

This systematic review of 58 observational studies identified hypothetical causal mechanisms explaining the effects of short and long intervals between pregnancies on maternal, perinatal, infant, and child health, and critically examined the scientific evidence for each causal mechanism hypothesized. The following hypothetical causal mechanisms for explaining the association between short intervals and adverse outcomes were identified: maternal nutritional depletion, folate depletion, cervical insufficiency, vertical transmission of infections, suboptimal lactation related to breastfeeding-pregnancy overlap, sibling competition, transmission of infectious diseases among siblings, incomplete healing of uterine scar from previous cesarean delivery, and abnormal remodeling of endometrial blood vessels. Women's physiological regression is the only hypothetical causal mechanism that has been proposed to explain the association between long intervals and adverse outcomes. We found growing evidence supporting most of these hypotheses.

Interbirth spacing and offspring mental health outcomes

BACKGROUND

The perinatal or early life environment may influence the development of mental illness in adulthood. It is not clear how, or when, any such influences might be mediated. Foetal exposure to maternal stress in the intrauterine environment has been suggested as a possible mediator of foetal origins of mental illness but the postnatal environment may also be of importance. This study aimed to test the foetal origins hypothesis by using retrograde and antegrade interbirth intervals (time to mother's most recent and next deliveries respectively) as proxy measures of antenatal and postnatal maternal stress.

METHOD

Linked datasets of the Scottish Morbidity Record (SMR) were used to identify a birth cohort. Where applicable, the dates of each mother's most recent previous and/or next subsequent delivery were noted, allowing birth intervals to be calculated. The cohort was followed up into young adulthood, using self-harm, substance misuse, psychotic disorder and affective disorder as outcome measures. Data were analysed using Cox regression.

RESULTS

No significant relationship was observed between affective disorders and interbirth interval, neither retrograde nor antegrade. Short (<18-month) antegrade birth intervals were independently associated with increased risk of psychotic disorder and self-harm. Long (>72-month) retrograde intervals were associated with increased risk of self-harm and substance misuse.

CONCLUSIONS

The data do not provide evidence for the foetal origins of mental disorders but, in the cases of psychotic disorders, and of self-harm, suggest that the early postnatal rather than the antenatal environment may be of greater importance.

Interbirth interval is associated with childhood type 1 diabetes risk

Short interbirth interval has been associated with maternal complications and childhood autism and leukemia, possibly due to deficiencies in maternal micronutrients at conception or increased exposure to sibling infections. A possible association between interbirth interval and subsequent risk of childhood type 1 diabetes has not been investigated. A secondary analysis of 14 published observational studies of perinatal risk factors for type 1 diabetes was conducted. Risk estimates of diabetes by category of interbirth interval were calculated for each study. Random effects models were used to calculate pooled odds ratios (ORs) and investigate heterogeneity between studies. Overall, 2,787 children with type 1 diabetes were included. There was a reduction in the risk of childhood type 1 diabetes in children born to mothers after interbirth intervals <3 years compared with longer interbirth intervals (OR 0.82 [95% CI 0.72-0.93]). Adjustments for various potential confounders little altered this estimate. In conclusion, there was evidence of a 20% reduction in the risk of childhood diabetes in children born to mothers after interbirth intervals <3 years.

Epigenetic epidemiology in psychiatry: A translational neuroscience perspective

Accumulating evidence from the field of neuroscience indicates a crucial role for epigenetic regulation of gene expression in development and aging of nervous system and suggests that aberrations in the epigenetic machinery are involved in the etiology of psychiatric disorders. Epidemiologic evidence on epigenetics in psychiatry, however, is currently very sparsely available, but is consistent with a mediating role for epigenetic mechanisms in bringing together inherited and acquired risk factors into a neurodevelopmental etiological model of psychiatric disorders. Here, we review evidence from the epidemiological and neuroscience literature, and aim to converge the evidence into an etiological model of psychiatric disorders that encompasses environmental, genetic and epigenetic contributions. Given the dynamic nature of the epigenetic machinery and the potential reversibility of epigenetic modifications, future well-designed interdisciplinary and translational studies will be of key importance in order to identify new targets for prevention and therapeutic strategies.

Pre-conception inter-pregnancy interval and risk of schizophrenia

It is hypothesised that the risk of schizophrenia may be elevated in children conceived following a short inter-pregnancy interval, when maternal folate stores are still being replenished. We examined the relationship between inter-pregnancy interval and schizophrenia risk in a longitudinal, population-based cohort. Risk of schizophrenia was increased by approximately 150% in those born following a pregnancy interval of ≤6 months, but was not increased if the interval after birth of the participant, before conception of the subsequent sibling, was ≤6 months. These findings support the hypothesis that folate (or other micronutrient) deficiency during fetal development may be an important risk factor for schizophrenia.

Advanced maternal age, short interpregnancy interval, and perinatal outcome

OBJECTIVE

The purpose of this study was to evaluate whether the association between short interpregnancy intervals and perinatal outcome varies with maternal age.

STUDY DESIGN

We performed a retrospective cohort study among 263,142 Dutch women with second deliveries that occurred between 2000 and 2007. Outcome variables were preterm delivery (<37 weeks of gestation), low birthweight in term deliveries (<2500 g) and small-for-gestational age (<10th percentile for gestational age on the basis of sex- and parity-specific Dutch standards).

RESULTS

Short interpregnancy intervals (<6 months) was associated positively with preterm delivery and low birthweight, but not with being small for gestational age. The association of short interpregnancy interval with the risk of preterm delivery was weaker among older than younger women. There was no clear interaction between short interpregnancy interval and maternal age in relation to low birthweight or small for gestational age.

CONCLUSION

The results of this study indicate that the association of short interpregnancy interval with preterm delivery attenuates with increasing maternal age.

Advanced paternal age is a risk factor for schizophrenia in Iranians

BACKGROUND

Since 1958 many, but not all studies have demonstrated that paternal age is a risk factor for schizophrenia. There may be many different explanations for differences between studies, including study design, sample size, collection criteria, heterogeneity and the confounding effects of environmental factors that can for example perturb epigenetic programming and lead to an increase in disease risk. The small number of children in Western families makes risk comparisons between siblings born at different paternal ages difficult. In contrast, more Eastern families have children both at early and later periods of life. In the present study, a cross-sectional population study in an Iranian population was performed to compare frequency of schizophrenia in younger offspring (that is, older paternal age) versus older offspring.

METHODS

A total of 220 patients with the diagnosis of schizophrenia (cases) from both psychiatric hospitals and private clinics and 220 individuals from other hospital wards (controls), matched for sex and age were recruited for this study. Patients with neurological problem, substance abuse, mental retardation and mood disorder were excluded from both groups.

RESULTS

Birth rank comparisons revealed that 35% vs 24% of the cases vs the controls were in the third or upper birth rank (P = 0.01). Also, the mean age of fathers at birth in case group (30 ± 6.26 years) was significantly more than the control group (26.45 ± 5.64 years; P = 0.0001). The age of 76 fathers at birth in case group was over 32 versus 33 fathers in control group. Individuals whose fathers' age was more than 32 (at birth) were at higher risk (2.77 times) for schizophrenia versus others (P < 0.0001, 95% CI 1.80 to 4.27). The maternal age at parturition of the case versus controls groups was 26.1 ± 5.41 vs 25.07 ± 4.47 (P = 0.02). Logistic regression analysis suggests that maternal age is less likely to be involved in the higher risk of schizophrenia than advanced parental age.

DISCUSSION

This study demonstrates a relationship between paternal age and schizophrenia in large families of an Iranian population. Arguments have been put forth that DNA bases changes or epigenetic changes in sperm account for the increased risk associated with older fathers. However, it would not be surprising that both de novo germline mutations and epigenetic changes contribute to disease occurrence because DNA replication and DNA methylation are closely linked at both the macromolecular level (that is, methylation closely follows replication), and at the metabolic level (both processes require folate), and susceptible to modulation by the environment. Further research on samples such as those collected here are needed to sort out the contributions of de novo mutations versus epigenetic changes to schizophrenia.

Closely spaced pregnancies are associated with increased odds of autism in California sibling births

OBJECTIVE

To determine whether the interpregnancy interval (IPI) is associated with the risk of autism in subsequent births.

METHODS

Pairs of first- and second-born singleton full siblings were identified from all California births that occurred from 1992 to 2002 using birth records, and autism diagnoses were identified by using linked records of the California Department of Developmental Services. IPI was calculated as the time interval between birth dates minus the gestational age of the second sibling. In the primary analysis, logistic regression models were used to determine whether odds of autism in second-born children varied according to IPI. To address potential confounding by unmeasured family-level factors, a case-sibling control analysis determined whether affected sibling (first versus second) varied with IPI.

RESULTS

An inverse association between IPI and odds of autism among 662 730 second-born children was observed. In particular, IPIs of <12, 12 to 23, and 24 to 35 months were associated with odds ratios (95% confidence intervals) for autism of 3.39 (3.00-3.82), 1.86 (1.65-2.10), and 1.26 (1.10-1.45) relative to IPIs of ≥ 36 months. The association was not mediated by preterm birth or low birth weight and persisted across categories of sociodemographic characteristics, with some attenuation in the oldest and youngest parents. Second-born children were at increased risk of autism relative to their firstborn siblings only in pairs with short IPIs.

CONCLUSIONS

These results suggest that children born after shorter intervals between pregnancies are at increased risk of developing autism; the highest risk was associated with pregnancies spaced <1 year apart.

Is family size related to adolescence mental hospitalization?

The aim of this study was to investigate the association between family size and psychiatric disorders of underage adolescent psychiatric inpatients. The study sample consisted of 508 adolescents (age 12-17) admitted to psychiatric impatient care between April 2001 and March 2006. Diagnostic and Statistical Manual of Mental Disorders, fourth edition-based psychiatric diagnoses and variables measuring family size were obtained from the Schedule for Affective Disorder and Schizophrenia for School-Age Children Present and Lifetime (K-SADS-PL). The family size of the general Finnish population was used as a reference population. There was a significant difference between the family size of the inpatient adolescents and the general population: 17.0% of adolescents came from large families (with 6 or more children) while the percentage in the general population was 3.3. A girl from a large family had an about 4-fold risk of psychosis other than schizophrenia. However, large family size was not associated with a risk for schizophrenia. Large family size was overrepresented among underage adolescents admitted for psychiatric hospitalization in Northern Finland.

Epigenetic mediation of environmental influences in major psychotic disorders

The major psychotic disorders schizophrenia and bipolar disorder are etiologically complex involving both heritable and nonheritable factors. The absence of consistently replicated major genetic effects, together with evidence for lasting changes in gene expression after environmental exposures, is consistent with the concept that the biologic underpinnings of these disorders are epigenetic in form rather than DNA sequence based. Psychosis-associated environmental exposures, particularly at key developmental stages, may result in long-lasting epigenetic alterations that impact on the neurobiological processes involved in pathology. Although direct evidence for epigenetic dysfunction in both schizophrenia and bipolar disorder is still limited, methodological technologies in epigenomic profiling have advanced. This means that we are at the exciting stage where it is feasible to start investigating molecular modifications to DNA and histones and examine the mechanisms by which environmental factors can act upon the genome to bring about epigenetic changes in gene expression involved in the etiology of these disorders. Given the dynamic nature of the epigenetic machinery and potential reversibility of epigenetic modifications, the understanding of such mechanisms is of key relevance for clinical psychiatry and for identifying new targets for prevention and/or intervention.

Gene-environment interactions in schizophrenia: review of epidemiological findings and future directions

Concern is building about high rates of schizophrenia in large cities, and among immigrants, cannabis users, and traumatized individuals, some of which likely reflects the causal influence of environmental exposures. This, in combination with very slow progress in the area of molecular genetics, has generated interest in more complicated models of schizophrenia etiology that explicitly posit gene-environment interactions (EU-GEI. European Network of Schizophrenia Networks for the Study of Gene Environment Interactions. Schizophrenia aetiology: do gene-environment interactions hold the key? [published online ahead of print April 25, 2008] Schizophr Res; S0920-9964(08) 00170-9). Although findings of epidemiological gene-environment interaction (G x E) studies are suggestive of widespread gene-environment interactions in the etiology of schizophrenia, numerous challenges remain. For example, attempts to identify gene-environment interactions cannot be equated with molecular genetic studies with a few putative environmental variables "thrown in": G x E is a multidisciplinary exercise involving epidemiology, psychology, psychiatry, neuroscience, neuroimaging, pharmacology, biostatistics, and genetics. Epidemiological G x E studies using indirect measures of genetic risk in genetically sensitive designs have the advantage that they are able to model the net, albeit nonspecific, genetic load. In studies using direct molecular measures of genetic variation, a hypothesis-driven approach postulating synergistic effects between genes and environment impacting on a final common pathway, such as "sensitization" of mesolimbic dopamine neurotransmission, while simplistic, may provide initial focus and protection against the numerous false-positive and false-negative results that these investigations engender. Experimental ecogenetic approaches with randomized assignment may help to overcome some of the limitations of observational studies and allow for the additional elucidation of underlying mechanisms using a combination of functional enviromics and functional genomics.

Schizophrenia and neural tube defects: comparisons from an epidemiological perspective

In this review, we examine and compare epidemiological studies of schizophrenia and neural tube defects (NTDs). Although there is no apparent link between these 2 disparate disorders in terms of clinical manifestation or phenotypes, overlapping patterns in the variation of incidence of schizophrenia with that of NTDs indicate the existence of one or more shared etiological risk factors. Evidence in support of such a phenomenon may enhance our understanding of underlying pathological mechanisms and may guide future studies of etiology and prevention. The similarities that occur in a number of epidemiological observations for these disorders are in keeping with a hypothesis of nutritional deficiencies in utero acting as a risk factor for both schizophrenia and NTDs. Programes of periconceptual folate and multivitamin supplementation aimed to reduce the risk of NTDs are already in place in many countries. Nevertheless, evidence of additional effects of specific maternal micronutrient deficiency on risk of schizophrenia may not only increase enthusiasm for expansion of such programes but also enhance understanding of etiology of this disorder and offer the potential for targeted interventions in high-risk groups.

Why are immigrants at increased risk for psychosis? Vitamin D insufficiency, epigenetic mechanisms, or both?

European researchers have observed that schizophrenia is 3 times more frequent in immigrants than in native-born subjects. This increased risk is even higher in dark-skinned immigrants, and the second generation is more affected than the first one. Immigrant status is an important environmental risk factor not only for schizophrenia but also for other psychoses. The explanations proposed to date have been mainly related to epidemiological biases and psychological reasons, such as racism or social defeat, but no biological hypotheses have been tested so far. This article proposes two biological hypotheses related to changes in sun exposure, changes in diet, and stress associated with immigration, which would explain the increased risk for psychosis associated with immigrant status. (1) Vitamin D insufficiency has been proposed as a risk factor for schizophrenia. The main source of vitamin D is through photosynthesis by sun exposure, and dark skins need more sun exposure to maintain adequate blood levels. Vitamin D insufficiency in adulthood could explain why dark-skinned immigrants develop psychosis when moving to high latitude countries, and its insufficiency during pregnancy could explain why the observed risk is higher in the second generation. (2) The second hypothesis is that of epigenetics, with psychosis resulting from modifications in gene expression caused by changes in diet and/or stress related to immigration. The role of homocysteine and the vitamin B-complex, especially folic acid, in these changes in DNA transcription would vary according to the polymorphism of the methylenetetrahydrofolate reductase gene. The vitamin D insufficiency and epigenetics hypotheses are consistent with yet unexplained findings well known in the epidemiology of schizophrenia, such as the increased risk in the urban environment, the excess of winter births, the excess of schizophrenia births after maternal famine, and the shorter interbirth period before a schizophrenia birth. In order to test these hypotheses, epidemiological studies of psychosis and immigration should include objective measures of skin color, which is predicted to be a more important risk factor than ethnicity. They should measure vitamin D, homocysteine and vitamin B-complex status and assess the polymorphisms of the vitamin D receptors and the methylenetetrahydrofolate reductase gene. If confirmed, these hypotheses would lead to effective and inexpensive preventive measures which would markedly decrease the rates of psychosis and schizophrenia, as well as the burden and stigma of these diseases, and greatly improve the mental health of immigrants.

Folate and long-chain polyunsaturated fatty acids in psychiatric disease

Schizophrenia, autism and depression do not inherit by Mendel's law, and the search for a genetic basis seems unsuccessful. Schizophrenia and autism relate to low birth weight and pregnancy complications, which are associated with developmental adaptations by "programming". Epigenetics might constitute the basis of programming and depend on folate status and one-carbon metabolism in general. Early folate status of patients with schizophrenia might be compromised as suggested by (i) coinciding incidences of schizophrenia and neural tube defects (NTDs) in the Dutch hunger winter, (ii) coinciding seasonal fluctuations in birth of patients with schizophrenia and NTDs, (iii) higher schizophrenia incidence in immigrants and (iv) higher incidence in methylene tetrahydrofolate reductase 677C-->T homozygotes. Recent studies in schizophrenia and autism point at epigenetic silencing of critical genes or chromosomal loci. The long-chain polyunsaturated fatty acids (LCPUFA), arachidonic acid (AA, from meat) and docosahexaenoic acid (fish) are components of brain phospholipids and modulators of signal transduction and gene expression. Patients with schizophrenia and, possibly, autism exhibit abnormal phospholipid metabolism that might cause local AA depletion and impaired eicosanoid-mediated signal transduction. National fish intakes relate inversely with major and postpartum depressions. Five out of six randomized controlled trials with eicosapentaenoic acid (fish) have shown positive effects in schizophrenia, and 4 of 6 were favorable in depression and bipolar disorders. We conclude that folate and LCPUFA might be important in both the etiology and severity of at least some psychiatric diseases.

Evolutionary neuropathology & congenital mental retardation: Environmental cues predictive of maternal deprivation influence the fetus to minimize cerebral metabolism in order to express bioenergetic thrift

This article will propose that humans have an adaptive vulnerability to certain forms of mental retardation, specifically, neuropathological disorders that cause decreased energy expenditure in the hippocampus and the cerebral cortex. This hypothesis will be analyzed in terms of the thrifty phenotype paradigm according to which adverse prenatal events can cause differential gene expression resulting in a phenotype that is better suited, metabolically, for a deprived environment. For example, a malnourished mother has an increased propensity to give birth to offspring that feature a "thrifty phenotype" which permits highly efficient calorie utilization, increased fat deposition and a sedentary nature. This article interprets several prenatal occurrences, including maternal malnourishment, low birth weight, multiparity, short birth interval, advanced maternal age and maternal stress--which are currently identified by the epidemiological literature as risk factors for neuropathology--to be environmental cues that communicate to the fetus that, because it will be neglected of maternal investment, developing a metabolically conservative brain will be the most effective ecological strategy. Success in hunting and foraging in mammals, primates and especially humans is known to be dependent on prolonged maternal investment. Low levels of maternal care are known to result in low survivorship of offspring, largely because the offspring are forced to subsist using simple, low-yield foraging strategies. A predictive, adaptive response, marked by cerebral hypometabolism, may produce a level of metabolic conservancy that mitigates the risks associated with low levels of maternal care. This article will suggest that certain, human neuropathological phenotypes would have been well suited for an ecological niche that closely resembled the less skill-intensive niche of our less encephalized, primate ancestors. The forms of congenital neuropathology discussed in this article do not cause damage to vital homeostatic systems; most simply decrease the size and energy expenditure of the cerebral cortex and the hippocampus, the two structures known to show plasticity during changes in ecological rigor in vertebrates. Also, many disorders that present comorbidly with neuropathology, such as tendency toward obesity, decrement in anabolic hormones, hypotonic musculature, up-regulation of the hypothalamic-pituitary-adrenal axis, and decreased thyroid output are associated with energy conservancy and the thrifty phenotype, further implicating neuropathology in an ecological strategy. Determining the relative impact of evolutionary causation on neuropathological disease should prove informative for medical and gene therapeutic treatment modalities. Furthermore, use of the maternal deprivation paradigm presented here may help researchers more precisely identify the risk factors that determine cognitive trajectory.

Aberrant folate status in schizophrenic patients: what is the evidence?

A vast amount of case reports, open studies and, to a lesser extent, case-control studies have been published on the topic of psychopathology and folate deficiency. These studies reported a high incidence of serum folate deficiency in patients with various psychiatric disorders. Folate deficiency seems to be a particular consistent finding in depressive patients. The evidence for an association between aberrant folate status and schizophrenia seems less convincing. The lack of stringent methodology such as inclusion of age- and sex-matched controls was thought to be the main reason for the inconclusive results. The purpose of this article is to review the published case-control studies that provide data on folate levels in the population of patients with schizophrenia. Data extracted from these studies comprised methodological design, clinical characteristics and folate measurements. We found that none of the 7 case-control studies included in this review (in total 325 cases and 560 control subjects) explicitly reported on all critical factors in the assessment of folate. In addition, only three studies found lower plasma folate levels more frequently in patients with schizophrenia compared to controls. Further research on this topic is required to clarify the relationship between folate status and schizophrenia and should avoid the methodological pitfalls mentioned in this review. In addition, research should also focus on polymorphisms of genes related to folate metabolism.

The schizophrenia envirome

PURPOSE OF REVIEW

To show which aspects of the environment increase the risk for schizophrenia and how they interact with pre-existing liability for psychosis.

RECENT FINDINGS

Not only does cannabis survive as a risk factor for psychosis, but the evidence is showing concrete synergistic effects between cannabis and pre-existing liability to psychosis. The urban environment is, in terms of attributable risk, the most important proxy environmental risk factor. There is evidence that it interacts with genetic risk and it has been hypothesized that the mechanism involves the cumulative effects of altered social interactions at the individual level and possibly also at the level of the wider social environment, such as the neighbourhood. Early trauma is another aspect of the environment that has recently been linked prospectively to psychosis, and meta-analytic work demonstrates conclusively that minority status is a risk factor, part of which may be mediated by chronic exposure to discrimination. Prenatal environmental effects may involve folate or vitamin D deficiency, viral infections or adverse effects associated with low or high birth weight. The mechanism by which the environment is likely to impact on risk is through cognitive and emotional pathways on the one hand, and biological pathways, possibly involving dopamine sensitization, on the other.

SUMMARY

Several synergistic mechanisms involving proxy measures of genes and proxy measures of the environment, such as gene-cannabis, gene-urbanicity and gene-stress interactions, offer concrete avenues to pursue research that stands a good chance of elucidating at least some of the causes of schizophrenia.