Role of the 5-HTTLPR and SNP Promoter Polymorphisms on Serotonin Transporter Gene Expression: a Closer Look at Genetic Architecture and In Vitro Functional Studies of Common and Uncommon Allelic Variants

How do probiotics alleviate constipation? A narrative review of mechanisms

Constipation is a common gastrointestinal condition, which may occur at any age and affects countless people. The search for new treatments for constipation is ongoing as current drug treatments fail to provide fully satisfactory results. In recent years, probiotics have attracted much attention because of their demonstrated therapeutic efficacy and fewer side effects than pharmaceutical products. Many studies attempted to answer the question of how probiotics can alleviate constipation. It has been shown that different probiotic strains can alleviate constipation by different mechanisms. The mechanisms on probiotics in relieving constipation were associated with various aspects, including regulation of the gut microbiota composition, the level of short-chain fatty acids, aquaporin expression levels, neurotransmitters and hormone levels, inflammation, the intestinal environmental metabolic status, neurotrophic factor levels and the body's antioxidant levels. This paper summarizes the perception of the mechanisms on probiotics in relieving constipation and provides some suggestions on new research directions.

Pharmacogenetics of selective serotonin reuptake inhibitors (SSRI): A serotonin reuptake transporter (SERT)-based approach

Neuropsychiatric disorders are considered to be the most common cause of disability worldwide. Serotonin and its transporter is a prominent paradigm in mood disorders. Response to selective serotonin reuptake inhibitors (SSRI) is altered due to heterogeneity in the serotonin transporter gene, SLC6A4 (solute carrier family 6 member 4). The reported polymorphisms are found to be in different regions of the transporter gene: promoter region (5-HTTLPR and various single nucleotide polymorphisms within it), intron (STin2), and exon 9 (I425V). The long and short alleles of the 5-HTTLPR gene, which are prevalent among variations, may mediate differential effects. In long allelic variant carriers, an increased response to SSRI and timely recovery is due to increased availability of SERT. Whereas, SERT availability is significantly decreased in short allelic carriers, necessitating a reduction in SSRI dosage due to the increased risk of adverse drug reactions. Thus, pharmacogenetic investigations are required to understand the impact of functional variations on the efficacy and tolerability of SSRI. Identifying the carrier variants may aid in clear-decision making of the treatment regimen, aiding the approach of personalized medication.

Research progress on antidepressant effects and mechanisms of berberine

Depression, a global health problem with growing prevalence, brings serious impacts on the daily life of patients. However, the antidepressants currently used in clinical are not perfectly effective, which greatly reduces the compliance of patients. Berberine is a natural quaternary alkaloid which has been shown to have a variety of pharmacological effects, such as hypoglycemic, lipid-regulation, anti-cancer, antibacterial, anti-oxidation, anti-inflammatory, and antidepressant. This review summarizes the evidence of pharmacological applications of berberine in treating depression and elucidates the mechanisms of berberine regulating neurotransmitter levels, promoting the regeneration of hippocampal neurons, improving hypothalamic-pituitary-adrenal axis dysfunction, anti-oxidative stress, and suppressing inflammatory status in order to provide a reference for further research and clinical application of berberine.

Organic cation transporters in psychiatric and substance use disorders

Psychiatric and substance use disorders inflict major public health burdens worldwide. Their widespread burden is compounded by a dearth of effective treatments, underscoring a dire need to uncover novel therapeutic targets. In this review, we summarize the literature implicating organic cation transporters (OCTs), including three subtypes of OCTs (OCT1, OCT2, and OCT3) and the plasma membrane monoamine transporter (PMAT), in the neurobiology of psychiatric and substance use disorders with an emphasis on mood and anxiety disorders, alcohol use disorder, and psychostimulant use disorder. OCTs transport monoamines with a low affinity but high capacity, situating them to play a central role in regulating monoamine homeostasis. Preclinical evidence discussed here suggests that OCTs may serve as promising targets for treatment of psychiatric and substance use disorders and encourage future research into their therapeutic potential.

Genetic variants in the TAC1 transcriptional regulatory region affect on trainability and excitability levels in Belgian Malinois dogs

BACKGROUND

Trainability in dogs is affected by learning aptitude and memory capacity. While this trait has a heritable basis in canines, the specific genetic loci responsible for it remain unknown. Our previous results suggested that the BDNF, CCK and TAC1 genes are associated with learning and memory in canines. Experimental validation is crucial to confirm the effects of these candidate genes on trainability. Understanding the genetic foundation of this trait would offer insight into the inheritance pattern of complex behavioural characteristics.

OBJECTIVE

This study aimed to assess the genetic variations within candidate genes and explore their potential associations with behavioural phenotypes in dogs.

METHODS

The behavioural characteristics of 123 male Belgian Malinois dogs were assessed using a customised questionnaire. Target regions of candidate genes were screened for genetic variation by single-strand conformational polymorphism (SSCP). Following that, SSCP banding patterns were sequenced, and putative transcription factor binding sites were predicted using bioinformatics tools. Quantitative association analysis between identified genetic variants and behavioural trait scores was performed using the general linear model (GLM).

RESULTS

Sequencing the coding and flanking regions revealed three mutations (c.-89C>T, c.-162G>C and c.*33T>A) in the dog TAC1 gene. Bioinformatics analysis predicted two single nucleotide polymorphisms (SNPs) were located within the putative TAC1 promoter and could disrupt transcription factor binding sites. Statistical tests revealed that the c.-89C>T was significantly associated with excitability (p < 0.01), while the c.-162G>C was significantly associated with trainability level (p < 0.05).

CONCLUSION

In summary, we identified two regulatory SNPs in the 5'-UTR promoter region of the TAC1 gene that are associated with excitability and trainability in Belgian Malinois dogs. These genetic variations have the potential to alter the binding sites of transcription factors NRF1 and OTX1, consequently influencing TAC1 expression and related behavioural characteristics. Our findings implicate TAC1 polymorphisms as candidates influencing breed-specific behavioural characteristics in canines. Further studies on diverse breeds of dogs are necessary to validate these SNPs' effects.

A Bibliometric and Visual Analysis of Single Nucleotide Polymorphism Studies in Depression

BACKGROUND

Genetic polymorphism has been proven to have an important association with depression, which can influence the risk of developing depression, the efficacy of medications, and adverse effects via metabolic and neurological pathways. Nonetheless, aspects of the association between single nucleotide polymorphisms and depression have not been systematically investigated by bibliometric analysis.

OBJECTIVE

The aim of this study was to analyze the current status and trends of single nucleotide polymorphism research on depression through bibliometric and visual analysis.

METHODS

The Web of Science Core Collection was used to retrieve 10,043 articles that were published between 1998 and 2021. CiteSpace (6.1 R4) was used to perform collaborative network analysis, co-citation analysis, co-occurrence analysis, and citation burst detection.

RESULTS

The most productive and co-cited journals were the Journal of Affective Disorders and Biological Psychiatry, respectively, and an analysis of the references showed that the most recent research focused on the largest thematic cluster, "5-HT", reflecting the important research base in this area. "CYP2D6" has been in the spotlight since its emergence in 2009 and has become a research hotspot since its outbreak in 2019. However, "BDNF ", "COMT ", "older adults", "loci", and "DNA methylation" are also the new frontier of research, and some of them are currently in the process of exploration.

CONCLUSION

These findings offer a useful perspective on existing research and potential future approaches in the study of the association between single nucleotide polymorphisms and depression, which may assist researchers in selecting appropriate collaborators or journals.

[The association of polymorphisms of the serotonin transporter gene SLC6A4 with depression]

OBJECTIVE

To study the relationship of polymorphic variants of the SLC6A4 gene with depression among people aged 25-44 years in Novosibirsk.

MATERIAL AND METHODS

Under the WHO program «MONICA-psychosocial (MOPSY)», a random representative sample of people aged 25-44 years from the population of the Oktyabrsky district of Novosibirsk (men n=725, mean age 43.4±0.4 years, response - 71.3%, women n=710, mean age 44.8±0.4 years, response - 72%). Depression was assessed using the MONICA-MOPSY psychosocial questionnaire. Every fourth respondent was examined for polymorphic variants of 5HTTLPR-VNTR SNP rs25531 A>G of the SLC6A4 gene. The study was carried out within the framework of the budget topic Reg. No. 122031700094-5.

RESULTS

The high level of depression among people aged 25-44 was 12.8% (for men 9.1%, for women - 15.92%); the average level of depression occurred in 24.5% of the population (among men in 21.24%, among women in 26.76%) (χ2=17.071, df=2, p<0.001). The most common genotype of the SLC6A4 gene, among people aged 25--4 years old in Novosibirsk, was SLA - 43.29%, LALA - 26.53% - in second place, SS - 17.87% - third, LALG - 6 genotypes were less represented genotypes. 74%, SLG - 4.18%, LGLG - 1.39%. Carrying the SLA genotype (53.3% and 63.6%) increased the chance of developing both the average level of depression by 2.359 (95% CI 1.278-4.355) times, and depression in general by 1.933 (95% CI 1.142-3.271) times, compared with persons carrying the LALA genotype (32.0% and 46.9%), (χ2=7.674, df=1, p<0.01 and χ2=6.095, df=1, p<0.05). Persons carrying the LALG genotype (54.5%) also had a higher chance of developing a mean level of depression RR=2.929 (95% CI 1.039-8.261), compared with carriers of the LALA genotype (32.0%) (χ2=4.326, df =1, p<0.05) (p<0.05).

CONCLUSION

Associative links between polymorphic variants of the SLC6A4 gene and depression have been established.

Analytical description of adolescent binge drinking patients

BACKGROUND

Binge drinking is a widespread health compromising behavior among adolescents and young adults, leading to significant health problems, injuries and mortality. However, data on alcohol consumption is often unreliable, as it is mainly based on self-reporting surveys. In this five-year study (2014-2019) at the University Children's Hospital Zurich, we analyzed blood samples from adolescent binge drinking patients to investigate blood alcohol concentrations (BACs), co-ingestion of drugs, assess compliance between self-reported and measured substance use, and test for genetic components of innate alcohol tolerance. Furthermore, hair analysis was performed to retrospectively access drug exposure and to evaluate the potential of hair analysis to assess binge drinking.

METHODS

In a prospective, single-center study, patients with alcohol intoxications aged 16 years and younger were included. Blood and hair samples were analyzed by sensitive liquid chromatography - tandem mass spectrometry drug analysis. HTTLPR genotyping was performed with PCR and fragment analysis.

RESULTS

Among 72 cases, 72 blood and 13 hair samples were analyzed. BACs ranged from 0.08-3.20‰ (mean 1.63‰, median 1.60‰), while a mean concentration of 3.64 pg/mg hair (median 3.0 pg/mg) of the alcohol marker ethyl glucuronide (EtG) was detected in eleven hair samples, providing no evidence of chronic excessive drinking. In 47% of the cases, co-ingested drugs were qualitatively detected next to ethanol, but only 9% of the detected drugs had blood concentrations classified as pharmacologically active. Cannabis consumption (22%) and stimulant intake (16%) were the most frequently observed drugs. Compliance between patients' statements and measured substances matched well. Although we investigated the genetic contribution to innate alcohol tolerance via the 5-HTTLPR polymorphism, the diverse genetic background of the cohort and small sample size did not allow any conclusions to be drawn.

CONCLUSION

Almost half of our binge drinking patients tested positive for other substances, primarily cannabis. We anticipate that our study enhances understanding of consumption behavior of young people and encourage continued efforts to address the harmful effects of binge drinking and co-occurring substance use.

Distribution of pharmacogene allele and phenotype frequencies in Brazilian psychiatric patients

Purpose: This work was designed to identify the pharmacogenetic profile of Brazilian psychiatric patients receiving psychoactive drug treatment according to ethnicity. Methods: Based on the GnTech® database, this cross-sectional study analyzed data from self-reported sociodemographic and genetic results from the next-generation sequencing panel composed of 26 pharmacogenes from 359 psychotropic drug users. Results: Variant frequencies of multiple pharmacogenes presented differences between ethnicities (CYP3A5, CYP2D6, CYP1A2, CYP2B6, CYP3A4, UGT1A4, UGT2B15, ABCB1 rs1045642, ADRA2A rs1800544, COMT rs4680, GRIK4 rs1954787, GSK3B rs334558, GSK3B rs6438552, HTR1A rs6295, HTR2A rs7997012, HTR2C rs1414334, MTHFR rs1801131, OPRM1 rs1799971 and 5-HTTLPR), endorsing the necessity of individual-level analyses in drug treatment. Conclusion: A discussion of pharmacogenomic test implementation in psychiatric clinical practice is needed to improve treatment choices, especially in Brazil, a multiethnic country.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2D6, CYP2C19, CYP2B6, SLC6A4, and HTR2A Genotypes and Serotonin Reuptake Inhibitor Antidepressants

Serotonin reuptake inhibitor antidepressants, including selective serotonin reuptake inhibitors (SSRIs; i.e., citalopram, escitalopram, fluoxetine, fluvoxamine, paroxetine, and sertraline), serotonin and norepinephrine reuptake inhibitors (i.e., desvenlafaxine, duloxetine, levomilnacipran, milnacipran, and venlafaxine), and serotonin modulators with SSRI-like properties (i.e., vilazodone and vortioxetine) are primary pharmacologic treatments for major depressive and anxiety disorders. Genetic variation in CYP2D6, CYP2C19, and CYP2B6 influences the metabolism of many of these antidepressants, which may potentially affect dosing, efficacy, and tolerability. In addition, the pharmacodynamic genes SLC6A4 (serotonin transporter) and HTR2A (serotonin-2A receptor) have been examined in relation to efficacy and side effect profiles of these drugs. This guideline updates and expands the 2015 Clinical Pharmacogenetics Implementation Consortium (CPIC) guideline for CYP2D6 and CYP2C19 genotypes and SSRI dosing and summarizes the impact of CYP2D6, CYP2C19, CYP2B6, SLC6A4, and HTR2A genotypes on antidepressant dosing, efficacy, and tolerability. We provide recommendations for using CYP2D6, CYP2C19, and CYP2B6 genotype results to help inform prescribing these antidepressants and describe the existing data for SLC6A4 and HTR2A, which do not support their clinical use in antidepressant prescribing.

Intersection of Sex and Depression: Pathogenesis, Presentation, and Treatments

Major Depressive Disorder (MDD) is a highly prevalent, debilitating disorder. According to the World Health Organization, approximately 5% of adults suffer from depression worldwide and more women than men are affected. Yet, we have a very limited understanding of the pathogenesis of the disease, how sex and genetics influence the pathophenotype of MDD, and how they contribute to the responses to pharmacological treatment. This chapter addresses key theories about the etiology of depression, the variations in epidemiology and presentation, and the treatment options with respect to sex and gender. Additionally, we discuss the emerging wave of treatment modalities, diagnosis, and research focusing on MDD.

Serotonin transporter in the temporal lobe, hippocampus and amygdala in SUDEP

Several lines of evidence link deficient serotonin function and SUDEP. Chronic treatment with serotonin reuptake inhibitors (SRIs) reduces ictal central apnoea, a risk factor for SUDEP. Reduced medullary serotonergic neurones, modulators of respiration in response to hypercapnia, were reported in a SUDEP post‐mortem series. The amygdala and hippocampus have high serotonergic innervation and are functionally implicated in seizure‐related respiratory dysregulation. We explored serotonergic networks in mesial temporal lobe structures in a surgical and post‐mortem epilepsy series in relation to SUDEP risk. We stratified 75 temporal lobe epilepsy patients with hippocampal sclerosis (TLE/HS) into high (N = 16), medium (N = 11) and low risk (N = 48) groups for SUDEP based on generalised seizure frequency. We also included the amygdala in 35 post‐mortem cases, including SUDEP (N = 17), epilepsy controls (N = 10) and non‐epilepsy controls (N = 8). The immunohistochemistry labelling index (LI) and axonal length (AL) of serotonin transporter (SERT)‐positive axons were quantified in 13 regions of interest with image analysis. SERT LI was highest in amygdala and subiculum regions. In the surgical series, higher SERT LI was observed in high risk than low risk cases in the dentate gyrus, CA1 and subiculum (p < 0.05). In the post‐mortem cases higher SERT LI and AL was observed in the basal and accessory basal nuclei of the amygdala and peri‐amygdala cortex in SUDEP compared to epilepsy controls (p < 0.05). Patients on SRI showed higher SERT in the dentate gyrus (p < 0.005) and CA4 (p < 0.05) but there was no difference in patients with or without a psychiatric history. Higher SERT in hippocampal subfields in TLE/HS cases with SUDEP risk factors and higher amygdala SERT in post‐mortem SUDEP cases than epilepsy controls supports a role for altered serotonergic networks involving limbic regions in SUDEP. This may be of functional relevance through reduced 5‐HT availability.

Novel GxE effects and resilience: A case:control longitudinal study of psychosocial stress with war-affected youth

Responses to early life adversity differ greatly across individuals. Elucidating which factors underlie this variation can help us better understand how to improve health trajectories. Here we used a case:control study of refugee and non-refugee youth, differentially exposed to war-related trauma, to investigate the effects of genetics and psychosocial environment on response to trauma. We investigated genetic variants in two genes (serotonin transporter, 5-HTT, and catechol-O-methyltransferase, COMT) that have been implicated in response to trauma. We collected buccal samples and survey data from 417 Syrian refugee and 306 Jordanian non-refugee youth who were enrolled in a randomized controlled trial to evaluate a mental health-focused intervention. Measures of lifetime trauma exposure, resilience, and six mental health and psychosocial stress outcomes were collected at three time points: baseline, ~13 weeks, and ~48 weeks. We used multilevel models to identify gene x environment (GxE) interactions and direct effects of the genetic variants in association with the six outcome measures over time. We did not identify any interactions with trauma exposure, but we did identify GxE interactions with both genes and resilience; 1) individuals with high expression (HE) variants of 5-HTTLPR and high levels of resilience had the lowest levels of perceived stress and 2) individuals homozygous for the Val variant of COMT with high levels of resilience showed stable levels of post-traumatic stress symptoms. We also identified a direct protective effect of 5-HTTLPR HE homozygotes on perceived insecurity. Our results point to novel interactions between the protective effects of genetic variants and resilience, lending support to ideas of differential susceptibility and altered stress reactivity in a cohort of war-affected adolescents.

Serotonin Transporter Genetic Variation and Antidepressant Response and Tolerability: A Systematic Review and Meta-Analysis

Antidepressants are used to treat several psychiatric disorders; however, a large proportion of patients do not respond to their first antidepressant therapy and often experience adverse drug reactions (ADR). A common insertion–deletion polymorphism in the promoter region (5-HTTLPR) of the serotonin transporter (SLC6A4) gene has been frequently investigated for its association with antidepressant outcomes. Here, we performed a systematic review and meta-analysis to assess 5-HTTLPR associations with antidepressants: (1) response in psychiatric disorders other than major depressive disorder (MDD) and (2) tolerability across all psychiatric disorders. Literature searches were performed up to January 2021, yielding 82 studies that met inclusion criteria, and 16 of these studies were included in the meta-analyses. Carriers of the 5-HTTLPR LL or LS genotypes were more likely to respond to antidepressant therapy, compared to the SS carriers in the total and European ancestry-only study populations. Long (L) allele carriers taking selective serotonin reuptake inhibitors (SSRIs) reported fewer ADRs relative to short/short (SS) carriers. European L carriers taking SSRIs had lower ADR rates than S carriers. These results suggest the 5-HTTLPR polymorphism may serve as a marker for antidepressant outcomes in psychiatric disorders and may be particularly relevant to SSRI treatment among individuals of European descent.

5-HTTLPR polymorphism and depression risk in Parkinson's disease: an updated meta-analysis

The relationship between the 5-hydroxytryptamine transporter gene-linked polymorphic region (5-HTTLPR) and depression in Parkinson's disease (PD) has remained controversial. Therefore, we conducted this meta-analysis to evaluate the relationship between 5-HTTLPR polymorphisms and depression in PD. Relevant online databases were searched for cross-sectional, case-control or cohort studies examining relations between 5-HTTLPR polymorphisms (S/L) and the risk of developing depression of PD using a meta-analysis. Odd ratios (ORs) of 5-HTTLPR polymorphisms (S/L allele genotype) were calculated between depression in PD and PD for each study. Five observational studies were identified. Overall ORs for 5-HTTLPR S-Allele genotype was 1.98 (95% CI 0.92-4.26) in the dominant model, 1.43 (95% CI 1.08-1.90) in the recessive model, 2.64 (95% CI 1.01-6.88) in the additive model, independently. The overall ORs of S-Allele genotype was 1.51 (95% CI 0.63-3.64) for the Caucasian subgroup, and 1.44 (95% CI 1.05-1.98) for the non-Caucasian subgroup in the recessive model. This meta-analysis indicates that the 5-HTTLPR genotype (S/S-Allele) is correlated with an increased depression risk in PD, and this highlights the needs for these people to take some effective approaches (if any) in prevention of depression of PD before its onset.

Effects of Polymorphisms in the Serotonin Transporter Promoter-Linked Polymorphic Region on Postthoracotomy Pain Severity

Purpose

Serotonin (5-HT) is highly associated with pain modulation. The human 5-HT transporter (5-HTT) gene (SLC6A4) features several polymorphisms in its promoter region (5-HTTLPR) that affect the 5-HTT expression. The S allele of 5-HTTLPR induces low 5-HT tone, and it may influence the modulation of chronic pain. Meanwhile, pain occurs in 40–50% of patients after thoracic surgery, and its mechanism remains under investigation. This study assessed the role of 5-HTTLPR polymorphisms in postthoracotomy pain severity.

Patients and Methods

A total of 178 patients undergoing pneumonectomy were enrolled. The genotypes of 5-HTTLPR were divided into two groups: S/S group and S/L or L/L group. Linear mixed-effects models were used to assess the association between 5-HTTLPR genotypes and the numerical rating scale (NRS) score change over time.

Results

Among the participants, data were obtained for 162 patients. The genotype distribution was as follows: S/S, 67.3%; S/L or L/L, 32.7%. No significant difference in patient characteristics was found between the genotype groups. There was no significant interaction between the 5-HTTLPR genotypes and the NRS score change over time (p = 0.842).

Conclusion

Polymorphisms in 5-HTTLPR were not associated with postthoracotomy pain severity.

5-HTTLPR-rs25531 and Antidepressant Treatment Outcomes in Korean Patients with Major Depression

INTRODUCTION

Despite the ethnic differences in 5-HTTLPR (S allele relates to better antidepressant response in Korean and Japanese people, while L allele with better response in Caucasians), it is unclear whether 5-HTTLPR and its high expression locus rs25531 are interactively associated with antidepressant treatment outcome. We investigated the individual and interaction effects of these polymorphisms on antidepressant treatment outcomes in the Korean population.

METHODS

A total of 464 Korean subjects with major depressive disorder completed 6 weeks of antidepressant monotherapy. Venous blood was extracted for genotyping 5-HTTLPR and rs25531 by polymerase chain reaction and DNA sequencing. We used logistic regression analyses to verify the main and interaction effects of 5-HTTLPR and rs25531 on response and remission after antidepressant treatment.

RESULTS

After adjusting for covariates, the SS genotype of 5-HTTLPR was significantly associated with better treatment outcomes (p<0.001, odds ratio [OR] [95% confidence interval (CI)]=2.435 [1.551, 3.823] in response; p<0.001, OR [95% CI]=2.912 [1.730, 4.903] in remission), while G-containing genotype (AG+GG) of rs25531 was only associated with remission (p=0.034, OR [95% CI]=2.104 [1.058, 4.181]). The interaction effect of 5-HTTLPR and rs25531 on response and remission was insignificant (all p>0.05).

DISCUSSION

Our findings suggest variations in allelic frequency and functionality of 5-HTTLPR and rs25531 among the different ethnicities. We found a minor advantage of rs25531 in achieving remission. However, there was no interaction effect with 5-HTTLPR.

Association Study of SLC6A4 (5-HTTLPR) Polymorphism and Its Promoter Methylation with Rehabilitation Outcome in Patients with Subacute Stroke

Recently it has been suggested that serotonin transporter (SLC6A4) and its 5HTTLPR polymorphism could be involved in post stroke recovery. Here, we characterized the methylation profile of two different CpG islands within the SLC6A4 promoter region in the whole blood of 50 patients with subacute stroke before and after a six-week rehabilitation treatment. These patients were genotyped for 5HTTLPR polymorphism identifying patients on the basis of short (S) and L (L) alleles: 17 patients LL, 22 patients LS and 11 patients SS. At baseline, all CpG sites for both CpG islands displayed a heterogeneous methylation percentage that were not influenced by the different genotypes. After rehabilitation, we found a significant variation in the methylation levels (increase/decrease) in the specific CpG sites of both CpG islands. The statistical analysis showed a significant relationship between the LL, LS and SS alleles and the outcome of the rehabilitation intervention (χ² (2,50) = 6.395, p = 0.041). Specifically, we found a significant difference between patients with or without a favorable outcome in the LL (11.1% with a favorable outcome) and in the SS (54.4% with a favorable outcome) groups. Our data suggest that 5-HTTLPR polymorphisms and SLC6A4 promoter methylation may be employed as a non-invasive biological marker of recovery in patients with stroke undergoing rehabilitation.

Identification and functional characterization of the extremely long allele of the serotonin transporter-linked polymorphic region

SLC6A4, which encodes the serotonin transporter, has a functional polymorphism called the serotonin transporter-linked polymorphic region (5-HTTLPR). The 5-HTTLPR consists of short (S) and long (L) alleles, each of which has 14 or 16 tandem repeats. In addition, the extralong (XL) and other rare alleles have been reported in 5-HTTLPR. Although they are more frequent in Asian and African than in other populations, the extent of variations and allele frequencies (AFs) were not addressed in a large population. Here, we report the AFs of the rare alleles in a large number of Japanese subjects (N = 2894) consisting of two cohorts. The first cohort (case-control study set, CCSS) consisted of 1366 subjects, including 485 controls and 881 patients with psychosis (bipolar disorder or schizophrenia). The second cohort (the Arao cohort study set, ACSS) consisted of 1528 elderly subjects. During genotyping, we identified 11 novel 5-HTTLPR alleles, including 3 XL alleles. One novel allele had the longest subunit ever reported, consisting of 28 tandem repeats. We named this XL_28-A. An in vitro luciferase assay revealed that XL_28-A has no transcriptional activity. XL_28-A was found in two unrelated patients with bipolar disorder in the CCSS and one healthy subject in the ACSS who did not show depressive symptoms or a decline in cognitive function. Therefore, it is unlikely that XL_28-A is associated with psychiatric disorders, despite its apparent functional deficit. Our results suggest that unraveling the complex genetic variations of 5-HTTLPR will be important for further understanding its role in psychiatric disorders.

Racial differences in platelet serotonin polymorphisms in acute coronary syndrome

INTRODUCTION

Genetic differences between races have been hypothesized to contribute to differences in outcome from acute coronary syndromes (ACS). Our objective was to assess racial differences in genetic variations in the platelet serotonin transporter (5HTT) and receptor in patients with ACS.

MATERIALS AND METHODS

127 consecutive patients, African Americans (AA) = 27; Caucasian (C) =100, admitted with ACS were evaluated for platelet function by serotonin (5HT) induced platelet activation. All patients were genotyped for two polymorphisms in the serotonin-transporter-linked polymorphic region (5-HTTLPR) S/L and L_G/L_A and one polymorphism of the serotonin 2A receptor (5-HT2A, T102C) gene. All patients were followed for major and minor adverse cardiac events at 12 months.

RESULTS

AA when compared to C had a lower prevalence of the HTTLPR S allele (21% vs 45%, p = 0.0003) and a higher prevalence of the L_G allele (24% vs 4.5%, p = 0.0001). Allelic frequency of the 5-HT2A T102C allele was not significantly different between the races. Platelet activation was lower in AA compared to C, median EC50 5HT was 12.08 μg vs 2.14 μg (p = 0.001). The 5-HTTLPR and the 5-HT2A polymorphisms were not associated with platelet functional responses to serotonin. There were no significant differences in major or minor adverse cardiac events in patients with serotonin transporter or receptor polymorphisms.

CONCLUSION

We found a lower prevalence of the S allele and a higher prevalence of the G allele in AA with ACS. We also found decreased platelet activation in AA which did not correlate with serotonin-related platelet polymorphisms. It is unclear if other contributing factors may explain these platelet functional differences.

Association of serotonin system-related genes with homicidal behavior and criminal aggression in a prison population of Pakistani Origin

The serotonin transporter (SLC6A4), 5-HT_2A (HTR2A) and 5-HT_2B (HTR2B) recepter genes, express proteins that are important regulators of serotonin reuptake and signaling, and thereby may contribute to the pathogenesis of aggressive criminal behavior. 370 sentenced murderers in Pakistani prisons and 359 men without any history of violence or criminal delinquency were genotyped for six candidate polymorphisms in SLC6A4, HTR2A and HTR2B genes. An association of higher expressing L/L and L_A/L_A variants of the 5-HTTLPR polymorphism was observed with homicidal behavior (bi-allelic: OR = 1.29, p = 0.016, tri-allelic: OR = 1.32, p = 0.015) and in the murderer group only with response to verbal abuse (OR = 2.11, p = 0.015), but not with other measures of self-reported aggression. L/L and L_A/L_A genotypes of the 5-HTTLPR polymorphism were associated with higher aggression scores on STAX1 scale of aggression compared to lower expressing genotypes (S/S, S/L_G, L_G/L_G) in prison inmates. No associations were apparent for other serotonergic gene polymorphisms analyzed. Using the Braineac and GTEx databases, we demonstrated significant eQTL based functional effects for rs25531 in HTTLPR and other serotonergic polymorphisms analyzed in different brain regions and peripheral tissues. In conclusion, these findings implicate SLC6A4* HTTLPR as a major genetic determinant associated with criminal aggression. Future studies are needed to replicate this finding and establish the biologic intermediate phenotypes mediating this relationship.

The effects of 5-HTTLPR/rs25531 serotonin transporter gene polymorphisms on antisocial personality disorder among criminals in a sample of the Turkish population

Antisocial personality disorder (ASPD) is a cluster B personality disorder characterized by a disposition for criminal behaviors. It has been determined by previous studies that ASPD may have a genetic origin and the human serotonin transporter gene (SLC6A4) is one of the two serotonergic genes expected to be associated with this disorder. 5-HTT-linked polymorphic promoter region (5-HTTLPR) is a degenerate repeat polymorphic region in SLC6A4, the gene that codes for the serotonin transporter. Among many polymorphisms in SLC6A4, 5-HTTLPR an insertion/deletion (indel) polymorphism and rs25531 single nucleotide polymorphism (SNP) in the 5-HTTLPR polymorphic region contribute to the regulation of SLC6A4 expression. In this study, we aimed to reveal the relationship between frequencies of 5-HTTLPR variants and ASPD among criminals in the Turkish population. Moreover, it was also attempted to figure out the SLC6A4 gene expression level differences regarding these polymorphisms. The 5-HTTLPR/rs25531 genotypes were determined by PCR and restriction length polymorphism (RFLP) analyses and quantitative real-time-PCR was done for measuring the gene expression levels in the case and control groups. Although no significant difference was observed in the distributions of the 5-HTTLPR/rs25531 polymorphisms between the case and control groups, SLC6A4 expression level in the control group was found significantly higher than the case group (p < 0.0001). There was also no significant difference between genotypes in terms of mRNA expression levels in either the control or the case group. According to our results, ASPD in Turkish society is associated with the SLC6A4 gene expression levels, though the distributions of 5-HTTLPR polymorphisms are not different. This study sheds light on future relevant studies as the first study which is conducted in criminals with ASPD in the Turkish community.

Phased Haplotype Resolution of the SLC6A4 Promoter Using Long-Read Single Molecule Real-Time (SMRT) Sequencing

The SLC6A4 gene has been implicated in psychiatric disorder susceptibility and antidepressant response variability. The SLC6A4 promoter is defined by a variable number of homologous 20–24 bp repeats (5-HTTLPR), and long (L) and short (S) alleles are associated with higher and lower expression, respectively. However, this insertion/deletion variant is most informative when considered as a haplotype with the rs25531 and rs25532 variants. Therefore, we developed a long-read single molecule real-time (SMRT) sequencing method to interrogate the SLC6A4 promoter region. A total of 120 samples were subjected to SLC6A4 long-read SMRT sequencing, primarily selected based on available short-read sequencing data. Short-read genome sequencing from the 1000 Genomes (1KG) Project (~5X) and the Genetic Testing Reference Material Coordination Program (~45X), as well as high-depth short-read capture-based sequencing (~330X), could not identify the 5-HTTLPR short (S) allele, nor could short-read sequencing phase any identified variants. In contrast, long-read SMRT sequencing unambiguously identified the 5-HTTLPR short (S) allele (frequency of 0.467) and phased SLC6A4 promoter haplotypes. Additionally, discordant rs25531 genotypes were reviewed and determined to be short-read errors. Taken together, long-read SMRT sequencing is an innovative and robust method for phased resolution of the SLC6A4 promoter, which could enable more accurate pharmacogenetic testing for both research and clinical applications.

5HTTLPR Genetic Variant and Major Depressive Disorder: A Review

Major Depressive Disorder (MDD) is a disease that involves biological, psychological, and social interactions. Studies have shown the importance of genetics contribution to MDD development. The SCL6A4 protein (5HTTLPR) functions transporting serotonin, a neurotransmitter linked to mood and emotion, to the synaptic cleft. Hence, this study seeks, through a literature review, a better comprehension of the 5HTTLPR genetic variant association with MDD. For this purpose, a search was performed on the Virtual Health Library Portal for articles that related 5HTTLPR to MDD. Most of the articles found were conducted in the American continent, with one (1) study implemented in Brazil. 5HTTLPR associations were found regarding changes in the nervous system, pharmacology, and risk factors seen in MDD patients. When verifying the allelic distribution, the S allele had a higher frequency in most of the studies analyzed. Despite not finding a commonality in the different studies, the tremendous genetic variation found demonstrates the MDD complexity. For this reason, further studies in diverse populations should be conducted to assist in the understanding and treatment of the disease.

AVPR1A main effect and OXTR-by-environment interplay in individual differences in depression level

Background

Multiple studies of depression indicated a significant role of gene-by-environment interactions; however, they are mainly limited to the examination of modulating effect of recent stressful life events. Other environmental factors occurring at different stages of ante- and postnatal development may affect the association between multiple genes and depression. The study aimed to analyze the main and haplotype-based effect of serotonergic system and HPA-axis gene polymorphisms on depression and to detect gene-by-environment interaction models explaining individual variance in depression in mentally healthy young adults from Russia.

Methods

Depression score was assessed using Beck Depression Inventory (BDI) in 623 healthy individuals (81% women; 17-25 years) of Caucasian origin (Russians, Tatars, Udmurts) from Russia. The main- and gene-based effects of 12 SNPs in SLC6A4 (5-HTTLPR, rs1042173), HTR2A (rs7322347), OXTR (rs7632287, rs2254298, rs13316193, rs53576, rs2228485, rs237911), AVPR1A (rs3803107, rs1042615), and AVPR1B (rs33911258) genes, and gene-by-environment interactions were tested with linear regression models (PLINK v.1.9) adjusted for multiple comparisons.

Results

We observed ethnicity-specific main effect of the AVPR1A rs3803107 (P = 0.003; P_FDR = 0.047) and gene-based effect of the OXTR gene (Р = 0.005; P_perm = 0.034) on BDI-measured depression, and modifying effect of paternal care on OXTR rs53576 (P = 0.004; P_FDR = 0.012) and birth order on OXTR rs237911 (P = 0.006; P_FDR = 0.018) association with depression level.

Limitations

A hypothesis driven candidate gene approach, which examined a limited number of genetic variants in a moderately large sample, was used.

Conclusions

Our preliminary findings indicate that familial environment may play a permissive role modulating the manifestation of OXTR-based depression variance in mentally healthy subjects.

Evaluation of i-Motif Formation in the Serotonin Transporter-Linked Polymorphic Region

Neuropsychiatric disorders such as major depressive disorder (MDD) arise from a complex set of genetic and environmental factors. The serotonin transporter (SERT) is a key regulator of synaptic serotonin (5-HT), and its inhibition is an important pharmacological target for treating MDD. The SERT-linked polymorphic region (5-HTTLPR) contains two major variants (short and long) that have been implicated in modulating susceptibility to MDD by altering the level of expression of SERT. Both variants contain C-rich repeats that conform to consensus i-motif folding sequences. i-Motifs are quadruplex DNA structures that have been proposed to have a role in transcription regulation. With spectroscopic techniques, we demonstrate that both alleles are able to form i-motifs at acidic pH, and at neutral pH under conditions of molecular crowding. This highlights the potential for i-motif formation to contribute to transcriptional regulation of the serotonin transporter, with a potential role in the pathophysiology of neuropsychiatric disorders.

Gender Differences in Depression: Evidence From Genetics

Compared with men, female accounts for a larger proportion of patients with depression. Behavioral genetics researches find gender differences in genetic underpinnings of depression. We found that gender differences exist in heritability and the gene associated with depression after reviewing relevant research. Both genes and gene-environment interactions contribute to the risk of depression in a gender-specific manner. We detailed the relationships between serotonin transporter gene-linked promoter region (5-HTTLPR) and depression. However, the results of these studies are very different. We explored the reasons for the contradictory conclusions and provided some suggestions for future research on the gender differences in genetic underpinnings of depression.

Gene Variants in Premature Ejaculation: Systematic Review and Future Directions

INTRODUCTION

A growing number of genetic association studies have been performed to investigate the association between the genetic susceptibility alleles and the risk of premature ejaculation (PE); however, the results remain inconclusive.

OBJECTIVES

This systematic review aimed: (i) to determine whether an association exists between gene(s) or allelic variant(s) and PE; (ii) to assess whether the associations are consistent across studies in magnitude and direction, and (iii) to identify any limitation, gap, or shortcoming in the included studies.

METHODS

The literature search was conducted in PubMed, MEDLINE, Scopus, Cochrane Library, EMBASE, Academic Search Complete, Google Scholar, and CINAHL databases.

RESULTS

Different gene variants associated with PE were assessed. 25 genetic association studies met the inclusion criteria that investigated 11 genes, 2,624 men with PE compared with 9,346 men as controls, twins, and siblings. 19 studies demonstrated a significant association with PE, whereas 4 studies denied such a relationship. SLC6A4 gene polymorphism was investigated in 11 studies (7 studies demonstrated a significant relationship with PE, and 4 studies denied such a relationship). Dopamine transporter gene (DAT1) polymorphism was investigated in 4 studies exhibiting a significant relationship. Androgen receptor gene polymorphisms were investigated in 2 studies, 1 with a significant relationship and the other with a non-significant relationship. Oxytocin gene polymorphisms and tryptophan hydroxylase 2 gene polymorphisms were investigated in 2 studies with a significant relationship.

CONCLUSION

While this review has highlighted several genes that may be potentially associated with PE such as SLC6A4, limitations such as variance in study methods, lack of robust findings, small sample sizes, lack of reproducibility, quality of reporting, and quality of assessment remain a major concern. Further efforts such as standardizing reporting, exploring complementary designs, and the use of genome-wide association studies technology are warranted to test the reproducibility of these early findings. Mostafa T, Abdel-Hamid IA, Taymour M, et al. Gene Variants in Premature Ejaculation: Systematic Review and Future Directions. Sex Med Rev 2020;8:586-602.

Promoter Activity-Based Case-Control Association Study on SLC6A4 Highlighting Hypermethylation and Altered Amygdala Volume in Male Patients With Schizophrenia

Associations between altered DNA methylation of the serotonin transporter (5-HTT)-encoding gene SLC6A4 and early life adversity, mood and anxiety disorders, and amygdala reactivity have been reported. However, few studies have examined epigenetic alterations of SLC6A4 in schizophrenia (SZ). We examined CpG sites of SLC6A4, whose DNA methylation levels have been reported to be altered in bipolar disorder, using 3 independent cohorts of patients with SZ and age-matched controls. We found significant hypermethylation of a CpG site in SLC6A4 in male patients with SZ in all 3 cohorts. We showed that chronic administration of risperidone did not affect the DNA methylation status at this CpG site using common marmosets, and that in vitro DNA methylation at this CpG site diminished the promoter activity of SLC6A4. We then genotyped the 5-HTT-linked polymorphic region (5-HTTLPR) and investigated the relationship among 5-HTTLPR, DNA methylation, and amygdala volume using brain imaging data. We found that patients harboring low-activity 5-HTTLPR alleles showed hypermethylation and they showed a negative correlation between DNA methylation levels and left amygdala volumes. These results suggest that hypermethylation of the CpG site in SLC6A4 is involved in the pathophysiology of SZ, especially in male patients harboring low-activity 5-HTTLPR alleles.

Pharmacogenetic Implications for Antidepressant Pharmacotherapy in Late-Life Depression: A Systematic Review of the Literature for Response, Pharmacokinetics and Adverse Drug Reactions

Affecting up to 15% of older adults, late-life depression (LLD) is characterized by the occurrence of depressive symptoms after the age of 50-65 years and maybe pathophysiologically distinct from depression in younger adults. Therefore, LLD is challenging to treat, and predictive genetic testing might be essential to improve treatment in this vulnerable population. The current review aims to provide a summary of the literature exploring genetic associations with antidepressant treatment outcomes in late-life. We conducted a systematic search of three integrated electronic databases. We identified 29 articles investigating genetic associations with antidepressant treatment outcomes, pharmacokinetic parameters, and adverse drug reactions in older adults. Given the small number of investigations conducted in older adults, it is difficult to conclude the presence or absence of genetic associations with the outcomes of interest. In sum, the most substantial amount of evidence exists for the CYP2D6 metabolizer status, SLC6A4 5-HTTLPR, and BDNF rs6265. These findings are consistent in the literature when not restricting to older adults, suggesting that similar treatment recommendations may be provided for older adults regarding genetic variation, such as those outlined for CYP2D6 by the Clinical Pharmacogenetics Implementation Consortium. Nonetheless, further studies are required in well-characterized samples, including genome-wide data, to validate if similar treatment adjustments are appropriate in older adults, given that there appear to be significant effects of genetic variation on antidepressant treatment factors.

Identification of the CD200R1 promoter and the association of its polymorphisms with the risk of Parkinson's disease

BACKGROUND AND PURPOSE

Neuroinflammation is known to be involved in the pathogenesis of Parkinson's disease (PD). Abnormal activation of microglia plays a key role in this pathological process. CD200R1 is a membrane glycoprotein that is expressed primarily on myeloid cells including microglia and is involved in the maintenance of microglia in a stationary state. Our previous study reported that the regulation of CD200R1 expression is altered in PD patients. Such alteration will lead to neuroinflammation and is related to the pathogenesis of PD. The possible role of promoter polymorphisms for abnormal CD200R1 expression in PD was examined in this study.

METHOD

The UCSC database and dual-luciferase assays were used to confirm the promoter region of CD200R1. The promoter of CD200R1 was sequenced in 457 PD patients and 520 matched healthy controls from the Chinese Han population. Dual-luciferase assays were conducted to examine the promoter activity of CD200R1.

RESULTS

It was confirmed that the promoter of CD200R1 is located in the region 876-146 bp upstream of the coding DNA sequence. The frequencies of rs144721913 (P = 0.001) and rs72952157 (P = 0.022) in the promoter were significantly different between the PD group and control group. rs144721913 increases the risk of PD by approximately 14-fold and rs72952157 by 2.6-fold. The dual-luciferase assay indicated that the rs144721913 T allele and the rs72952157 G allele reduced the transcriptional activity of the CD200R1 promoter.

CONCLUSIONS

For the first time the promoter region of CD200R1 has been defined and two potential risk polymorphisms (rs144721913 and rs72952157) in the region for PD in Chinese Han populations have been reported.

Translational Studies in the Complex Role of Neurotransmitter Systems in Anxiety and Anxiety Disorders

Discovery of innovative anxiolytics is severely hampering. Existing anxiolytics are developed decades ago and are still the therapeutics of choice. Moreover, lack of new drug targets forecasts a severe jeopardy in the future treatment of the huge population of CNS-diseased patients. We simply lack the knowledge on what is wrong in brains of anxious people (normal and diseased). Translational research, based on interacting clinical and preclinical research, is extremely urgent. In this endeavor, genetic and genomic approaches are part of the spectrum of contributing factors. We focus on three druggable targets: serotonin transporter, 5-HT_1A, and GABA_A receptors. It is still uncertain whether and how these targets are involved in normal and diseased anxiety processes. For serotonergic anxiolytics, the slow onset of action points to indirect effects leading to plasticity changes in brain systems leading to reduced anxiety. For GABA_A benzodiazepine drugs, acute anxiolytic effects are found indicating primary mechanisms directly influencing anxiety processes. Close translational collaboration between fundamental academic and discovery research will lead to badly needed breakthroughs in the search for new anxiolytics.

THE EXPOSOME IN HUMAN EVOLUTION: FROM DUST TO DIESEL

Global exposures to air pollution and cigarette smoke are novel in human evolutionary history and are associated with about 16 million premature deaths per year. We investigate the history of the human exposome for relationships between novel environmental toxins and genetic changes during human evolution in six phases. Phase I: With increased walking on savannas, early human ancestors inhaled crustal dust, fecal aerosols, and spores; carrion scavenging introduced new infectious pathogens. Phase II: Domestic fire exposed early Homo to novel toxins from smoke and cooking. Phases III and IV: Neolithic to preindustrial Homo sapiens incurred infectious pathogens from domestic animals and dense communities with limited sanitation. Phase V: Industrialization introduced novel toxins from fossil fuels, industrial chemicals, and tobacco at the same time infectious pathogens were diminishing. Thereby, pathogen-driven causes of mortality were replaced by chronic diseases driven by sterile inflammogens, exogenous and endogenous. Phase VI: Considers future health during global warming with increased air pollution and infections. We hypothesize that adaptation to some ancient toxins persists in genetic variations associated with inflammation and longevity.

Genetic Association Study in Multigenerational Kindreds With Vasovagal Syncope: Evidence for Involvement of Sex-Specific Serotonin Signaling

BACKGROUND

Several studies suggest that vasovagal syncope has a genetic origin, but this is unclear. We assessed whether plausible gene variants associate with vasovagal syncope.

METHODS

We studied 160 subjects in 9 kindreds comprising 82 fainters and 78 controls. The diagnosis was ascertained with the Calgary Syncope Score. Common genetic variants were genotyped for 12 genes for vascular signaling, potassium channels, the HTR1A(serotonin 5-HT1A receptor), SLC6A4(serotonin reuptake transporter), and COMT(catecholamine O-methyltransferase). Sex-specific associations between genotypes and phenotypes were tested.

RESULTS

In 9 out of 12 variants, there was no significant association between genotype and phenotype. However, the HTR1A(-1019) G alleles associated with syncope in males, but not in females ( P=0.005). CC and GG males had 9% versus 77% likelihoods of syncope. The SLC6A4 promoter L alleles associated with decreased syncope in males but increased in females ( P=0.059). The LL and SS males had 25% and 47% syncope likelihoods, whereas females had 75% and 50% syncope likelihoods. The COMT c.472 A alleles associated with decreased syncope in males but increased in females ( P=0.017). The GG and AA males had 50% and 15% syncope likelihoods, whereas females had 52% and 73% syncope likelihoods.

CONCLUSIONS

There is a sex-dependent effect of alleles of serotonin signaling and vasovagal syncope, supporting the serotonin hypothesis of the physiology of vasovagal syncope.

Anxiety-related Endophenotypes and Hazardous Alcohol Use in Young Adults are Associated with a Functional Polymorphism in the SLC6A4 Gene

Background:

A functional polymorphism (5-HTTLPR, rs4795541) in the serotonin transporter (SLC6A4) gene has been shown as an important candidate for several psychiatric and behavioral traits.

Objective:

The objective of this study was to examine the possible interaction of this polymorphism with physical neglect in childhood on the presentation of anxiety traits and hazardous alcohol consumption in young Colombian subjects.

Methods:

272 young adults (mean age: 21.3 years) were evaluated with the Childhood Trauma Questionnaire, the Zung Self-rating Anxiety Scale, the Big Five Inventory, the Cohen’s Perceived Stress Scale, the Alcohol, Smoking, Substance Involvement Screening Test and the Alcohol Use Disorders Identification Test. Genotyping for the 5-HTTLPR polymorphism was carried out using conventional PCR. A linear regression model, corrected by age and gender, was used.

Results:

We found that individuals with the L/L genotype showed higher scores on physical neglect (p=0.0047), anxiety symptoms (p=0.028), neuroticism (p=0.019) and perceived stress (p=0.035). L/L genotype was a risk factor for hazardous alcohol use in young adults (OR=3.06, p=0.0003). No GxE interactions were observed in our data.

Conclusion:

Our results provide novel evidence for the role of a functional polymorphism in the SLC6A4 gene on the relationship of childhood trauma, anxiety-related traits and risky consumption of alcohol.

Adaptive developmental plasticity in rhesus macaques: the serotonin transporter gene interacts with maternal care to affect juvenile social behaviour

Research has increasingly highlighted the role that developmental plasticity-the ability of a particular genotype to produce variable phenotypes in response to different early environments-plays as an adaptive mechanism. One of the most widely studied genetic contributors to developmental plasticity in humans and rhesus macaques is a serotonin transporter gene-linked polymorphic region (5-HTTLPR), which determines transcriptional efficiency of the serotonin transporter gene in vitro and modifies the availability of synaptic serotonin in these species. A majority of studies to date have shown that carriers of a loss-of-function variant of the 5-HTTLPR, the short (s) allele, develop a stress-reactive phenotype in response to adverse early environments compared with long (l) allele homozygotes, leading to the prevalent conceptualization of the s-allele as a vulnerability allele. However, this framework fails to address the independent evolution of these loss-of-function mutations in both humans and macaques as well as the high population prevalence of s-alleles in both species. Here we show in free-ranging rhesus macaques that s-allele carriers benefit more from supportive early social environments than l-allele homozygotes, such that s-allele carriers which receive higher levels of maternal protection during infancy demonstrate greater social competence later in life. These findings provide, to our knowledge, the first empirical support for the assertion that the s-allele grants high undirected biological sensitivity to context in primates and suggest a mechanism through which the 5-HTTLPR s-allele is maintained in primate populations.

SLC6A4 Repeat and Single-Nucleotide Polymorphisms Are Associated With Depression and Rest Tremor in Parkinson's Disease: An Exploratory Study

Introduction: Level of serotonin is mainly regulated by the serotonin reuptake transporter encoded by SLC6A4. The promoter region of SLC6A4 bears a repeat polymorphism 5-HTTLPR and a single nucleotide polymorphism rs25531. We have previously studied the association between these two variants and sporadic PD. The objective of the current study was to determine whether the SLC6A4 polymorphisms were associated with key motor and non-motor symptoms of PD.

Methods: A total of 370 PD patients of Han Chinese were included. Associations between the SLC6A4 polymorphisms and PD symptoms including depression, intellectual impairment, tremor and rigidity were analyzed.

Results: 5-HTTLPR was associated with depression in PD patients and presence of the LL genotype was protective against the depression risk. The rs25531 was associated with rest tremor in PD and the A allele serves as a recessive risk allele. No associations were found in the two polymorphisms with respect to intellectual impairment and rigidity in the cohort.

Conclusion: The current study reveals two PD symptoms associated with SLC6A4 polymorphisms, and provides new insight into how serotonergic system genetically participates in the symptomatic progression of PD. Further study is warranted in additional populations.

Hydroxytryptamine transporter gene-linked polymorphic region (5HTTLPR) is associated with delusions in Alzheimer's disease

Background

Serotoninergic pathways underlying delusion symptoms in Alzheimer's disease (AD) have not been fully clarified. 5-Hydroxytryptamine transporter gene-linked polymorphic region (5-HTTLPR) is a variable number tandem repeats in the promoter region of serotonin transporter encoding-gene affecting transcription.

Methods

We investigated the association of 5-HTTLPR with delusions in a total of 257 consecutive patients clinically diagnosed as AD according to the National Institute on Aging-Alzheimer's Association criteria. All participants underwent a comprehensive evaluation with a standardized comprehensive geriatric assessment and Neuropsychiatric Inventory.

Results

Delusion symptoms were observed in 171 patients (66.54%). In respect to AD patients without delusions, AD patients with delusions showed a low prevalence of S-plus carriers (5-HTTLPR-L/S + 5-HTTLPR-S/S genotypes) [p < 0.001; odds ratio (OR) = 0.240, 95% confidence interval (CI) = 0.121-0.471]. Logistic regression analysis adjusted for the apolipoprotein E polymorphism showed that in AD patients with delusions the presence of an 5-HTTLPR-S allele may reduce disease duration (p = 0.005; OR = 0.680, 95% CI = 0.522-0.886) and increase aberrant motor activity (p = 0.013; OR = 2.257, 95% CI = 1.195-4.260). The present findings suggested that 5-HTTLPR might be associated with delusions in AD. S-plus carriers might be associated with protective effect against delusions in AD.

Conclusions

More studies on wider samples of high selected demented patients are needed to confirm our results. However, the present findings suggested that a genetic factor related to serotonin metabolism might exert a protective role on the clinical expression of neuropsychiatric clusters in AD with important implications regarding mechanisms underlying delusions and their possible treatment across the AD and dementia spectrum.

Influence of Serotonin Transporter SLC6A4 Genotype on the Effect of Psychosocial Stress on Cognitive Performance: An Exploratory Pilot Study

BACKGROUND AND OBJECTIVE

Previous research has shown an effect of various psychosocial stressors on unconstrained cognitive flexibility, such as searching through a large set of potential solutions in the lexical-semantic network during verbal problem-solving. Functional magnetic resonance imaging has shown that the presence of the short (S) allele (lacking a 43-base pair repeat) of the promoter region of the gene (SLC6A4) encoding the serotonin transporter (5-HTT) protein is associated with a greater amygdalar response to emotional stimuli and a greater response to stressors. Therefore, we hypothesized that the presence of the S-allele is associated with greater stress-associated impairment in performance on an unconstrained cognitive flexibility task, anagrams.

METHODS

In this exploratory pilot study, 28 healthy young adults were genotyped for long (L)-allele versus S-allele promoter region polymorphism of the 5-HTT gene, SLC6A4. Participants solved anagrams during the Trier Social Stress Test, which included public speaking and mental arithmetic stressors. We compared the participants' cognitive response to stress across genotypes.

RESULTS

A Gene×Stress interaction effect was observed in this small sample. Comparisons revealed that participants with at least one S-allele performed worse during the Stress condition.

CONCLUSIONS

Genetic susceptibility to stress conferred by SLC6A4 appeared to modulate unconstrained cognitive flexibility during psychosocial stress in this exploratory sample. If confirmed, this finding may have implications for conditions associated with increased stress response, including performance anxiety and cocaine withdrawal. Future work is needed both to confirm our findings with a larger sample and to explore the mechanisms of this proposed effect.

Stress response genes associated with attention deficit hyperactivity disorder: A case-control study in Chinese children

To explore the associations between stress response genes and attention deficit hyperactivity disorder (ADHD) in children, we conducted a case-control study consisting of 406 newly diagnosed ADHD cases and 432 controls in Wuhan, China. We genotyped the candidate genes, nuclear receptor subfamily 3 group C member 1(NR3C1) and solute carrier family 6 member 4(SLC6A4), using the Sequenom MassARRAY technology. After correction by Bonferroni (α' = 0.05/6 = 0.008), the rs6191 SNP was found to be associated with a reduced risk of ADHD in the dominant model (OR = 0.564, 95% CI = 0.389-0.819, P = 0.003) while the rs25531 SNP was associated with an increased risk of ADHD in the multiplicative model (OR = 1.380, 95% CI = 1.111-1.714, P = 0.004). Additionally, both the rs6191 and rs25531 SNPs were significantly associated with the attention deficit factor (P = 0.006, P = 0.003, respectively) but not with the hyperactivity/impulsivity factor in the Swanson, Nolan and Pelham-IV Questionnaire (SNAP-IV) scale. Furthermore, we found that these two SNPs were significantly associated with pure ADHD, and not affected by the comorbidities (P =  0.001, P =  0.007, respectively). Besides, there was an interaction between these two SNPs. This study demonstrated the role of NR3C1 and SLC6A4 polymorphisms in ADHD, yet independent replication of the findings of this study in multi-center and multi-stage studies with large samples is warranted in the future.

Association Between 5-HTTLPR Polymorphism and the Risk of Autism: A Meta-Analysis Based on Case-Control Studies

Background: Recently, many case-control studies have reported the association between 5-HTTLPR polymorphism and autism risk. However, the results are inconclusive and conflicting. To investigate the genetic association of 5-HTTLPR polymorphism and autism risk, we conducted a comprehensive meta-analysis based on previous case-control studies. Methods: Literature search was performed through PubMed, Embase, Web of Knowledge and CNKI databases until June 27, 2018. The strength of the association was assessed by relative risk (RR) and its corresponding 95% confidence interval (CI). Fixed or random effect model was selected based on the results of heterogeneity test. Further, subgroup analyses were conducted to explore the association of 5-HTTLPR polymorphism and autism risk in different population. Results: Eleven studies with 930 cases and 1234 controls were identified. Although there was a significant association between 5-HTTLPR polymorphism and autism risk under the dominant model after removing the studies causing heterogeneity, the significance did not exist after Bonferroni's correction. Subgroup analyses also showed similar results after Bonferroni's correction. In addition, there was no obvious publication bias in our meta-analysis. Conclusions: Our present meta-analysis does not support a direct effect of 5-HTTLPR polymorphism on autism risk according to present results. Further analyses of the effect of genetic networks and more well designed studies with larger sample size are required.

Effects of long-term administration of Lactobacillus reuteri DSM-17938 on circulating levels of 5-HT and BDNF in adults with functional constipation

Accumulated evidence shows that some probiotic strains ameliorate functional constipation (FC) via the modulation of specific gastrointestinal peptide pathways. The aims of this study were to investigate: (1) the effects of long-term administration of Lactobacillus reuteri (LR) DSM 17938 on the serum levels of serotonin (5-HT) and brain-derived neurotrophic factor (BDNF); (2) the possible link between 5-HT, BDNF, and specific constipation-related symptoms; (3) whether genetic variability at the 5-HTT gene-linked polymorphic region (5-HTTLPR) and BDNF Val66Met loci could be associated with serum 5-HT and BDNF variations. LR DSM 17938 was administered to 56 FC patients for 105 days in a randomised, double-blind manner. The fasting blood samples were collected during the randomisation visit (V₁), at day 15 (induction period, V₂), day 60 (intermediate evaluation, V₃), and day 105 (V₄) and the Constipaq questionnaire (the sum of Constipation Scoring System (CSS) and patient assessment constipation quality of life (PAC-QoL)) was administered. A group of healthy subjects was enrolled as controls (HC). At V1, the mean serum 5-HT level in the whole patient group was significantly higher (P=0.027) than in HC subjects, while serum BDNF did not. At the end of probiotic administration (V4), 5-HT and BDNF levels were significantly lower than the initial values (V1) (P=0.008 and P=0.015, respectively). 5-HT and BDNF serum concentration were significantly associated (r=0.355; P=0.007). Neither 5-HT nor BDNF serum levels correlated with the CSS item scores and with the PAC-QoL. Lastly, the regression analysis demonstrated that the presence of the S allele of the 5-HTTLPR accounted for the reduction in the 5-HT concentration at V4. In conclusion, the long-term administration of LR DSM 17938 demonstrated that such a probiotic strain could improve FC by affecting 5-HT and BDNF serum concentrations.

Individual biological sensitivity to environmental influences: testing the differential susceptibility properties of the 5HTTLPR polymorphism in relation to depressive symptoms and delinquency in two adolescent general samples

The gene–environment interaction research field in psychiatry has traditionally been dominated by the diathesis–stress framework, where certain genotypes are assumed to confer increased risk for adverse outcomes in a stressful environment. In later years, theories of differential susceptibility, or biological sensitivity, suggest that candidate genes that interact with environmental events do not exclusively confer a risk for behavioural or psychiatric disorders but rather seem to alter the sensitivity to both positive and negative environmental influences. The present study investigates the susceptibility properties of the serotonin transporter-linked polymorphic region (5HTTLPR) in relation to depressive symptoms and delinquency in two separate adolescent community samples: n = 1457, collected in 2006; and n = 191, collected in 2001. Two-, three-, and four-way interactions between the 5HTTLPR, positive and negative family environment, and sex were found in relation to both depressive symptoms and delinquency. However, the susceptibility properties of the 5HTTLPR were distinctly less pronounced in relation to depressive symptoms. If the assumption that the 5HTTLPR induces differential susceptibility to both positive and negative environmental influences is correct, the previous failures to measure and control for positive environmental factors might be a possible explanation for former inconsistent findings within the research field.

Membrane cholesterol removal and replenishment affect rat and monkey brain monoamine transporters

The dopamine transporter (DAT) is abundantly expressed in the striatum where it removes extracellular dopamine into the cytosol of presynaptic nerve terminals. It is the target of drugs of abuse and antidepressants. There is a loss of the DAT in Parkinson's disease affecting release of levodopa implicated in levodopa-induced dyskinesias. This study investigated the effect of cholesterol on DAT, serotonin transporter (SERT) and vesicular monoamine transporter 2 (VMAT2) in monkey and rat brains in vitro. DAT protein levels measured by Western blot remained unchanged with in vitro methyl-β-cyclodextrin (MCD) incubations to remove membrane cholesterol or with incubations to increase membrane cholesterol content. By contrast, striatal DAT specific binding labelled with [¹²⁵I]RTI-121 or with [¹²⁵I]RTI-55 decreased with increasing concentrations of MCD and increased with cholesterol loading. Moreover, [¹²⁵I]RTI-121 specific binding of striatal membranes depleted of cholesterol with MCD was restored to initial DAT content with addition of cholesterol showing its rapid and reversible effect. By contrast, striatal VMAT2 and SERT specific binding showed no or limited changes by cholesterol manipulations. Similar results were obtained for monkey caudate nucleus, putamen and nucleus accumbens. Membrane microviscosity was assessed by fluorescence polarization spectroscopy, using the probe 1,6-diphenyl-1,3,5-hexatriene. DAT changes positively correlated with changes of membrane microviscosity in rat and monkey brain regions investigated and with membrane cholesterol contents. Similar findings were observed with desmosterol but to a lower extent than with cholesterol. These results show an important effect of cholesterol on the DAT associated with microviscosity changes that should be considered in drug therapies.

Extending Previous cG×I Findings on 5-HTTLPR's Moderation of Intervention Effects on Adolescent Substance Misuse Initiation

This study addresses replication in candidate gene × environment interaction (cG×E) research by investigating if the key findings from Brody, Beach, Philibert, Chen, and Murry (2009) can be detected using data (N = 1,809) from the PROSPER substance use preventive intervention delivery system. Parallel to Brody et al., this study tested the hypotheses that substance misuse initiation would increase faster from age 11 to age 14 and be higher at age 14 among: (a) 5-HTTLPR short carrier adolescents versus long homozygotes, (b) control versus intervention adolescents, and (c) 5-HTTLPR short carriers in the control condition versus all other participants. The hypotheses were generally supported and results were consistent with Brody et al.'s cG×I finding. Results are discussed in light of replication issues in cG×E research and implications for intervention.

Neuroplasticity of selective attention: Research foundations and preliminary evidence for a gene by intervention interaction

This article reviews the trajectory of our research program on selective attention, which has moved from basic research on the neural processes underlying selective attention to translational studies using selective attention as a neurobiological target for evidence-based interventions. We use this background to present a promising preliminary investigation of how genetic and experiential factors interact during development (i.e., gene × intervention interactions). Our findings provide evidence on how exposure to a family-based training can modify the associations between genotype (5-HTTLPR) and the neural mechanisms of selective attention in preschool children from lower socioeconomic status backgrounds.