Association of neurexin 3 polymorphisms with smoking behavior

Structure, function, and pathology of Neurexin-3

Neurexin-3 is primarily localized in the presynaptic membrane and forms complexes with various ligands located in the postsynaptic membrane. Neurexin-3 has important roles in synapse development and synapse functions. Neurexin-3 mediates excitatory presynaptic differentiation by interacting with leucine-rich-repeat transmembrane neuronal proteins. Meanwhile, neurexin-3 modulates the expression of presynaptic α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors and γ-aminobutyric acid A receptors by interacting with neuroligins at excitatory and inhibitory synapses. Numerous studies have documented the potential contribution of neurexin-3 to neurodegenerative and neuropsychiatric disorders, such as Alzheimer's disease, addiction behaviors, and other diseases, which raises hopes that understanding the mechanisms of neurexin-3 may hold the key to developing new strategies for related illnesses. This review comprehensively covers the literature to provide current knowledge of the structure, function, and clinical role of neurexin-3.

Traumatic events during childhood and its risks to substance use in adulthood: an observational and genome-wide by environment interaction study in UK Biobank

We aimed to explore the underlying genetic mechanisms of traumatic events during childhood affecting the risks of adult substance use in present study. Using UK Biobank cohort, linear regression model was first applied to assess the relationships between cigarette smoking and alcohol drinking in adults with traumatic events during childhood, including felt hated by family member (41,648-111,465), felt loved (46,394-124,481) and sexually molested (47,598-127,766). Using traumatic events as exposure variables, genome-wide by environment interaction study was then performed by PLINK 2.0 to identify cigarette smoking and alcohol drinking associated genes interacting with traumatic events during childhood. We found that the frequency of cigarette smoking was significantly associated with felt hated by family member (coefficient = 0.42, P < 1.0 × 10^-9), felt loved (coefficient = -0.31, P < 1.0 × 10^-9) and sexually molested (coefficient = 0.46, P < 1.0 × 10^-9). We also observed weaker associations of alcohol drinking with felt hated by family member (coefficient = 0.08, P = 3.10 × 10^-6) and felt loved (coefficient = -0.06, P = 3.15 × 10^-7). GWEIS identified multiple candidate loci interacting with traumatic events, such as CTNNA3 (rs189142060, P = 4.23 × 10^-8) between felt hated by family member and the frequency of cigarette smoking, GABRG3 (rs117020886, P = 2.77 × 10^-8) between felt hated by family member and the frequency of alcohol drinking. Our results suggested the significant impact of traumatic events during childhood on the risk of cigarette smoking and alcohol drinking.

Maternal smoking during pregnancy and risks to depression and anxiety in offspring: An observational study and genome-wide gene-environment interaction analysis in UK biobank cohort

BACKGROUND

Maternal smoking during pregnancy (MSDP) has been reported to be associated with increased anxiety and depression behaviors in offspring. However, there is still scant evidence to support the link between MSDP and anxiety/depression.

METHODS

Using the subjects from the UK Biobank cohort (n = 371,903-432,881). Logistic regression analyses were first conducted to test the correlation between MSDP and anxiety/depression in offspring. Second, genome-wide gene-environment interaction study (GWGEIS) analyses were conducted by PLINK, using MSDP as environmental factor. Genetic correlation analysis of anxiety/depression and smoking was conducted by the LDSC software using the published genome-wide association study (GWAS) summary data of four smoking traits (n = 337,334-1,232,091), anxiety (n = 31,880) and depression (n = 490,359). Finally, pathway enrichment analysis was carried out to detect the pathway involved in the development of offspring anxiety caused by the interaction of MSDP × SNPs.

RESULTS

Observational analyses showed that anxiety and depression status in offspring were significantly associated with MSDP (all p < 0.0001). Further GWEGI analyses observed significant MSDP-gene interaction effects at UNC80 gene for anxiety (p = 9.09 × 10^-9). LDSC did not detect significant genetic correlation between anxiety and smoking traits. Pathway analysis identified 19 significant pathways for anxiety, such as MANALO_HYPOXIA_UP (FDR = 5.50 × 10^-4), REACTOME_ADHERENS_JUNCTIONS_INTERACTIONS (FDR = 0.0304) and ONDER_CDH1_TARGETS_2_UP (FDR = 0.0371).

CONCLUSION

Our study results suggested the important impact of MDSP on the risk of anxiety in offspring, partly attributing to environment-gene interactions effects.

Pharmacogenetics factors influencing smoking cessation success; the importance of nicotine metabolism

Introduction: Smoking remains a worldwide epidemic, and despite an increase in public acceptance of the harms of tobacco use, it remains the leading cause of preventable death. It is estimated that up to 70% of all smokers express a desire to quit, but only 3-5% of them are successful.Areas covered: The goal of this review was to evaluate the current status of smoking cessation treatments and the feasibility of implementing personalized-medicine approaches to these pharmacotherapies. We evaluated the genetics associated with higher levels of nicotine addiction and follow with an analysis of the genetic variants that affect the nicotine metabolic ratio (NMR) and the FDA approved treatments for smoking cessation. We also highlighted the gaps in the process of translating current laboratory understanding into clinical practice, and the benefits of personalized treatment approaches for a successful smoking cessation strategy.Expert opinion: Evidence supports the use of tailored therapies to ensure that the most efficient treatments are utilized in an individual's smoking cessation efforts. An understanding of the genetic effects on the efficacy of individualized smoking cessation pharmacotherapies is key to smoking cessation, ideally utilizing a polygenetic risk score that considers all genetic variation.

Common genetic substrates of alcohol and substance use disorder severity revealed by pleiotropy detection against GWAS catalog in two populations

Alcohol and other substance use disorders (AUD and SUD) are complex diseases that are postulated to have a polygenic inheritance and are often comorbid with other disorders. The comorbidities may arise partially through genetic pleiotropy. Identification of specific gene variants accounting for large parts of the variance in these disorders has yet to be accomplished. We describe a flexible strategy that takes a variant-trait association database and determines if a subset of disease/straits are potentially pleiotropic with the disorder under study. We demonstrate its usage in a study of use disorders in two independent cohorts: alcohol, stimulants, cannabis (CUD), and multi-substance use disorders (MSUD) in American Indians (AI) and AUD and CUD in Mexican Americans (MA). Using a machine learning method with variants in GWAS catalog, we identified 229 to 246 pleiotropic variants for AI and 153 to 160 for MA for each SUD. Inflammation was the most enriched for MSUD and AUD in AIs. Neurological disorder was the most significantly enriched for CUD in both cohorts, and for AUD and stimulants in AIs. Of the select pleiotropic genes shared among substances-cohorts, multiple biological pathways implicated in SUD and other psychiatric disorders were enriched, including neurotrophic factors, immune responses, extracellular matrix, and circadian regulation. Shared pleiotropic genes were significantly up-regulated in brain regions playing important roles in SUD, down-regulated in esophagus mucosa, and differentially regulated in adrenal gland. This study fills a gap for pleiotropy detection in understudied admixed populations and identifies pleiotropic variants that may be potential targets of interest for SUD.

Genome-wide association studies for diabetic macular edema and proliferative diabetic retinopathy

Background

Diabetic macular edema (DME) and proliferative diabetic retinopathy (PDR) are sight-threatening complications of diabetes mellitus and leading causes of adult-onset blindness worldwide. Genetic risk factors for diabetic retinopathy (DR) have been described previously, but have been difficult to replicate between studies, which have often used composite phenotypes and been conducted in different populations. This study aims to identify genetic risk factors for DME and PDR as separate complications in Australians of European descent with type 2 diabetes.

Methods

Caucasian Australians with type 2 diabetes were evaluated in a genome-wide association study (GWAS) to compare 270 DME cases and 176 PDR cases with 435 non-retinopathy controls. All participants were genotyped by SNP array and after data cleaning, cases were compared to controls using logistic regression adjusting for relevant covariates.

Results

The top ranked SNP for DME was rs1990145 (p = 4.10 × 10^− 6, OR = 2.02 95%CI [1.50, 2.72]) on chromosome 2. The top-ranked SNP for PDR was rs918519 (p = 3.87 × 10^− 6, OR = 0.35 95%CI [0.22, 0.54]) on chromosome 5. A trend towards association was also detected at two SNPs reported in the only other reported GWAS of DR in Caucasians; rs12267418 near MALRD1 (p = 0.008) in the DME cohort and rs16999051 in the diabetes gene PCSK2 (p = 0.007) in the PDR cohort.

Conclusion

This study has identified loci of interest for DME and PDR, two common ocular complications of diabetes. These findings require replication in other Caucasian cohorts with type 2 diabetes and larger cohorts will be required to identify genetic loci with statistical confidence. There is considerable overlap in the patient cohorts with each retinopathy subtype, complicating the search for genes that contribute to PDR and DME biology.

Electronic supplementary material

The online version of this article (10.1186/s12881-018-0587-8) contains supplementary material, which is available to authorized users.

The Role of Cell Adhesion Molecule Genes Regulating Neuroplasticity in Addiction

A variety of genetic approaches, including twin studies, linkage studies, and candidate gene studies, has established a firm genetic basis for addiction. However, there has been difficulty identifying the precise genes that underlie addiction liability using these approaches. This situation became especially clear in genome-wide association studies (GWAS) of addiction. Moreover, the results of GWAS brought into clarity many of the shortcomings of those early genetic approaches. GWAS studies stripped away those preconceived notions, examining genes that would not previously have been considered in the study of addiction, consequently creating a shift in our understanding. Most importantly, those studies implicated a class of genes that had not previously been considered in the study of addiction genetics: cell adhesion molecules (CAMs). Considering the well-documented evidence supporting a role for various CAMs in synaptic plasticity, axonal growth, and regeneration, it is not surprising that allelic variation in CAM genes might also play a role in addiction liability. This review focuses on the role of various cell adhesion molecules in neuroplasticity that might contribute to addictive processes and emphasizes the importance of ongoing research on CAM genes that have been implicated in addiction by GWAS.

Neurexins and neuropsychiatric disorders

Neurexins are a family of presynaptic single-pass transmembrane proteins that act as synaptic organizers in mammals. The neurexins consist of three genes (NRXN1, NRXN2, and NRXN3), each of which produces a longer α- and shorter β-form. Genomic alterations in NRXN genes have been identified in a wide variety of neuropsychiatric disorders, including autism spectrum disorders (ASD), schizophrenia, intellectual disability (ID), and addiction. Remarkably, a bi-allelic deficiency of NRXN1 was recently linked to Pitt-Hopkins syndrome. The fact that some mono-allelic functional variants of NRXNs are also found in healthy controls indicates that other genetic or environmental factors affect the penetrance of NRXN deficiency. In this review, we summarize the common research methods and representative results of human genetic studies that have implicated NRXN variants in various neuropsychiatric disorders. We also summarize studies of rodent models with NRXN deficiencies that complement our knowledge of human genetics.

Converging findings from linkage and association analyses on susceptibility genes for smoking and other addictions

Experimental approaches to genetic studies of complex traits evolve with technological advances. How do discoveries using different approaches advance our knowledge of the genetic architecture underlying complex diseases/traits? Do most of the findings of newer techniques, such as genome-wide association study (GWAS), provide more information than older ones, for example, genome-wide linkage study? In this review, we address these issues by developing a nicotine dependence (ND) genetic susceptibility map based on the results obtained by the approaches commonly used in recent years, namely, genome-wide linkage, candidate gene association, GWAS and targeted sequencing. Converging and diverging results from these empirical approaches have elucidated a preliminary genetic architecture of this intractable psychiatric disorder and yielded new hypotheses on ND etiology. The insights we obtained by putting together results from diverse approaches can be applied to other complex diseases/traits. In sum, developing a genetic susceptibility map and keeping it updated are effective ways to keep track of what we know about a disease/trait and what the next steps may be with new approaches.

Synaptic Plasticity and Signal Transduction Gene Polymorphisms and Vulnerability to Drug Addictions in Populations of European or African Ancestry

AIM

Drug addiction is characterized, in part, by deregulation of synaptic plasticity in circuits involved in reward, stress, cue learning, and memory. This study was designed to assess whether 185 variants in 32 genes central to synaptic plasticity and signal transduction contribute to vulnerability to develop heroin and/or cocaine addiction.

METHODS

Analyses were conducted in a sample of 1860 subjects divided according to ancestry (African and European) and drug of abuse (heroin or cocaine).

RESULTS

Eighteen SNPs in 11 genes (CDK5R1, EPHA4, EPHA6, FOSL2, MAPK3, MBP, MPDZ, NFKB1, NTRK2, NTSR1, and PRKCE) showed significant associations (P < 0.01), but the signals did not survive correction for multiple testing. SNP rs230530 in the NFKB1 gene, encoding the transcription regulator NF-kappa-B, was the only SNP indicated in both ancestry groups and both addictions. This SNP was previously identified in association with alcohol addiction. SNP rs3915568 in NTSR1, which encodes neurotensin receptor, and SNP rs1389752 in MPDZ, which encodes the multiple PDZ domain protein, were previously associated with heroin addiction or alcohol addiction, respectively.

CONCLUSIONS

The study supports the involvement of genetic variation in signal transduction pathways in heroin and cocaine addiction and provides preliminary evidence suggesting several new risk or protective loci that may be relevant for diagnosis and treatment success.

Molecular analysis of cluster headache

OBJECTIVES

Cluster headache (CH) is characterized by severe, recurrent, unilateral attacks of extreme intensity and brief duration. Variants in a myriad of genes were studied in sporadic CH patients, often with conflicting results.

METHODS

We studied gene mutations in some candidate genes, hypocretin receptor 2, Clock, and alcohol dehydrogenase 4 (ADH4), in 54 unrelated sporadic CH patients and in 200 controls in 8 kindreds/families that included more affected and nonaffected cases. Furthermore, we performed the whole-genome scanning by comparative genomic hybridization, searching for rearrangements associated with DNA gain or loss in a subset of sporadic and familial CH and control participants.

RESULTS

The analysis of candidate genes revealed that only allele and genotype frequency of the 2 ADH4 mutations resulted significantly between sporadic CH and controls; the same mutations were homozygous in CH patients from 2 families. The comparative genomic hybridization analysis revealed 2 novel rearrangements that involved the intron regions of thyrotropin-releasing hormone-degrading enzyme and neurexin 3 (NRXN3) genes, respectively. The first arrangement was present either in CH or in controls, whereas the second one was specifically found in some sporadic and familial CH cases.

CONCLUSIONS

Our data (although obtained on a small number of cases) confirm the genetic heterogeneity of CH, suggesting that mutations in the ADH4 gene and a novel rearrangement involving NRXN3 gene might be related to CH in a subset of cases.

Gene network analysis shows immune-signaling and ERK1/2 as novel genetic markers for multiple addiction phenotypes: alcohol, smoking and opioid addiction

Background

Addictions to alcohol and tobacco, known risk factors for cancer, are complex heritable disorders. Addictive behaviors have a bidirectional relationship with pain. We hypothesize that the associations between alcohol, smoking, and opioid addiction observed in cancer patients have a genetic basis. Therefore, using bioinformatics tools, we explored the underlying genetic basis and identified new candidate genes and common biological pathways for smoking, alcohol, and opioid addiction.

Results

Literature search showed 56 genes associated with alcohol, smoking and opioid addiction. Using Core Analysis function in Ingenuity Pathway Analysis software, we found that ERK1/2 was strongly interconnected across all three addiction networks. Genes involved in immune signaling pathways were shown across all three networks. Connect function from IPA My Pathway toolbox showed that DRD2 is the gene common to both the list of genetic variations associated with all three addiction phenotypes and the components of the brain neuronal signaling network involved in substance addiction. The top canonical pathways associated with the 56 genes were: 1) calcium signaling, 2) GPCR signaling, 3) cAMP-mediated signaling, 4) GABA receptor signaling, and 5) G-alpha i signaling.

Conlusions

Cancer patients are often prescribed opioids for cancer pain thus increasing their risk for opioid abuse and addiction. Our findings provide candidate genes and biological pathways underlying addiction phenotypes, which may be future targets for treatment of addiction. Further study of the variations of the candidate genes could allow physicians to make more informed decisions when treating cancer pain with opioid analgesics.

Electronic supplementary material

The online version of this article (doi:10.1186/s12918-015-0167-x) contains supplementary material, which is available to authorized users.

Distinct circuit-dependent functions of presynaptic neurexin-3 at GABAergic and glutamatergic synapses

α- and β-neurexins are presynaptic cell-adhesion molecules whose general importance for synaptic transmission is well documented. The specific functions of neurexins, however, remain largely unknown because no conditional neurexin knockouts are available and targeting all α- and β-neurexins produced by a particular gene is challenging. Using newly generated constitutive and conditional knockout mice that target all neurexin-3α and neurexin-3β isoforms, we found that neurexin-3 was differentially required for distinct synaptic functions in different brain regions. Specifically, we found that, in cultured neurons and acute slices of the hippocampus, extracellular sequences of presynaptic neurexin-3 mediated trans-synaptic regulation of postsynaptic AMPA receptors. In cultured neurons and acute slices of the olfactory bulb, however, intracellular sequences of presynaptic neurexin-3 were selectively required for GABA release. Thus, our data indicate that neurexin-3 performs distinct essential pre- or postsynaptic functions in different brain regions by distinct mechanisms.

Gene-smoking interactions identify several novel blood pressure loci in the Framingham Heart Study

BACKGROUND

Cardiovascular diseases are among the most significant health problems in the United States. Blood pressure (BP) variability has a genetic component, and most of the genetic variance remains to be identified. One promising strategy for gene discovery is genome-wide analysis of interactions between single nucleotide polymorphisms (SNPs) and environmental factors related to cardiovascular diseases.

METHODS

We investigated SNP-smoking interaction effects on BP in genome-wide data in 6,889 participants from the Framingham Heart Study. We performed the standard 1 degree of freedom (df) test of the interaction effect and the joint 2 df test of main and interaction effects. Three smoking measures were used: cigarettes per day (CPD), pack years of smoking, and smoking status.

RESULTS

We identified 7 significant and 21 suggestive BP loci. Identified through the joint 2 df test, significant SBP loci include: rs12149862 (P = 3.65×10(-9)) in CYB5B, rs2268365 (P = 4.85×10(-8)) in LRP2, rs133980 (P = 1.71×10(-8) with CPD and P = 1.07×10(-8) with pack-years) near MN1, and rs12634933 (P = 4.05×10(-8)) in MECOM. Through 1 df interaction analysis, 1 suggestive SBP locus at SNP rs8010717 near NRXN3 was identified using all 3 smoking measures (P = 3.27×10(-7) with CPD, P = 1.03×10(-7) with pack-years, and P = 1.19×10(-7) with smoking status).

CONCLUSIONS

Several of these BP loci are biologically plausible, providing physiological connection to BP regulation. Our study demonstrates that SNP-smoking interactions can enhance gene discovery and provide insight into novel pathways and mechanisms regulating BP.

Phenome-wide association study (PheWAS) in EMR-linked pediatric cohorts, genetically links PLCL1 to speech language development and IL5-IL13 to Eosinophilic Esophagitis

Objective: We report the first pediatric specific Phenome-Wide Association Study (PheWAS) using electronic medical records (EMRs). Given the early success of PheWAS in adult populations, we investigated the feasibility of this approach in pediatric cohorts in which associations between a previously known genetic variant and a wide range of clinical or physiological traits were evaluated. Although computationally intensive, this approach has potential to reveal disease mechanistic relationships between a variant and a network of phenotypes.

Method: Data on 5049 samples of European ancestry were obtained from the EMRs of two large academic centers in five different genotyped cohorts. Recently, these samples have undergone whole genome imputation. After standard quality controls, removing missing data and outliers based on principal components analyses (PCA), 4268 samples were used for the PheWAS study. We scanned for associations between 2476 single-nucleotide polymorphisms (SNP) with available genotyping data from previously published GWAS studies and 539 EMR-derived phenotypes. The false discovery rate was calculated and, for any new PheWAS findings, a permutation approach (with up to 1,000,000 trials) was implemented.

Results: This PheWAS found a variety of common variants (MAF > 10%) with prior GWAS associations in our pediatric cohorts including Juvenile Rheumatoid Arthritis (JRA), Asthma, Autism and Pervasive Developmental Disorder (PDD) and Type 1 Diabetes with a false discovery rate < 0.05 and power of study above 80%. In addition, several new PheWAS findings were identified including a cluster of association near the NDFIP1 gene for mental retardation (best SNP rs10057309, p = 4.33 × 10⁻⁷, OR = 1.70, 95%CI = 1.38 − 2.09); association near PLCL1 gene for developmental delays and speech disorder [best SNP rs1595825, p = 1.13 × 10⁻⁸, OR = 0.65(0.57 − 0.76)]; a cluster of associations in the IL5-IL13 region with Eosinophilic Esophagitis (EoE) [best at rs12653750, p = 3.03 × 10⁻⁹, OR = 1.73 95%CI = (1.44 − 2.07)], previously implicated in asthma, allergy, and eosinophilia; and association of variants in GCKR and JAZF1 with allergic rhinitis in our pediatric cohorts [best SNP rs780093, p = 2.18 × 10⁻⁵, OR = 1.39, 95%CI = (1.19 − 1.61)], previously demonstrated in metabolic disease and diabetes in adults.

Conclusion: The PheWAS approach with re-mapping ICD-9 structured codes for our European-origin pediatric cohorts, as with the previous adult studies, finds many previously reported associations as well as presents the discovery of associations with potentially important clinical implications.

Identification of candidate single-nucleotide polymorphisms in NRXN1 related to antipsychotic treatment response in patients with schizophrenia

Neurexins are presynaptic neuronal adhesion molecules that interact with postsynaptic neuroligins to form an inter-synaptic complex required for synaptic specification and efficient neurotransmission. Deletions and point mutations in the neurexin 1 (NRXN1) gene are associated with a broad spectrum of neuropsychiatric and neurodevelopmental disorders, including autism, intellectual disability, epilepsy, developmental delay, and schizophrenia. Recently, small nucleotide polymorphisms in NRXN1 have been associated with antipsychotic drug response in patients with schizophrenia. Based on previous suggestive evidence of an impact on clozapine response in patients with schizophrenia, we conducted an association study of NRXN1 polymorphisms (rs12467557 and rs10490162) with antipsychotic treatment response in 54 patients with schizophrenia in a double blind, placebo-controlled NIMH inpatient crossover trial and examined for association with risk for schizophrenia in independent case-control and family-based clinical cohorts. Pharmacogenetic analysis in the placebo controlled trial revealed significant association of rs12467557and rs10490162 with drug response, whereby individuals homozygous for the A allele, at either SNP, showed significant improvement in positive symptoms, general psychopathology, thought disturbance, and negative symptoms, whereas patients carrying the G allele showed no overall response. Although we did not find evidence of the same NRXN1 SNPs being associated with results of the NIMH sponsored CATIE trial, other SNPs showed weakly positive signals. The family and case-control analyses for schizophrenia risk were negative. Our results provide confirmatory evidence of genetically determined differences in drug response in patients with schizophrenia related to NRXN1 variation. Furthermore, these findings potentially implicate NRXN1 in the therapeutic actions of antipsychotic drugs.

DNA pooling base genome-wide association study identifies variants at NRXN3 associated with delayed encephalopathy after acute carbon monoxide poisoning

Delayed encephalopathy after acute carbon monoxide poisoning (DEACMP) is more characteristic of anoxic encephalopathy than of other types of anoxia. Those who have the same poisoning degree and are of similar age and gender have a greater risk of getting DEACMP. This has made it clear that there are obvious personal differences. Genetic factors may play a very important role. The authors performed a genome-wide association study involving pooling of DNA obtained from 175 patients and 244 matched acute carbon monoxide poisoning without delayed encephalopathy controls. The Illumina HumanHap 660 Chip array was used for DNA pools. Allele frequencies of all SNPs were compared between delayed encephalopathy after acute carbon monoxide poisoning and control groups and ranked. A total of 123 SNPs gave an OR >1.4. Of these, 46 mapped in or close to known genes. Forty-eight SNPs located in 19 genes were associated with DEACMP after correction for 5% FDR in the genome-wide association of pooled DNA. Two SNPs (rs11845632 and rs2196447) locate in the Neurexin 3 gene were selected for individual genotyping in all samples and another cohort consisted of 234 and 271 controls. There were significant differences in the genotype and allele frequencies of rs11845632 and rs2196447 between the DEACMP group and controls group (all P-values <0.05). This study describes a positive association between Neurexin 3 and controls in the Han Chinese population, and provides genetic evidence to support the susceptibility of DEACMP, which may be the resulting interaction of environmental and genetic factors.

Gene × smoking interactions on human brain gene expression: finding common mechanisms in adolescents and adults

BACKGROUND

Numerous studies have examined gene × environment interactions (G × E) in cognitive and behavioral domains. However, these studies have been limited in that they have not been able to directly assess differential patterns of gene expression in the human brain. Here, we assessed G × E interactions using two publically available datasets to assess if DNA variation is associated with post-mortem brain gene expression changes based on smoking behavior, a biobehavioral construct that is part of a complex system of genetic and environmental influences.

METHODS

We conducted an expression quantitative trait locus (eQTL) study on two independent human brain gene expression datasets assessing G × E for selected psychiatric genes and smoking status. We employed linear regression to model the significance of the Gene × Smoking interaction term, followed by meta-analysis across datasets.

RESULTS

Overall, we observed that the effect of DNA variation on gene expression is moderated by smoking status. Expression of 16 genes was significantly associated with single nucleotide polymorphisms that demonstrated G × E effects. The strongest finding (p = 1.9 × 10⁻¹¹) was neurexin 3-alpha (NRXN3), a synaptic cell-cell adhesion molecule involved in maintenance of neural connections (such as the maintenance of smoking behavior). Other significant G × E associations include four glutamate genes.

CONCLUSIONS

This is one of the first studies to demonstrate G × E effects within the human brain. In particular, this study implicated NRXN3 in the maintenance of smoking. The effect of smoking on NRXN3 expression and downstream behavior is different based upon SNP genotype, indicating that DNA profiles based on SNPs could be useful in understanding the effects of smoking behaviors. These results suggest that better measurement of psychiatric conditions, and the environment in post-mortem brain studies may yield an important avenue for understanding the biological mechanisms of G × E interactions in psychiatry.

Examining the association of NRXN3 SNPs with borderline personality disorder phenotypes in heroin dependent cases and socio-economically disadvantaged controls

BACKGROUND

Borderline personality disorder (BPD) and substance use disorders frequently co-occur; their dual presence predicts poor prognosis. The genetic underpinnings of BPD have not been well-characterized and could offer insight into comorbidity. The current report focuses on the association of neurexin 3 (NRXN3) single nucleotide polymorphisms (SNPs) with BPD symptoms in heroin dependent cases and controls.

METHODS

The sample of the Comorbidity and Trauma Study, a genetic association study of heroin dependence, consists of Australian heroin dependent cases ascertained from opioid replacement therapy clinics and controls ascertained in nearby economically disadvantaged neighborhoods. The assessment included a screening instrument for BPD, used previously in Australian population surveys. Genotypic and BPD phenotypic data were available for 1439 cases and 507 controls. We examined the association of 1430 candidate gene SNPs with BPD phenotypes.

RESULTS

One or more NRXN3 SNPs were nominally associated with all BPD phenotypes; however, none met the conservative significance threshold we employed to correct for multiple testing. The most strongly associated SNPs included rs10144398 with identity disturbance (p=4.9×10(-5)) and rs10151731 with affective instability (p=8.8×10(-5)). The strongest association with screening positive for BPD was found for the NRXN3 SNP, rs10083466 (p=.0013). Neither the correlation of BPD phenotypes nor the linkage disequilibrium relationships of the SNPs account for the number of observed associations involving NRXN3 SNPs.

CONCLUSIONS

Our findings provide intriguing preliminary evidence for the association of NRXN3 with BPD phenotypes. The strongest associations were found for traits (i.e., affective instability; identity disturbance) also observed with other disorders.