Schizophrenia and vitamin D related genes could have been subject to latitude-driven adaptation

Recent natural selection conferred protection against schizophrenia by non-antagonistic pleiotropy

Schizophrenia is a debilitating psychiatric disorder associated with a reduced fertility and decreased life expectancy, yet common predisposing variation substantially contributes to the onset of the disorder, which poses an evolutionary paradox. Previous research has suggested balanced selection, a mechanism by which schizophrenia risk alleles could also provide advantages under certain environments, as a reliable explanation. However, recent studies have shown strong evidence against a positive selection of predisposing loci. Furthermore, evolutionary pressures on schizophrenia risk alleles could have changed throughout human history as new environments emerged. Here in this study, we used 1000 Genomes Project data to explore the relationship between schizophrenia predisposing loci and recent natural selection (RNS) signatures after the human diaspora out of Africa around 100,000 years ago on a genome-wide scale. We found evidence for significant enrichment of RNS markers in derived alleles arisen during human evolution conferring protection to schizophrenia. Moreover, both partitioned heritability and gene set enrichment analyses of mapped genes from schizophrenia predisposing loci subject to RNS revealed a lower involvement in brain and neuronal related functions compared to those not subject to RNS. Taken together, our results suggest non-antagonistic pleiotropy as a likely mechanism behind RNS that could explain the persistence of schizophrenia common predisposing variation in human populations due to its association to other non-psychiatric phenotypes.

Eating disorder symptoms and their associations with anthropometric and psychiatric polygenic scores

Background

Eating disorder (ED) symptoms are prevalent in the general population, but their shared genetic underpinnings with psychiatric, metabolic, and anthropometric traits are not known. Here, we examined if polygenic scores (PGSs) of traits associated with anorexia nervosa are also associated with adolescent ED symptoms in the Avon Longitudinal Study of Parents and Children (ALSPAC).

Methods

A total of 8654 participants with genotype data and at least one phenotypic measure were included from the ALSPAC study. We associated PGS from 25 traits (16 psychiatric, 4 metabolic, and 5 anthropometric) with eight ED symptoms, including behaviours such as fasting for weight loss and cognitions such as body dissatisfaction.

Results

Higher attention deficit hyperactivity disorder PGS and lower educational attainment PGS were associated with fasting for weight loss. Higher insomnia PGS was associated with increased body dissatisfaction. We found no evidence of an association between metabolic trait PGS and any ED symptom. Fat‐free mass, fat mass, and body fat percentage PGSs, were positively associated with binge eating, excessive exercise, fasting for weight loss, body dissatisfaction, and weight and shape concern.

Conclusions

ED symptoms are genetically associated with psychiatric and anthropometric, but not with metabolic traits. Our findings provide insights for future genetic research investigating on why some individuals with ED symptoms progress to develop threshold EDs while others do not.

Several eating disorder symptoms (i.e., binge eating, fasting for weight loss, and body dissatisfaction) in this study were significantly associated with both psychiatric and anthropometric polygenic scores emphasising the genetic complexity of these traits.

Eating disorder symptoms as present in the general population and threshold eating disorders may be partially etiologically related (i.e., psychiatric and anthropometric origins), but metabolic genetic factors may differentiate between symptoms and threshold eating disorders.

Metabolic disturbances could therefore be the catalyst that puts some individuals on a developmental trajectory leading to threshold eating disorders.

Independent and Interactive Influences of Environmental UVR, Vitamin D Levels, and Folate Variant MTHFD1-rs2236225 on Homocysteine Levels

Elevated homocysteine (Hcy) levels are a risk factor for vascular diseases. Recently, increases in ultraviolet radiation (UVR) have been linked to decreased Hcy levels. This relationship may be mediated by the status of UVR-responsive vitamins, vitamin D and folate, and/or genetic variants influencing their levels; however, this has yet to be examined. Therefore, the independent and interactive influences of environmental UVR, vitamin D and folate levels and related genetic variants on Hcy levels were examined in an elderly Australian cohort (n = 619). Red blood cell folate, 25-hydroxyvitamin D (25(OH)D), and plasma Hcy levels were determined, and genotyping for 21 folate and vitamin D-related variants was performed. Erythemal dose rate accumulated over six-weeks (6W-EDR) and four-months (4M-EDR) prior to clinics were calculated as a measure of environmental UVR. Multivariate analyses found interactions between 6W-EDR and 25(OH)D levels (pinteraction = 0.002), and 4M-EDR and MTHFD1-rs2236225 (pinteraction = 0.006) in predicting Hcy levels. The association between 6W-EDR and Hcy levels was found only in subjects within lower 25(OH)D quartiles (<33.26 ng/mL), with the association between 4M-EDR and Hcy occurring only in subjects carrying the MTHFD1-rs2236225 variant. 4M-EDR, 6W-EDR, and MTHFD1-rs2236225 were also independent predictors of Hcy. Findings highlight nutrient-environment and gene-environment interactions that could influence the risk of Hcy-related outcomes.

Distribution of variants in multiple vitamin D-related loci (DHCR7/NADSYN1, GC, CYP2R1, CYP11A1, CYP24A1, VDR, RXRα and RXRγ) vary between European, East-Asian and Sub-Saharan African-ancestry populations

BACKGROUND

The frequency of vitamin D-associated gene variants appear to reflect changes in long-term ultraviolet B radiation (UVB) environment, indicating interactions exist between the primary determinant of vitamin D status, UVB exposure and genetic disposition. Such interactions could have health implications, where UVB could modulate the impact of vitamin D genetic variants identified as disease risk factors. However, the current understanding of how vitamin D variants differ between populations from disparate UVB environments is limited, with previous work examining a small pool of variants and restricted populations only.

METHODS

Genotypic data for 46 variants within multiple vitamin D-related loci (DHCR7/NADSYN1, GC, CYP2R1, CYP11A1, CYP27A1, CYP24A1, VDR, RXRα and RXRγ) was collated from 60 sample sets (2633 subjects) with European, East Asian and Sub-Saharan African origin via the NCBI 1000 Genomes Browser and ALFRED (Allele Frequency Database), with the aim to examine for patterns in the distribution of vitamin D-associated variants across these geographic areas.

RESULTS

The frequency of all examined genetic variants differed between populations of European, East Asian and Sub-Saharan African ancestry. Changes in the distribution of variants in CYP2R1, CYP11A1, CYP24A1, RXRα and RXRγ genes between these populations are novel findings which have not been previously reported. The distribution of several variants reflected changes in the UVB environment of the population's ancestry. However, multiple variants displayed population-specific patterns in frequency that appears not to relate to UVB changes.

CONCLUSIONS

The reported population differences in vitamin D-related variants provides insight into the extent by which activity of the vitamin D system can differ between cohorts due to genetic variance, with potential consequences for future dietary recommendations and disease outcomes.

A trans-ethnic two-stage polygenetic scoring analysis detects genetic correlation between osteoporosis and schizophrenia

BACKGROUNDS

To explore the genetic correlation between schizophrenia (SCZ) and osteoporosis (OP).

DESIGN, SETTING, PARTICIPANTS, MEASUREMENTS

We conducted a trans-ethnic two-stage genetic correlation analysis of OP and SCZ, totally invoking 2286 Caucasia subjects in discovery stage and 4124 Chinese subjects in replication stage. The bone mineral density (BMD) and bone area values of ulna & radius, hip and spine were measured using Hologic 4500W dual energy X-ray absorptiometry machine. SCZ was diagnosed according to DSM-IV criteria. For the genome-wide association study (GWAS) of Caucasian OP, Chinese OP and Chinese SCZ, SNP genotyping was performed using Affymetrix SNP 6.0 array. For the GWAS of Caucasian SCZ, SNP genotyping was conducted using the Affymetrix 5.0 array, Affymetrix 6.0 array and Illumina 550 K array. Polygenetic risk scoring (PRS) analysis was conducted by PRSice software. Also, Linkage disequilibrium score regression (LD Score regression) analysis was performed to evaluate the genetic correlation between OP and SCZ. Multi-trait analysis of GWAS (MTAG) was performed to detect novel candidate genes for osteoporosis and SCZ.

RESULTS

In the Caucasia discovery samples, significant genetic correlations were observed for ulna & radius BMD vs. SCZ (P value = 0.010), ulna & radius area vs. SCZ (P value = 0.031). In the Chinese replication samples, we observed significant correlation for ulna & radius area vs. SCZ (P value = 0.019). In addition, LD Score regression also identified significant genetic correlations between SCZ and bone phenotypes in Caucasian and Chinese sample respectively. MTAG analysis identified several novel candidate genes, such as CTNNA2 (MTAG P value = 2.24 × 10-6) for SCZ and FADS2 (MTAG P value = 2.66 × 10-7) for osteoporosis.

CONCLUSIONS

Our study results support the overlapped genetic basis for osteoporosis and SCZ, and provide novel clues for elucidating the biological mechanism of increased osteoporosis risk in SCZ patients.

Williams Syndrome, Human Self-Domestication, and Language Evolution

Language evolution resulted from changes in our biology, behavior, and culture. One source of these changes might be human self-domestication. Williams syndrome (WS) is a clinical condition with a clearly defined genetic basis which results in a distinctive behavioral and cognitive profile, including enhanced sociability. In this paper we show evidence that the WS phenotype can be satisfactorily construed as a hyper-domesticated human phenotype, plausibly resulting from the effect of the WS hemideletion on selected candidates for domestication and neural crest (NC) function. Specifically, we show that genes involved in animal domestication and NC development and function are significantly dysregulated in the blood of subjects with WS. We also discuss the consequences of this link between domestication and WS for our current understanding of language evolution.

Exploring the relationship between vitamin D and mania: correlations between serum vitamin D levels and disease activity

BACKGROUND

Several studies suggest an association between hypovitaminosis D and mood disorders including major depressive disorder, seasonal affective disorder and premenstrual dysphoric disorder. On the other hand, there is not enough study about acute manic episode and hypovitaminosis D. This data insufficient zone led us to study on whether vitamin D deficiency is associated with acute manic episode and has an impact on disease activity Methods: Thirty-one patients with bipolar disorder in remission, 26 patients with acute manic episode and 40 healthy controls with no major psychopathology were recruited in this study. Hamilton Depression Rating Scale (HAM-D), Young Mania Rating Scale (YMRS) and the Clinical Global Impression - Severety scale (CGI-S) were used to evaluate disease activity. Total vitamin D (D2 + D3) values were measured.

RESULTS

Patients in acute manic episode had significantly lower (p = .002) vitamin D serum concentrations than healthy controls (respectively 15.16 ± 7.48 and 22.31 ± 8.8) but remission group's serum concentrations (18.40 ± 7.30) did not differ significantly from healthy controls or acute manic episode patients (p > .05). We observed negative and moderate correlations between vitamin D levels and YMRS scores (r: -0.641, p < .001), vitamin D levels and CGI scores (r: -0.559, p= .003).

CONCLUSIONS

Our results contribute to the idea that vitamin D deficiency and acute manic episode may have interactions with many pathways. Future trials may investigate this association with longer follow up. We recommend that serum vitamin D levels should be measured in patients with bipolar disorder especially in long term care.

Vitamin D-related genes are subjected to significant de novo mutation burdens in autism spectrum disorder

Vitamin D deficiency is a putative environmental risk factor for autism spectrum disorder (ASD). Besides, de novo mutations (DNMs) play essential roles in ASD. However, it remains unclear whether vitamin D-related genes (VDRGs) carry a strong DNM burden. For the 943 reported VDRGs, we analyzed publicly-available DNMs from 4,327 ASD probands and 3,191 controls. We identified 126 and 44 loss-of-function or deleterious missense mutations in the probands and the controls, respectively, representing a significantly higher DNM burden (p = 1.06 × 10^-5 ; odds ratio = 2.11). Specifically, 18 of the VDRGs were found to harbor recurrent functional DNMs in the probands, compared with only one in the controls. In addition, we found that 108 VDRGs with functional DNMs in the probands were significantly more likely to exhibit haploinsufficiency and genic intolerance (p < 0.0078). These VDRGs were also significantly interconnected and co-expressed, and also with other known ASD-risk genes (p < 0.0014), thereby forming a functional network enriched in chromatin modification, transcriptional regulation, and neuronal function. We provide straightforward genetic evidences for the first time that VDRGs with a strong degree of DNM burden in ASD and DNMs of VDRGs could be involved in the mechanism underlying in ASD pathogenesis.

Association Between Vitamin D Status and Schizophrenia: A First Psychotic Episode Study

Vitamin D deficiency has been linked with schizophrenia. We aimed to determine whether patients with a first episode of psychosis (FEP) had lower vitamin D levels compared with controls considering their final diagnosis. We conducted a cross-sectional study determining 25-hydroxyvitamin D blood levels. 25-Hydroxyvitamin D levels were considered optimum at 20 ng/mL or greater. A group of 45 adult patients with FEP and a group of 22 healthy controls matched for age were recruited. The patient group was subdivided in two final diagnosis groups (schizophrenia versus other psychoses) after a 6-month follow-up. Average vitamin D values were deficient for FEP patients, especially those 22 with a final diagnosis of schizophrenia. These results relating vitamin D and schizophrenia generate interest to further examine this association.

An evaluation of variation in published estimates of schizophrenia prevalence from 1990─2013: a systematic literature review

BACKGROUND

There is a lack of consistency in findings across studies on the prevalence of schizophrenia, and no recent systematic review of the literature exists. The purpose of this study is to provide an updated systematic review of population-based prevalence estimates and to understand the factors that could account for this variation in prevalence estimates.

METHODS

MEDLINE, Embase, and PsycInfo databases were searched for observational studies describing schizophrenia prevalence in general populations from 2003-2013 and supplemented by studies from a prior review covering 1990-2002. Studies reporting prevalence estimates from specialized populations such as institutionalized, homeless, or incarcerated persons were excluded. Prevalence estimates were compared both across and within studies by factors that might contribute to variability using descriptive statistics.

RESULTS

Sixty-five primary studies were included; thirty-one (48 %) were from Europe and 35 (54 %) were conducted in samples of ≥50,000 persons. Among 21 studies reporting 12-month prevalence, the median estimate was 0.33 % with an interquartile range (IQR) of 0.26 %-0.51 %. The median estimate of lifetime prevalence among 29 studies was 0.48 % (IQR: 0.34 %-0.85 %). Prevalence across studies appeared to vary by study design, geographic region, time of assessment, and study quality scores; associations between study sample size and prevalence were not observed. Within studies, age-adjusted estimates were higher than crude estimates by 17 %-138 %, the use of a broader definition of schizophrenia spectrum disorders compared to schizophrenia increased case identification by 18 %-90 %, identification of cases from inpatient-only settings versus any setting decreased prevalence by 60 %, and no consistent trends were noted by differing diagnostic criteria.

CONCLUSIONS

This review provides updated information on the epidemiology of schizophrenia in general populations, which is vital information for many stakeholders. Study characteristics appear to play an important role in the variation between estimates. Overall, the evidence is still sparse; for many countries no new studies were identified.

Vitamin D as a neurosteroid affecting the developing and adult brain

Vitamin D deficiency is prevalent throughout the world, and growing evidence supports a requirement for optimal vitamin D levels for the healthy developing and adult brain. Vitamin D has important roles in proliferation and differentiation, calcium signaling within the brain, and neurotrophic and neuroprotective actions; it may also alter neurotransmission and synaptic plasticity. Recent experimental studies highlight the impact that vitamin D deficiency has on brain function in health and disease. In addition, results from recent animal studies suggest that vitamin D deficiency during adulthood may exacerbate underlying brain disorders and/or worsen recovery from brain stressors. An increasing number of epidemiological studies indicate that vitamin D deficiency is associated with a wide range of neuropsychiatric disorders and neurodegenerative diseases. Vitamin D supplementation is readily available and affordable, and this review highlights the need for further research.

Correlation between total vitamin D levels and psychotic psychopathology in patients with schizophrenia: therapeutic implications for add-on vitamin D augmentation

OBJECTIVES

Vitamin D deficiency is one of the implicated factors in ethio-pathogenesis of schizophrenia. Low serum vitamin D levels have been reported in many schizophrenia studies. However, the question is still not answered: Is there a correlation between disease activity and serum vitamin D levels? This is the first study evaluating the relationship between serum total vitamin D levels and disease activity, by comparing total vitamin D levels in two schizophrenia groups abruptly different in terms of disease activity.

METHODS

41 patients with schizophrenia in remission, 40 patients with schizophrenia those in an acute episode and 40 age- and sex -matched controls with no major psychopatology were recruited in this study. Positive and Negative Syndrome Scale (PANSS) and the Clinical Global Impression - Severety scale (CGI-S) were used to evaluate disease activity. A demographic data form that included entries on age, gender, ethnicity, weight, skin color, daily duration of sun exposure and nutritional assessment were used. Blood samples were taken from all patients and controls. Total vitamin D (D2+D3), calcium, phosphor, parathyroid hormone values were measured.

RESULTS

Patients in an acute episode had significantly lower vitamin D levels compared to patients in remission and to healthy controls (in terms of median values respectively, 7.18, 15.03, 15.02, p < 0.001). We observed negative and moderate correlations between vitamin D levels and CGI scores (r = -0.624, p < 0.001), vitamin D levels and PANNS scores (r = -0.508, p < 0.001). There were no significant differences between groups in terms of serum P, Ca and PTH levels (p = 0.099, p = 0.943, p = 0.762). We could not detect any significant impact of weekly duration of sun exposure, skin color, ethnicity or nutrition on total vitamin D levels.

CONCLUSIONS

Even though important factors for vitamin D synthesis were similar, there was severe vitamin D deficiency in patients presenting with an acute episode, significantly different from those in remission. Is vitamin D deficiency the result or the cause of an acute episode? Our results contribute to the idea that vitamin D deficiency and schizophrenia may have interactions with an unknown pathway. Present data points out a possible influence at a genomic level. Future trials may investigate this association with longer follow up. We recommend that, serum vitamin D levels should be measured in patients with schizophrenia especially in long term care. Appropriate further treatment with add-on vitamin D supplements and diets that are rich in vitamin D should be considered.

Possible contributions of skin pigmentation and vitamin D in a polyfactorial model of seasonal affective disorder

Seasonal affective disorder (SAD) is a polyfactorial and polygenetic disorder that involves biological and psychological sub-mechanisms that differentially involve depression, seasonality, circadian rhythms, retinal sensitivity, iris pigmentation, sleep factors, and the neurotransmitters involved with these systems. Within the framework of the polyfactorial conceptualization of SAD, we review the possible contributions of vitamin D3 with respect to the aforementioned sub-mechanisms. We hypothesize that rather than functioning primarily as a proximal or direct sub-mechanism in the etiology of SAD, vitamin D likely functions in a more foundational and regulative role in potentiating the sub-mechanisms associated with the depressive and seasonality factors. There are several reasons for this position: 1. vitamin D levels fluctuate in the body seasonally, with a lag, in direct relation to seasonally-available sunlight; 2. lower vitamin D levels have been observed in depressed patients (as well as in patients with other psychiatric disorders) compared to controls; 3. vitamin D levels in the central nervous system affect the production of both serotonin and dopamine; and 4. vitamin D and vitamin D responsive elements are found throughout the midbrain regions and are especially concentrated in the hypothalamus, a region that encompasses the circadian timing systems and much of its neural circuitry. We also consider the variable of skin pigmentation as this may affect levels of vitamin D in the body. We hypothesize that people with darker skin pigmentation may experience greater risks for lower vitamin D levels that, especially following their migration to regions of higher latitude, could contribute to the emergence of SAD and other psychiatric and physical health problems.

Review: the role of vitamin D in nervous system health and disease

Vitamin D and its metabolites have pleomorphic roles in both nervous system health and disease. Animal models have been paramount in contributing to our knowledge and understanding of the consequences of vitamin D deficiency on brain development and its implications for adult psychiatric and neurological diseases. The conflation of in vitro, ex vivo, and animal model data provide compelling evidence that vitamin D has a crucial role in proliferation, differentiation, neurotrophism, neuroprotection, neurotransmission, and neuroplasticity. Vitamin D exerts its biological function not only by influencing cellular processes directly, but also by influencing gene expression through vitamin D response elements. This review highlights the epidemiological, neuropathological, experimental and molecular genetic evidence implicating vitamin D as a candidate in influencing susceptibility to a number of psychiatric and neurological diseases. The strength of evidence varies for schizophrenia, autism, Parkinson's disease, amyotrophic lateral sclerosis, Alzheimer's disease, and is especially strong for multiple sclerosis.

Vitamin D and maternal and child health: overview and implications for dietary requirements

The essentiality of vitamin D for normal growth and development has been recognized for over 80 years, and vitamin D fortification programs have been in place in the United States for more than 70 years. Despite the above, vitamin D deficiency continues to be a common finding in certain population groups. Vitamin D deficiency has been suggested as a potential risk factor for the development of preeclampsia, and vitamin D deficiency during infancy and early childhood is associated with an increased risk for numerous skeletal disorders, as well as immunological and vascular abnormalities. Vitamin D deficiency can occur through multiple mechanisms including the consumption of diets low in this vitamin and inadequate exposure to environmental ultraviolet B rays. The potential value of vitamin D supplementation in high-risk pregnancies and during infancy and early childhood is discussed. Currently, there is vigorous debate concerning what constitutes appropriate vitamin D intakes during early development as exemplified by differing recommendations from the Institute of Medicine Dietary Reference Intake report and recent recommendations by the Endocrine Society. As is discussed, a major issue that needs to be resolved is what key biological endpoint should be used when making vitamin D recommendations for the pregnant woman and her offspring.

A proximity-based method to identify genomic regions correlated with a continuously varying environmental variable

Knowledge of markers in the human genome which show spatial patterns and display extreme correlation with different environmental determinants play an important role in understanding the factors which affect the biological evolution of our species. We used the genotype data of more than half a million single nucleotide polymorphisms (SNPs) from the data set Human Genome Diversity Panel (HGDP-CEPH -CEPH) and we calculated Spearman's correlation between absolute latitude and one of the two allele frequencies of each SNP. We selected SNPs with a correlation coefficient within the upper 1% tail of the distribution. We then used a criterion of proximity between significant variants to focus on DNA regions showing a continuous signal over a portion of the genome. Based on external information and genome annotations, we demonstrated that most regions with the strongest signals also have biological relevance. We believe this proximity requirement adds an edge to our novel method compared to the existing literature, highlighting several genes (for example DTNB, DOT1L, TPCN2, RELN, MSRA, NRG3) related to body size or shape, human height, hair color, and schizophrenia. Our approach can be applied generally to any measure of association between polymorphic frequencies and continuously varying environmental variables.

Genome-wide association analysis of eating disorder-related symptoms, behaviors, and personality traits

Eating disorders (EDs) are common, complex psychiatric disorders thought to be caused by both genetic and environmental factors. They share many symptoms, behaviors, and personality traits, which may have overlapping heritability. The aim of the present study is to perform a genome-wide association scan (GWAS) of six ED phenotypes comprising three symptom traits from the Eating Disorders Inventory 2 [Drive for Thinness (DT), Body Dissatisfaction (BD), and Bulimia], Weight Fluctuation symptom, Breakfast Skipping behavior and Childhood Obsessive-Compulsive Personality Disorder trait (CHIRP). Investigated traits were derived from standardized self-report questionnaires completed by the TwinsUK population-based cohort. We tested 283,744 directly typed SNPs across six phenotypes of interest in the TwinsUK discovery dataset and followed-up signals from various strata using a two-stage replication strategy in two independent cohorts of European ancestry. We meta-analyzed a total of 2,698 individuals for DT, 2,680 for BD, 2,789 (821 cases/1,968 controls) for Bulimia, 1,360 (633 cases/727 controls) for Childhood Obsessive-Compulsive Personality Disorder trait, 2,773 (761 cases/2,012 controls) for Breakfast Skipping, and 2,967 (798 cases/2,169 controls) for Weight Fluctuation symptom. In this GWAS analysis of six ED-related phenotypes, we detected association of eight genetic variants with P < 10(-5) . Genetic variants that showed suggestive evidence of association were previously associated with several psychiatric disorders and ED-related phenotypes. Our study indicates that larger-scale collaborative studies will be needed to achieve the necessary power to detect loci underlying ED-related traits.

Exome sequencing followed by large-scale genotyping suggests a limited role for moderately rare risk factors of strong effect in schizophrenia

Schizophrenia is a severe psychiatric disorder with strong heritability and marked heterogeneity in symptoms, course, and treatment response. There is strong interest in identifying genetic risk factors that can help to elucidate the pathophysiology and that might result in the development of improved treatments. Linkage and genome-wide association studies (GWASs) suggest that the genetic basis of schizophrenia is heterogeneous. However, it remains unclear whether the underlying genetic variants are mostly moderately rare and can be identified by the genotyping of variants observed in sequenced cases in large follow-up cohorts or whether they will typically be much rarer and therefore more effectively identified by gene-based methods that seek to combine candidate variants. Here, we consider 166 persons who have schizophrenia or schizoaffective disorder and who have had either their genomes or their exomes sequenced to high coverage. From these data, we selected 5,155 variants that were further evaluated in an independent cohort of 2,617 cases and 1,800 controls. No single variant showed a study-wide significant association in the initial or follow-up cohorts. However, we identified a number of case-specific variants, some of which might be real risk factors for schizophrenia, and these can be readily interrogated in other data sets. Our results indicate that schizophrenia risk is unlikely to be predominantly influenced by variants just outside the range detectable by GWASs. Rather, multiple rarer genetic variants must contribute substantially to the predisposition to schizophrenia, suggesting that both very large sample sizes and gene-based association tests will be required for securely identifying genetic risk factors.

The effects of vitamin D on brain development and adult brain function

A role for vitamin D in brain development and function has been gaining support over the last decade. Multiple lines of evidence suggest that this vitamin is actually a neuroactive steroid that acts on brain development, leading to alterations in brain neurochemistry and adult brain function. Early deficiencies have been linked with neuropsychiatric disorders, such as schizophrenia, and adult deficiencies have been associated with a host of adverse brain outcomes, including Parkinson's disease, Alzheimer's disease, depression and cognitive decline. This review summarises the current state of research on the actions of vitamin D in the brain and the consequences of deficiencies in this vitamin. Furthermore, we discuss specific implications of vitamin D status on the neurotransmitter, dopamine.