The role of brain-derived neurotrophic factor (BDNF) gene variants in antipsychotic response and antipsychotic-induced weight gain

The BDNF Val66Met polymorphism serves as a potential marker of body weight in patients with psychiatric disorders

Brain-derived neurotrophic factor (BDNF) is a predominant neurotrophic factor in the brain, indispensable for neuronal growth, synaptic development, neuronal repair, and hippocampal neuroplasticity. Among its genetic variants, the BDNF Val66Met polymorphism is widespread in the population and has been associated with the onset and aggravation of diverse pathologies, including metabolic conditions like obesity and diabetes, cardiovascular ailments, cancer, and an array of psychiatric disorders. Psychiatric disorders constitute a broad category of mental health issues that influence mood, cognition, and behavior. Despite advances in research and treatment, challenges persist that hinder our understanding and effective intervention of these multifaceted conditions. Achieving and maintaining stable body weight is pivotal for overall health and well-being, and the relationship between psychiatric conditions and body weight is notably intricate and reciprocal. Both weight gain and loss have been linked to varying mental health challenges, making the disentanglement of this relationship critical for crafting holistic treatment strategies. The BDNF Val66Met polymorphism's connection to weight fluctuation in psychiatric patients has garnered attention. This review investigated the effects and underlying mechanisms by which the BDNF Val66Met polymorphism moderates body weight among individuals with psychiatric disorders. It posits the polymorphism as a potential biomarker, offering prospects for improved monitoring and therapeutic approaches for mental illnesses.

Clinical Utility and Implementation of Pharmacogenomics for the Personalisation of Antipsychotic Treatments

Decades of pharmacogenetic research have revealed genetic biomarkers of clinical response to antipsychotics. Genetic variants in antipsychotic targets, dopamine and serotonin receptors in particular, and in metabolic enzymes have been associated with the efficacy and toxicity of antipsychotic treatments. However, genetic prediction of antipsychotic response based on these biomarkers is far from accurate. Despite the clinical validity of these findings, the clinical utility remains unclear. Nevertheless, genetic information on CYP metabolic enzymes responsible for the biotransformation of most commercially available antipsychotics has proven to be effective for the personalisation of clinical dosing, resulting in a reduction of induced side effects and in an increase in efficacy. However, pharmacogenetic information is rarely used in psychiatric settings as a prescription aid. Lack of studies on cost-effectiveness, absence of clinical guidelines based on pharmacogenetic biomarkers for several commonly used antipsychotics, the cost of genetic testing and the delay in results delivery hamper the implementation of pharmacogenetic interventions in clinical settings. This narrative review will comment on the existing pharmacogenetic information, the clinical utility of pharmacogenetic findings, and their current and future implementations.

Associations of BDNF/BDNF-AS SNPs with Depression, Schizophrenia, and Bipolar Disorder

Brain-Derived Neurotrophic Factor (BDNF) is crucial for various aspects of neuronal development and function, including synaptic plasticity, neurotransmitter release, and supporting neuronal differentiation, growth, and survival. It is involved in the formation and preservation of dopaminergic, serotonergic, GABAergic, and cholinergic neurons, facilitating efficient stimulus transmission within the synaptic system and contributing to learning, memory, and overall cognition. Furthermore, BDNF demonstrates involvement in neuroinflammation and showcases neuroprotective effects. In contrast, BDNF antisense RNA (BDNF-AS) is linked to the regulation and control of BDNF, facilitating its suppression and contributing to neurotoxicity, apoptosis, and decreased cell viability. This review article aims to comprehensively overview the significance of single nucleotide polymorphisms (SNPs) in BDNF/BDNF-AS genes within psychiatric conditions, with a specific focus on their associations with depression, schizophrenia, and bipolar disorder. The independent influence of each BDNF/BDNF-AS gene variation, as well as the interplay between SNPs and their linkage disequilibrium, environmental factors, including early-life experiences, and interactions with other genes, lead to alterations in brain architecture and function, shaping vulnerability to mental health disorders. The potential translational applications of BDNF/BDNF-AS polymorphism knowledge can revolutionize personalized medicine, predict disease susceptibility, treatment outcomes, and guide the selection of interventions tailored to individual patients.

Novel ketamine and zinc treatment for anorexia nervosa and the potential beneficial interactions with the gut microbiome

Anorexia nervosa (AN) is a severe illness with diverse aetiological and maintaining contributors including neurobiological, metabolic, psychological, and social determining factors. In addition to nutritional recovery, multiple psychological and pharmacological therapies and brain-based stimulations have been explored; however, existing treatments have limited efficacy. This paper outlines a neurobiological model of glutamatergic and γ-aminobutyric acid (GABA)-ergic dysfunction, exacerbated by chronic gut microbiome dysbiosis and zinc depletion at a brain and gut level. The gut microbiome is established early in development, and early exposure to stress and adversity contribute to gut microbial disturbance in AN, early dysregulation to glutamatergic and GABAergic networks, interoceptive impairment, and inhibited caloric harvest from food (e.g., zinc malabsorption, competition for zinc ions between gut bacteria and host). Zinc is a key part of glutamatergic and GABAergic networks, and also affects leptin and gut microbial function; systems dysregulated in AN. Low doses of ketamine in conjunction with zinc, could provide an efficacious combination to act on NMDA receptors and normalise glutamatergic, GABAergic and gut function in AN.

The Progress and Pitfalls of Pharmacogenetics-Based Precision Medicine in Schizophrenia Spectrum Disorders: A Systematic Review and Meta-Analysis

The inadequate efficacy and adverse effects of antipsychotics severely affect the recovery of patients with schizophrenia spectrum disorders (SSD). We report the evidence for associations between pharmacogenetic (PGx) variants and antipsychotics outcomes, including antipsychotic response, antipsychotic-induced weight/BMI gain, metabolic syndrome, antipsychotic-related prolactin levels, antipsychotic-induced tardive dyskinesia (TD), clozapine-induced agranulocytosis (CLA), and drug concentration level (pharmacokinetics) in SSD patients. Through an in-depth systematic search in 2010–2022, we identified 501 records. We included 29 meta-analyses constituting pooled data from 298 original studies over 69 PGx variants across 39 genes, 4 metabolizing phenotypes of CYP2D9, and 3 of CYP2C19. We observed weak unadjusted nominal significant (p < 0.05) additive effects of PGx variants of DRD1, DRD2, DRD3, HTR1A, HTR2A, HTR3A, and COMT (10 variants) on antipsychotic response; DRD2, HTR2C, BDNF, ADRA2A, ADRB3, GNB3, INSIG2, LEP, MC4R, and SNAP25 (14 variants) on weight gain; HTR2C (one variant) on metabolic syndrome; DRD2 (one variant) on prolactin levels; COMT and BDNF (two variants) on TD; HLA-DRB1 (one variant) on CLA; CYP2D6 (four phenotypes) and CYP2C19 (two phenotypes) on antipsychotics plasma levels. In the future, well-designed longitudinal naturalistic multi-center PGx studies are needed to validate the effectiveness of PGx variants in antipsychotic outcomes before establishing any reproducible PGx passport in clinical practice.

Genetic determinants associated with response to clozapine in schizophrenia: an umbrella review

OBJECTIVE

Clozapine response varies widely from person to person, which may be due to inter-individual genetic variability. This umbrella review aims to summarize the current evidence on associations between pharmacodynamic genes and response to clozapine treatment.

METHODS

Following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis methodology, a systematic literature search was conducted in the PubMed and EMBASE databases from inception to November 2021 to identify systematic reviews and meta-analyses of studies that examined genetic determinants of clozapine response. The quality of the reviews was assessed with the AMSTAR-2 tool.

RESULTS

From a total of 128 records, 10 studies representing nine systematic reviews and one meta-analysis met our inclusion criteria. The overall quality of the included studies was poor. All systematic reviews concluded that the results of primary studies were largely negative or conflicting. Most evidence was found for an association with clozapine response and rs6313 and rs6314 within HTR2A and rs1062613 within HTR3A in the serotonergic system.

CONCLUSIONS

Conclusive evidence for associations between genetic variants and clozapine response is still lacking. Hypothesis-generating genetic studies in large, well-characterized study populations are urgently needed to obtain more consistent and clinically informative results. Future studies may also include multi-omics approaches to identify novel genetic determinants associated with clozapine response.

Pharmacogenetics of Antipsychotic Treatment in Schizophrenia

Antipsychotics are the mainstay treatment for schizophrenia. There is large variability between individuals in their response to antipsychotics, both in efficacy and adverse effects of treatment. While the source of interindividual variability in antipsychotic response is not completely understood, genetics is a major contributing factor. The identification of pharmacogenetic markers that predict antipsychotic efficacy and adverse reactions is a growing area of research and holds the potential to replace the current trial-and-error approach to treatment selection in schizophrenia with a personalized medicine approach.In this chapter, we provide an overview of the current state of pharmacogenetics in schizophrenia treatment. The most promising pharmacogenetic findings are presented for both antipsychotic response and commonly studied adverse reactions. The application of pharmacogenetics to schizophrenia treatment is discussed, with an emphasis on the clinical utility of pharmacogenetic testing and directions for future research.

The association between BDNF levels and risperidone-induced weight gain is dependent on the BDNF Val66Met polymorphism in antipsychotic-naive first episode schizophrenia patients: a 12-week prospective study

A growing number of studies have shown that brain-derived neurotrophic factor (BDNF) is associated with weight gain during antipsychotic treatment in schizophrenia patients. However, there is still a lack of research results in the initial stage of antipsychotic treatment. This study aimed to evaluate the relationship between weight gain caused by risperidone monotherapy for 12 weeks and BDNF level in antipsychotic-naive and first-episode (ANFE) patients with schizophrenia, and we hypothesize that this may depend on BDNF Val66Met gene polymorphism. In a 12-week longitudinal trial, 225 ANFE patients were enrolled and treated with risperidone. Body weight was measured at baseline and during the 12-week follow-up. After treatment, the average weight of ANFE patients increased by 2.6 kg. Furthermore, we found that in patients with Val/Val genotype, the increase in serum BDNF levels was negatively correlated with risperidone-induced weight gain (r = -0.44, p = 0.008). Regression analysis showed that the baseline BDNF level was a predictor of weight gain after treatment (β = -0.45, t = -3.0, p = 0.005). Our results suggest that the BDNF signaling may be involved in weight gain caused by risperidone treatment. Furthermore, the negative association between weight gain and increased BDNF levels during risperidone treatment in ANFE schizophrenia depends on the BDNF Val66Met polymorphism.

The Burden of Antipsychotic-Induced Weight Gain and Metabolic Syndrome in Children

Antipsychotic medications are critical to child and adolescent psychiatry, from the stabilization of psychotic disorders like schizophrenia, bipolar disorder, and psychotic depression to behavioral treatment of autism spectrum disorder, tic disorders, and pediatric aggression. While effective, these medications carry serious risk of adverse events-most commonly, weight gain and cardiometabolic abnormalities. Negative metabolic consequences affect up to 60% of patients and present a major obstacle to long-term treatment. Since antipsychotics are often chronically prescribed beginning in childhood, cardiometabolic risk accumulates. An increased susceptibility to antipsychotic-induced weight gain (AIWG) has been repeatedly documented in children, particularly rapid weight gain. Associated cardiometabolic abnormalities include central obesity, insulin resistance, dyslipidemia, and systemic inflammation. Lifestyle interventions and medications such as metformin have been proposed to reduce risk but remain limited in efficacy. Furthermore, antipsychotic medications touted to be weight-neutral in adults can cause substantial weight gain in children. A better understanding of the biological underpinnings of AIWG could inform targeted and potentially more fruitful treatments; however, little is known about the underlying mechanism. As yet, modest genetic studies have nominated a few risk genes that explain only a small percentage of the risk. Recent investigations have begun to explore novel potential mechanisms of AIWG, including a role for gut microbiota and microbial metabolites. This article reviews the problem of AIWG and AP metabolic side effects in pediatric populations, proposed mechanisms underlying this serious side effect, and strategies to mitigate adverse impact. We suggest future directions for research efforts that may advance the field and lead to improved clinical interventions.

Gut microbiota: An intermediary between metabolic syndrome and cognitive deficits in schizophrenia

Gut microbiome interacts with the central nervous system tract through the gut-brain axis. Such communication involves neuronal, endocrine, and immunological mechanisms, which allows for the microbiota to affect and respond to various behaviors and psychiatric conditions. In addition, the use of atypical antipsychotic drugs (AAPDs) may interact with and even change the abundance of microbiome to potentially cause adverse effects or aggravate the disorders inherent in the disease. The regulate effects of gut microbiome has been described in several psychiatric disorders including anxiety and depression, but only a few reports have discussed the role of microbiota in AAPDs-induced Metabolic syndrome (MetS) and cognitive disorders. The following review systematically summarizes current knowledge about the gut microbiota in behavior and psychiatric illness, with the emphasis of an important role of the microbiome in the metabolism of schizophrenia and the potential for AAPDs to change the gut microbiota to promote adverse events. Prebiotics and probiotics are microbiota-management tools with documented efficacy for metabolic disturbances and cognitive deficits. Novel therapies for targeting microbiota for alleviating AAPDs-induced adverse effects are also under fast development.

Pharmacogenetics of Antipsychotic Drug Treatment: Update and Clinical Implications

Numerous genetic variants have been shown to be associated with antipsychotic response and adverse effects of schizophrenia treatment. However, the clinical application of these findings is limited. The aim of this narrative review is to summarize the most recent publications and recommendations related to the genetics of antipsychotic treatment and shed light on the clinical utility of pharmacogenetics/pharmacogenomics (PGx). We reviewed the literature on PGx studies with antipsychotic drugs (i.e., antipsychotic response and adverse effects) and commonly used commercial PGx tools for clinical practice. Publications and reviews were included with emphasis on articles published between January 2015 and April 2018. We found 44 studies focusing on antipsychotic response and 45 studies on adverse effects (e.g., antipsychotic-induced weight gain, movement disorders, hormonal abnormality, and clozapine-induced agranulocytosis/granulocytopenia), albeit with mixed results. Overall, several gene variants related to antipsychotic response and adverse effects in the treatment of patients with schizophrenia have been reported, and several commercial pharmacogenomic tests have become available. However, further well-designed investigations and replication studies in large and well-characterized samples are needed to facilitate the application of PGx findings to clinical practice.

Brain-derived neurotrophic factor and schizophrenia

The brain-derived neurotrophic factor (BDNF) is a secretory growth factor that promotes neuronal proliferation and survival, synaptic plasticity and long-term potentiation in the central nervous system. Brain-derived neurotrophic factor biosynthesis and secretion are chrono-topically regulated processes at the cellular level, accounting for specific localizations and functions. Given its role in regulating brain development and activity, BDNF represents a potentially relevant gene for schizophrenia, and indeed BDNF and its non-synonymous functional variant, rs6265 (C → T, Val → Met) have been widely studied in psychiatric genetics. Human and animal studies have indicated that brain-derived neurotrophic factor is relevant for schizophrenia-related phenotypes, and that: (1) fine-tuned regulation of brain-derived neurotrophic factor secretion and activity is necessary to guarantee brain optimal development and functioning; (2) the Val → Met substitution is associated with impaired activity-dependent secretion of brain-derived neurotrophic factor; (3) disruption of brain-derived neurotrophic factor signaling is associated with altered synaptic plasticity and neurodevelopment. However, genome-wide association studies failed to associate the BDNF locus with schizophrenia, even though a sub-threshold association exists. Here, we will review studies focused on the relationship between the genetic variation of BDNF and schizophrenia, trying to fill the gap between genetic risk per se and insights from molecular biology. A deeper understanding of brain-derived neurotrophic factor biology and of the epigenetic regulation of brain-derived neurotrophic factor and its interactome during development may help clarifying the potential role of this gene in schizophrenia, thus informing development of brain-derived neurotrophic factor-based strategies of prevention and treatment of this disorder.

Progress in Genetic Polymorphisms Related to Lipid Disturbances Induced by Atypical Antipsychotic Drugs

Metabolic side effects such as weight gain and disturbed lipid metabolism are often observed in the treatment of atypical antipsychotic drugs (AAPDs), which contribute to an excessive prevalence of metabolic syndrome among schizophrenic patients. Great individual differences are observed but the underlying mechanisms are still uncertain. Research on pharmacogenomics indicates that gene polymorphisms involved in the pathways controlling food intake and lipid metabolism may play a significant role. In this review, relevant genes (HTR2C, DRD2, LEP, NPY, MC4R, BDNF, MC4R, CNR1, INSIG2, ADRA2A) and genetic polymorphisms related to metabolic side effects of AAPDs especially dyslipidemia were summarized. Apart from clinical studies, in vitro and in vivo evidence is also analyzed to support related theories. The association of central and peripheral mechanisms is emphasized, enabling the possibility of using peripheral gene expression to predict the central status. Novel methodological development of pharmacogenomics is in urgent need, so as to provide references for individualized medication and further to shed some light on the mechanisms underlying AAPD-induced lipid disturbances.

Does metabolic status affect serum levels of BDNF and MMP-9 in patients with schizophrenia?

The purpose of the article: Brain-derived neurotrophic factor (BDNF) and matrix metalloproteinase-9 (MMP-9) are involved in the processes of neurogenesis, synaptic plasticity, learning and memory. Growing number of studies shows a relationship between BDNF or MMP-9 and schizophrenia. Also, BDNF and MMP-9 levels may be affected by metabolic parameters, such as obesity or dyslipidemia. Our hypothesis is that alterations of BDNF or MMP-9 levels in schizophrenia might be secondary to metabolic abnormalities, often found among schizophrenia patients. Materials and methods: We have compared BDNF and MMP-9 between patients with schizophrenia (n = 64, age 49 ± 8.2 y) and healthy controls (n = 32, age 51 ± 8.9 y) in the context of cardio-metabolic parameters. Serum levels of BDNF and MMP-9 were measured using ELISA test, body composition parameters were determined using bioelectric impedance analysis. Results and conclusions: Our results showed significantly lowered serum BDNF concentration in the schizophrenia group (schizophrenia: 23.8 ± 7.83 ng/mL, control: 27.69 ± 8.11 ng/mL, p = 0.03). Serum MMP-9 concentration in schizophrenia group did not differ compared with the control group (schizophrenia: 456.8 ± 278.4 ng/mL, control: 341.5 ± 162.4 ng/mL, p = 0.07). After adjusting for age, all anthropometric parameters, body composition and laboratory tests BDNF were still significantly lower in the schizophrenia group. However, MMP-9 became significantly elevated in the schizophrenia group after adjusting for several anthropometric and body composition covariates. Our results confirmed reduced serum BDNF concentration in patients with schizophrenia. Also, this reduction seems to be independent of metabolic abnormalities. On the other hand, our hypothesis that MMP-9 level in schizophrenia is altered due to metabolic abnormalities might be true.

Sex difference in the association of body mass index and BDNF levels in Chinese patients with chronic schizophrenia

RATIONALE AND OBJECTIVE

Schizophrenia displays sex differences in many aspects. Decreased brain-derived neurotrophic factor (BDNF) levels have been reported to be associated with high body weight or obesity as well as other psychopathological aspects in schizophrenia patients. This study aimed to explore sex differences in the relationship between serum BDNF levels and obesity in patients with chronic schizophrenia.

METHODS

We recruited 132 Chinese patients with chronic schizophrenia (98 males and 34 females) and compared sex differences in the body mass index (BMI), obesity, serum BDNF levels, and their associations. Psychopathology symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS). A regression model with various demographic and clinical variables was applied to predict the serum levels of BDNF.

RESULTS

Female patients had a higher rate of obesity and higher BMI, but lower BDNF levels than male schizophrenia patients. A significantly negative correlation was observed between BMI and BDNF levels only in female patients but not in male patients. The multiple regression model with demographic and clinical variables significantly predicted BDNF levels only in female patients, with a medium size effect. And only in female patients, BMI made a significant contribution to this prediction.

CONCLUSION

Our results indicate significant sex differences in the obesity, BMI, BDNF levels, and their association in chronic patients with schizophrenia, showing a significant inverse correlation between BMI and BDNF levels only in female patients. Thus, sex needs to be considered when assessing the relationship between BDNF and metabolic syndromes in schizophrenia.

Pharmacogenetic Correlates of Antipsychotic-Induced Weight Gain in the Chinese Population

Antipsychotic-induced weight gain (AIWG) is a common adverse effect of this treatment, particularly with second-generation antipsychotics, and it is a major health problem around the world. We aimed to review the progress of pharmacogenetic studies on AIWG in the Chinese population to compare the results for Chinese with other ethnic populations, identify the limitations and problems of current studies, and provide future research directions in China. Both English and Chinese electronic databases were searched to identify eligible studies. We determined that > 25 single-nucleotide polymorphisms in 19 genes have been investigated in association with AIWG in Chinese patients over the past few decades. HTR2C rs3813929 is the most frequently studied single-nucleotide polymorphism, and it seems to be the most strongly associated with AIWG in the Chinese population. However, many genes that have been reported to be associated with AIWG in other ethnic populations have not been included in Chinese studies. To explain the pharmacogenetic reasons for AIWG in the Chinese population, genome-wide association studies and multiple-center, standard, unified, and large samples are needed.

BDNF as a pharmacogenetic target for antipsychotic treatment of schizophrenia

Antipsychotic drugs remain the mainstay of pharmacotherapy for schizophrenia. As there are large individual variations in efficacy and side-effects of antipsychotic drugs, there is a strong demand for personalized medication to treat schizophrenia. Pharmacogenetic research into antipsychotic drugs has examined a number of genetic variants and only a few polymorphisms have been found which promise to be associated with the therapeutic efficacy and side-effects of antipsychotic drugs. Brain-derived neurotrophic factor (BDNF) is a neurotrophin that plays a major role in neurogenesis and neuroplasticity, and in the modulation of several neurotransmitter systems including the dopaminergic system involved in the pathophysiology of schizophrenia. This review focused on the association between the BDNF gene Val66Met polymorphism and antipsychotic drugs. The BDNF Val66Met polymorphism has been related to the pathophysiology of schizophrenia, psychotic symptomatology, cognition, efficacy and side-effects of antipsychotic drugs. The BDNF Val66Met variants could be a promising target for antipsychotic medication options or developing next generation antipsychotic drugs. However, some studies showed inconsistent results due to sample size, ethnic differences and different antipsychotic drugs. Further studies will be required in this area to confirm the effect of the BDNF Val66Met polymorphism in the pathophysiology of schizophrenia and patients' response to antipsychotic drugs, especially in a larger sample size and in different ethnic populations.

BDNF Val66Met polymorphism and clinical response to antipsychotic treatment in schizophrenia and schizoaffective disorder patients: a meta-analysis

Brain-derived neurotrophic factor (BDNF) plays an important role in dopaminergic and serotonergic neurotransmission by modulating dopaminergic neuron differentiation and establishment. Multiple studies have analyzed the functional BDNF Val66Met variant in relation to antipsychotic response in schizophrenia (SCZ) patients, yielding mixed results. A meta-analysis was thus performed to examine the relationship between this variant and symptom improvement during antipsychotic treatment. Searches using PubMed, Web of Science, and PsycInfo until October 2017 yielded 11 studies that met inclusion criteria (total n = 3774). These studies investigated the BDNF Val66Met variant and antipsychotic response in patients with SCZ or schizoaffective disorder. Responders to antipsychotics were defined using the original criteria applied in each study. Effect sizes were computed using odds ratios, which were pooled according to the Mantel-Haenszel method. The BDNF Val66Met variant was not associated with the total number of responders and non-responders (p > 0.05) under dominant, recessive, or allelic models. Secondary analyses stratifying for individuals of each ethnicity and drug type also revealed no significant associations. Our findings suggest that the BDNF Val66Met variant is not associated with response to antipsychotics in individuals with SCZ. However, considering the current sample size, small effects cannot be ruled out. Moreover, recent studies have suggested that Val66Met forms haplotypes with other BDNF variants. Future studies should examine the Val66Met variant in conjunction with these other variants in relation to antipsychotic response. Moreover, since illness duration appears to influence BDNF levels in SCZ patients, future studies should aim to control for this potential confounding factor in response analyses.

Brain-derived neurotrophic factor as a biomarker for cognitive recovery in acute schizophrenia: 12-week results from a prospective longitudinal study

RATIONALE

It is generally accepted that impaired cognitive function is a core feature of schizophrenia. There is evidence for the role of brain-derived neurotrophic factor (BDNF) in cognitive function. Olanzapine was reported to yield cognitive improvement in patients with schizophrenia.

OBJECTIVES

In this study, we performed a prospective, open-label, 12-week observation trial to investigate whether peripheral BDNF may represent a potential biomarker for the effect of cognitive improvement induced by olanzapine in patients with schizophrenia.

METHODS

In total, 95 patients with acute schizophrenia were enrolled in the study. We also recruited 72 healthy individuals for a control group. The Positive and Negative Syndrome Scale (PANSS) was used to evaluate symptom severity and treatment response. Cognitive function was evaluated using the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). Plasma BDNF levels were measured with an enzyme-linked immunosorbent assay.

RESULTS

Of the 95 patients consented into the study, 68 completed the 12-week follow up. Our results showed that schizophrenia patients with acute exacerbation had significantly poorer performance than that of the controls (Ps < 0.01). A significantly decreased plasma level of BDNF in patients was observed compared with the controls (F = 7.77, P = 0.006). A significant improvement in each PANSS subscore and total score was observed when the patients completed this study (Ps < 0.01). Additionally, 12-week olanzapine treatment exhibited significant improvements in RBANS immediate memory, attention, and total scores (P = 0.018, 0.001, and 0.007, respectively). Along with the clinical improvement, plasma BDNF levels after 12-week olanzapine monotherapy (4.67 ± 1.74 ng/ml) were also significantly increased compared with those at baseline (3.38 ± 2.11 ng/ml) (P < 0.01). Spearman's correlation analysis showed that the increase in plasma levels of BDNF is significantly correlated with the change in the RBANS total scores (r = 0.28, P = 0.02) but not with the change in the PANSS total scores (r = - 0.18, P = 0.13). There is a significant correlation of BDNF increase with the change of RBANS attention subscore (r = 0.27, P = 0.028).

CONCLUSIONS

Our findings suggest that olanzapine improves psychiatric symptoms and cognitive dysfunction, particularly attention and immediate memory, in patients with acute schizophrenia, in parallel with increased plasma BDNF levels. Plasma BDNF levels may be a potential biomarker for cognitive recovery in acute schizophrenia.

Functional analysis of schizophrenia genes using GeneAnalytics program and integrated databases

Schizophrenia (SCZ) is a chronic debilitating neuropsychiatric disorder with multiple risk factors involving numerous complex genetic influences. We examined and updated a master list of clinically relevant and susceptibility genes associated with SCZ reported in the literature and genomic databases dedicated to gene discovery for characterization of SCZ genes. We used the commercially available GeneAnalytics computer-based gene analysis program and integrated genomic databases to create a molecular profile of the updated list of 608 SCZ genes to model their impact in select categories (tissues and cells, diseases, pathways, biological processes, molecular functions, phenotypes and compounds) using specialized GeneAnalytics algorithms. Genes for schizophrenia were predominantly expressed in the cerebellum, cerebral cortex, medulla oblongata, thalamus and hypothalamus. Psychiatric/behavioral disorders incorporating SCZ genes included ADHD, bipolar disorder, autism spectrum disorder and alcohol dependence as well as cancer, Alzheimer's and Parkinson's disease, sleep disturbances and inflammation. Function based analysis of major biological pathways and mechanisms associated with SCZ genes identified glutaminergic receptors (e.g., GRIA1, GRIN2, GRIK4, GRM5), serotonergic receptors (e.g., HTR2A, HTR2C), GABAergic receptors (e.g., GABRA1, GABRB2), dopaminergic receptors (e.g., DRD1, DRD2), calcium-related channels (e.g., CACNA1H, CACNA1B), solute transporters (e.g., SLC1A1, SLC6A2) and for neurodevelopment (e.g., ADCY1, MEF2C, NOTCH2, SHANK3). Biological mechanisms involving synaptic transmission, regulation of membrane potential and transmembrane ion transport were identified as leading molecular functions associated with SCZ genes. Our approach to interrogate SCZ genes and their interactions at various levels has increased our knowledge and insight into the disease process possibly opening new avenues for therapeutic intervention.

Metabolic adverse effects of olanzapine on cognitive dysfunction: A possible relationship between BDNF and TNF-alpha

OBJECTIVE

There is accumulating evidence indicating that long-term treatment with second-generation antipsychotics (SGAs) results in metabolic syndrome (MetS) and cognitive impairment. This evidence suggests an intrinsic link between antipsychotic-induced MetS and cognitive dysfunction in schizophrenia patients. Olanzapine is a commonly prescribed SGA with a significantly higher MetS risk than that of most antipsychotics. In this study, we hypothesized that olanzapine-induced MetS may exacerbate cognitive dysfunction in patients with schizophrenia.

METHODS

A sample of 216 schizophrenia patients receiving long-term olanzapine monotherapy were divided into two groups, MetS and non-MetS, based on the diagnostic criteria of the National Cholesterol Education Program's Adult Treatment Panel III. We also recruited 72 healthy individuals for a control group. Cognitive function was evaluated using the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). Plasma brain-derived neurotrophic factor (BDNF) and tumor necrosis factor-alpha (TNF-alpha) were measured by an enzyme-linked immunosorbent assay for 108 patients and 47 controls.

RESULTS

Among the 216 schizophrenia patients receiving olanzapine monotherapy, MetS was found in 95/216 (44%). Patients with MetS had more negative symptoms, higher total scores in PANSS (Ps<0.05) and lower immediate memory, attention, delayed memory and total scores in RBANS (Ps<0.01). Stepwise multivariate linear regression analysis revealed that increased glucose was the independent risk factor for cognitive dysfunction (t=-2.57, P=0.01). Patients with MetS had significantly lower BDNF (F=6.49, P=0.012) and higher TNF-alpha (F=5.08, P=0.026) levels than those without MetS. There was a negative correlation between the BDNF and TNF-alpha levels in the patients (r=-0.196, P=0.042).

CONCLUSION

Our findings provide evidence suggesting that the metabolic adverse effects of olanzapine may aggravate cognitive dysfunction in patients with schizophrenia through an interaction between BDNF and TNF-alpha.

Theranostic Biomarkers for Schizophrenia

Schizophrenia is a highly heritable, chronic, severe, disabling neurodevelopmental brain disorder with a heterogeneous genetic and neurobiological background, which is still poorly understood. To allow better diagnostic procedures and therapeutic strategies in schizophrenia patients, use of easy accessible biomarkers is suggested. The most frequently used biomarkers in schizophrenia are those associated with the neuroimmune and neuroendocrine system, metabolism, different neurotransmitter systems and neurotrophic factors. However, there are still no validated and reliable biomarkers in clinical use for schizophrenia. This review will address potential biomarkers in schizophrenia. It will discuss biomarkers in schizophrenia and propose the use of specific blood-based panels that will include a set of markers associated with immune processes, metabolic disorders, and neuroendocrine/neurotrophin/neurotransmitter alterations. The combination of different markers, or complex multi-marker panels, might help in the discrimination of patients with different underlying pathologies and in the better classification of the more homogenous groups. Therefore, the development of the diagnostic, prognostic and theranostic biomarkers is an urgent and an unmet need in psychiatry, with the aim of improving diagnosis, therapy monitoring, prediction of treatment outcome and focus on the personal medicine approach in order to improve the quality of life in patients with schizophrenia and decrease health costs worldwide.

TOX and ADIPOQ Gene Polymorphisms Are Associated with Antipsychotic-Induced Weight Gain in Han Chinese

To find the genetic markers related to the antipsychotic-induced weight gain (AIWG), we analyzed associations among candidate gene single-nucleotide polymorphisms (SNPs) and quantitative traits of weight changes and lipid profiles in a Chinese Han population. A total of 339 schizophrenic patients, including 86 first-episode patients (FEPs), meeting the entry criteria were collected. All patients received atypical antipsychotic drug monotherapy and hospitalization and were followed for 12 weeks. Forty-three SNPs in 23 candidate genes were calculated for quantitative genetic association with AIWG, performed by PLINK. The TOX gene SNP rs11777927 (P = 0.009) and the ADIPOQ gene SNP rs182052 (P = 0.019) were associated with AIWG (in body mass index, BMI). In addition, the BDNF SNP rs6265 (P = 0.002), BDAF SNP rs11030104 SNP (P = 0.001), and ADIPOQ SNPs rs822396 (P = 0.003) were significantly associated with the change of waist-to-hip ratio (WHR) induced by atypical antipsychotics. These results were still significant after age and gender adjustments. These findings provide preliminary evidence supporting the role of TOX, ADIPOQ and BDNF in weight and WHR gain induced by atypical antipsychotics.

Differential gene expression profiles in neurons generated from lymphoblastoid B-cell line-derived iPS cells from monozygotic twin cases with treatment-resistant schizophrenia and discordant responses to clozapine

Schizophrenia is a chronic psychiatric disorder with complex genetic and environmental origins. While many antipsychotics have been demonstrated as effective in the treatment of schizophrenia, a substantial number of schizophrenia patients are partially or fully unresponsive to the treatment. Clozapine is the most effective antipsychotic drug for treatment-resistant schizophrenia; however, clozapine has rare but serious side-effects. Furthermore, there is inter-individual variability in the drug response to clozapine treatment. Therefore, the identification of the molecular mechanisms underlying the action of clozapine and drug response predictors is imperative. In the present study, we focused on a pair of monozygotic twin cases with treatment-resistant schizophrenia, in which one twin responded well to clozapine treatment and the other twin did not. Using induced pluripotent stem (iPS) cell-based technology, we generated neurons from iPS cells derived from these patients and subsequently performed RNA-sequencing to compare the transcriptome profiles of the mock or clozapine-treated neurons. Although, these iPS cells similarly differentiated into neurons, several genes encoding homophilic cell adhesion molecules, such as protocadherin genes, showed differential expression patterns between these two patients. These results, which contribute to the current understanding of the molecular mechanisms of clozapine action, establish a new strategy for the use of monozygotic twin studies in schizophrenia research.

Is treatment-resistant schizophrenia categorically distinct from treatment-responsive schizophrenia? a systematic review

BACKGROUND

Schizophrenia is a highly heterogeneous disorder, and around a third of patients are treatment-resistant. The only evidence-based treatment for these patients is clozapine, an atypical antipsychotic with relatively weak dopamine antagonism. It is plausible that varying degrees of response to antipsychotics reflect categorically distinct illness subtypes, which would have significant implications for research and clinical practice. If these subtypes could be distinguished at illness onset, this could represent a first step towards personalised medicine in psychiatry. This systematic review investigates whether current evidence supports conceptualising treatment-resistant and treatment-responsive schizophrenoa as categorically distinct subtypes.

METHOD

A systematic literature search was conducted, using PubMed, EMBASE, PsycInfo, CINAHL and OpenGrey databases, to identify all studies which compared treatment-resistant schizophrenia (defined as either a lack of response to two antipsychotic trials or clozapine prescription) to treatment-responsive schizophrenia (defined as known response to non-clozapine antipsychotics).

RESULTS

Nineteen studies of moderate quality met inclusion criteria. The most robust findings indicate that treatment-resistant patients show glutamatergic abnormalities, a lack of dopaminergic abnormalities, and significant decreases in grey matter compared to treatment-responsive patients. Treatment-resistant patients were also reported to have higher familial loading; however, no individual gene-association study reported their findings surviving correction for multiple comparisons.

CONCLUSIONS

Tentative evidence supports conceptualising treatment-resistant schizophrenia as a categorically different illness subtype to treatment-responsive schizophrenia. However, research is limited and confirmation will require replication and rigorously controlled studies with large sample sizes and prospective study designs.

Treatment-resistant schizophrenia: current insights on the pharmacogenomics of antipsychotics

Up to 30% of people with schizophrenia do not respond to two (or more) trials of dopaminergic antipsychotics. They are said to have treatment-resistant schizophrenia (TRS). Clozapine is still the only effective treatment for TRS, although it is underused in clinical practice. Initial use is delayed, it can be hard for patients to tolerate, and clinicians can be uncertain as to when to use it. What if, at the start of treatment, we could identify those patients likely to respond to clozapine - and those likely to suffer adverse effects? It is likely that clinicians would feel less inhibited about using it, allowing clozapine to be used earlier and more appropriately. Genetic testing holds out the tantalizing possibility of being able to do just this, and hence the vital importance of pharmacogenomic studies. These can potentially identify genetic markers for both tolerance of and vulnerability to clozapine. We aim to summarize progress so far, possible clinical applications, limitations to the evidence, and problems in applying these findings to the management of TRS. Pharmacogenomic studies of clozapine response and tolerability have produced conflicting results. These are due, at least in part, to significant differences in the patient groups studied. The use of clinical pharmacogenomic testing - to personalize clozapine treatment and identify patients at high risk of treatment failure or of adverse events - has moved closer over the last 20 years. However, to develop such testing that could be used clinically will require larger, multicenter, prospective studies.

Pharmacogenetic Associations of Antipsychotic Drug-Related Weight Gain: A Systematic Review and Meta-analysis

Although weight gain is a serious but variable adverse effect of antipsychotics that has genetic underpinnings, a comprehensive meta-analysis of pharmacogenetics of antipsychotic-related weight gain is missing. In this review, random effects meta-analyses were conducted for dominant and recessive models on associations of specific single nucleotide polymorphisms (SNP) with prospectively assessed antipsychotic-related weight or body mass index (BMI) changes (primary outcome), or categorical increases in weight or BMI (≥7%; secondary outcome). Published studies, identified via systematic database search (last search: December 31, 2014), plus 3 additional cohorts, including 222 antipsychotic-naïve youth, and 81 and 141 first-episode schizophrenia adults, each with patient-level data at 3 or 4 months treatment, were meta-analyzed. Altogether, 72 articles reporting on 46 non-duplicated samples (n = 6700, mean follow-up = 25.1wk) with 38 SNPs from 20 genes/genomic regions were meta-analyzed (for each meta-analysis, studies = 2-20, n = 81-2082). Eleven SNPs from 8 genes were significantly associated with weight or BMI change, and 4 SNPs from 2 genes were significantly associated with categorical weight or BMI increase. Combined, 13 SNPs from 9 genes (Adrenoceptor Alpha-2A [ADRA2A], Adrenoceptor Beta 3 [ADRB3], Brain-Derived Neurotrophic Factor [BDNF], Dopamine Receptor D2 [DRD2], Guanine Nucleotide Binding Protein [GNB3], 5-Hydroxytryptamine (Serotonin) Receptor 2C [HTR2C], Insulin-induced gene 2 [INSIG2], Melanocortin-4 Receptor [MC4R], and Synaptosomal-associated protein, 25kDa [SNAP25]) were significantly associated with antipsychotic-related weight gain (P-values < .05-.001). SNPs in ADRA2A, DRD2, HTR2C, and MC4R had the largest effect sizes (Hedges' g's = 0.30-0.80, ORs = 1.47-1.96). Less prior antipsychotic exposure (pediatric or first episode patients) and short follow-up (1-2 mo) were associated with larger effect sizes. Individual antipsychotics did not significantly moderate effect sizes. In conclusion, antipsychotic-related weight gain is polygenic and associated with specific genetic variants, especially in genes coding for antipsychotic pharmacodynamic targets.

Association of the BDNF Val66Met polymorphism with BMI in chronic schizophrenic patients and healthy controls

Several lines of evidence suggest that a functional variant of the brain-derived neurotrophic factor gene (BDNF Val66Met) correlates with a number of eating disorders. Studies have also shown that the BDNF Val66Met polymorphism was associated with weight gain in patients with schizophrenia on long-term antipsychotic treatment. This study aimed to determine whether there was a relationship between the BDNF Val66Met polymorphism and BMI values in patients with chronic schizophrenia. We compared 308 Han Chinese patients with schizophrenia on long-term antipsychotic medication with 304 healthy normal controls on BDNF polymorphism. Body weight and BMI were measured before breakfast on the day blood samples were taken. The symptomatology of schizophrenia was assessed using the Positive and Negative Syndrome Scale. The results showed that the BDNF Val66Met polymorphism was associated with the BMI value, with genotype having a strong effect on the mean BMI value in male but not in female patients. Our results suggest that variation in the BDNF gene may be a risk factor for weight gain in male patients with schizophrenia on long-term antipsychotic treatment.

Catechol-O-Methyltransferase Val158Met Polymorphism and Clinical Response to Antipsychotic Treatment in Schizophrenia and Schizo-Affective Disorder Patients: a Meta-Analysis

BACKGROUND

The catechol-O-methyltransferase (COMT) enzyme plays a crucial role in dopamine degradation, and the COMT Val158Met polymorphism (rs4680) is associated with significant differences in enzymatic activity and consequently dopamine concentrations in the prefrontal cortex. Multiple studies have analyzed the COMT Val158Met variant in relation to antipsychotic response. Here, we conducted a meta-analysis examining the relationship between COMT Val158Met and antipsychotic response.

METHODS

Searches using PubMed, Web of Science, and PsycInfo databases (03/01/2015) yielded 23 studies investigating COMT Val158Met variation and antipsychotic response in schizophrenia and schizo-affective disorder. Responders/nonresponders were defined using each study's original criteria. If no binary response definition was used, authors were asked to define response according to at least 30% Positive and Negative Syndrome Scale score reduction (or equivalent in other scales). Analysis was conducted under a fixed-effects model.

RESULTS

Ten studies met inclusion criteria for the meta-analysis. Five additional antipsychotic-treated samples were analyzed for Val158Met and response and included in the meta-analysis (ntotal=1416). Met/Met individuals were significantly more likely to respond than Val-carriers (P=.039, ORMet/Met=1.37, 95% CI: 1.02-1.85). Met/Met patients also experienced significantly greater improvement in positive symptoms relative to Val-carriers (P=.030, SMD=0.24, 95% CI: 0.024-0.46). Posthoc analyses on patients treated with atypical antipsychotics (n=1207) showed that Met/Met patients were significantly more likely to respond relative to Val-carriers (P=.0098, ORMet/Met=1.54, 95% CI: 1.11-2.14), while no difference was observed for typical-antipsychotic-treated patients (n=155) (P=.65).

CONCLUSIONS

Our findings suggest that the COMT Val158Met polymorphism is associated with response to antipsychotics in schizophrenia and schizo-affective disorder patients. This effect may be more pronounced for atypical antipsychotics.

BDNF Val66Met and clinical response to antipsychotic drugs: A systematic review and meta-analysis

BACKGROUND

The polymorphic brain-derived neurotrophic factor (BDNF) gene has been postulated to be involved in inter-individual variability response to antipsychotic drugs.

PURPOSE

To perform a qualitative and quantitative synthesis of studies evaluating the influence of BDNF genetic variation on clinical response to antipsychotics.

METHODS

The review protocol was published in the PROSPERO database (Reg. n(o) CRD42015024614). A comprehensive search was performed through PubMed, Web of Knowledge and Cochrane databases up to July 2015. The methodological quality of identified studies was assessed using the MINORS criteria. Publication bias was estimated and potential sources of heterogeneity were investigated via meta-regression, subgroup and sensitivity analyses.

RESULTS

Nine studies including a total of 2461 antipsychotic-treated patients fulfilled inclusion criteria for meta-analysis of BDNF Val66Met. Using the random-effects model, the pooled results showed no significant association with antipsychotic response for the dominant (Met carriers vs Val/Val, OR: 0.93, 95% CI: 0.72-1.19, P=0.55), codominant (Met/Met vs Val/Val, OR: 0.82, 95% CI: 0.59-1.15, P=0.25), recessive (Met/Met vs Val carriers, OR: 0.81, 95% CI 0.60-1.10, P=0.18) or the allelic contrast (Met vs Val, OR: 0.92, 95% CI 0.76-1.10, P=0.34). Visual inspection of funnel plots and further evaluation with Egger's test did not suggest evidence of publication bias. Despite lack of significant heterogeneity in most comparisons, no evidence of association also emerged in the subgroup and sensitivity analyses conducted.

CONCLUSION

The present meta-analysis excludes a clinically relevant effect of BDNF Val66Met on antipsychotic drug response per se. Nevertheless, further investigation is still needed to clarify in well-designed, large sample-based studies, the impact of BDNF haplotypes containing the Val66Met polymorphism.

Serum brain-derived neurotrophic factor and cortical thickness are differently related in patients with schizophrenia and controls

Brain-derived neurotrophic factor (BDNF) has been implicated in neuronal plasticity, a key process related to the pathophysiology of schizophrenia. However, the relationship of peripheral levels of BDNF to cortical thickness and subcortical structures has not been extensively investigated. This study aims to investigate the relationship of peripheral serum BDNF levels to cortical thickness and volumes of the hippocampus and amygdala. Twenty-nine patients with schizophrenia and 32 healthy controls were included in this study. Structural magnetic resonance imaging (MRI) scans obtained in a 1.5 T scanner were performed in all subjects. Images were processed using Freesurfer software. Blood samples were collected on the same day of the MRI scan for BDNF peripheral levels. Vertex-wise analysis revealed significantly thinner cortex in patients compared with controls. BDNF levels and cortical thickness showed different patterns of correlation for patients and healthy controls in one cluster in the right hemisphere distributed across the supramarginal, postcentral, and inferior frontal cortices.

Pharmacogenetics of clozapine treatment response and side-effects in schizophrenia: an update

INTRODUCTION

Clozapine (CLZ) is the most effective treatment for treatment-resistant schizophrenia (SCZ) patients, with potential added benefits of reduction in suicide risk and aggression. However, CLZ is also mainly underused due to its high risk for the potentially lethal side-effect of agranulocytosis as well as weight gain and related metabolic dysregulation. Pharmacogenetics promises to enable the prediction of patient treatment response and risk of adverse effects based on patients' genetics, paving the way toward individualized treatment.

AREA COVERED

This article reviews pharmacogenetics studies of CLZ response and side-effects with a focus on articles from January 2012 to February 2015, as an update to the previous reviews. Pharmacokinetic genes explored primarily include CYP1A2, while pharmacodynamic genes consisted of traditional pharmacogenetic targets such as brain-derived neurotrophic factor as well novel mitochondrial genes, NDUFS-1 and translocator protein.

EXPERT OPINION

Pharmacogenetics is a promising avenue for individualized medication of CLZ in SCZ, with several consistently replicated gene variants predicting CLZ response and side-effects. However, a large proportion of studies have yielded mixed results. Large-scale Genome-wide association studies (e.g., CRESTAR) and targeted gene studies with standardized designs (response measurements, treatment durations, plasma level monitoring) are required for further progress toward clinical translation. Additionally, in order to improve study quality, we recommend accounting for important confounders, including polypharmacy, baseline measurements, treatment duration, gender, and age at onset.

The brain-derived neurotrophic factor (BDNF) Val66Met polymorphism is associated with increased body mass index and insulin resistance measures in bipolar disorder and schizophrenia

OBJECTIVES

We tested the hypothesis that a common functional variant in brain-derived neurotrophic factor (BDNF), Val66Met, which has been shown to be associated with increased body mass index (BMI) in schizophrenia (SCZ) and schizoaffective disorder (SAD), is also associated with antipsychotic-induced weight gain in bipolar disorder (BPD). Association of Val66Met with other metabolic measures, including high- and low-density cholesterol, triglycerides, total cholesterol, fasting blood glucose, and hemoglobin A1c, was also tested.

METHODS

This was a 12-month, prospective, randomized trial of two atypical antipsychotic drugs (APDs) with moderate (risperidone) or high (olanzapine) risk to cause weight gain. Subjects were diagnosed as having BPD (n = 90) and SCZ or SAD (n = 76).

RESULTS

BMI was significantly greater in all diagnoses for Met66 allele carriers at six months (p = 0.01). Met66 carriers with BPD showed a greater increase in the triglycerides/high-density (HDL) cholesterol ratio (p = 0.01), a key marker for metabolic syndrome related to insulin resistance, and log-triglycerides (p = 0.04), after three or six months of treatment. Met66 carriers had the greatest increase in log-triglycerides (p = 0.03) and triglycerides/HDL cholesterol ratio after three months of treatment with risperidone (p = 0.003), and the highest BMI at six months (p = 0.01).

CONCLUSIONS

The positive association of BNDF Val66Met with high BMI values replicates previous findings in patients with SCZ and indicates the BDNF Val66Met genotype as a potential risk factor for obesity and insulin resistance measures in patients with BPD receiving antipsychotics as well.

The BDNF gene Val66Met polymorphism as a modifier of psychiatric disorder susceptibility: progress and controversy

Brain-derived neurotrophic factor (BDNF) has a primary role in neuronal development, differentiation and plasticity in both the developing and adult brain. A single-nucleotide polymorphism in the proregion of BDNF, termed the Val66Met polymorphism, results in deficient subcellular translocation and activity-dependent secretion of BDNF, and has been associated with impaired neurocognitive function in healthy adults and in the incidence and clinical features of several psychiatric disorders. Research investigating the Val66Met polymorphism has increased markedly in the past decade, and a gap in integration exists between and within academic subfields interested in the effects of this variant. Here we comprehensively review the role and relevance of the Val66Met polymorphism in psychiatric disorders, with emphasis on suicidal behavior and anxiety, eating, mood and psychotic disorders. The cognitive and molecular neuroscience of the Val66Met polymorphism is also concisely reviewed to illustrate the effects of this genetic variant in healthy controls, and is complemented by a commentary on the behavioral neuroscience of BDNF and the Val66Met polymorphism where relevant to specific disorders. Lastly, a number of controversies and unresolved issues, including small effect sizes, sampling of allele inheritance but not genotype and putative ethnicity-specific effects of the Val66Met polymorphism, are also discussed to direct future research.

BDNF Val66Met polymorphism and hippocampal volume in neuropsychiatric disorders: A systematic review and meta-analysis

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is a neurotrophin involved in neurogenesis and synaptic plasticity in the central nervous system, especially in the hippocampus, and has been implicated in the pathophysiology of several neuropsychiatric disorders. Its Val66Met polymorphism (refSNP Cluster Report: rs6265) is a functionally relevant single nucleotide polymorphism affecting the secretion of BDNF and is implicated in differences in hippocampal volumes.

METHODS

This is a systematic meta-analytical review of findings from imaging genetic studies on the impact of the rs6265 SNP on hippocampal volumes in neuropsychiatric patients with major depressive disorder, anxiety, bipolar disorder or schizophrenia.

RESULTS

The overall sample size of 18 independent clinical cohorts comprised 1695 patients. Our results indicated no significant association of left (Hedge's g=0.08, p=0.12), right (g=0.07, p=0.22) or bilateral (g=0.07, p=0.16) hippocampal volumes with BDNF rs6265 in neuropsychiatric patients. There was no evidence for a publication bias or any demographic, clinical, or methodological moderating effects. Both Val/Val homozygotes (g=0.32, p=0.004) and Met-carriers (g=0.20, p=0.004) from the patient sample had significantly smaller hippocampal volumes than the healthy control sample with the same allele. The magnitude of these effects did not differ between the two genotypes.

CONCLUSION

This meta-analysis suggests that there is no association between this BDNF polymorphism and hippocampal volumes. For each BDNF genotype, the hippocampal volumes were significantly lower in neuropsychiatric patients than in healthy controls.

[No effect of the BDNF Val66Met polymorphism on cognitive deficit in patients with schizophrenia and on the risk of the disease in their relatives]

OBJECTIVE

The brain-derived neurotrophic factor (BDNF) gene is thought to be a candidate gene for schizophrenia. At the same time, many studies failed to find the association between BDNF and the disease though the contribution of the BDNF Val66Met polymorphism to the variance of characteristics of schizophrenia has been confirmed. Authors suggested that this contribution was the consequence of the involvement of this gene in the formation of "cognitive reserve" that had a protective effect on the different aspects of the disease. This protective effect should emerge in relatively intact cognitive function in patients with the protective Val66Met genotype as well as in the accumulation of the protective genotypes in unaffected relatives.

MATERIAL AND METHODS

We examined 169 patients with schizophrenia spectrum disorders, 320 their first-degree relatives and control groups using molecular-genetic and experimental psychological methods.

RESULTS

No effect of the Val66Met polymorphism on verbal memory, executive functions and total index of cognitive functioning was found. Besides, we did not find any differences in Val66Met genotype frequencies in first-degree relatives of patients with schizophrenia and healthy people without family history of schizophrenia.

CONCLUSION

The results do not support our hypothesis that BDNF is a gene of "cognitive reserve".

Association of LEPR and ANKK1 Gene Polymorphisms with Weight Gain in Epilepsy Patients Receiving Valproic Acid

BACKGROUND

Weight gain is the most frequent adverse effect of valproic acid (VPA) treatment, resulting in poor compliance and many endocrine disturbances. Similarities in the weight change of monozygotic twins receiving VPA strongly suggests that genetic factors are involved in this effect. However, few studies have been conducted to identify the relevant genetic polymorphisms. Additionally, the causal relationship between the VPA concentration and weight gain has been controversial. Thus, we investigated the effects of single nucleotide polymorphisms (SNPs) in several appetite stimulation and energy homeostasis genes and the steady state plasma concentrations (Css) of VPA on the occurrence of weight gain in patients.

METHODS

A total of 212 epilepsy patients receiving VPA were enrolled. Nineteen SNPs in 11 genes were detected using the Sequenom MassArray iPlex platform, and VPA Css was determined by high-performance liquid chromatography (HPLC).

RESULTS

After 6 months of treatment, 20.28% of patients were found to gain a significant amount of weight (weight gained ≥7%). Three SNPs in the leptin receptor (LEPR), ankyrin repeat kinase domain containing 1 (ANKK1), and α catalytic subunit of adenosine monophosphate-activated protein kinase (AMPK) showed significant associations with VPA-induced weight gain (p < 0.001, p = 0.017 and p = 0.020, respectively). After Bonferroni correction for multiple tests, the genotypic association of LEPR rs1137101, the allelic association of LEPR rs1137101, and ANKK1 rs1800497 with weight gain remained significant. However, the VPA Css in patents who gained weight were not significantly different from those who did not gain weight (p = 0.121).

CONCLUSIONS

LEPR and ANKK1 genetic polymorphisms may have value in predicting VPA-induced weight gain.

Association study of GABAA α2 receptor subunit gene variants in antipsychotic-associated weight gain

Schizophrenia treatment has been hampered by undesirable adverse effects, including weight gain and associated complications. Recent candidate gene studies have been exploring the appetite regulation pathways in antipsychotic-associated weight gain (AAWG) with some promising leads. Genome-wide association studies of obesity have pointed to a number of potential candidate genes, such as MC4R, that were later found to be shared with AAWG. GABAA α2 receptor subunit (GABRA2) was another potential candidate gene for obesity from genome-wide association studies; however, it has not been explored in AAWG. We examined 9 single nucleotide polymorphisms across the GABRA2 gene. Prospective weight change was assessed for a total of 160 schizophrenia patients of European ancestry. The rs279858 marker was associated with percent weight change, with the patients homozygous for the TT genotype experiencing higher percentage weight gain on average than the C allele carriers (P = 0.009). When we performed the analysis considering each clinical site using a meta-analytic method, the results remained statistically significant (P = 1.4e-4). These findings became even more significant when we considered only patients taking clozapine or olanzapine, the 2 medications with higher risk for weight gain (P < 1e-10). GABRA2 genetic variants may play a role in predicting AAWG. However, replication in larger and independent samples is required.

Fat mass- and obesity-associated (FTO) gene and antipsychotic-induced weight gain: an association study

OBJECTIVES

Genetic variation in the fat mass- and obesity-associated gene (FTO) has been associated with obesity in the general population. In this study we have investigated these variants for association with antipsychotic-induced weight gain (AIWG).

METHODS

A total of 218 patients with chronic schizophrenia or schizoaffective disorder treated mostly with clozapine or olanzapine for up to 14 weeks were included in the study. We analyzed 4 polymorphisms in intron 1 of the FTO gene (rs1421085, rs8050136, rs9939609, rs9930506) for association with AIWG using ANCOVA.

RESULTS

No statistically significant associations were observed between the single nucleotide polymorphisms and AIWG. However, patients homozygous for the A-allele of rs9939609 gained numerically higher weight than the other genotypic groups (AA: 5.26 ± 6.7%; TA: 4.66 ± 5.6%; TT: 4.21 ± 5.3%).

CONCLUSION

Our current observations suggest that the FTO gene variants investigated may not play a major role in AIWG.

The role of genetic variation across IL-1β, IL-2, IL-6, and BDNF in antipsychotic-induced weight gain

OBJECTIVES

Antipsychotics with high weight gain-inducing propensities influence the expression of immune and neurotrophin genes, which have been independently related to obesity indices. Thus, we investigated whether variants in the genes encoding interleukin (IL)-1β, IL-2, and IL-6 and brain-derived neurotrophic factor (BDNF) Val66Met are associated with antipsychotic-induced weight gain (AIWG).

METHODS

Nineteen polymorphisms were genotyped using Taqman(®) assays in 188 schizophrenia patients on antipsychotic treatment for up to 14 weeks. Mean weight change (%) from baseline was compared across genotypic groups using analysis of covariance (ANCOVA). Epistatic effects between cytokine polymorphisms and BDNF Val66Met were tested using Model-Based Multifactor Dimensionality Reduction.

RESULTS

In European patients, IL-1β rs16944*GA (P = 0.013, Pcorrected = 0.182), IL-1β rs1143634*G (P = 0.001, Pcorrected = 0.014), and BDNF Val66Met (Val/Val, P = 0.004, Pcorrected = 0.056) were associated with greater AIWG, as were IL-1β rs4849127*A (P = 0.049, Pcorrected = 0.784), and IL-1β rs16944*GA (P = 0.012, Pcorrected = 0.192) in African Americans. BDNF Val66Met interacted with both IL-1β rs13032029 (Val/Met+ TT, PPerm = 0.029), and IL-6 rs2069837 (Val/Val+ AA, PPerm = 0.021) in Europeans, in addition to IL-1β rs16944 (Val/Val+ GA, PPerm = 0.006) in African Americans.

CONCLUSIONS

SNPs across IL-1β and BDNF Val66Met may influence AIWG. Replication of these findings in larger, independent samples is warranted.

Investigation of TSPO variants in schizophrenia and antipsychotic treatment outcomes

Aim: TSPO is a neuroinflammatory biomarker and emerging therapeutic target in psychiatric disorders. We evaluated whether TSPO polymorphisms contribute to interindividual variability in schizophrenia, antipsychotic efficacy and antipsychotic-induced weight gain. Patients & methods: We analyzed TSPO polymorphisms in 670 schizophrenia cases and 775 healthy controls. Gene–gene interactions between TSPO and other mitochondrial membrane protein-encoding genes (VDAC1 and ANT1) were explored. Positive findings were evaluated in two independent samples (Munich, n = 300; RUPP, n = 119). Results: TSPO rs6971 was independently associated with antipsychotic-induced weight gain in the discovery (puncor = 0.04) and RUPP samples (p = 3.00 × 10-3), and interacted with ANT1 rs10024068 in the discovery (p = 1.15 × 10-3) and RUPP samples (p = 2.76 × 10-4). Conclusion: Our findings highlight TSPO as a candidate for future investigations of antipsychotic-induced weight gain, and support the involvement of mitochondrial membrane components in this serious treatment side effect.

Original submitted 20 August 2014; Revision submitted 3 November 2014

Analyzing the influence of BDNF heterozygosity on spatial memory response to 17β-estradiol

The recent use of estrogen-based therapies as adjunctive treatments for the cognitive impairments of schizophrenia has produced promising results; however the mechanism behind estrogen-based cognitive enhancement is relatively unknown. Brain-derived neurotrophic factor (BDNF) regulates learning and memory and its expression is highly responsive to estradiol. We recently found that estradiol modulates the expression of hippocampal parvalbumin-positive GABAergic interneurons, known to regulate neuronal synchrony and cognitive function. What is unknown is whether disruptions to the aforementioned estradiol-parvalbumin pathway alter learning and memory, and whether BDNF may mediate these events. Wild-type (WT) and BDNF heterozygous (+/-) mice were ovariectomized (OVX) at 5 weeks of age and simultaneously received empty, estradiol- or progesterone-filled implants for 7 weeks. At young adulthood, mice were tested for spatial and recognition memory in the Y-maze and novel-object recognition test, respectively. Hippocampal protein expression of BDNF and GABAergic interneuron markers, including parvalbumin, were assessed. WT OVX mice show impaired performance on Y-maze and novel-object recognition test. Estradiol replacement in OVX mice prevented the Y-maze impairment, a Behavioral abnormality of dorsal hippocampal origin. BDNF and parvalbumin protein expression in the dorsal hippocampus and parvalbumin-positive cell number in the dorsal CA1 were significantly reduced by OVX in WT mice, while E2 replacement prevented these deficits. In contrast, BDNF(+/-) mice showed either no response or an opposite response to hormone manipulation in both behavioral and molecular indices. Our data suggest that BDNF status is an important biomarker for predicting responsiveness to estrogenic compounds which have emerged as promising adjunctive therapeutics for schizophrenia patients.

Association between the brain-derived neurotrophic factor Val66Met polymorphism and therapeutic response to olanzapine in schizophrenia patients

RATIONALE

Brain-derived neurotrophic factor (BDNF) is a neurotrophin that plays a major role in neurogenesis and neuroplasticity, and in the modulation of several neurotransmitter systems including the dopaminergic system. There are mixed reports about the association between the BDNF Val66Met polymorphism, schizophrenia, and treatment response to antipsychotic drugs.

OBJECTIVES

The present study evaluated the association of the BDNF Val66Met polymorphism with treatment response to atypical antipsychotic olanzapine in schizophrenia and the possible predictive value of the BDNF Val66Met genotype status in treatment response to antipsychotic medication.

METHODS

The study included 590 ethnically homogenous Caucasian patients with schizophrenia (diagnosed using the SCID), 40.2 ± 12.0 years old, treated with olanzapine monotherapy (10-20 mg/day), or with other antipsychotics such as risperidone (3-6 mg/day), clozapine (100-500 mg/day), haloperidol (3-115 mg/day), fluphenazine (4-25 mg/day), and quetiapine (50-800 mg/day). Patients were subdivided into responders and non-responders according to a 50 % reduction in the Positive and Negative Syndrome Scale (PANSS) total and subscale scores after 8 weeks of treatment.

RESULTS

The results, corrected for possible effects of gender and age, showed a significant association between the BDNF Val66Met polymorphism and treatment response to olanzapine in patients. The Val/Val genotype was observed more frequently in treatment responders to olanzapine, and this genotype was associated with an improvement in clinical symptoms.

CONCLUSIONS

Our results suggest that BDNF Val66Met variants might influence the response to 8 weeks of monotherapy with olanzapine, in a relatively large sample of patients with schizophrenia.

Genetic variations of PIP4K2A confer vulnerability to poor antipsychotic response in severely ill schizophrenia patients

Literature suggests that disease severity and neurotransmitter signaling pathway genes can accurately identify antipsychotic response in schizophrenia patients. However, putative role of signaling molecules has not been tested in schizophrenia patients based on severity of illness, despite its biological plausibility. In the present study we investigated the possible association of polymorphisms from five candidate genes RGS4, SLC6A3, PIP4K2A, BDNF, PI4KA with response to antipsychotic in variably ill schizophrenia patients. Thus in present study, a total 53 SNPs on the basis of previous reports and functional grounds were examined for their association with antipsychotic response in 423 schizophrenia patients segregated into low and high severity groups. Additionally, haplotype, diplotype, multivariate logistic regression and multifactor-dimensionality reduction (MDR) analyses were performed. Furthermore, observed associations were investigated in atypical monotherapy (n = 355) and risperidone (n = 260) treated subgroups. All associations were estimated as odds ratio (OR) and 95% confidence interval (CI) and test for multiple corrections was applied. Single locus analysis showed significant association of nine variants from SLC6A3, PIP4K2A and BDNF genes with incomplete antipsychotic response in schizophrenia patients with high severity. We identified significant association of six marker diplotype ATTGCT/ATTGCT (rs746203-rs10828317-rs7094131-rs2296624-rs11013052-rs1409396) of PIP4K2A gene in incomplete responders (corrected p-value = 0.001; adjusted-OR = 3.19, 95%-CI = 1.46–6.98) with high severity. These associations were further observed in atypical monotherapy and risperidone sub-groups. MDR approach identified gene-gene interaction among BDNF_rs7103411-BDNF_rs1491851-SLC6A3_rs40184 in severely ill incomplete responders (OR = 7.91, 95%-CI = 4.08–15.36). While RGS4_rs2842026-SLC6A3_rs2975226 interacted synergistically in incomplete responders with low severity (OR = 4.09, 95%-CI = 2.09–8.02). Our findings provide strong evidence that diplotype ATTGCT/ATTGCT of PIP4K2A gene conferred approximately three-times higher incomplete responsiveness towards antipsychotics in severely ill patients. These results are consistent with the known role of phosphatidyl-inositol-signaling elements in antipsychotic action and outcome. Findings have implication for future molecular genetic studies as well as personalized medicine. However more work is warranted to elucidate underlying causal biological pathway.

Brain-derived neurotrophic factor, but not body weight, correlated with a reduction in depression scale scores in men with metabolic syndrome: a prospective weight-reduction study

BACKGROUND

Obesity, a critical component of metabolic syndrome (MetS), is associated with depression. Deficiency of brain-derived neurotrophic factor (BDNF) is involved in the mechanism of depression. We hypothesized that weight reduction would improve depressive symptoms via increasing BDNF levels in obese men.

METHODS

Male adults with obesity were enrolled in a weight-reduction program for twelve weeks. All subjects underwent daily caloric restriction and an exercise program which was regularly assessed in group classes. Fasting blood samples and Zung Self-Rating Depression Scale (Zung SDS) scores were collected for assessments before and after the study.

RESULTS

A total of 36 subjects completed this program. The average reduction in body weight was 8.4 ± 5.1 kg (8.8 ± 5.1%, P < 0.001). Fasting serum BDNF significantly increased after the study (from 40.4 ± 7.8 to 46.9 ± 8.9 ng/ml, P < 0.001). However, the depression symptoms, as assessed by the Zung Self-Rating Depression Scale (Zung SDS), did not reduce significantly (P = 0.486). Divided into subgroups based on changes in BDNF, Zung SDS scores were significantly reduced in subjects with greater BDNF increase than in those with minor BDNF change (-3.9 ± 6.2 vs. 2.3 ± 6.7, P = 0.009). The increased percentage of BDNF was inversely correlated with the change in Zung SDS (r = -0.380, P = 0.022). Multivariate regression analysis showed that reduction in BDNF was independently associated with change in Zung SDS (95% confidence interval -0.315 to -0.052, P = 0.008).

CONCLUSION

Zung SDS only significantly improved in men with increased fasting BDNF levels after a lifestyle intervention.

TRIAL REGISTRATION

(NCT01065753, ClinicalTrials.gov).