Genetic epidemiology and schizophrenia: a study of reproductive fitness

A functional schizophrenia-associated genetic variant near the TSNARE1 and ADGRB1 genes

Recent collaborative genome-wide association studies (GWAS) have identified >200 independent loci contributing to risk for schizophrenia (SCZ). The genes closest to these loci have diverse functions, supporting the potential involvement of multiple relevant biological processes, yet there is no direct evidence that individual variants are functional or directly linked to specific genes. Nevertheless, overlap with certain epigenetic marks suggest that most GWAS-implicated variants are regulatory. Based on the strength of association with SCZ and the presence of regulatory epigenetic marks, we chose one such variant near TSNARE1 and ADGRB1, rs4129585, to test for functional potential and assay differences that may drive the pathogenicity of the risk allele. We observed that the variant-containing sequence drives reporter expression in relevant neuronal populations in zebrafish. Next, we introduced each allele into human induced pluripotent cells and differentiated four isogenic clones homozygous for the risk allele and five clones homozygous for the non-risk allele into neural progenitor cells. Employing RNA sequencing, we found that the two alleles yield significant transcriptional differences in the expression of 109 genes at a false discovery rate (FDR) of <0.05 and 259 genes at a FDR of <0.1. We demonstrate that these genes are highly interconnected in pathways enriched for synaptic proteins, axon guidance, and regulation of synapse assembly. Exploration of genes near rs4129585 suggests that this variant does not regulate TSNARE1 transcripts, as previously thought, but may regulate the neighboring ADGRB1, a regulator of synaptogenesis. Our results suggest that rs4129585 is a functional common variant that functions in specific pathways likely involved in SCZ risk.

The cliff edge model of the evolution of schizophrenia: Mathematical, epidemiological, and genetic evidence

How has schizophrenia, a condition that significantly reduces an individual's evolutionary fitness, remained common across generations and cultures? Numerous theories about the evolution of schizophrenia have been proposed, most of which are not consistent with modern epidemiological and genetic evidence. Here, we briefly review this evidence and explore the cliff edge model of schizophrenia. It suggests that schizophrenia is the extreme manifestation of a polygenic trait or a combination of traits that, within a normal range of variation, confer cognitive, linguistic, and/or social advantages. Only beyond a certain threshold, these traits precipitate the onset of schizophrenia and reduce fitness. We provide the first mathematical model of this qualitative concept and show that it requires only very weak positive selection of the underlying trait(s) to explain today's schizophrenia prevalence. This prediction, along with expectations about the effect size of schizophrenia risk alleles, are surprisingly well matched by empirical evidence. The cliff edge model predicts a dynamic change of selection of risk alleles, which explains the contradictory findings of evolutionary genetic studies.

A Functional Schizophrenia-associated genetic variant near the TSNARE1 and ADGRB1 genes

Recent collaborative genome wide association studies (GWAS) have identified >200 independent loci contributing to risk for schizophrenia (SCZ). The genes closest to these loci have diverse functions, supporting the potential involvement of multiple relevant biological processes; yet there is no direct evidence that individual variants are functional or directly linked to specific genes. Nevertheless, overlap with certain epigenetic marks suggest that most GWAS-implicated variants are regulatory. Based on the strength of association with SCZ and the presence of regulatory epigenetic marks, we chose one such variant near TSNARE1 and ADGRB1, rs4129585, to test for functional potential and assay differences that may drive the pathogenicity of the risk allele. We observed that the variant-containing sequence drives reporter expression in relevant neuronal populations in zebrafish. Next, we introduced each allele into human induced pluripotent cells and differentiated 4 isogenic clones homozygous for the risk allele and 5 clones homozygous for the non-risk allele into neural precursor cells. Employing RNA-seq, we found that the two alleles yield significant transcriptional differences in the expression of 109 genes at FDR <0.05 and 259 genes at FDR <0.1. We demonstrate that these genes are highly interconnected in pathways enriched for synaptic proteins, axon guidance, and regulation of synapse assembly. Exploration of genes near rs4129585 suggests that this variant does not regulate TSNARE1 transcripts, as previously thought, but may regulate the neighboring ADGRB1, a regulator of synaptogenesis. Our results suggest that rs4129585 is a functional common variant that functions in specific pathways likely involved in SCZ risk.

The EEG multiverse of schizophrenia

Research on schizophrenia typically focuses on one paradigm for which clear-cut differences between patients and controls are established. Great efforts are made to understand the underlying genetical, neurophysiological, and cognitive mechanisms, which eventually may explain the clinical outcome. One tacit assumption of these "deep rooting" approaches is that paradigms tap into common and representative aspects of the disorder. Here, we analyzed the resting-state electroencephalogram (EEG) of 121 schizophrenia patients and 75 controls. Using multiple signal processing methods, we extracted 194 EEG features. Sixty-nine out of the 194 EEG features showed a significant difference between patients and controls, indicating that these features detect an important aspect of schizophrenia. Surprisingly, the correlations between these features were very low. We discuss several explanations to our results and propose that complementing "deep" with "shallow" rooting approaches might help in understanding the underlying mechanisms of the disorder.

Genetic variations in evolutionary accelerated regions disrupt cognition in schizophrenia

Cognition is believed to be a product of human evolution, while schizophrenia is ascribed as the by-product with cognitive impairment as it's genetically mediated endophenotype. Genomic loci associated with these traits are enriched with recent evolutionary markers such as Human accelerated regions (HARs). HARs are markedly different in humans since their divergence with chimpanzees and mostly regulate gene expression by binding to transcription factors and/or modulating chromatin interactions. We hypothesize that variants within HARs may alter such functions and thus contribute to disease pathogenesis. 49 systematically prioritized variants from 2737 genome-wide HARs were genotyped in a north-Indian schizophrenia cohort (331 cases, 235 controls). Six variants were significantly associated with cognitive impairment in schizophrenia, thirteen with general cognition in healthy individuals. These variants were mapped to 122 genes; predicted to alter 79 transcription factors binding sites and overlapped with promoters, enhancers and/or repressors. These genes and TFs are implicated in neurocognitive phenotypes, autism, schizophrenia and bipolar disorders; a few are targets of common or repurposable antipsychotics suggesting their draggability; and enriched for immune response and brain developmental pathways. Immune response has been more strongly targeted by natural selection during human evolution and has a prominent role in neurodevelopment. Thus, its disruption may have deleterious consequences for neuronal and cognitive functions. Importantly, among the 15 associated SNPs, 12 showed association in several independent GWASs of different neurocognitive functions. Further analysis of HARs may be valuable to understand their role in cognition biology and identify improved therapeutics for schizophrenia.

Revisiting Schizophrenia from an Evolutionary Perspective: An Association Study of Recent Evolutionary Markers and Schizophrenia

The persistence of schizophrenia in human populations at a high prevalence and with a large heritability estimate despite reduced fertility and increased mortality rate is a Darwinian paradox. This may be likely if the genomic components that predispose to schizophrenia are also advantageous for the acquisition of important human traits, such as language and cognition. Accordingly, an emerging group of genomic markers of recent evolution in humans, namely human accelerated regions (HARs), since our divergence from chimpanzees, are gaining importance for neurodevelopmental disorders, such as schizophrenia. We hypothesize that variants within HARs may affect the expression of genes under their control, thus contributing to disease etiology. A total of 49 HAR single nucleotide polymorphisms (SNPs) were prioritized from the complete repertoire of HARs (n = 2737) based on their functional relevance and prevalence in the South Asian population. Test of association using 2 independent schizophrenia case-control cohorts of north Indian ethnicity (discovery: n = 930; replication: n = 1104) revealed 3 SNPs (rs3800926, rs3801844, and rs764453) from chromosome 7 and rs77047799 from chromosome 3 to be significantly associated (combined analysis: Bonferroni corrected P < .002-.000004). Of note, these SNPs were found to alter the expression of neurodevelopmental genes such as SLC25A13, MAD1L1, and ULK4; a few from the HOX gene family; and a few genes that are implicated in mitochondrial function. These SNPs may most likely alter binding sites of transcription factors, including TFCP2, MAFK, SREBF2, E2F1, and/or methylation signatures around these genes. These findings reiterate a neurodevelopmental basis of schizophrenia and also open up a promising avenue to investigate HAR-mediated mitochondrial dysfunction in schizophrenia etiology.

Interrogating the Evolutionary Paradox of Schizophrenia: A Novel Framework and Evidence Supporting Recent Negative Selection of Schizophrenia Risk Alleles

Schizophrenia is a psychiatric disorder with a worldwide prevalence of ∼1%. The high heritability and reduced fertility among schizophrenia patients have raised an evolutionary paradox: why has negative selection not eliminated schizophrenia associated alleles during evolution? To address this question, we examined evolutionary markers, known as modern-human-specific (MD) sites and archaic-human-specific sites, using existing genome-wide association study (GWAS) data from 34,241 individuals with schizophrenia and 45,604 healthy controls included in the Psychiatric Genomics Consortium (PGC). By testing the distribution of schizophrenia single nucleotide polymorphisms (SNPs) with risk and protective effects in the human-specific sites, we observed a negative selection of risk alleles for schizophrenia in modern humans relative to archaic humans (e.g., Neanderthal and Denisovans). Such findings indicate that risk alleles of schizophrenia have been gradually removed from the modern human genome due to negative selection pressure. This novel evidence contributes to our understanding of the genetic origins of schizophrenia.

The Concept of Schizophrenia: From Unity to Diversity

After over 100 years of research without clarifying the aetiology of schizophrenia, a look at the current state of knowledge in epidemiology, genetics, precursors, psychopathology, and outcome seems worthwhile. The disease concept, created by Kraepelin and modified by Bleuler, has a varied history. Today, schizophrenia is considered a polygenic disorder with onset in early adulthood, characterized by irregular psychotic episodes and functional impairment, but incident cases occur at all ages with marked differences in symptoms and social outcome. Men’s and women’s lifetime risk is nearly the same. At young age, women fall ill a few years later and less severely than men, men more rarely and less severely later in life. The underlying protective effect of oestrogen is antagonized by genetic load. The illness course is heterogeneous and depressive mood the most frequent symptom. Depression and schizophrenia are functionally associated, and affective and nonaffective psychoses do not split neatly. Most social consequences occur at the prodromal stage. Neither schizophrenia as such nor its main symptom dimensions regularly show pronounced deterioration over time. Schizophrenia is neither a residual state of a neurodevelopmental disorder nor a progressing neurodegenerative process. It reflects multifactorial CNS instability, which leads to cognitive deficits and symptom exacerbations.

Cognitive mapping deficits in schizophrenia: a critical overview

Hippocampal deficits are an established feature of schizophrenia and are complementary with recent evidences of marked allocentric processing deficits being reported in this disorder. By "Cognitive mapping" we intend to refer to the concepts from the seminal works of O'Keefe and Nadel (1978) that led to the development of cognitive map theory of hippocampal function. In this review, we summarize emerging evidences and issues that indicate that "Cognitive mapping deficits" form one of the important cognitive aberrations in schizophrenia. The importance has been placed upon hippocampally mediated allocentric processing deficits and their role in pathology of schizophrenia, for spatial/representational cognitive deficits and positive symptoms in particular. It is modestly summarized that emerging evidences point toward a web of spatial and cognitive representation errors concurrent with pronounced hippocampal dysfunction. In general, it can be stated that there are clear and consistent evidences that favor the cognitive mapping theory in explaining certain deficits of schizophrenia and for drawing out a possible and promising endophenotype/biomarkers. Further research in this regard demands attention.

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.

Genetics of the schizophrenias: a model accounting for their persistence and myriad phenotypes

This article addresses the classic enigma about schizophrenia (SZ). The disease occurs with a lifetime prevalence of 1%, 80% of which is attributable to genetic factors. Females with SZ produce 50% as many children as normals, and males with SZ produce 25%. Genetic factors responsible for SZ should behave like lethal genes. Yet the prevalence of SZ remains around 1% throughout the world. How can that be? Additionally, CATIE concluded that the response of each individual with SZ to treatment with antipsychotic agents (effectiveness, side-effect profile, or long-term prognosis) cannot be predicted. Every case seems to be unique. Several recent publications have reported increased frequencies of single-nucleotide polymorphisms (SNPs) and of copy-number variants (CNVs) containing large regions of DNA in patients with SZ. These genetic perturbations often include neurodevelopmental genes. The overwhelming majority of SNPs and CNVs are post-fertilization mutations, occurring in somatic tissue, not germinal tissue. These mutations are a normal aspect of somatic cell division but occur more frequently in patients with SZ. Somatic mutations are not passed on to subsequent generations and therefore cannot account for the inheritance of SZ. Our speculation is that the genetic platform for SZ is the gene or genes that increase the number of de novo mutations in patients with SZ. We argue that balanced polymorphism is the most plausible hypothesis to account for the preservation of non-adaptive genes in nature-and, in particular, in SZ. Maladaptive genes in different combinations can confer increased fitness to the entire population, thus insuring their preservation in the gene pool. Somatic mutations explain both the sporadic occurrence of SZ within families and the wide variations in phenotypic expression of SZ. Increased frequency of somatic mutations may confirm greater overall fitness via balanced polymorphism to explain the maintenance of the SZ gene or genes within the human population.

A systematic review and meta-analysis of the fertility of patients with schizophrenia and their unaffected relatives

OBJECTIVE

We aimed to systematically evaluate the empirical evidence for the commonly held view that the reduced reproductive output in patients with schizophrenia is compensated for by an increased fitness in unaffected relatives. Secondary aims were to quantify the magnitude of the fertility disadvantage and the apparent gender difference in fertility of patients with schizophrenia.

METHOD

We carried out a systematic review and meta-analysis of studies investigating the fertility of patients with schizophrenia, their siblings, their parents and the general population.

RESULTS

Patients with schizophrenia had reduced fertility compared with the general population, [Fertility Ratio (FR)=0.39 (95% Confidence Interval (CI)=0.35-0.44)]. Siblings of patients with schizophrenia had somewhat fewer offspring than the general population (FR=0.96, 95% CI=0.93-1.00). Parents of patients with schizophrenia had fertility similar to the general population (FR=1.17, 95% CI=0.94-1.46). Men had a greater impairment in fertility than women, both in patients (FR=0.54, 95% CI=0.50-0.57) and in their unaffected siblings (FR=0.81, 95% CI=0.71-0.92).

CONCLUSION

Compensatory fitness advantage in siblings and parents cannot explain the maintenance of schizophrenia in the population. Alternative explanations include mutation-selection balance and the role of quantitative traits.

Reduced fertility in patients' families is consistent with the sexual selection model of schizophrenia and schizotypy

Background

Schizophrenia is a mental disorder marked by an evolutionarily puzzling combination of high heritability, reduced reproductive success, and a remarkably stable prevalence. Recently, it has been proposed that sexual selection may be crucially involved in the evolution of schizophrenia. In the sexual selection model (SSM) of schizophrenia and schizotypy, schizophrenia represents the negative extreme of a sexually selected indicator of genetic fitness and condition. Schizotypal personality traits are hypothesized to increase the sensitivity of the fitness indicator, thus conferring mating advantages on high-fitness individuals but increasing the risk of schizophrenia in low-fitness individuals; the advantages of successful schzotypy would be mediated by enhanced courtship-related traits such as verbal creativity. Thus, schizotypy-increasing alleles would be maintained by sexual selection, and could be selectively neutral or even beneficial, at least in some populations. However, most empirical studies find that the reduction in fertility experienced by schizophrenic patients is not compensated for by increased fertility in their unaffected relatives. This finding has been interpreted as indicating strong negative selection on schizotypy-increasing alleles, and providing evidence against sexual selection on schizotypy.

Methodology

A simple mathematical model is presented, showing that reduced fertility in the families of schizophrenic patients can coexist with selective neutrality of schizotypy-increasing alleles, or even with positive selection on schizotypy in the general population. If the SSM is correct, studies of patients' families can be expected to underestimate the true fertility associated with schizotypy.

Significance

This paper formally demonstrates that reduced fertility in the families of schizophrenic patients does not constitute evidence against sexual selection on schizotypy-increasing alleles. Futhermore, it suggests that the fertility estimates derived from extant studies may be biased to an unknown extent. These results have important implications for the evolutionary genetics of psychosis.

The relation between maternal schizophrenia and low birth weight is modified by paternal age

OBJECTIVE

Paternal characteristics have never been considered in the relation between maternal schizophrenia and adverse pregnancy outcomes. The aim of our study was to consider different paternal ages while investigating the relation between maternal schizophrenia and low birth weight (LBW), using a nationwide population-based dataset.

METHOD

Our study used data from the 2001 to 2003 Taiwan National Health Insurance Research Dataset and birth certificate registry. A total of 543 394 singleton live births were included. We performed multivariate logistic regression analyses to explore the relation between maternal schizophrenia and the risk of LBW, taking different paternal age groups into account (aged 29 years or younger, 30 to 39 years, and 40 years and older), and after adjusting for other characteristics of infant, mother, and father as well as the difference between the parent's ages.

RESULTS

Mothers with schizophrenia had a higher percentage of LBW infants than mothers who did not (11.8%, compared with 6.8%). For infants whose mothers had schizophrenia, the adjusted odds ratios of LBW were 1.47 (95% CI 1.02 to 2.27, P < 0.05) and 2.80 (95% CI 1.42 to 5.51, P < 0.01) times greater than for infants whose mothers did not have schizophrenia, for paternal age groups of 30 to 39 years and 40 years or older, respectively. However, maternal schizophrenia was not a significant predictor of LBW for infants whose fathers were aged 29 years and younger.

CONCLUSIONS

The relation between LBW and maternal schizophrenia is modified by paternal age. More attention should be paid to the interaction of paternal characteristics and maternal psychiatric disorders in producing adverse pregnancy outcomes.

Illusions and delusions: relating experimentally-induced false memories to anomalous experiences and ideas

The salience hypothesis of psychosis rests on a simple but profound observation that subtle alterations in the way that we perceive and experience stimuli have important consequences for how important these stimuli become for us, how much they draw our attention, how they embed themselves in our memory and, ultimately, how they shape our beliefs. We put forward the idea that a classical memory illusion – the Deese–Roediger–McDermott (DRM) effect – offers a useful way of exploring processes related to such aberrant belief formation. The illusion occurs when, as a consequence of its relationship to previous stimuli, a stimulus that has not previously been presented is falsely remembered. Such illusory familiarity is thought to be generated by the surprising fluency with which the stimulus is processed. In this respect, the illusion relates directly to the salience hypothesis and may share common cognitive underpinnings with aberrations of perception and attribution that are found in psychosis. In this paper, we explore the theoretical importance of this experimentally-induced illusion in relation to the salience model of psychosis. We present data showing that, in healthy volunteers, the illusion relates directly to self reported anomalies of experience and magical thinking. We discuss this finding in terms of the salience hypothesis and of a broader Bayesian framework of perception and cognition which emphasizes the salience both of predictable and unpredictable experiences.

Increased number of offspring in first degree relatives of psychotic individuals: a partial explanation for the persistence of psychotic illnesses

OBJECTIVE

As patients with psychotic illness have fewer offspring than controls, the persistence of psychotic illness is puzzling. We hypothesized that unaffected first-degree relatives of patients have more offspring than controls.

METHOD

Probands were 4904, individuals with non-affective psychotic disorders identified from a hospitalization registry. Unaffected first degree relatives and matched controls were identified from the Israeli Population Registry. The number of offspring of unaffected parents, biological siblings and controls was ascertained.

RESULTS

Unaffected parents of psychotic patients had more offspring/person than controls; 4.5 +/- 2.7 vs. 3.4 +/- 2.2, P = 0.000. Unaffected parents from familial psychosis families (more than one affected family member) had 1.83 more offspring than controls; unaffected parents from non-familial psychosis families had 0.97 more offspring than controls (both P < 0.001).

CONCLUSION

These findings might imply that genes which increase susceptibility for schizophrenia may be associated with increased number of offspring, perhaps supplying a partial explanation for the persistence of psychosis.

Association between paternal schizophrenia and low birthweight: a nationwide population-based study

Using a nationwide population-based dataset, the aim of the present study was to investigate the association between paternal schizophrenia and the risk of low birthweight (LBW). This study linked the 2001 Taiwan National Health Insurance Research Dataset with Taiwan's birth and death certificate registries. In total, 220 465 singleton live births were included. The key dependent variable was whether or not an infant's father was diagnosed with schizophrenia, while the independent variable of interest was whether an infant had LBW. Multivariate logistic regression analysis was performed to explore the relationship between paternal schizophrenia and the risk of LBW, after adjusting for the infant and parents' characteristics. The results show that infants whose fathers had schizophrenia were more likely to have LBW than those whose fathers did not (12.6% vs 8.0%). Infants whose fathers had schizophrenia were found to be 1.58 (95% confidence interval = 1.10-2.52, P < .05) times more likely to have LBW than their counterparts whose fathers did not have schizophrenia, following adjustment for gestational week at birth, parity, paternal age and highest educational level, family monthly incomes, and marital status. We conclude that the offspring whose fathers had a diagnosis of schizophrenia had increased risk of LBW compared with those whose fathers had no schizophrenia. This finding paves the way for further studies and suggests that there may be potential benefit to early intervention to prevent LBW in pregnant women with husbands with schizophrenia.

Is a Successful High-K Fitness Strategy Associated with Better Mental Health?

This study examined the associations between a high-K fitness strategy and mental health. These associations were tested on a sample of 1400 disaster workers who had exposure to a singular traumatic event and who underwent psychological evaluations. The results showed that high-K was an important negative predictor of psychopathology, accounting for significant variance in PTSD, general psychopathology, functional disability, anger, and sleep disturbances. Implications of the results are discussed.

Reconciling 'the new epidemiology' with an evolutionary genetic basis for schizophrenia

Recent epidemiological findings of variable incidence and prevalence pose a problem for evolutionary genetic analyses of schizophrenia. The author rejects models of psychosis based on balanced polymorphism and develops an alternative evolutionary model incorporating concepts of anatagonistic pleiotropy, 'cliff-edged fitness' and gene-environment interactions. In essence, genes for psychosis are considered as 'normal genes' that play a fundamental role in neurodevelopment. A spectrum of genetic vulnerability exists in the population, which in the context of a toxic social environment is expressed as a continuum of psychosis. Complex bidirectional gene-environment interactions operate throughout neurodevelopment to mediate expression of the disorder. Harmful social conditions lead to epigenetic alterations in the expression of susceptibility genes/alleles. This in turn alters the trajectory of normal brain development resulting in abnormalities of neural connectivity, dysregulation of neurotransmitter and other biochemical systems, and resulting psychotic illness. In this manner, the evolved genetic make-up that defines the unique social cognitive abilities of modern Homo sapiens, also carries with it an inherent genetic vulnerability to harmful features of the social environment. Psychosis therefore, is not just a costly by-product of social brain evolution in modern humans, but is also a consequence of the unhealthy societies we create around us.

Problems with the imprinting hypothesis of schizophrenia and autism

Crespi & Badcock (C&B) convincingly argue that autism and schizophrenia are diametric malfunctions of the social brain, but their core imprinting hypothesis is less persuasive. Much of the evidence they cite is unrelated to their hypothesis, is selective, or is overstated; their hypothesis lacks a clearly explained mechanism; and it is unclear how their explanation fits in with known aspects of the disorders.

Psychosis and autism as diametrical disorders of the social brain

Autistic-spectrum conditions and psychotic-spectrum conditions (mainly schizophrenia, bipolar disorder, and major depression) represent two major suites of disorders of human cognition, affect, and behavior that involve altered development and function of the social brain. We describe evidence that a large set of phenotypic traits exhibit diametrically opposite phenotypes in autistic-spectrum versus psychotic-spectrum conditions, with a focus on schizophrenia. This suite of traits is inter-correlated, in that autism involves a general pattern of constrained overgrowth, whereas schizophrenia involves undergrowth. These disorders also exhibit diametric patterns for traits related to social brain development, including aspects of gaze, agency, social cognition, local versus global processing, language, and behavior. Social cognition is thus underdeveloped in autistic-spectrum conditions and hyper-developed on the psychotic spectrum.;>We propose and evaluate a novel hypothesis that may help to explain these diametric phenotypes: that the development of these two sets of conditions is mediated in part by alterations of genomic imprinting. Evidence regarding the genetic, physiological, neurological, and psychological underpinnings of psychotic-spectrum conditions supports the hypothesis that the etiologies of these conditions involve biases towards increased relative effects from imprinted genes with maternal expression, which engender a general pattern of undergrowth. By contrast, autistic-spectrum conditions appear to involve increased relative bias towards effects of paternally expressed genes, which mediate overgrowth. This hypothesis provides a simple yet comprehensive theory, grounded in evolutionary biology and genetics, for understanding the causes and phenotypes of autistic-spectrum and psychotic-spectrum conditions.

Schizotypy versus openness and intelligence as predictors of creativity

Schizophrenia-spectrum risk alleles may persist in the population, despite their reproductive costs in individuals with schizophrenia, through the possible creativity benefits of mild schizotypy in non-psychotic relatives. To assess this creativity-benefit model, we measured creativity (using 6 verbal and 8 drawing tasks), schizotypy, Big Five personality traits, and general intelligence in 225 University of New Mexico students. Multiple regression analyses showed that openness and intelligence, but not schizotypy, predicted reliable observer ratings of verbal and drawing creativity. Thus, the 'madness-creativity' link seems mediated by the personality trait of openness, and standard creativity-benefit models seem unlikely to explain schizophrenia's evolutionary persistence.

Fertility of first-degree relatives of patients with schizophrenia: a three generation perspective

We explored the fertility in three generations; fertility of parents, siblings and offspring to patients with schizophrenia, to test the hypothesis that the decreased reproductive rate in the patients is compensated by an increased rate in their first-degree relatives. A population-based national database was created by linking the Swedish Multi-Generation and Hospital Discharge Registers. To maximize follow-up time for schizophrenia and reproductive history, three birth cohorts were selected: parental generation, born 1918-1927 (n=274464); affected generation, born 1932-1941 (n=108502) and offspring to affected generation, born 1951-1960 (n=103105). Ratios of estimated mean number of offspring were measured (fertility ratios), comparing the study subjects to the general population. The fertility among males with schizophrenia was decreased by over 70% (fertility ratio(patients/population)=0.29, 95% CI 0.25-0.35), whereas female patients had less than half as many offspring as the general female population (fertility ratio(patients/population)=0.48, 95% CI 0.42-0.55). When accounting for selection bias of larger families, no statistically significant difference was found among parents of patients with and without a diagnosis of schizophrenia. Further, the fertility among siblings of schizophrenic patients did not differ from the general population. A reduction in fertility was found among offspring to patients with schizophrenia, male offspring had 12% fewer offspring (fertility ratio(offspring/population)=0.88, 95%CI 0.77-1.01), while female offspring had 6% fewer offspring (fertility ratio(offspring/population)=0.94, 95% CI 0.84-1.05). In conclusion, we found reduced fertility in patients with schizophrenia and among their offspring that was not compensated by higher parental or sibling fertility.

The evolution of personality variation in humans and other animals

A comprehensive evolutionary framework for understanding the maintenance of heritable behavioral variation in humans is yet to be developed. Some evolutionary psychologists have argued that heritable variation will not be found in important, fitness-relevant characteristics because of the winnowing effect of natural selection. This article propounds the opposite view. Heritable variation is ubiquitous in all species, and there are a number of frameworks for understanding its persistence. The author argues that each of the Big Five dimensions of human personality can be seen as the result of a trade-off between different fitness costs and benefits. As there is no unconditionally optimal value of these trade-offs, it is to be expected that genetic diversity will be retained in the population.

Psychosis: a costly by-product of social brain evolution in Homo sapiens

The plethora of varied and often conflictual research evidence on the functional psychoses calls for a unifying explanatory framework. An evolutionary framework is appropriate in view of the paradoxical epidemiology of the disorders. Evolutionary models that rely on balanced polymorphism or group selection models are not supported by the evidence. Rather, a hypothesis is presented arguing that the spectrum of psychoses should be regarded as a costly by-product of social brain evolution in Homo sapiens. Under social selective pressures, hominid ancestors evolved a sophisticated neural network supporting social cognition and adaptive interpersonal behaviour--this is termed the 'social brain'. The functional psychoses (and schizophrenia in particular) are characterised by functional and structural deficits in these fronto-temporal and fronto-parietal circuits; hence the epithet 'social brain disorders' is fitting. I argue that accumulating evidence for an evolved social brain calls for a new philosophy of mind; a philosophy focussed on the social and interpersonal nature of human experience and derived from the philosophies of Fromm, Heidegger and Merleau-Ponty. Such a paradigm shift would aid modern neuroscience in finally abandoning Cartesian dualism and would guide psychiatry towards an integrated and 'socio-neurologically' embedded understanding of mental disorders.

Schizotypy, creativity and mating success in humans

There is an evolutionary puzzle surrounding the persistence of schizophrenia, since it is substantially heritable and associated with sharply reduced fitness. However, some of the personality traits which are predictive of schizophrenia are also associated with artistic creativity. Geoffrey Miller has proposed that artistic creativity functions to attract mates. Here, we investigate the relationship between schizotypal personality traits, creative activity, and mating success in a large sample of British poets, visual artists, and other adults. We show that two components of schizotypy are positively correlated with mating success. For one component, this relationship is mediated by creative activity. Results are discussed in terms of the evolution of human creativity and the genesis of schizophrenia.

Schizophrenia as one extreme of a sexually selected fitness indicator

Schizophrenia remains an evolutionary paradox. Its delusions, hallucinations and other symptoms begin in adolescence or early adulthood and so devastate sexual relationships and reproductive success that selection should have eliminated the disorder long ago. Yet it persists as a moderately heritable disorder at a global 1% prevalence--too high for new mutations at a few genetic loci. We suggest that schizophrenia persists and involves many loci because it is the unattractive, low-fitness extreme of a highly variable mental trait that evolved as a fitness ("good genes") indicator through mutual mate choice. Here we show that this hypothesis explains many key features of schizophrenia and predicts that some families carry modifier alleles that increase the indicator's neurodevelopmental sensitivity to heritable fitness and condition. Such alleles increase the extent to which high-fitness family members develop impressive courtship abilities and achieve high reproductive success, but also increase the extent to which low-fitness family members develop schizophrenia. Here we introduce this fitness indicator model of schizophrenia, discuss its explanatory power, explain how it resolves the evolutionary paradox, discuss its implications for gene hunting, and identify some empirically testable predictions as directions for further research.

The prevalence of panic attacks in the United States: 1980 to 1995

OBJECTIVE

The purpose of this study was to determine the difference in the prevalence of panic attacks among adults in the US population between 1980 and 1995.

METHODS

Data were drawn from the Epidemiologic Catchment Area Program study (1980) and the Midlife Development in the United States Survey (1996), which are epidemiologic survey studies with samples representative of the US adult population. A chi-square test was used to determine the difference between the prevalence of panic attack in 1980 and 1995.

RESULTS

There was a statistically significant increase in the prevalence of panic attacks among adults 25 to 74 years of age from 1980 to 1995 in the United States (12.7% versus 5.3%; chi(2)=135.2, df=1, P<.0001).

CONCLUSIONS

These data suggest that there may have been an increase in the prevalence of panic attacks among adults 25 to 74 years of age in the general US population over the past two decades.

The glial growth factors deficiency and synaptic destabilization hypothesis of schizophrenia

BACKGROUND

A systems approach to understanding the etiology of schizophrenia requires a theory which is able to integrate genetic as well as neurodevelopmental factors.

PRESENTATION OF THE HYPOTHESIS

Based on a co-localization of loci approach and a large amount of circumstantial evidence, we here propose that a functional deficiency of glial growth factors and of growth factors produced by glial cells are among the distal causes in the genotype-to-phenotype chain leading to the development of schizophrenia. These factors include neuregulin, insulin-like growth factor I, insulin, epidermal growth factor, neurotrophic growth factors, erbB receptors, phosphatidylinositol-3 kinase, growth arrest specific genes, neuritin, tumor necrosis factor alpha, glutamate, NMDA and cholinergic receptors. A genetically and epigenetically determined low baseline of glial growth factor signaling and synaptic strength is expected to increase the vulnerability for additional reductions (e.g., by viruses such as HHV-6 and JC virus infecting glial cells). This should lead to a weakening of the positive feedback loop between the presynaptic neuron and its targets, and below a certain threshold to synaptic destabilization and schizophrenia.

TESTING THE HYPOTHESIS

Supported by informed conjectures and empirical facts, the hypothesis makes an attractive case for a large number of further investigations.

IMPLICATIONS OF THE HYPOTHESIS

The hypothesis suggests glial cells as the locus of the genes-environment interactions in schizophrenia, with glial asthenia as an important factor for the genetic liability to the disorder, and an increase of prolactin and/or insulin as possible working mechanisms of traditional and atypical neuroleptic treatments.