Functional polymorphisms in dopamine and serotonin pathway genes

Psychopharmacology and ethnicity: A comparative study on Senegalese and Italian men

Objectives: Ethnicity represents a crucial factor in influencing response to psychotropic drugs. Some data indicate that functional polymorphisms of two candidate genes of the serotonin (5-HT) transporter (SERT) may affect the response to selective 5-HT reuptake inhibitors (SSRIs). The present study aimed to compare the platelet SERT, through the specific [³H]paroxetine ([³H]Par) binding, and plasma oxytocin (OT) levels in 20 Senegalese and in 20 Italian men.Methods: No subjects had family or personal history of any major psychiatric disorder, or had ever regularly taken psychotropic drugs, or were suffering from any physical illness.Results: Senegalese men showed statistically significant higher density (B_max, fmol/mg protein, mean ± SD) of [³H]Par binding sites (2105.00 ± 473.15 vs 1139.85 ± 213.58, P < 0.001), as well as more elevated plasma OT levels (pg/ml, mean ± SD) (OT: 18.08 ± 4.46 vs 6.62 ± 2.91) than Italian men.Conclusions: These differences, possibly due to genetic or dietary reasons, or even to gender, might affect the response to psychopharmacological compounds. Our findings would suggest specific caution when administering psychotropic compounds to non-European individuals, and the need of further studies in this emerging field of neuropsychopharmacology.

Association of serotonin and GABA pathway gene polymorphisms with alcohol dependence: A preliminary study

BACKGROUND

Alcohol dependence (AD), characterized by profound disruptions in specific circuits of the brain is influenced by both environmental, which play a significant role in developing addiction and genetic factors, which make some individuals more susceptible to disruptions. Various polymorphisms in the neurotransmitter genes are reported to increase the risk of developing dependence. The present study aimed to identify association of serotonin and GABA polymorphisms with AD in Indian subjects.

METHOD

The study group comprised of 141 AD cases recruited as per DSM IV TR criteria from the outpatient Department of Psychiatry and 110 volunteers from the general population. Clinical and family history was noted and 5 ml blood drawn for genetic studies. Polymorphisms 5-HTTLPR and STin2 of serotonin and rs2279020 and rs3219151 of the GABA pathway were analyzed and results correlated with age at first use quantity consumed, duration of use, dependence and age at onset of dependence.

RESULTS

The marker frequencies were similar between cases and controls except for rs3219151. 5-HTTLPR was significantly associated with high AUDIT scores and alcohol intake (p < 0.0001), GABA_A rs2279020 and rs3219151 with age at first use (p < 0.0001); rs2279020 with higher AUDIT score (p = 0.002) and rs3219151 with quantity (p = 0.0001). High frequency of GABRA6 rs3219151 TT genotype in AD and its association with lower age at first use, higher intake/day, and higher duration of dependence appears to confer risk.

CONCLUSIONS

This preliminary study, though on a smaller sample size, suggests an association of 5-HTTLPR and GABA_A receptor polymorphisms with AD in our population.

Non-invasive genotyping with a massively parallel sequencing panel for the detection of SNPs in HPA-axis genes

We designed a genotyping panel for the investigation of the genetic underpinnings of inter-individual differences in aggression and the physiological stress response. The panel builds on single nucleotide polymorphisms (SNPs) in genes involved in the three subsystems of the hypothalamic-pituitary-adrenal (HPA)-axis: the catecholamine, serotonin and corticoid metabolism. To promote the pipeline for use with wild animal populations, we used non-invasively collected faecal samples from a wild population of Assamese macaques (Macaca assamensis). We targeted loci of 46 previously reported SNPs in 21 candidate genes coding for elements of the HPA-axis and amplified and sequenced them using next-generation Illumina sequencing technology. We compared multiple bioinformatics pipelines for variant calling and variant effect prediction. Based on this strategy and the application of different quality thresholds, we identified up to 159 SNPs with different types of predicted functional effects among our natural study population. This study provides a massively parallel sequencing panel that will facilitate integrating large-scale SNP data into behavioural and physiological studies. Such a multi-faceted approach will promote understanding of flexibility and constraints of animal behaviour and hormone physiology.

Different contributions of preparatory activity in the basal ganglia and cerebellum for self-timing

The ability to flexibly adjust movement timing is important for everyday life. Although the basal ganglia and cerebellum have been implicated in monitoring of supra- and sub-second intervals, respectively, the underlying neuronal mechanism remains unclear. Here, we show that in monkeys trained to generate a self-initiated saccade at instructed timing following a visual cue, neurons in the caudate nucleus kept track of passage of time throughout the delay period, while those in the cerebellar dentate nucleus were recruited only during the last part of the delay period. Conversely, neuronal correlates of trial-by-trial variation of self-timing emerged earlier in the cerebellum than the striatum. Local inactivation of respective recording sites confirmed the difference in their relative contributions to supra- and sub-second intervals. These results suggest that the basal ganglia may measure elapsed time relative to the intended interval, while the cerebellum might be responsible for the fine adjustment of self-timing.

Genome-wide association meta-analysis highlights light-induced signaling as a driver for refractive error

Refractive errors, including myopia, are the most frequent eye disorders worldwide and an increasingly common cause of blindness. This genome-wide association meta-analysis in 160,420 participants and replication in 95,505 participants increased the number of established independent signals from 37 to 161 and showed high genetic correlation between Europeans and Asians (>0.78). Expression experiments and comprehensive in silico analyses identified retinal cell physiology and light processing as prominent mechanisms, and also identified functional contributions to refractive-error development in all cell types of the neurosensory retina, retinal pigment epithelium, vascular endothelium and extracellular matrix. Newly identified genes implicate novel mechanisms such as rod-and-cone bipolar synaptic neurotransmission, anterior-segment morphology and angiogenesis. Thirty-one loci resided in or near regions transcribing small RNAs, thus suggesting a role for post-transcriptional regulation. Our results support the notion that refractive errors are caused by a light-dependent retina-to-sclera signaling cascade and delineate potential pathobiological molecular drivers.

Polygonum aviculare L. extract reduces fatigue by inhibiting neuroinflammation in restraint-stressed mice

BACKGROUND

Chronic fatigue patients experience various neuropsychological symptoms, including fatigue behaviors, chronic pain, and depression. They also display immune system dysregulation. Polygonum aviculare L. extract (PAE) is a traditional herbal medicine used to treat inflammatory diseases by reportedly decreasing pro-inflammatory cytokine production.

HYPOTHESIS/PURPOSE

We hypothesized that the anti-inflammatory properties of PAE would attenuate fatigue symptoms in a mouse model of restraint stress.

STUDY DESIGN

We evaluated the effects of PAE on fatigue using three experimental groups: unstressed, vehicle-treated stressed, and PAE-treated stressed mice. This restraint stress paradigm, comprised of restraint for 3 h daily for 15 days, was used to model chronic fatigue.

METHODS

We compared lethargy-like behavior between our experimental groups using forced-swim, sucrose preference, and open-field tests once per week on days 7 and 14 of restraint stress. We also used histology and western blotting to evaluate pro-inflammatory cytokine expression in the brain and serum, and microglial activation in the brain. Finally, we used liquid chromatography/mass spectroscopy (LC/MS) to identify individual components of PAE, and applied cell culture techniques to test the effects of these components on neuronal cells in vitro.

RESULTS

In restraint-stressed mice, PAE treatment decreased lethargy-like behavior relative to vehicle-treated animals. PAE treatment also reduced expression of fatigue-related factors such as corticosterone, serotonin, and catecholamines (adrenaline and noradrenaline) in the brain and serum, and decreased expression of CD68, Ibal-1, and the inflammatory cytokines TNF-α, IL-6, and IL-1β in the brain. Together, these data indicate that PAE reduced fatigue and is anti-inflammatory. Furthermore, histopathological analyses indicated that PAE treatment recovered atrophic volumes and hepatic injuries. Finally, LC/MS analysis of PAE identified four individual chemicals: myricitrin, isoquercitrin, avicularin, and quercitrin. In neuronal cell cultures, treatment with these PAE components inhibited TNF-α production, confirming that PAE treatment reduces neuroinflammation.

CONCLUSIONS

PAE treatment may reduce fatigue by suppressing neuroinflammation and the expression of fatigue-related hormones.

Gene-environment interaction and psychiatric disorders: Review and future directions

Empirical studies suggest that psychiatric disorders result from a complex interplay between genetic and environmental factors. Most evidence for such gene-environment interaction (GxE) is based on single candidate gene studies conducted from a Diathesis-Stress perspective. Recognizing the short-comings of candidate gene studies, GxE research has begun to focus on genome-wide and polygenic approaches as well as drawing on different theoretical concepts underlying GxE, such as Differential Susceptibility. After reviewing evidence from candidate GxE studies and presenting alternative theoretical frameworks underpinning GxE research, more recent approaches and findings from whole genome approaches are presented. Finally, we suggest how future GxE studies may unpick the complex interplay between genes and environments in psychiatric disorders.

Genetic Consideration of Schizotypal Traits: A Review

Schizotypal traits are of interest and importance in their own right and also have theoretical and clinical associations with schizophrenia. These traits comprise attenuated psychotic symptoms, social withdrawal, reduced cognitive capacity, and affective dysregulation. The link between schizotypal traits and psychotic disorders has long since been debated. The status of knowledge at this point is such schizotypal traits are a risk for psychotic disorders, but in and of themselves only confer liability, with other risk factors needing to be present before a transition to psychosis occurs. Investigation of schizotypal traits also has the possibility to inform clinical and research pursuits concerning those who do not make a transition to psychotic disorders. A growing body of literature has investigated the genetic underpinnings of schizotypal traits. Here, we review association, family studies and describe genetic disorders where the expression of schizotypal traits has been investigated. We conducted a thorough review of the existing literature, with multiple search engines, references, and linked articles being searched for relevance to the current review. All articles and book chapters in English were sourced and reviewed for inclusion. Family studies demonstrate that schizotypal traits are elevated with increasing genetic proximity to schizophrenia and some chromosomal regions have been associated with schizotypy. Genes associated with schizophrenia have provided the initial start point for the investigation of candidate genes for schizotypal traits; neurobiological pathways of significance have guided selection of genes of interest. Given the chromosomal regions associated with schizophrenia, some genetic disorders have also considered the expression of schizotypal traits. Genetic disorders considered all comprise a profile of cognitive deficits and over representation of psychotic disorders compared to the general population. We conclude that genetic variations associated with schizotypal traits require further investigation, perhaps with targeted phenotypes narrowed to assist in refining the clinical end point of significance.

Gene-environment interactions in psychopathology throughout early childhood: a systematic review

Up to 20% of children and adolescents worldwide suffer from mental health problems. Epidemiological studies have shown that some of these problems are already present at an early age. The recognition that psychopathology is a result of an interaction between individual experiences and genetic characteristics has led to an increase in the number of studies using a gene-environment approach (G×E). However, to date, there has been no systematic review of G×E studies on psychopathology in the first 6 years of life. Following a literature search and a selection process, 14 studies were identified and most (n=12) of the studies found at least one significant G×E effect. This review provides a systematic characterization of the published G×E studies, providing insights into the neurobiological and environmental determinants involved in the etiology of children's psychopathology.

Differential Muscle Involvement in Mice and Humans Affected by McArdle Disease

McArdle disease (muscle glycogenosis type V) is caused by myophosphorylase deficiency, which leads to impaired glycogen breakdown. We investigated how myophosphorylase deficiency affects muscle physiology, morphology, and glucose metabolism in 20-week-old McArdle mice and compared the findings to those in McArdle disease patients. Muscle contractions in the McArdle mice were affected by structural degeneration due to glycogen accumulation, and glycolytic muscles fatigued prematurely, as occurs in the muscles of McArdle disease patients. Homozygous McArdle mice showed muscle fiber disarray, variations in fiber size, vacuoles, and some internal nuclei associated with cytosolic glycogen accumulation and ongoing regeneration; structural damage was seen only in a minority of human patients. Neither liver nor brain isoforms of glycogen phosphorylase were upregulated in muscles, thus providing no substitution for the missing muscle isoform. In the mice, the tibialis anterior (TA) muscles were invariably more damaged than the quadriceps muscles. This may relate to a 7-fold higher level of myophosphorylase in TA compared to quadriceps in wild-type mice and suggests higher glucose turnover in the TA. Thus, despite differences, the mouse model of McArdle disease shares fundamental physiological and clinical features with the human disease and could be used for studies of pathogenesis and development of therapies.

Genetic mechanisms of parenting

This article is part of a Special Issue "Parental Care". The complexities of parenting behavior in humans have been studied for decades. Only recently did we begin to probe the genetic and epigenetic mechanisms underlying these complexities. Much of the research in this field continues to be informed by animal studies, where genetic manipulations and invasive tools allow to peek into and directly observe the brain during the expression of maternal behavior. In humans, studies of adult twins who are parents can suggest dimensions of parenting that might be more amenable to a genetic influence. Candidate gene studies can test specific genes in association with parental behavior based on prior knowledge of those genes' function. Gene-by-environment interactions of a specific kind indicating differential susceptibility to the environment might explain why some parents are more resilient and others are more vulnerable to stressful life events. Epigenetic studies can provide the bridge often necessary to explain why some individuals behave differently from others despite common genetic influences. There is a much-needed expansion in parenting research to include not only mothers as the focus-as has been the case almost exclusively to date-but also fathers, grandparents, and other caregivers.

Dyskinesias and impulse control disorders in Parkinson's disease: From pathogenesis to potential therapeutic approaches

Dopaminergic treatment in Parkinson's disease (PD) reduces the severity of motor symptoms of the disease. However, its chronic use is associated with disabling motor and behavioral side effects, among which levodopa-induced dyskinesias (LID) and impulse control disorders (ICD) are the most common. The underlying mechanisms and pathological substrate of these dopaminergic complications are not fully understood. Recently, the refinement of imaging techniques and the study of the genetics and molecular bases of LID and ICD indicate that, although different, they could share some features. In addition, animal models of parkinsonism with LID have provided important knowledge about mechanisms underlying such complications. In contrast, animal models of parkinsonism and abnormal impulsivity, although useful regarding some aspects of human ICD, do not fully resemble the clinical phenotype of ICD in patients with PD, and until now have provided limited information. Studies on animal models of addiction could complement the previous models and provide some insights into the background of these behavioral complications given that ICD are regarded as behavioral addictions. Here we review the most relevant advances in relation to imaging, genetics, biochemistry and pharmacological interventions to treat LID and ICD in patients with PD and in animal models with a view to better understand the overlapping and unique maladaptations to dopaminergic therapy that are associated with LID and ICD.

The role of serotonin and its receptors in activation of immune responses and inflammation

Serotonin or 5-hydroxytryptamine (5-HT) is a neurotransmitter and hormone that contributes to the regulation of various physiological functions by its actions in the central nervous system (CNS) and in the respective organ systems. Peripheral 5-HT is predominantly produced by enterochromaffin (EC) cells of the gastrointestinal (GI) tract. These gut-resident cells produce much more 5-HT than all neuronal and other sources combined, establishing EC cells as the main source of this biogenic amine in the human body. Peripheral 5-HT is also a potent immune modulator and affects various immune cells through its receptors and via the recently identified process of serotonylation. Alterations in 5-HT signalling have been described in inflammatory conditions of the gut, such as inflammatory bowel disease. The association between 5-HT and inflammation, however, is not limited to the gut, as changes in 5-HT levels have also been reported in patients with allergic airway inflammation and rheumatoid arthritis. Based on searches for terms such as '5-HT', 'EC cell', 'immune cells' and 'inflammation' in pubmed.gov as well as by utilizing pertinent reviews, the current review aims to provide an update on the role of 5-HT in biological functions with a particular focus on immune activation and inflammation.

The serotonin transporter gene polymorphism 5-HTTLPR moderates the effects of stress on attention-deficit/hyperactivity disorder

INTRODUCTION

The role of the serotonin transporter gene polymorphism 5-HTTLPR in attention-deficit/hyperactivity disorder (ADHD) is unclear. Heterogeneity of findings may be explained by gene-environment interactions (GxE), as it has been suggested that S-allele carriers are more reactive to psychosocial stress than L-allele homozygotes. This study aimed to investigate whether 5-HTTLPR genotype moderates the effects of stress on ADHD in a multisite prospective ADHD cohort study.

METHODS

5-HTTLPR genotype, as well as the number of stressful life events in the past 5 years and ongoing long-term difficulties, was determined in 671 adolescents and young adults with ADHD, their siblings, and healthy controls (57.4% male, average age 17.3 years). Linear mixed models, accounting for family relatedness, were applied to investigate the effects of genotype, experienced stress, and their interaction on ADHD severity at time point T2, while controlling for ADHD severity at T1 (mean follow-up time 5.9 years) and for comorbid internalizing problems at T2.

RESULTS

The interaction between genotype and stress significantly predicted ADHD severity at T2 (p = .006), which was driven by the effect on hyperactivity-impulsivity (p = .004). Probing of the interaction effect made clear that S-allele carriers had a significantly more positive correlation between stress and ADHD severity than L-allele homozygotes.

CONCLUSION

The results show that the interaction between 5-HTTLPR and stress is a mechanism involved particularly in the hyperactivity/impulsivity dimension of ADHD, and that this is independent of comorbid internalizing problems. Further research into the neurobiological mechanisms underlying this interaction effect is warranted.

Androgen receptor and monoamine oxidase polymorphism in wild bonobos

Androgen receptor gene (AR), monoamine oxidase A gene (MAOA) and monoamine oxidase B gene (MAOB) have been found to have associations with behavioral traits, such as aggressiveness, and disorders in humans. However, the extent to which similar genetic effects might influence the behavior of wild apes is unclear. We examined the loci AR glutamine repeat (ARQ), AR glycine repeat (ARG), MAOA intron 2 dinucleotide repeat (MAin2) and MAOB intron 2 dinucleotide repeat (MBin2) in 32 wild bonobos, Pan paniscus, and compared them with those of chimpanzees, Pan troglodytes, and humans. We found that bonobos were polymorphic on the four loci examined. Both loci MAin2 and MBin2 in bonobos showed a higher diversity than in chimpanzees. Because monoamine oxidase influences aggressiveness, the differences between the polymorphisms of MAin2 and MBin2 in bonobos and chimpanzees may be associated with the differences in aggression between the two species. In order to understand the evolution of these loci and AR, MAOA and MAOB in humans and non-human primates, it would be useful to conduct future studies focusing on the potential association between aggressiveness, and other personality traits, and polymorphisms documented in bonobos.

Functional effects of dopamine transporter gene genotypes on in vivo dopamine transporter functioning: a meta-analysis

Much psychiatric genetic research has focused on a 40-base pair variable number of tandem repeats (VNTR) polymorphism located in the 3'-untranslated region (3'UTR) of the dopamine active transporter (DAT) gene (SLC6A3). This variant produces two common alleles with 9- and 10-repeats (9R and 10R). Studies associating this variant with in vivo DAT activity in humans have had mixed results. We searched for studies using positron emission tomography (PET) or single-photon emission computed tomography (SPECT) to evaluate this association. Random effects meta-analyses assessed the association of the 3'UTR variant with DAT activity. We also evaluated heterogeneity among studies and evidence for publication bias. We found twelve studies comprising 511 subjects, 125 from PET studies and 386 from SPECT studies. The PET studies provided highly significant evidence that the 9R allele was associated with increased DAT activity in human adults. The SPECT studies were highly heterogeneous. As a group, they suggested no association between the 3'UTR polymorphism and DAT activity. When the analysis was limited to the most commonly used ligand, [123I]β-CIT, stratification by affection status dramatically reduced heterogeneity and revealed a significant association of the 9R allele with increased DAT activity for healthy subjects. In humans, the 9R allele of the 3'UTR polymorphism of SLC6A3 regulates dopamine activity in the striatal brain regions independent of the presence of neuropsychiatric illness. Differences in study methodology account for the heterogeneous results across individual studies.

Treatment-resistant schizophrenia and DAT and SERT polymorphisms

One fifth to one third of all patients diagnosed with schizophrenia are resistant to drug treatment, which makes it a major clinical challenge. Genetic studies have focused on the association between treatment resistant schizophrenia (TRS) and a number of candidate genes, including serotonin and dopamine system genes. We explored associations between carefully characterized TRS and DAT-VNTR, SERT-PR and SERT-in2 polymorphisms. There were 173 patients enrolled in the study that were clinically evaluated using Positive and Negative Syndrome Scale and Clinical Global Impressions Scales and divided into two groups based on treatment resistance (92 patients in TRS group). Patients with a combination of SERT-in2 ll and DAT 9/10, 9/11, 9/9 and 6/6 genotypes were more likely to have TRS, compared to those with 10/10 or 10/12 genotype (OR=5.1; 95% CI=1.6-16.8). In the group of patients with DAT 10/10 or 10/12 genotype, those who also shared SERT-in2 ls or ss genotype were more likely to have TRS, compared to ll genotype carriers (OR=2.7; 95% CI=1.0-7.0). The model in which interaction between SERT-in2 and DAT polymorphisms is linked to TRS can possibly explain contradictory previous results regarding role of DAT and SERT in TRS, but further research is needed.

Mothers' prenatal stress and their children's antisocial outcomes--a moderating role for the dopamine D4 receptor (DRD4) gene

BACKGROUND

Maternal distress during pregnancy has been linked to aggressive behavior in offspring. This effect has been interpreted in terms of 'fetal programming'. The 7-repeat (7r) allele of a VNTR polymorphism in exon III of the human dopamine receptor D4 (DRD4) has consistently been associated with externalizing behavior problems, especially in the presence of adverse environmental factors. So far, it is not known whether the DRD4 genotype moderates the effect of prenatal maternal stress on the development of childhood antisocial behavior.

METHODS

As part of an ongoing epidemiological cohort study, prenatal maternal stress was assessed using self-report 3 months following child birth. When children were 8, 11, and 15 years old, mothers rated their children's externalizing behavior, and diagnoses of conduct disorder and/or oppositional defiant disorder (CD/ODD) according to DSM-IV were obtained. In a sample of N = 308 participants, the effects of the DRD4 genotype, prenatal maternal stress, and the interaction thereof on antisocial outcome were tested.

RESULTS

Under conditions of elevated prenatal maternal stress, children carrying one or two DRD4 7r alleles were at increased risk of a diagnosis of CD/ODD. Moreover, homozygous carriers of the DRD4 7r allele displayed more externalizing behavior following exposure to higher levels of prenatal maternal stress, while homozygous carriers of the DRD4 4r allele turned out to be insensitive to the effects of prenatal stress.

CONCLUSIONS

This study is the first to report a gene-environment interaction related to DRD4 and prenatal maternal stress using data from a prospective study, which extends earlier findings on the impact of prenatal maternal stress with respect to childhood antisocial behavior.

Association of functional DBH genetic variants with alcohol dependence risk and related depression and suicide attempt phenotypes: results from a large multicenter association study

OBJECTIVE

Dopamine-beta-hydroxylase (DBH) metabolizes the conversion of dopamine to noradrenaline. DBH, located on chromosome 9q34.2 has variants with potential functional consequences which may be related to alterations of neurotransmitter function and several psychiatric phenotypes, including alcohol dependence (AD), depression (MD) and suicidal behavior (SA). The aim of this association study in a large multicenter sample of alcohol-dependent individuals and controls is to investigate the role of DBH SNPs and haplotypes in AD risk and associated phenotypes (AD with MD or SA).

METHOD

1606 inpatient subjects with DSM-IV AD from four addiction treatment centers and 1866 control subjects were included. Characteristics of AD, MD and SA were obtained using standardized structured interviews. After subjects were genotyped for 4 DBH polymorphisms, single SNP case-control and haplotype analyses were conducted.

RESULTS

rs1611115 (near 5') C-allele and related haplotypes were significantly associated with alcohol dependence in females. This association with female alcohol dependence also accounts for the significant relationship between this variant and comorbid conditions and traits.

CONCLUSIONS

This study presents evidence for a potentially functional DBH variant influencing the risk for alcohol dependence while other comorbid conditions are not independently influenced by this SNP. However, the study also supports the possible role of the dopamine system in the etiology of female alcohol dependence.

Pharmacokinetics and pharmacodynamics of 3,4-methylenedioxymethamphetamine (MDMA): interindividual differences due to polymorphisms and drug-drug interactions

Clinical outcome following 3,4-methylenedioxymethamphetamine (MDMA) intake ranges from mild entactogenic effects to a life-threatening intoxication. Despite ongoing research, the clinically most relevant mechanisms causing acute MDMA-induced adverse effects remain largely unclear. This complicates the triage and treatment of MDMA users needing medical care. The user's genetic profile and interactions resulting from polydrug use are key factors that modulate the individual response to MDMA and influence MDMA pharmacokinetics and dynamics, and thus clinical outcome. Polymorphisms in CYP2D6, resulting in poor metabolism status, as well as co-exposure of MDMA with specific substances (e.g. selective serotonin reuptake inhibitors (SSRIs)) can increase MDMA plasma levels, but can also decrease the formation of toxic metabolites and subsequent cellular damage. While pre-exposure to e.g. SSRIs can increase MDMA plasma levels, clinical effects (e.g. blood pressure, heart rate, body temperature) can be reduced, possibly due to a pharmacodynamic interaction at the serotonin reuptake transporter (SERT). Pretreatment with inhibitors of the dopamine or norepinephrine reuptake transporter (DAT or NET), 5-HT(2A) or α-β adrenergic receptor antagonists or antipsychotics prior to MDMA exposure can also decrease one or more MDMA-induced physiological and/or subjective effects. Carvedilol, ketanserin and haloperidol can reduce multiple MDMA-induced clinical and neurotoxic effects. Thus besides supportive care, i.e. sedation using benzodiazepines, intravenous hydration, aggressive cooling and correction of electrolytes, it is worthwhile to investigate the usefulness of carvedilol, ketanserin and haloperidol in the treatment of MDMA-intoxicated patients.

Behavioral effects of prenatal ketamine exposure in rhesus macaques are dependent on MAOA genotype

Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist that is used in anesthetic, abuse, and therapeutic contexts. Recent evidence suggests that ketamine may affect not only glutamate systems, but may also act on receptors in the dopamine and serotonin systems. Because monoamine neurotransmitters play important trophic roles in prenatal development, we hypothesized that the behavioral consequences of prenatal exposure to ketamine may be moderated by genotype of the promoter in the monoamine oxidase-A (MAOA) gene. Eighty-two infant rhesus monkeys were identified that had known dates of conception and exposures to ketamine during gestation. Animals were tested at 3-4 months of age on a battery of tests assessing responsiveness to maternal separation, recognition memory, and contact with novel objects. Animals were classified by putative activity levels for the MAOA genotype. The effects of prenatal ketamine exposure were seen only in the context of MAOA genotype. Greater exposure to ketamine resulted in increased activity, less willingness to perform in the memory task, and reduced emotionality and novel-object contact, but only for individuals with the low-activity genotype. Nearly all effects of ketamine were the result of first- and second-trimester exposure. MAOA genotype moderates the role of prenatal ketamine exposure at time points in gestation earlier than have been shown in past research, and is particularly evident for measures of emotionality. These results support the idea that ketamine's use might be best considered in light of individuals' genetic characteristics.

Pharmacogenetically driven treatments for alcoholism: are we there yet?

Pharmacogenetic analyses of treatments for alcohol dependence attempt to predict treatment response and side-effect risk for specific medications. We review the literature on pharmacogenetics relevant to alcohol dependence treatment, and describe state-of-the-art methods of pharmacogenetic research in this area. Two main pharmacogenetic study designs predominate: challenge studies and treatment-trial analyses. Medications studied include US FDA-approved naltrexone and acamprosate, both indicated for treating alcohol dependence, as well as several investigational (and off-label) treatments such as sertraline, olanzapine and ondansetron. The best-studied functional genetic variant relevant to alcoholism treatment is rs1799971, a single-nucleotide polymorphism in exon 1 of the OPRM1 gene that encodes the μ-opioid receptor. Evidence from clinical trials suggests that the presence of the variant G allele of rs1799971 may predict better treatment response to opioid receptor antagonists such as naltrexone. Evidence from clinical trials also suggests that several medications interact pharmacogenetically with variation in genes that encode proteins involved in dopaminergic and serotonergic neurotransmission. Variation in the DRD4 gene, which encodes the dopamine D(4) receptor, may predict better response to naltrexone and olanzapine. A polymorphism in the serotonin transporter gene SLC6A4 promoter region appears related to differential treatment response to sertraline depending on the subject's age of onset of alcoholism. Genetic variation in SLC6A4 may also be associated with better treatment response to ondansetron. Initial pharmacogenetic efforts in alcohol research have identified functional variants with potential clinical utility, but more research is needed to further elucidate the mechanism of these pharmacogenetic interactions and their moderators in order to translate them into clinical practice.

MotifMap: integrative genome-wide maps of regulatory motif sites for model species

Background

A central challenge of biology is to map and understand gene regulation on a genome-wide scale. For any given genome, only a small fraction of the regulatory elements embedded in the DNA sequence have been characterized, and there is great interest in developing computational methods to systematically map all these elements and understand their relationships. Such computational efforts, however, are significantly hindered by the overwhelming size of non-coding regions and the statistical variability and complex spatial organizations of regulatory elements and interactions. Genome-wide catalogs of regulatory elements for all model species simply do not yet exist.

Results

The MotifMap system uses databases of transcription factor binding motifs, refined genome alignments, and a comparative genomic statistical approach to provide comprehensive maps of candidate regulatory elements encoded in the genomes of model species. The system is used to derive new genome-wide maps for yeast, fly, worm, mouse, and human. The human map contains 519,108 sites for 570 matrices with a False Discovery Rate of 0.1 or less. The new maps are assessed in several ways, for instance using high-throughput experimental ChIP-seq data and AUC statistics, providing strong evidence for their accuracy and coverage. The maps can be usefully integrated with many other kinds of omic data and are available at http://motifmap.igb.uci.edu/.

Conclusions

MotifMap and its integration with other data provide a foundation for analyzing gene regulation on a genome-wide scale, and for automatically generating regulatory pathways and hypotheses. The power of this approach is demonstrated and discussed using the P53 apoptotic pathway and the Gli hedgehog pathways as examples.

Dopaminergic, serotonergic, and oxytonergic candidate genes associated with infant attachment security and disorganization? In search of main and interaction effects

BACKGROUND AND METHODS

In two birth cohort studies with genetic, sensitive parenting, and attachment data of more than 1,000 infants in total, we tested main and interaction effects of candidate genes involved in the dopamine, serotonin, and oxytocin systems (DRD4, DRD2, COMT, 5-HTT, OXTR) on attachment security and disorganization. Parenting was assessed using observational rating scales for parental sensitivity (Ainsworth, Bell, & Stayton, 1974), and infant attachment was assessed with the Strange Situation Procedure.

RESULTS

We found no consistent additive genetic associations for attachment security and attachment disorganization. However, specific tests revealed evidence for a codominant risk model for COMT Val158Met, consistent across both samples. Children with the Val/Met genotype showed higher disorganization scores (combined effect size d = .22, CI = .10-.34, p < .001). Gene-by-environment interaction effects were not replicable across the two samples.

CONCLUSIONS

This unexpected finding might be explained by a broader range of plasticity in heterozygotes, which may increase susceptibility to environmental influences or to dysregulation of emotional arousal. This study is unique in combining the two largest attachment cohorts with molecular genetic and observed rearing environment data to date.

Catechol-O-methyltransferase Val158Met and the risk of dyskinesias in Parkinson's disease

BACKGROUND

The A-allele of the catechol-O-methyltransferase (COMT) Val158Met polymorphism is associated with decreased enzymatic activity and higher dopamine availability.

METHODS

We studied 219 patients with PD who were free of dyskinesias at baseline and underwent thorough annual examinations.

RESULTS

The A-allele of the COMT Val158Met polymorphism was related to an increased risk of developing dyskinesias during follow-up, in a dose-dependent manner (adjusted hazard ratios for the AG and AA genotypes [compared to GG]: 2.09 [95% confidence interval (CI), 1.07-4.06] and 2.81 [CI, 1.43-5.54], respectively).

CONCLUSIONS

This finding suggests that genetic factors may affect susceptibility to dyskinesias in PD.

Pharmacogenetic approach at the serotonin transporter gene as a method of reducing the severity of alcohol drinking

OBJECTIVE

Severe drinking can cause serious morbidity and death. Because the serotonin transporter (5-HTT) is an important regulator of neuronal 5-HT function, allelic differences at that gene may modulate the severity of alcohol consumption and predict therapeutic response to the 5-HT(3) receptor antagonist, ondansetron.

METHOD

The authors randomized 283 alcoholics by genotype in the 5'-regulatory region of the 5-HTT gene (LL/LS/SS), with additional genotyping for another functional single-nucleotide polymorphism (T/G), rs1042173, in the 3'-untranslated region, in a double-blind controlled trial. Participants received either ondansetron (4 μg/kg twice daily) or placebo for 11 weeks, plus standardized cognitive-behavioral therapy.

RESULTS

Individuals with the LL genotype who received ondansetron had a lower mean number of drinks per drinking day (-1.62) and a higher percentage of days abstinent (11.27%) than those who received placebo. Among ondansetron recipients, the number of drinks per drinking day was lower (-1.53) and the percentage of days abstinent higher (9.73%) in LL compared with LS/SS individuals. LL individuals in the ondansetron group also had a lower number of drinks per drinking day (-1.45) and a higher percentage of days abstinent (9.65%) than all other genotype and treatment groups combined. For both number of drinks per drinking day and percentage of days abstinent, 5'-HTTLPR and rs1042173 variants interacted significantly. LL/TT individuals in the ondansetron group had a lower number of drinks per drinking day (-2.63) and a higher percentage of days abstinent (16.99%) than all other genotype and treatment groups combined.

CONCLUSIONS

The authors propose a new pharmacogenetic approach using ondansetron to treat severe drinking and improve abstinence in alcoholics.

Genetics of depression: an overview of the current science

Most psychiatric disorders, including major depressive disorder (MDD), are known to involve complex interactions between genetic and environmental influences that impact the development and severity of symptomatology. Health care practitioner competencies have been expanded to include application of genetic knowledge in mental health. Yet this information is difficult to decipher and apply. To assist with these challenges, this article synthesizes recent literature related to the genetics of MDD and illustrates the genetic pathways for major depression.

From regulatory problems in infancy to attention-deficit/hyperactivity disorder in childhood: a moderating role for the dopamine D4 receptor gene?

OBJECTIVE

To examine whether the dopamine receptor D4 gene (DRD4) exon III VNTR moderates the risk of infants with regulatory disorders for developing attention-deficit/hyperactivity disorder (ADHD) later in childhood.

STUDY DESIGN

In a prospective longitudinal study of children at risk for later psychopathology, 300 participants were assessed for regulatory problems in infancy, DRD4 genotype, and ADHD symptoms and diagnoses from childhood to adolescence. To examine a potential moderating effect on ADHD measures, linear and logistic regressions were computed. Models were fit for the main effects of the DRD4 genotype (presence or absence of the 7r allele) and regulatory problems (presence or absence), with the addition of the interaction term. All models were controlled for sex, family adversity, and obstetric risk status.

RESULTS

In children without the DRD4-7r allele, a history of regulatory problems in infancy was unrelated to later ADHD. But in children with regulatory problems in infancy, the additional presence of the DRD4-7r allele increased the risk for ADHD in childhood.

CONCLUSIONS

The DRD4 genotype seems to moderate the association between regulatory problems in infancy and later ADHD. A replication study is needed before further conclusions can be drawn, however.

Global microsatellite content distinguishes humans, primates, animals, and plants

Microsatellites are highly mutable, repetitive sequences commonly used as genetic markers, but they have never been studied en masse. Using a custom microarray to measure hybridization intensities of every possible repetitive nucleotide motif from 1-mers to 6-mers, we examined 25 genomes. Here, we show that global microsatellite content varies predictably by species, as measured by array hybridization signal intensities, correlating with established taxonomic relationships, and particular motifs are characteristic of one species versus another. For instance, hominid-specific microsatellite motifs were identified despite alignment of the human reference, Celera, and Venter genomic sequences indicating substantial variation (30-50%) among individuals. Differential microsatellite motifs were mainly associated with genes involved in developmental processes, whereas those found in intergenic regions exhibited no discernible pattern. This is the first description of a method for evaluating microsatellite content to classify individual genomes.

Pharmacogenetic of response efficacy to antipsychotics in schizophrenia: pharmacodynamic aspects. Review and implications for clinical research

Pharmacogenetics constitutes a new and growing therapeutic approach in the identification of the predictive factors of the response to antipsychotic treatment. This review aims to summarize recent finding into pharmacodynamic approach of pharmacogenetics of antipsychotics and particularly second generation. Studies were identified in the MEDLINE database from 1993 to July 2008 by combining the following Medical Subject Heading search terms: genetic, polymorphism, single nucleotide polymorphism, pharmacogenetics, antipsychotics, and response to treatment as well as individual antipsychotics names. Only pharmacodynamics studies were analyzed and we focused on efficacy studies. We also reviewed the references of ll identified articles. Most studies follow a polymorphism-by-polymorphism approach, and concern polymorphisms of genes coding for dopamine and serotonin receptors. Haplotypic approach has been considered in some studies. Few have studied the combinations of polymorphisms of several genes as a predictive factor of the response to antipsychotics. We present this gene-by-gene approach while detailing the features of the polymorphisms being studied (functionality, linkage disequilibrium) and the features of the studies (studied treatment(s), prospective/retrospective study, pharmacological dosage). We discuss the heterogeneity of the results and their potential clinical implications and extract methodological suggestions for the future concerning phenotype characterization, genotypes variants studied and methodological and statistical approach.

Hypoxia-induced transcription of dopamine D3 and D4 receptors in human neuroblastoma and astrocytoma cells

Background

Dopaminergic pathways that influence mood and behaviour are severely affected in cerebral hypoxia. In contrast, hypoxia promotes the differentiation of dopaminergic neurons. In order to clarify the hypoxic sensitivity of key dopaminergic genes, we aimed to study their transcriptional regulation in the context of neuroblastoma and astrocytoma cell lines exposed to 1% hypoxia.

Results

Quantitative RT-PCR assays revealed that the transcription of both type D3 and D4 postsynaptic dopamine receptors (DRD3 and DRD4) was induced several fold upon 2-day hypoxia in a cell-specific manner, while the vascular endothelial growth factor gene was activated after 3-hr incubation in hypoxia. On the other hand, mRNA levels of type 2 dopamine receptor, dopamine transporter, monoamino oxidase and catechol-O-methyltransferase were unaltered, while those of the dopamine receptor regulating factor (DRRF) were decreased by hypoxia. Notably, 2-day hypoxia did not result in elevation of protein levels of DRD3 and DRD4.

Conclusion

In light of the relatively delayed transcriptional activation of the DRD3 and DRD4 genes, we propose that slow-reacting hypoxia sensitive transcription factors might be involved in the transactivation of DRD3 and DRD4 promoters in hypoxia.

Epistasis between IL1A, IL1B, TNF, HTR2A, 5-HTTLPR and TPH2 variations does not impact alcohol dependence disorder features

We assessed a set of biological (HDL, LDL, SGOT, SGPT, GGT, HTc, Hb and T levels) and psychometric variables (investigated through HAM-D, HAM-A, GAS, Liebowitz Social Anxiety Scale, Mark & Mathews Scale, Leyton scale, and Pilowski scale) in a sample of 64 alcohol dependent patients, at baseline and after a detoxification treatment. Moreover, we recruited 47 non-consanguineous relatives who did not suffer alcohol related disorders and underwent the same tests. In both groups we genotyped 11 genetic variations (rs1800587; rs3087258; rs1799724; 5-HTTLPR; rs1386493; rs1386494; rs1487275; rs1843809; rs4570625; rs2129575; rs6313) located in genes whose impact on alcohol related behaviors and disorders has been hypothesized (IL1A, IL1B, TNF, 5-HTTLPR, TPH2 and HTR2A). We analyzed the epistasis of these genetic variations upon the biological and psychological dimensions in the cases and their relatives. Further on, we analyzed the effects of the combined genetic variations on the short - term detoxification treatment efficacy. Finally, being the only not yet investigated variation within this sample, we analyzed the impact of the rs6313 alone on baseline assessment and treatment efficacy. We detected the following results: the couple rs6313 + rs2129575 affected the Leyton -Trait at admission (p = 0.01) (obsessive-compulsive trait), whilst rs1800587 + 5-HTTLPR impacted the Pilowski test at admission (p = 0.01) (hypochondriac symptoms). These results did not survive Bonferroni correction (p < or = 0.004). This lack of association may depend on the incomplete gene coverage or on the small sample size which limited the power of the study. On the other hand, it may reflect a substantial absence of relevance of the genotype variants toward the alcohol related investigated dimensions. Nonetheless, the marginal significance we detected could witness an informative correlation worth investigating in larger samples.

Genes within the serotonergic system are differentially expressed in human brain

Background

Serotonin is an important neurotransmitter with wide-ranging functions throughout the central nervous system. There is strong evidence to suggest that regulation of serotonergic gene expression might be related to genetic variability, and several studies have focused on understanding the functional effects of specific polymorphisms within these genes on expression levels. However, the combination of genotype together with gender and brain region could have an overall effect on gene expression. In this study, we report expression patterns of five serotonergic genes (TPH1, TPH2, 5-HT2A, 5-HT2C, 5-HTT) in seven different human post-mortem brain regions (superior frontal gyrus, superior temporal gyrus, striatum, cerebellum, hippocampus, midbrain and thalamus) using TaqMan™ real-time quantitative PCR. In addition, the effect of genotype and gender on their expression levels was determined.

Results

The data revealed that mRNA from the five genes investigated was detected in all brain regions and showed an overall significant difference in expression levels. Furthermore, the expression of 5-HT2C, 5-HT2A and TPH2 was found to be significantly different between the various brain regions. However, neither gender nor genotype showed significant effects on the expression levels of any of the genes assayed. Interestingly, TPH1 and TPH2 were expressed in all brain regions similarly except for within the striatum and cerebellum, where TPH1 was expressed at a significantly higher level than TPH2.

Conclusion

The effect of brain region has a greater influence on serotonergic gene expression than either genotype or gender. These data add to the growing body of evidence that effects of functional polymorphisms on gene expression in vitro are not observed ex vivo, and provide information that will aid in the design of expression studies of the serotonergic gene system within human post-mortem brain.

3B but which 3B and that's just one of the questions: the heterogeneity of human 5-HT3 receptors

The 5-hydroxytryptamine 3 (5-HT3) receptor is expressed widely in the central and peripheral nervous systems, where it mediates or modulates a wide range of physiological processes. The receptor is targeted by drugs administered for nausea and/or emesis and irritable bowel syndrome and has been proposed as a potential drug target in various psychiatric disorders. The 5-HT3 receptor is a pentameric ligand-gated ion channel and belongs to the Cys-loop receptor family. In contrast to the immense heterogeneity characterizing other Cysloop receptors, native 5-HT3 receptors historically have been considered a much more homogenous receptor population. However, the recent discovery of additional 5-HT3 subunits and the dawning realization that central and peripheral 5-HT3 receptor populations might comprise several subtypes characterized by distinct functional properties has emphasized the complexity of human 5-HT3 receptor signaling. In this review potential implications of these findings and of the entirely new layer of interindividual diversity introduced to the 5-HT3 receptor system by genetic variations will be outlined.

New genetic evidence for involvement of the dopamine system in migraine with aura

In order to systematically test the hypothesis that genetic variation in the dopamine system contributes to the susceptibility to migraine with aura (MA), we performed a comprehensive genetic association study of altogether ten genes from the dopaminergic system in a large German migraine with aura case-control sample. Based on the genotyping results of 53 variants across the ten genes in 270 MA cases and 272 controls, three genes-DBH, DRD2 and SLC6A3-were chosen to proceed to additional genotyping of 380 MA cases and 378 controls. Four of the 26 genotyped polymorphisms in these three genes displayed nominally significant allelic P-values in the sample of 650 MA patients and 650 controls. Three of these SNPs [rs2097629 in DBH (uncorrected allelic P value = 0.0012, OR = 0.77), rs7131056 in DRD2 (uncorrected allelic P value = 0.0018, OR = 1.28) and rs40184 in SLC6A3 (uncorrected allelic P value = 0.0082, OR = 0.81)] remained significant after gene-wide correction for multiple testing by permutation analysis. Further consideration of imputed genotype data from 2,937 British control individuals did not affirm the association with DRD2, but supported the associations with DBH and SLC6A3. Our data provide new evidence for an involvement of components of the dopaminergic system-in particular the dopamine-beta hydroxylase and dopamine transporter genes-to the pathogenesis of migraine with aura.

Mutations in human monoamine-related neurotransmitter pathway genes

Biosynthesis and metabolism of serotonin and catecholamines involve at least eight individual enzymes that are mainly expressed in tissues derived from the neuroectoderm, e.g., the central nervous system (CNS), pineal gland, adrenal medulla, enterochromaffin tissue, sympathetic nerves, and ganglia. Some of the enzymes appear to have additional biological functions and are also expressed in the heart and various other internal organs. The biosynthetic enzymes are tyrosine hydroxylase (TH), tryptophan hydroxylases type 1 and 2 (TPH1, TPH2), aromatic amino acid decarboxylase (AADC), dopamine beta-hydroxylase (DbetaH), and phenylethanolamine N-methyltransferase (PNMT), and the specific catabolic enzymes are monoamine oxidase A (MAO-A) and catechol O-methyltransferase (COMT). For the TH, DDC, DBH, and MAOA genes, many single nucleotide polymorphisms (SNPs) with unknown function, and small but increasing numbers of cases with autosomal recessive mutations have been recognized. For the remaining genes (TPH1, TPH2, PNMT, and COMT) several different genetic markers have been suggested to be associated with regulation of mood, pain perception, and aggression, as well as psychiatric disturbances such as schizophrenia, depression, suicidality, and attention deficit/hyperactivity disorder. The genetic markers may either have a functional role of their own, or be closely linked to other unknown functional variants. In the future, molecular testing may become important for the diagnosis of such conditions. Here we present an overview on mutations and polymorphisms in the group of genes encoding monoamine neurotransmitter metabolizing enzymes. At the same time we propose a unified nomenclature for the nucleic acid aberrations in these genes. New variations or details on mutations will be updated in the Pediatric Neurotransmitter Disorder Data Base (PNDDB) database (www.bioPKU.org).

Effects of an attachment-based intervention on daily cortisol moderated by dopamine receptor D4: A randomized control trial on 1- to 3-year-olds screened for externalizing behavior

The effect of the Video-Feedback Intervention to Promote Positive Parenting and Sensitive Discipline (VIPP-SD) on daily cortisol production was tested in a randomized controlled trial with 130 families with 1- to 3-year-old children screened for their relatively high levels of externalizing behavior. Six 1.5-hr intervention sessions focusing on maternal sensitivity and discipline were conducted with individual families at their homes. Children in the intervention group showed lower cortisol levels, with a moderating role of the dopamine receptor D4 (DRD4) VNTR exon III polymorphism. The VIPP-SD program proved to be effective in decreasing daily cortisol production in childrenwiththeDRD47-repeat allele, but not in childrenwithouttheDRD47-repeat allele. Our findings indicate that children are differentially susceptible to intervention effects dependent on the presence of the 7-repeatDRD4allele.

Oxytocin receptor (OXTR) and serotonin transporter (5-HTT) genes associated with observed parenting

Both oxytocin and serotonin modulate affiliative responses to partners and offspring. Animal studies suggest a crucial role of oxytocin in mammalian parturition and lactation but also in parenting and social interactions with offspring. The serotonergic system may also be important through its influence on mood and the release of oxytocin. We examined the role of serotonin transporter (5-HTT) and oxytocin receptor (OXTR) genes in explaining differences in sensitive parenting in a community sample of 159 Caucasian, middle-class mothers with their 2-year-old toddlers at risk for externalizing behavior problems, taking into account maternal educational level, maternal depression and the quality of the marital relationship. Independent genetic effects of 5-HTTLPR SCL6A4 and OXTR rs53576 on observed maternal sensitivity were found. Controlling for differences in maternal education, depression and marital discord, parents with the possibly less efficient variants of the serotonergic (5-HTT ss) and oxytonergic (AA/AG) system genes showed lower levels of sensitive responsiveness to their toddlers. Two-way and three-way interactions with marital discord or depression were not significant. This first study on the role of both OXTR and 5-HTT genes in human parenting points to molecular genetic differences that may be implicated in the production of oxytocin explaining differences in sensitive parenting.

Inhibition of serotonin but not norepinephrine transport during development produces delayed, persistent perturbations of emotional behaviors in mice

Serotonin (5-HT) acts as a neurotransmitter, but also modulates brain maturation during early development. The demonstrated influence of genetic variants on brain function, personality traits, and susceptibility to neuropsychiatric disorders suggests a critical importance of developmental mechanisms. However, little is known about how and when developmentally perturbed 5-HT signaling affects circuitry and resulting behavior. The 5-HT transporter (5-HTT) is a key regulator of extracellular 5-HT levels and we used pharmacologic strategies to manipulate 5-HTT function during development and determine behavioral consequences. Transient exposure to the 5-HTT inhibitors fluoxetine, clomipramine, and citalopram from postnatal day 4 (P4) to P21 produced abnormal emotional behaviors in adult mice. Similar treatment with the norepinephrine transporter (NET) inhibitor, desipramine, did not adversely affect adult behavior, suggesting that 5-HT and norepinephrine (NE) do not share the same effects on brain development. Shifting our period of treatment/testing to P90/P185 failed to mimic the effect of earlier exposure, demonstrating that 5-HT effects on adult behavior are developmentally specific. We have hypothesized that early-life perturbations of 5-HT signaling affect corticolimbic circuits that do not reach maturity until the peri-adolescent period. In support of this idea, we found that abnormal behaviors resulting from postnatal fluoxetine exposure have a post-pubescent onset and persist long after reaching adult age. A better understanding of the underlying 5-HT sensitive circuits and how they are perturbed should lead to new insights into how various genetic polymorphisms confer their risk to carriers. Furthermore, these studies should help determine whether in utero exposure to 5-HTT blocking drugs poses a risk for behavioral abnormalities in later life.

Advances in genetic findings on attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) is a common, childhood-onset neurodevelopmental disorder with adverse consequences during adult life. Family, twin and adoption studies show that genetic factors contribute to the aetiology of ADHD and that environmental factors also play a role. Family and twin studies have shown the importance of genetic influences on continuity in ADHD over time and in accounting for the co-occurrence of ADHD and conduct disorder problems. In meta-analyses of molecular genetic studies, the 48-bp variable number tandem repeat (VNTR) variant in the dopamine D4 gene and the CA(n) microsatellite marker in the D5 receptor gene have been found to be repeatedly associated with ADHD. Results from meta-analyses of the 480-bp VNTR in the dopamine transporter gene are mixed. Several genetic studies have also identified genetic variants that are related to specific clinical and developmental features of ADHD. In the next few years, a new generation of much larger-scale genetic studies should lead to the identification of further ADHD susceptibility genes. Such studies will also need to be integrated with other areas of neuroscience, clinical and epidemiological research to investigate how specific gene variants exert risk effects, interact with environmental factors and enable identification of the underlying causal mechanisms that lead to ADHD.

In vitro assays fail to predict in vivo effects of regulatory polymorphisms

A typical paradigm in the investigation of complex human disease is to assess the effects of cis-regulatory polymorphisms implicated in association studies on transcription in cellular expression systems. Evidence from in vitro transfection studies is often assumed to be sufficient evidence for the in vivo functional importance of a polymorphism in the context of human disease, even though many confounding effects (e.g. temporal regulation, tissue specificity, genetic background) are not considered. In this study, we evaluate this assumption directly by examining the translation of in vitro results on allele-specific expression to an in vivo system using four genes that have been well documented through reporter assays to have promoter polymorphisms affecting transcription level: monoamine oxidase A (MAOA), neuropeptide Y (NPY), endothelial nitric oxide synthase (NOS3), and prodynorphin (PDYN). In our study, MAOA was found to have large allelic imbalances, which indicates that there is in vivo variation in the expression of this gene. However, the imbalances observed were not correlated with genotype at the putatively functional polymorphism. PDYN, NOS3 and NPY did not have large allelic imbalances. Overall, there was no statistically significant effect of these polymorphisms on expression level as measured by imbalance ratios in any of these genes. These results suggest that the functional effects of a polymorphism on gene expression may be more complicated and context dependent than is often assumed and also imply that the use of cell-based expression studies to support the role of such polymorphisms in disease etiology should be treated with caution.