Durante lo sviluppo, l’esperienza gioca un ruolo determinante nel guidare l’emergere del comportamento in maniera individuo specifica all’interno di un trend maturativo comune alla specie. La presenza di un determinato background genetico costituisce la situazione al contorno in cui l’esperienza opera. Costituisce, ovvero, la base della formazione dei circuiti neurali sulla cui maturazione l’esperienza agisce per guidare l’emergenza del comportamento Patrimonio genetico = potenzialità ma anche vincolo, limite per l’azione dell’esperienza E’ sempre più evidente che fattori genetici e fattori ambientali non sono indipendenti tra loro nel controllare lo sviluppo del sistema nervoso e del comportamento; ciò che è importante è l’interazione tra essi. Donald Hebb riassunse molto efficacemente questa idea rispondendo a un giornalista che gli chiedeva chi, tra geni e ambiente, contribuisse maggiormente alla personalità. Hebb rispose domandando al giornalista se per l’area di un rettangolo fosse più importante la base o l’altezza. Studi che esaminano nell’uomo le interazioni geni-ambiente nella probabilità di sviluppare disturbi del comportamento o del tono dell’umore Approcci allo studio del ruolo di fattori genetici nel comportamento e nei suoi disturbi La storia recente della ricerca sul ruolo di fattori genetici nello sviluppo del comportamento e nei suoi disturbi ha seguito tre grandi approcci, ciascuno con la sua logica e le sue assunzioni. Il primo approccio assume che vi sia una relazione diretta fra geni e comportamento. In particolare, assume che i geni causino i disturbi del comportamento. Lo scopo di questo approccio è stato di correlare la presenza di disturbi nel comportamento con differenze individuali nella sequenza del DNA. “This has been attempted using both linkage analysis and association analysis, with regard to many psychiatric conditions such as depression, schizophrenia and addiction. Although a few genes have accumulated replicated evidence of association with disorder, replication failures are routine and overall progress has been slow.” (Caspi et al., 2006) “Because of inconsistent findings, many scientists have despaired of the search for a straightforward association between genotype and diagnosis, that is, for direct main effects.” (Caspi et al., 2006). Caspi et al. Nature Reviews Neuroscience 7, 583–590 (July 2006) | doi:10.1038/nrn1925 Il secondo approccio ha cercato di aggirare questo scoglio cercando correlazioni fra il genotipo individuale e fenotipi intermedi, chiamati endofenotipi. “Endophenotypes are heritable neurophysiological, biochemical, endocrinological, neuroanatomical or neuropsychological constituents of disorders (es. from ASDs).” (Caspi et al., 2006) Si assume che gli endofenotipi abbiano cause genetiche più semplici rispetto al fenotipo completo. Quindi, l’assunzione dietro questo approccio è che è più semplice identificare i geni associati con endofenotipi che identificare i geni associati con il disturbo con cui tali endofenotipi sono correlati. Anche questo approccio, però, cerca un effetto principale di fattori genetici nelle differenze interindividuali. Caspi et al. Nature Reviews Neuroscience 7, 583–590 (July 2006) | doi:10.1038/nrn1925 Il terzo e più nuovo approccio cerca di incorporare nello studio delle differenze interindividuali nel comportamento l’effetto dell’ambiente. Questo approccio, detto approccio “interazioni geni-ambiente” differisce in maniera forte dai due approcci precedenti, che cercano un “effetto principale” dei fattori genetici. “Main-effect approaches assume that genes cause disorder, an assumption carried forward from early work that identified single-gene causes of rare Mendelian conditions. “ (Caspi eta l., 2006). L’approccio “interazioni geni-ambiente” (Gene x Environment, G x E) invece assume che patogeni ambientali possano causare disturi del comportamento e che il genotipo influenzi la suscettibilità a tali patogeni. Si assume quindi che i geni siano fattori di rischio per la suscettibilità a patogeni ambientali. In contrasto con gli studi che cercano effetti principali del genotipo, secondo l’approccio G xE non c’è attesa per una associazione diretta genecomportamento in assenza di patogeni ambientali (e viceversa). Caspi et al. Nature Reviews Neuroscience 7, 583–590 (July 2006) | doi:10.1038/nrn1925 L’approccio G x E è scaturito da due tipi di osservazioni: 1. Disturbi del comportamento e del tono dell’umore hanno cause legate all’ambiente ed all’esperienza individuale; 2. C’è eterogeneità nella risposta a “patogeni” ambientali (resilienza/vulnerabilità) “Like other non-communicable diseases that have common prevalence in the population and complex multi-factorial aetiology, most mental disorders have known non-genetic, environmental risk factors (that is, predictors whose causal status is unproven). Environmental risk factors for mental disorders discovered to date include (but are not limited to): maternal stress during pregnancy, maternal substance abuse during pregnancy, low birth weight, birth complications, deprivation of normal parental care during infancy, childhood physical maltreatment, childhood neglect, premature parental loss, exposure to family conflict and violence, stressful life events involving loss or threat, substance abuse, toxic exposures” Caspi et al., 2006 I patogeni ambientali sono quindi in realtà non “causali”, ma sono fattori di rischio. L’esposizione ad essi non sempre causa un disturbo del comportamento. Sia gli studi nell’uomo che gli studi in modelli animali hanno consistentemente mostrato una grande variabilità interindividuale nelle risposte comportamentali a patogeni ambientali. “Heterogeneity of response characterizes all known environmental risk factors for psychopathology, including even the most overwhelming of traumas. Such response heterogeneity is associated with pre-existing individual differences in temperament, personality, cognition and autonomic physiology, all of which are known to be under genetic influence.” (Caspi et al., 2006). “The hypothesis of genetic moderation implies that differences between individuals, originating in the DNA sequence, bring about differences between individuals in their resilience or vulnerability to the environmental causes of many pathological conditions of the mind and body.” Caspi et al., 2006 Esempi di interazioni geni x ambiente: Sovraespressione del gene NMDA2B x ambiente arricchito, (memoria migliore per animali wild type, ceiling effect per animali con mutazione) G x E nella suscettibilità a sviluppare dipendenza da sostanze: Esempio: Cabib et al., 2000 Uso di linee di topi “Inbred”, largamente usati per la genetica del comportamento. Prima di entrare nel vivo dell’argomento, vi introduco il sistema endogeno della ricompensa Qui andare al file sistema endogeno della ricompensa Saline Drug of abuse appaiato Place preference non appaiato C57B6J DBA C57B6J DBA Conditioned place preference test, due background genetici diversi. C57, più suscettibili a sviluppare dipendenza da sostanze d’abuso dei DBA Descrizione del “conditioned Place Preference “test Un periodo moderato di carenza di cibo (“food shortage”), che costituisce una esperienza “ecologica” e piuttosto comune in natura, può invertire o cancellare le differenze fra le linee C57 e DBA nella risposta comportamentale alla esposizione a psicostimolanti. Quindi, una “sfida” ambientale può annullare la differenza fra i genotipi. Neuromodulatory system lesion Ambiente normale Food shortage Place preference C57 unpaired paired Place preference DBA unpaired paired “The period of food shortage occurred when the animals were mature and was terminated before the administration of amphetamine. Strain differences in behavior appear highly dependent on environmental experiences. Consequently, to identify biological determinants of behavior, in this case resilience to addiction, an integrated approach considering the interaction between environmental and genetic factors needs to be used.” Cabib et al., 2000 Ventura et al., 2003 Trasformare i C57 in DBA modificando la trasmissione cortico striatale La corteccia prefrontale esercita un forte effetto modulatorio sui meccanismi di dipendenza. La trasmissione noradrenergica nella corteccia prefrontale mediale (mpFC) modula ad esempio l’effetto della anfetamina a livello del comportamento. Il lavoro di Ventura et al mira a verificare che l’azione modulatoria della noradrenaline (NE) a livello prefrontale sia coinvolta nello sviluppo di dipendenza dalle anfetamine. Metodo: Deplezione selettiva di NE nella mPFC nei C57BL/6J, (molto suscettibili allo sviluppo di dipendenza da anfetamine). Scopo: Valutare lo sviluppo di dipendenza da anfetamine con il conditioned place preference. Risultati: Assenza di conditioned place preference nei topi C57 con deplezione prefrontale di NE (C57 sono diventati DBA). Effects of prefrontal cortical norepinephrine depletion on the preference scores shown by saline (A) and amphetamine (B)-treated groups of C57 mice in conditioned place preference test. All data are expressed as mean ± SE. *p < 0.05 compared with the unpaired compartment. Ventura et al., 2003 In un secondo gruppo di esperimenti, Ventura et al., (2003) hanno mostrato che la deplezione noradrenergica a livello prefrontale riduce fortemente l’effetto della anfetamina nell’aumentare il rilascio di dopamina dalla VTA al nucleo accumbens, in linea con l’assenza di dipendenza. “These results indicate that noradrenergic prefrontal transmission, by allowing increased dopamine release in the nucleus accumbens induced by amphetamine, is a critical factor for the rewardingreinforcing effects of this drug.” Ventura et al., 2003 “Later studies have shown that C57 and DBA mice differ in their sensitivity to other drugs of abuse (cocaine and morphine) in terms of drug induced conditioned place preference and suggest that the two strains differ in sensitivity to the positive incentive properties of drugs of abuse (Orsini et al., 2005).” (Pascucci et al., 2007) Sembrerebbe quindi che lo sviluppo di dipendenza dall’assunzione di sostanze, legato al rilascio di dopamina nel nucleo accumbens (dopamina che è rilasciata dai neuroni della VTA), sia sotto il controllo opponente del sistema noradrenergico e dopaminergico a livello della corteccia prefrontale. (Pascucci et al., 2007). In ultima analisi, il bilancio fra attività noradrenergica e dopaminergica a livello prefrontale potrebbe, regolando il rilascio di dopamina nel nucleo accumbens, determinare la suscettibilità allo sviluppo di dipendenza da sostanze, attraverso una interazione geni x ambiente. Risultati simili per la risposta allo stress. Esposizione a stressors inibisce il rilascio di dopamina nel nucleo accumbens. Nei C57, questo effetto è accompaganto da una forte attivazione del sistema dopaminergico mesocorticale; a livello comportamentale, questo corrisponde ad una messa in atto di comportamenti “rinunciatari” e alla presenza di anedonia. Nei DBA si ha invece una risposta neuromodulatoria prefrontale e comportamentale opposta. “There may be a genetic control over the balance between mesocortical and mesoaccumbens dopamine responses to drugs and stress, which sets the level of susceptibility for drug addiction, stressful events and ultimately, interactions with the environment.” (Pascucci et al., 2007) I polimorfismi: fattori di rischio, fattori protettivi nei confronti di “patogeni” ambientali. (Si parla di polimorfismo genetico quando una variazione genetica ha una prevalenza maggiore dell'1% nella popolazione. La variazione genetica può essere determinata da sostituzioni, delezioni o inserzioni di basi nel DNA e può riguardare regioni codificanti e regioni non codificanti.) Lavoro capostipite: Caspi et al., 2002 Role of genotype in the cycle of violence in maltreated children “Childhood maltreatment is a universal risk factor for antisocial behavior. Boys who experience abuse--and, more generally, those exposed to erratic, coercive, and punitive parenting--are at risk of developing conduct disorder, antisocial personality symptoms, and of becoming violent offenders. The earlier children experience maltreatment, the more likely they are to develop these problems. But there are large differences between children in their response to maltreatment. Although maltreatment increases the risk of later criminality by about 50%, most maltreated children do not become delinquents or adult criminals. The reason for this variability in response is largely unknown, but it may be that vulnerability to adversities is conditional, depending on genetic susceptibility factors.” In questo studio, viene indagata l’ipotesi di una suscettibilità genetica al maltrattamento infantile. Si ipotizza in particolare che differenze interindividuali nella funzionalità del gene per la monoamminoossidasi A (MAOA), dovute ad un polimorfismo nel promotore del gene stesso, influenzino la resilienza ad un ambiente avverso precoce. Ipotesi: “polimorphism in MAOA gene modifies the influence of maltreatment on children's development of antisocial behavior.” Il gene per la MAOA è localizzato sul cromosoma X. Esso codifica per l’enzima MAOA, che metabolizza neurotrasmettitori quali la Noradrenalina (NE), serotonina (5-HT), e dopamina (DA), rendendoli inattivi e facendone quindi terminare l’azione a livello sinaptico. Una mutazione che determina la produzione di una versione meno funzionale della MAOA prolunga la vita media del neurotrasmettitore, aumentandone l’efficacia sinapitca. Deficit nella attività della MAOA dovuti a polimorfismi genetici sono stati messi in relazione con fenotipi a maggior aggressività sia in modelli animali che nell’uomo. 1: Increased aggression and increased levels of brain NE, 5-HT, and DA were observed in a transgenic mouse line in which the gene encoding MAOA was deleted, and aggression was normalized by restoring MAOA expression. 2: In humans, a null allele at the MAOA locus was linked with male antisocial behavior in a Dutch kindred. Because MAOA is an X-linked gene, affected males with a single copy produced no MAOA enzyme--effectively, a human knockout. However, this mutation is extremely rare. Evidence for an association between MAOA and aggressive behavior in the human general population remains inconclusive. Circumstantial evidence suggests the hypothesis that childhood maltreatment predisposes most strongly to adult violence among children whose MAOA is insufficient to constrain maltreatmentinduced changes to neurotransmitter systems. Indeed, animal studies document that maltreatment stress (e.g., maternal deprivation, peer rearing) in early life alters NE, 5-HT, and DA neurotransmitter systems in ways that can persist into adulthood and can influence aggressive behaviors (Harlow, Meaney). “Maltreatment has lasting neurochemical correlates in human children: psychobiological sequelae of child maltreatment may be regarded as an environmentally induced complex developmental disorder, and although no study has ascertained whether MAOA plays a role, it exerts an effect on all aforementioned neurotransmitter systems. Posttraumatic stress disorder in maltreated children is associated with dysregulation of biological stress systems, adverse brain development, and neuronal loss in the anterior cingulate region of the medial prefrontal cortex.” (Caspi et al., 2000) Deficient MAOA activity may dispose the organism toward neural hyperreactivity to threat. McDermott et al., 2009 Monoamine oxidase A gene (MAOA) has earned the nickname “warrior gene” because it has been linked to aggression in observational and survey-based studies. McDermott and coworkers have performed an experiment, synthesizing work in psychology and behavioral economics, which suggests that aggression occurs with greater intensity and frequency as provocation is experimentally manipulated upwards, especially among low activity MAOA (MAOA-L) subjects. Low MAOA activity may be particularly problematic early in life, because there is insufficient MAOB (a homolog of MAOA with broad specificity to neurotransmitter amines) to compensate for an MAOA deficiency. Based on the hypothesis that MAOA genotype can moderate the influence of childhood maltreatment on neural systems implicated in antisocial behavior, Caspi et al. tested whether antisocial behavior would be predicted by an interaction between a gene (MAOA) and an environment (maltreatment). A well-characterized variable number tandem repeat (VNTR) polymorphism exists at the promoter of the MAOA gene, which is known to affect gene expression. Caspi’s group genotyped this polymorphism in members of the Dunedin Multidisciplinary Health and Development Study. This birth cohort of 1,037 children (52% male) has been assessed at ages 3, 5, 7, 9, 11, 13, 15, 18, and 21 and was virtually intact (96%) at age 26 years. The Dunedin Multidisciplinary Health and Development Study (often referred to as the Dunedin Longitudinal Study) is a longrunning cohort study of 1037 people born over the course of a year in Dunedin, New Zealand. The original pool of study members were selected from those born between 1 April 1972 and 31 March 1973 and still living in the Otago region 3 years later. Study members were assessed at age 3, and then at ages 5, 7, 9, 11, 13, 15, 18, 21, 26, 32 and, most recently, at age 38 (20102012). Future assessments are scheduled for ages 44 and 50. Avshalom Caspi and Terrie Moffitt During an assessment, study members are brought back to Dunedin from wherever in the world they live. They participate in a day of interviews, tests and surveys. Sub-studies of the Dunedin Study include the on-going Parenting Study which focuses on the Dunedin Study member and their first three-year-old child; and the Next Generation Study which involves the offspring of Dunedin Study members as they turn 15 and looks at the lifestyles, behaviours, attitudes and health of today's teenagers, and aims to see how these have changed from when the original Study Members were 15 (in 1987-88). This means that information across three generations of the same families will be available. Great emphasis is placed on retention of study members. At the most recent (age 38) assessments, 96% of all living eligible study members, or 961 people, participated. This is unprecedented for a longitudinal study, with many others worldwide experiencing 20– 40% drop-out rates. The Caspi et al. 2002 study. The study offers three advantages for testing gene-environment (G × E) interactions. First, in contrast to studies of clinical samples, this study of a representative general population sample avoids potential distortions in association between variables. Second, the sample has well-characterized environmental adversity histories. Between the ages of 3 and 11 years, 8% of the study children experienced "severe" maltreatment, 28% experienced "probable" maltreatment, and 64% experienced no maltreatment. (Maltreatment groups did not differ on MAOA activity, suggesting that genotype did not influence exposure to maltreatment.) Third, the study has ascertained antisocial outcomes rigorously. Antisocial behavior is a complicated phenotype, and each method and data source used to measure it (e.g., clinical diagnoses, personality checklists, official conviction records) is characterized by different strengths and limitations. Using information from independent sources appropriate to different stages of development, Caspi et al., examined four outcome measures. A common-factor model fit the four measures of antisocial behavior well, with factor loadings ranging from 0.64 to 0.74, showing that all four measures index liability to antisocial behavior. 1 Adolescent conduct disorder was assessed according to criteria of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV); 2 Convictions for violent crimes were identified via the Australian and New Zealand police; 3 A personality disposition toward violence was measured as part of a psychological assessment at age 26; 4 Symptoms of antisocial personality disorder were ascertained at age 26 by collecting information about the study members from people they nominated as "someone who knows you well." Means on the composite index of antisocial behavior as a function of MAOA activity and a childhood history of maltreatment . MAOA activity is the gene expression level associated with allelic variants of the functional promoter polymorphism, grouped into low and high activity; childhood maltreatment is grouped into 3 categories of increasing severity. The antisocial behavior composite is standardized (z score) to a M = 0 and SD = 1; group differences are interpretable in SD unit differences (d). A test of the interaction between MAOA activity and maltreatment revealed a significant G × E interaction (P = 0.01). This interaction within each genotype group showed that effect of childhood maltreatment on antisocial behavior was significantly weaker among males with high MAOA activity (P = 0.03) than among males with low MAOA activity (P < 0.001). * * * Fin qui 14 ottobre * * * Effect of maltreatment significant Association between childhood maltreatment and subsequent antisocial behavior as a function of MAOA activity. (A) Percentage of males (and standard errors) meeting diagnostic criteria for Conduct Disorder between ages 10 and 18. In a hierarchical logistic regression model, the interaction between maltreatment and MAOA activity was in the predicted direction, P = 0.06. Probing the interaction within each genotype group showed that the effect of maltreatment was highly significant in the low-MAOA activity P < 0.001, and marginally significant in the high-MAOA group P = 0.09). (B) Percentage of males convicted of a violent crime by age 26. The G × E interaction was in the predicted direction, p = 0.05. Probing the interaction, the effect of maltreatment was significant in the low-MAOA activity P < 0.001), but was not significant in the high MAOA group P = 0.17. (C) Mean z scores (M = 0, SD = 1) on the Disposition Toward Violence Scale at age 26. G × E interaction was in the predicted direction, P = 0.10); the effect of maltreatment was significant in the lowMAOA activity P = 0.002) but not in the high MAOA group P = 0.17). (D) Mean z scores (M = 0, SD = 1) on the Antisocial Personality Disorder symptom scale at age 26. The G × E interaction was in the predicted direction P = 0.04); the effect of maltreatment was significant in the lowMAOA activity P < 0.001) but not in the high MAOA group P = 0.12). Although individuals having the combination of low-activity MAOA genotype and maltreatment were only 12% of the male birth cohort, they accounted for 44% of the cohort's violent convictions, yielding an attributable risk fraction (11%) comparable to that of the major risk factors associated with cardiovascular disease. Moreover, 85% of cohort males having a lowactivity MAOA genotype who were severely maltreated developed some form of antisocial behavior. “These findings provide initial evidence that a functional polymorphism in the MAOA gene moderates the impact of early childhood maltreatment on the development of antisocial behavior in males.” (Caspi et al., 2000) Questo lavoro è stato il primo a mostrare chiaramente che un fattore genetico poteva rendere resilienti nei confronti di un patogeno ambientale. “With regard to research in psychiatric genetics, knowledge about environmental context might help gene-hunters refine their phenotypes. Genetic effects in the population may be diluted across all individuals in a given sample, if the effect is apparent only among individuals exposed to specific environmental risks. Environment effect in the population may be masked across all individuals in a given sample, if the effect is apparent only among individuals carrying a specific polymorphism” “With regard to research on child health, knowledge about specific genetic risks may help to clarify risk processes. The search has focused on social experiences that may protect some children, overlooking a potential protective role of genes. Genes are assumed to create vulnerability to disease, but from an evolutionary perspective they are equally likely to protect against environmental insult. Maltreatment studies may benefit from ascertaining genotypes associated with sensitivity to stress, and the known functional properties of MAOA may point toward hypotheses, based on neurotransmitter system development, about how stressful experiences are converted into antisocial behavior toward others in some, but not all, victims of maltreatment. Caspi et al., 2003 Influence of Life Stress on Depression: Moderation by a Polymorphism in the 5-HTT Gene “Across the life span, stressful life events that involve threat, loss, humiliation, or defeat influence the onset and course of depression. However, not all people who encounter a stressful life experience succumb to its depressogenic effect.” Costello et al., 2002 The NIMH convened a multidisciplinary Workgroup of scientists to review the field and the NIMH portfolio and to generate specific recommendations. To encourage a balanced and creative set of proposals, experts were included within and outside this area of research, as well as public stakeholders. The Workgroup identified the need for expanded knowledge of mood disorders in children and adolescents, noting important gaps in understanding the onset, course, and recurrence of earlyonset unipolar and bipolar disorder. Recommendations included the need for a multidisciplinary research initiative on the pathogenesis of unipolar depression encompassing genetic and environmental risk and protective factors. Whether specific genes exacerbate or buffer the effect of stressful life events on depression is beginning to be unravelled. In this study, a functional polymorphism in the promoter region of the serotonin transporter gene (5-HTT) was used to characterize genetic vulnerability to depression and to test whether 5-HTT gene variation moderates the influence of life stress on depression. The 5-HT system provides a logical source of candidate genes for depression, because this system is the target of selective serotonin reuptake–inhibitor drugs that are effective in treating depression. The 5-HTT has received particular attention because it is involved in the reuptake of serotonin at brain synapses. The promoter activity of the 5-HTT gene is modified by sequence elements within the proximal 5' regulatory region, designated the 5-HTT gene-linked polymorphic region (5-HTTLPR). The short ("s") allele in the 5-HTTLPR is associated with lower transcriptional efficiency of the promoter compared with the long ("l") allele. Up to Caspi’s work, evidence for an association between the short promoter variant and depression was inconclusive. Although the 5-HTT gene may not be directly associated with depression, it could moderate the serotonergic response to stress. Three lines of experimental research suggested this hypothesis of a gene-by-environment (G x E) interaction. First, in mice with disrupted 5-HTT, homozygous and heterozygous (5-HTT –/– and +/–) strains exhibited more fearful behavior; in response to stress they showed greater increases in the stress hormone (plasma) adrenocorticotropin compared to homozygous (5HTT +/+) controls, but in the absence of stress no differences related to genotype were observed. 5-HTT KO mice Behaviour in the elevated plus maze The 5-HT1A receptor antagonist, WAY 100635, produced anxiolytic-like effects in the EPM Second, in rhesus macaques, whose length variation of the 5-HTTLPR is analogous to that of humans, the short allele is associated with decreased serotonergic function [lower cerebro-spinal fluid (CSF) concentrations of 5-HT metabolites] among monkeys reared in stressful conditions but not among normally reared monkeys. Monkeys with deleterious early rearing experiences were differentiated by genotype in cerebrospinal fluid concentrations of the 5-HT metabolite, 5hydroxyindoleacetic acid, while monkeys reared normally were not. Questi risultati dimostrano che l’effetto del genotipo (s/s, l/l, s/l) del 5-HTT sulla funzione serotoninergica nel SNC dipende dall’ambiente. Una cosa molto importante è che anche la risposta allo stress è modificata in s/s carriers esposti a stress precoce (peer rearing) Caspi et al. Nature Reviews Neuroscience 7, 583–590 (July 2006) | doi:10.1038/nrn1925 Influence of exposure to early stress (peer rearing) on subsequent exaggerated responses of the HPA responses to stress is conditioned by serotonin transporter gene promoter variation (rh-5HTTLPR) in rhesus macaques. When exposed to stress later in life, peer-reared animals with the s/l genotype had higher ACTH levels than animals with the l/l genotype. There were no differences between genotypes among animals reared with their mothers l/l Trattatemi con cura, sono un s/s s/s An alert monkey and a depressed monkey. "Depressed monkeys do not appear responsive to potential threats. It's that slumped, collapsed body posture accompanied by a lack of responsiveness to environmental events.“ As in humans, monkey depression is deeper than just mopey behavior. The depressed macaques had less body fat, higher levels of stress hormones, lower bone density (consistent with osteoporosis), higher cholesterol concentrations and high heart rates. They were often subordinate in the community hierarchy and socially stressed by dominant animals. Third, human neuroimaging research suggests that the fear response (and therefore the stress response) is mediated by variations in the 5-HTTLPR. Humans with one or two copies of the s allele exhibit greater amygdala neuronal activity to fearful stimuli compared to individuals homozygous for the l Effect of 5-HTT genotype on right allele. amygdala activity. Bar graphs represent the mean BOLD fMRI percent signal change in a region of interest (ROI) comprising the entire right amygdala in the s (n = 14) and l (n = 14) groups collapsed across both cohorts. Individual circles represent the activity for each subject in this ROI. Consistent with the statistical parametric maps (Fig. 2), which identified significant voxels within the right amygdala, analysis of variance for the entire amygdala ROI, including voxels that were not differentially activated according to statistical parametric mapping, still revealed significant group differences in the mean (±SEM) BOLD fMRI percent signal change [s group = 0.28 ± 0.08 and l group = 0.03 ± 0.05; F(1,26) = 6.84, P = 0.01]. Presi nel loro insieme, questi risultati costituiscono un sufficiente razionale per formulare l’ipotesi che variazioni a carico del gene del 5-HTT possano moderare le reazioni ad esperienze avverse, rendendo gli individui resilienti o vulnerabili. Caspi tested this G x E hypothesis among members of the Dunedin Multidisciplinary Health and Development Study. This representative birth cohort of 1037 children (52% male) has been assessed at ages 3, 5, 7, 9, 11, 13, 15, 18, and 21 and was virtually intact (96%) at the age of 26 years. Stressful life events occurring after the 21st birthday and before the 26th birthday were assessed with the aid of a life-history calendar, a highly reliable method for ascertaining life-event histories. The 14 events included employment, financial, housing, health, and relationship stressors. 30% of the study members experienced no stressful life events; 25% experienced one event; 20%, two events; 11%, three events; and 15%, four or more events. There were no significant differences between the three genotype groups in the number of life events they experienced, F(2,846) = 0.56, P = 0.59, suggesting that 5-HTTLPR genotype did not influence exposure to stressful life events. * Main effect of 5-HTT genotype significance * (p 0.06) Results of multiple regression analyses estimating the association between number of stressful life events (between ages 21 and 26 years) and depression outcomes at age 26 as a function of 5HT T genotype. (A) Self-reports of depression symptoms. The main effect of 5-HT TLPR (i.e., an effect not conditional on other variables) was marginally significant (P = 0.06), the main effect of stressful life events was significant (P < 0.001), and the interaction between 5-HT TLPR and life events was in the predicted direction (P = 0.02). The interaction showed that the effect of life events on self-reports of depression symptoms was stronger among individuals carrying an s allele (P < 0.001 among s/s homozygotes, and P < 0.001 among s/l heterozygotes) than among l/l homozygotes ( P = 0.08). (B) Probability of major depressive episode. The main effect of 5-HT TLPR was not significant (P = 0.29), the main effect of life events was significant (P < 0.001), and the G x E was in the predicted direction (P = 0.056). Life events predicted a diagnosis of major depression among s carriers (P = 0.001 among s/s homozygotes, and P < 0.001 among s/l heterozygotes) but not among l/l homozygotes (P = 0.24). Probability of suicide ideation or attempt. The main effect of 5-HT TLPR was not significant (P = 0.99), the main effect of life events was significant (P < 0.001), and the G x E interaction was in the predicted direction (P = 0.051). Life events predicted suicide ideation or attempt among s carriers (, P = 0.09 among s/s homozygotes, and P < 0.001 among s/l heterozygotes) but not among l/l homozygotes (P = 0.62). Caspi reasoned that if measure of life events represents environmental stress, then the timing of life events relative to depression must follow cause-effect order and life events that occur after depression should not interact with 5-HTTLPR to postdict depression. Caspi tested this hypothesis by substituting the age-26 measure of depression with depression assessed in this longitudinal study when study members were 21 and 18 years old, before the occurrence of the measured life events between the ages of 21 and 26 years. Whereas the 5-HTTLPR x life events interaction predicted depression at the age of 26 years, this same interaction did not postdict depression reported at age 21 nor at the age of 18 years, indicating that the above related finding is a true G x E interaction. If 5-HTT genotype moderates the depressogenic influence of stressful life events, it should moderate the effect of life events that occurred not just in adulthood but also of stressful experiences that occurred in earlier developmental periods. Based on this hypothesis, Caspi tested whether adult depression was predicted by the interaction between 5-HTTLPR and childhood maltreatment that occurred during the first decade of life. Consistent with the G x E hypothesis, the longitudinal prediction from childhood maltreatment to adult depression was significantly moderated by 5-HTTLPR. The interaction showed that childhood maltreatment predicted adult depression only among individuals carrying an s allele but not among l/l homozygotes. Results of regression analysis estimating the association between childhood maltreatment (between the ages of 3 and 11 years) and adult depression (ages 18 to 26), as a function of 5HT T genotype. Among the 147s/s homozygotes, 92 (63%), 39 (27%), and 16 (11%) study members were in the no maltreatment, probable maltreatment, and severe maltreatment groups, respectively. Among the 435 s/l heterozygotes, 286 (66%), 116 (27%), and 33 (8%) were in the no, probable, and severe maltreatment groups. Among the 265 l/l homozygotes, 172 (65%), 69 (26%), and 24 (9%) were in the no, probable, and severe maltreatment groups. The main effect of 5-HT TLPR was not significant (b = –0.14, SE = 0.11, z = 1.33, P = 0.19), the main effect of childhood maltreatment was significant (b = 0.30, SE = 0.10, z = 3.04, P = 0.002), and the G x E interaction was in the predicted direction (b = –0.33, SE = 0.16, z = 2.01, P = 0.05). The interaction showed that childhood stress predicted adult depression only among individuals carrying an s allele (b = 0.60, SE = 0.26, z = 2.31, P = 0.02 among s/s homozygotes, and b = 0.45, SE = 0.16, z = 2.83, P = 0.01 among s/l heterozyotes) and not among l/l homozygotes (b = –0.01, SE = 0.21, z = 0.01, P = 0.99). Evidence of a direct relation between the 5-HTTLPR and depression had been inconsistent, perhaps because prior studies have not considered participants' stress histories. In this study, no direct association between the 5-HTT gene and depression was observed. Previous experimental paradigms, including 5-HTT knockout mice, stress-reared rhesus macaques, and human functional neuroimaging, have shown that the 5-HTT gene can interact with environmental conditions, although these experiments did not address depression. Caspi’s study demonstrates that this G x E interaction extends to the natural development of depression in a representative sample of humans. Cosa abbiamo imparato dai lavori di Caspi e da altri simili “The study of gene–environment interactions has been the province of epidemiology, in which genotypes, environmental pathogen exposures and disorder outcomes are studied as they naturally occur in the human population. “ However, genetic epidemiology is limited for understanding the biological mechanisms involved in an interaction, and therefore its potential will be better realized when it is integrated with experimental neuroscience (psychobiology). Psychobiology can complement psychiatric genetic epidemiology by specifying the more proximal role of nervous system reactivity in the gene–environment interaction. Caspi et al. Nature Reviews Neuroscience 7, 583–590 (July 2006) | doi:10.1038/nrn1925 The building blocks correspond to the three elements of the triad: the disorder, the environmental pathogen and the genotype. First, evidence is needed about which neural substrate is involved in the disorder. Second, evidence is needed that an environmental cause of the disorder has effects on variables indexing the same neural substrate. Third, evidence is needed that a candidate gene has functional effects on variables indexing that same neural substrate. It is this convergence of environmental and genotypic effects within the same neural substrate that allows for the possibility of gene– environment interactions. Caspi et al. Nature Reviews Neuroscience 7, 583–590 (July 2006) | doi:10.1038/nrn1925 Psychobiology provides the building blocks for constructing hypotheses about gene– environment interaction (a) that are tested against data (b), subsequently stimulating new studies to illuminate the black box of biology (c) between the gene (G), the environmental pathogen (E) and the disorder (D). Several studies have sought to replicate the interaction between the high- and low-activity MAOA genotypes and maltreatment found by Caspi et al.; a recent metaanalysis revealed a significant pooled effect. Positive replications of the interaction between 5HTT*long/5HTT*short genotypes and life stress have also appeared, along with two failures to replicate. Other studies have found G xE for other genes, such as BDNF (Val/Met polimorphism), in relation to mood disorders. Brain galanin system genes interact with life stresses in depression-related phenotypes. Juhasz G, Hullam G, Eszlari N, Gonda X, Antal P, Anderson IM, Hökfelt TG, Deakin JF, Bagdy G Proc Natl Acad Sci U S A. 2014 Apr 22;111(16):E1666-73 Galanin is a stress-inducible neuropeptide and cotransmitter in serotonin and norepinephrine neurons with a possible role in stress-related disorders. Galanin is widely distributed in the rodent and human brain. In rat it coexists with noradrenaline (NA) in the locus coeruleus (LC) and with 5-HT in the dorsal raphe complex. Like other peptide cotransmitters, galanin is released when neurons fire in high-frequency bursts in response to strong behavioral and pharmacological challenge Variants in genes for galanin (GAL) and its receptors (GALR1, GALR2, GALR3), conferred increased risk of depression and anxiety in people who experienced childhood adversity or recent negative life events in a European white population cohort totaling 2,361 from Manchester, United Kingdom and Budapest, Hungary. The results suggest that the galanin pathway plays an important role in the pathogenesis of depression in humans by increasing the vulnerability to early and recent psychosocial stress. The findings further emphasize the importance of modeling environmental interaction in finding new genes for depression Forebrain NAc (and dorsal Raphe) Caption for previous figure. Galanin, a neuropeptide, and its receptors are colocalized in some monoaminergic neurons in the brain. The galanin system is highly sensitive to experimental and naturalistic stressors. Recent analysis of human brain has shown that the GALR3 is the main galanin receptor in NA-LC and probably 5-HT dorsal raphe nucleus cells, and that the GALR1 is the main receptor in the forebrain. Antidepressive effects may be achieved by (i) GALR3 antagonists, by reinstating normal monoamine turnover in the brainstem, and by (ii) GALR1 antagonists in the forebrain by normalization of limbic system activity, or by (iii) agonists at GALR2, promoting neuroprotection. Genetic analysis suggests that GALR1 risk variants may compromise galanin signaling during childhood, whereas GALR2 signaling may be influenced by recent negative life events. In addition, all four galanin system genes have relevant roles in the development of depression-related phenotypes in those persons who were highly exposed to life stressors. Three-way interaction effect of 5-HTTLPR, BDNF Val66Met, and childhood adversity on depression: a replication study. Comasco E, Åslund C, Oreland L, Nilsson KW. Eur Neuropsychopharmacol. 2013 Oct;23(10):1300-6. Both the serotonin transporter linked promoter region (5HTTLPR) and the brain-derived neurotrophic factor (BDNF) Val66Met polymorphisms have been shown to interact with unfavourable environment in relation to depression symptoms and to depression diagnosis. Several attempts have been made to study a three-way interaction effect of these factors on depression, with contradictory results. This paper aimed to test the hypothesis of a three-way interaction effect and to attempt at replication in an independent population-based sample. Family maltreatment and depression were self-reported by an adolescent population-based cohort (N=1393) from the county of Västmanland, Sweden. DNA was isolated from saliva, and used for genotyping of the 5-HTTLPR and BDNF Val66Met polymorphisms. Neither 5-HTTLPR or BDNF genotypes separately, nor in interaction with each other had any relation to depression, however in an environment adjusted model a two-way interaction and a three-way interaction effect was found. Both 5-HTTLPR and BDNF Val66Met interacted with unfavourable environment in relation to depressive symptoms. Interazioni G x E nella lunghezza dei telomeri: effetti di esperienze precoci avverse sulla integrità del DNA tramite i telomeri I telomeri impediscono la degradazione progressiva dei cromosomi con rischio di perdita di informazione genetica. Social disadvantage, genetic sensitivity, and children's telomere length. Mitchell C, Hobcraft J, McLanahan SS, Siegel SR, Berg A, Brooks-Gunn J, Garfinkel I, Notterman D. Proc Natl Acad Sci U S A. 2014 Apr 22;111(16):5944-9. Disadvantaged social environments are associated with adverse health outcomes. This has been attributed, in part, to chronic stress. Results: Exposure to disadvantaged environments is associated with reduced telomere length (TL) by age 9 years. There is a significant associations between low income, low maternal education, unstable family structure, harsh parenting and TL. These effects were moderated by genetic variants in serotonergic and dopaminergic pathways. Consistent with the differential susceptibility hypothesis, subjects with the “vulnerable” genotype had the shortest TL when exposed to disadvantaged social environments and the longest TL when exposed to advantaged environments Other G x E interactions Evidence from studies around the world shows that cannabis use is a statistical risk factor for the emergence of psychosis, ranging from psychotic symptoms (such as hallucinations and delusions) to clinically significant disorders. However, most people who use cannabis do not develop psychosis, which suggests that some individuals may be genetically vulnerable to its effects. Which is the genetic risk factor? COMT gene polymorphism??? Individuals with one or more high-activity valine alleles (VAL/METor VAL/VAL) showed subsequent increased risk of psychotic symptoms and psychosis-spectrum disorder if they used cannabis. Cannabis use had no such adverse influence on individuals with two copies of the methionine allele (MET/MET). Results of an epidemiological study that traced a longitudinal cohort from prior to the onset of cannabis use (age 11 years), through to the peak risk period of psychosis onset (age 26 years) Cannabis affects in subjects with different genotype Subjects were tested on two occasions, separated by 1 week, as part of a double-blind, placebo controlled cross-over design. In randomized order, they received either 0 g or 300 g -9tetrahydrocannabinol (the principal component of cannabis) per kilogram bodyweight. Cannabis affected cognition and state psychosis, but this was conditional on COMT genotype. Individuals carrying two copies of the valine allele exhibited more cannabis-induced memory and attention impairments than carriers of the methionine allele, and were the most sensitive to cannabis-induced psychotic experiences. Vulnerabilità genetica verso la dipendenza da sostanze: dati nell’uomo In one experiment, the researchers investigated whether a polymorphism in the D4 dopamine receptor gene (DRD4) affected craving after priming doses and drug cues. Participants were tested on two occasions, randomly assigned to receive three alcoholic drinks on the first session and three control drinks on the second session, or the reverse. Individuals carrying the DRD4 long (L) allele reported a stronger urge to drink in the alcohol condition than in the placebo condition. By contrast, individuals with two short DRD4 alleles (S) reported no differences in the urge to drink between the two conditions. These findings suggest that the DRD4 polymorphism moderates craving after alcohol consumption, and indicate that DRD4*L individuals may be more susceptible to losing control over drinking But the DRD4 polymorphism is not simply a genetic risk for alcohol abuse. Individuals carrying the L allele also experience more craving and arousal after exposure to tobacco smoking cues, whereas DRD4*S individuals do not. This suggests that DRD4 may influence the incentive salience of appetitive stimuli more generally, and offers a clue as to why different addictive disorders tend to co-occur in the same individuals. Much genetic research has been guided by the assumption that genes cause diseases, but the expectation that direct paths will be found from gene to disease has not proven fruitful for complex psychiatric disorders. Findings of G x E interaction point to a different, evolutionary model. This model assumes that genetic variants maintained at high prevalence in the population probably act to promote organisms' resistance to environmental pathogens. They extend the concept of environmental pathogens to include traumatic, stressful life experiences and propose that the effects of genes may be uncovered when such pathogens are measured (in naturalistic studies) or manipulated (in experimental studies). Futura facenda The characterization of subjects' genetic vulnerability as opposed to their resilience needs to move beyond single genetic polymorphisms. New approaches will use information about biological pathways to identify gene systems and study sets of genetic polymorphisms that are active in the pathophysiology of a disorder. For example, in relation to depression, information about the psychobiology of psycho-social stress can be used as a first step to characterize a set of genes that define a genotype that is vulnerable as opposed to resilient to stressful life events. Incorporating information about genetic pathways into gene–environment interaction studies will enhance explanatory power, but it will also present unique statistical challenges related to the use of data-mining tools and the pooling of data across different studies. If environmental risk exposure differs between samples, candidate genes may fail replication. If environmental risk exposure differs among participants within a sample, genes may account for little variation in the phenotype. Hypothesis Some multifactorial disorders, instead of resulting from variations in many genes of small effect, may result from variations in fewer genes whose effects are conditional on exposure to environmental risks. Necessity of implementing gene x environment interaction research protocols Necessity of accurate phenotyping Interazioni geni ambiente nel Bucharest Early Intervention Project Fin qui 19 ottobre Charles Nelson III Cosa è il Bucharest Early Intervention project Science, 2008 Modification of depression by COMT val158met polymorphism in children exposed to early severe psychosocial deprivation. Drury SS, Theall KP, Smyke AT, Keats BJ, Egger HL, Nelson CA, Fox NA, Marshall PJ, Zeanah CH. (2010) OBJECTIVE: To examine the impact of the catechol-O-methyltransferase (COMT) val(158)met allele on depressive symptoms in young children exposed to early severe social deprivation as a result of being raised in institutions. METHODS: One hundred thirty six children from the Bucharest Early Intervention Project (BEIP) were randomized before 31 months of age to either care as usual (CAU) in institutions or placement in newly created foster care (FCG). At 54 months of age, a psychiatric assessment using the Preschool Age Psychiatric Assessment (PAPA) was completed. DNA was collected and genotyped for the COMT val(158)met polymorphism. Multivariate analysis examined the relationship between COMT alleles and depressive symptoms. RESULTS: Mean level of depressive symptoms was lower among participants with the met allele compared to those with two copies of the val allele (P<0.05). Controlling for group and gender, the rate of depressive symptoms was significantly lower among participants with the met/met or the met/val genotype [adjusted relative risk (aRR)=0.67, 95% CI=0.45, 0.99] compared to participants with the val/val genotype, indicating an intermediate impact for heterozygotes consistent with the biological impact of this polymorphism. The impact of genotype within groups differed significantly. There was a significant protective effect of the met allele on depressive symptoms within the CAU group, however there was no relationship seen within the FCG group. . CONCLUSIONS: This is the first study to find evidence of a gene x environment interaction in the setting of early social deprivation. These results support the hypothesis that individual genetic differences may explain some of the variability in recovery amongst children exposed to early severe social deprivation