Emanuel Miller Lecture: early onset depressions--meanings, mechanisms and processes

Mood Disorders in Young People With Acquired Brain Injury: An Integrated Model

Purpose/Objective

Young people with paediatric acquired brain injury (pABI) are twice as likely to develop a mood disorder as their peers, frequently have significant unmet socio-emotional needs, and are at over double the risk of going on to use adult mental health services. Recent years have seen significant advances in the development of interventions for young people with mood disorders. However, evidence-based approaches to mood disorders in pABI are lacking and surprisingly little work has evaluated clinical and neuro-developmental models of mood disorders in this population.

Method

We review the literature regarding key mechanisms hypothesised to account for the increased vulnerability to mood disorders in pABI: First, we summarise the direct neurocognitive consequences of pABI, considering the key areas of the brain implicated in vulnerability to mood disorders within a neurodevelopmental framework. Second, we outline five key factors that contribute to the heightened prevalence of mood disorders in young people following ABI. Finally, we synthesise these, integrating neuro-cognitive, developmental and systemic factors to guide clinical formulation.

Results and Implications

We present a framework that synthesises the key mechanisms identified in our review, namely the direct effects of pABI, neurocognitive and neuroendocrine factors implicated in mood and anxiety disorders, maladaptive neuroplasticity and trauma, structural and systemic factors, and psychological adjustment and developmental context. This framework is the first attempt to provide integrated guidance on the multiple factors that contribute to elevated life-long risk of mood disorders following pABI.

Inflammatory cytokines and depression in children with cancer: A review of the literature

Compared to the general pediatric population, pediatric cancer patients are at increased risk of experiencing depressive symptoms during and after their treatment. Clinically, there exist few resources to guide health care professionals in the care of children with cancer who report depressive symptomatology. Pediatric cancer patients experience unique inflammatory changes secondary to their disease and accompanying treatments. It has been reported that inflammatory changes in the context of illness are related to cytokine dysregulation which in turn may influence the expression of depressive symptoms. In this review of current literature, we summarize the existing knowledge, relevant models and studies in progress with respect to this concept.

Investigating the relationship between iron and depression

Lower levels of circulating iron have been associated with depression. Our objective was to investigate the phenotypic and genetic relationship between measures of circulating levels of iron (serum iron, transferrin, transferrin saturation, and ferritin) and depressive symptoms. Data were available from ongoing studies at QIMR Berghofer Medical Research Institute (QIMRB), including twin adolescents (mean age 15.1 years, standard deviation (SD) 3.2 years), and twin adults (mean age 23.2 years, SD 2.2 years). In the adolescent cohort, there were 3416 participants from 1688 families. In the adult cohort there were 9035 participants from 4533 families. We estimated heritabilities of, and phenotypic and genetic correlations between, traits. We conducted analyses that linked results from published large-scale genome-wide association studies (including iron and Major Depressive Disorder) with our study samples using single SNP and multi-SNP genetic risk score analyses, and LD score regression analyses. In both cohorts, measures of iron, transferrin, transferrin saturation, and log 10 of ferritin (L10Fer) were all highly heritable, while depressive measures were moderately heritable. In adolescents, depression measures were higher in those in the middle 10th versus top 10th percentile of transferrin saturation measures (p = 0.002). Genetic profile risk scores of the iron measures were not significantly associated with depression in study participants. LD score analyses showed no significant genetic relationship between iron and depression. Genetic factors strongly influence iron measures in adolescents and adults. Using several different strategies we find no evidence for a genetic contribution to the relationship between blood measures of iron and measures of depression.

Functional MRI of emotional memory in adolescent depression

INTRODUCTION

Major Depressive Disorder (MDD) is a leading cause of disease burden worldwide. Mood-congruent biases in memory tasks are frequently reported in MDD patients, with facilitated memory for negative stimuli. Most functional MRI studies to date have examined the neural correlates of these biases in depressed adults, with fewer studies in adolescents with MDD. Investigation of MDD in adolescence may aid greater understanding of the aetiology and development of the disorder.

METHODS

Cognitive biases were investigated in 56 MDD patients aged 11-17 years and a matched group of 30 healthy control participants with a self-referential memory task. Behavioural performance and BOLD fMRI data were collected during both encoding and retrieval stages.

RESULTS

The neural response to encoding in adolescents with MDD was found to differ significantly from controls. Additionally, neural responses during encoding and retrieval showed differential relationships with age between patient and control groups, specifically in medial, temporal, and prefrontal regions.

CONCLUSIONS

These findings suggest that during adolescence neurophysiological activity associated with emotional memory differs in those with depression compared to controls and may be age sensitive.

Neurodevelopment and ages of onset in depressive disorders

How and why do clinical depressive disorders emerge in adolescence? In this Personal View, we present a neurodevelopmental theory to address causes for adolescent onsets of clinical depressive disorders. We argue that theories should account for three perplexing aspects of depressive disorders in adolescence: the episodic nature of depression; differences between sexes in rates of depression across development; and age-differentiated onsets. We consider how theories such as psychosocial acceleration, heterochronic brain development, dual-process models, glucocorticoid vulnerability hypothesis linked to early life stress, and epigenetic and genetic susceptibility might explain some aspects of adolescent depressive disorders. We argue that some synthesis between existing theories might be needed to establish a sufficient neurodevelopmental theoretical framework to explain onsets of depressive disorders in adolescence.

Genes, environments and depressions in young people

Among the common mental illnesses in childhood and adolescence, the unipolar depressions are the most concerning. These mental illnesses are aetiologically and clinically heterogeneous and little is known about their pathophysiology. This selected review considers the contribution of genetic and environmental factors in the emergence of these illnesses in the second decade of life.

The influence of prenatal intimate partner violence exposure on hypothalamic–pituitary–adrenal axis reactivity and childhood internalizing and externalizing symptoms

This prospective longitudinal study examines the long-term influence of intimate partner violence (IPV) exposure in utero. We hypothesized that (a) prenatal IPV increases risk for internalizing and externalizing problems as well as for a profile of dysregulated cortisol reactivity, and (b) patterns of cortisol hyper- and hyporeactivity are differentially associated with internalizing and externalizing problems. The participants were 119 10-year-old children. Their mothers reported their IPV experiences and distress during pregnancy. Child and maternal reports of internalizing and externalizing problems as well as lifetime IPV exposure were obtained. Salivary cortisol was assessed at baseline, 20 min, and 40 min after challenge. The results partially supported our hypotheses: Exposure to IPV during pregnancy predicted child-reported internalizing and externalizing problems, mother ratings of child externalizing problems, and a profile of high cortisol secretion before and after stress challenge. The results were significant above and beyond the influence of maternal distress during pregnancy and IPV that occurred during the child's life. In addition, a profile of high cortisol secretion was associated with maternal reports of child internalizing behaviors. Findings support the growing consensus that prenatal stress can lead to lasting disruptions in adaptation and highlight the need for more longitudinal examinations of prenatal IPV exposure.

Higher cognitive ability buffers stress-related depressive symptoms in adolescent girls

Stress has been shown to have a causal effect on risk for depression. We investigated the role of cognitive ability as a moderator of the effect of stressful life events on depressive symptoms and whether this varied by gender. Data were analyzed in two adolescent data sets: one representative community sample aged 11–12 years (n = 460) and one at increased familial risk of depression aged 9–17 years (n = 335). In both data sets, a three-way interaction was found whereby for girls, but not boys, higher cognitive ability buffered the association between stress and greater depressive symptoms. The interaction was replicated when the outcome was a diagnosis of major depressive disorder. This buffering effect in girls was not attributable to coping efficacy. However, a small proportion of the variance was accounted for by sensitivity to environmental stressors. Results suggest that this moderating effect of cognitive ability in girls is largely attributable to greater available resources for cognitive operations that offer protection against stress-induced reductions in cognitive processing and cognitive control which in turn reduces the likelihood of depressive symptomatology.

Elevated morning cortisol is a stratified population-level biomarker for major depression in boys only with high depressive symptoms

Major depressive disorder (MD) is a debilitating public mental health problem with severe societal and personal costs attached. Around one in six people will suffer from this complex disorder at some point in their lives, which has shown considerable etiological and clinical heterogeneity. Overall there remain no validated biomarkers in the youth population at large that can aid the detection of at-risk groups for depression in general and for boys and young men in particular. Using repeated measurements of two well-known correlates of MD (self-reported current depressive symptoms and early-morning cortisol), we undertook a population-based investigation to ascertain subtypes of adolescents that represent separate longitudinal phenotypes. Subsequently, we tested for differential risks for MD and other mental illnesses and cognitive differences between subtypes. Through the use of latent class analysis, we revealed a high-risk subtype (17% of the sample) demarcated by both high depressive symptoms and elevated cortisol levels. Membership of this class of individuals was associated with increased levels of impaired autobiographical memory recall in both sexes and the greatest likelihood of experiencing MD in boys only. These previously unidentified findings demonstrate at the population level a class of adolescents with a common physiological biomarker specifically for MD in boys and for a mnemonic vulnerability in both sexes. We suggest that the biobehavioral combination of high depressive symptoms and elevated morning cortisol is particularly hazardous for adolescent boys.

Research review: the role of cytokines in depression in adolescents: a systematic review

BACKGROUND

While cytokines have been implicated in the pathophysiology of depression in adults, the potential role in younger age groups such as adolescents is less clear. This article therefore reviews the literature (a) to explore the relationship between cytokines and depression in adolescents, and (b) to examine how cytokines may be related to adolescent depression in the context of other neurobiological theories of depression.

METHOD

A systematic review of the scientific literature on the subject was conducted in February 2013, searching the Web of Knowledge, PubMed (Medline), PsycInfo and Cochrane electronic databases.

RESULTS

Eighteen studies were identified measuring both depression or depressive symptoms and cytokines or immune markers in adolescents. Adolescents with depression show age-specific characteristics of the immune and inflammatory system, specifically in NK cell activity and in pro-inflammatory cytokines (such as IL-1β and TNF-α). In addition, the role of cytokines in adolescent depression is influenced by neurodevelopment, hormonal changes, stress and trauma.

CONCLUSIONS

There may be differences in the neurobiology of adolescent major depressive disorder (MDD) compared with adult MDD. Increased understanding of the role of cytokines in adolescent MDD may lead to improved outcomes in the treatment of adolescent depression.

The role of gene-environment correlations and interactions in middle childhood depressive symptoms

Depression is known to be associated with a wide array of environmental factors. Such associations are due at least in part to genetic influences on both. This issue has been little explored with preadolescent children. Measures of family chaos and parenting style at age 9 and child depressive symptoms at age 12 were completed by 3,258 twin pairs from the Twins Early Development Study and their parents. Quantitative genetic modeling was used to explore common and unique genetic and environmental influences on both family environment and later depressive symptoms. Depressive symptoms at age 12 were significantly heritable. Moderate genetic effects influenced parenting style and family chaos at the age of 9, indicating gene-environment correlation. There were significant genetic correlations between family environment and depressive symptoms. There was some evidence of a Gene × Environment interaction, with stronger genetic effects on depressive symptoms for children with more suboptimal family environment. There was an Environment × Environment interaction, with effects of nonshared environment on depressive symptoms stronger for twins with more adverse parenting experiences. There is some evidence for gene-environment correlation between aspects of family environment in middle childhood and subsequent depressive symptoms. This suggests that one of the mechanisms by which genes lead to depressive symptoms may be by themselves influencing depressogenic environments.

Affective neuronal selection: the nature of the primordial emotion systems

Based on studies in affective neuroscience and evolutionary psychiatry, a tentative new proposal is made here as to the nature and identification of primordial emotional systems. Our model stresses phylogenetic origins of emotional systems, which we believe is necessary for a full understanding of the functions of emotions and additionally suggests that emotional organizing systems play a role in sculpting the brain during ontogeny. Nascent emotional systems thus affect cognitive development. A second proposal concerns two additions to the affective systems identified by Panksepp. We suggest there is substantial evidence for a primary emotional organizing program dealing with power, rank, dominance, and subordination which instantiates competitive and territorial behavior and is an evolutionary contributor to self-esteem in humans. A program underlying disgust reactions which originally functioned in ancient vertebrates to protect against infection and toxins is also suggested.

Future directions in vulnerability to depression among youth: integrating risk factors and processes across multiple levels of analysis

Depression is a developmental phenomenon. Considerable progress has been made in describing the syndrome, establishing its prevalence and features, providing clues as to its etiology, and developing evidence-based treatment and prevention options. Despite considerable headway in distinct lines of vulnerability research, there is an explanatory gap in the field's ability to more comprehensively explain and predict who is likely to become depressed, when, and why. Still, despite clear success in predicting moderate variance for future depression, especially with empirically rigorous methods and designs, the heterogeneous and multi-determined nature of depression suggests that additional etiologies need to be included to advance knowledge on developmental pathways to depression. This paper advocates for a multiple levels of analysis approach to investigating vulnerability to depression across the lifespan and providing a more comprehensive understanding of its etiology. One example of a multiple levels of analysis model of vulnerabilities to depression is provided that integrates the most accessible, observable factors (e.g., cognitive and temperament risks), intermediate processes and endophenotypes (e.g., information-processing biases, biological stress physiology, and neural activation and connectivity), and genetic influences (e.g., candidate genes and epigenetics). Evidence for each of these factors as well as their cross-level integration is provided. Methodological and conceptual considerations important for conducting integrative, multiple levels of depression vulnerability research are discussed. Finally, translational implications for how a multiple levels of analysis perspective may confer additional leverage to reduce the global burden of depression and improve care are considered.

Meta-review of depressive subtyping models

BACKGROUND

Increasing dissatisfaction with the non-specificity of major depression has led many to propose more specific depressive subtyping models. The present meta-review seeks to map dominant depressive subtype models, and highlight definitions and overlaps.

METHODS

A database search in Medline and EMBASE of proposed depressive subtypes, and limited to reviews published between 2000 and 2011, was undertaken. Of the more than four thousand reviews, 754 were judged as potentially relevant and provided the base for the present selective meta-review.

RESULTS

Fifteen subtype models were identified. The subtypes could be divided into five molar categories of (1) symptom-based subtypes, such as melancholia, psychotic depression, atypical depression and anxious depression, (2) aetiologically-based subtypes, exemplified by adjustment disorders, early trauma depression, reproductive depression, perinatal depression, organic depression and drug-induced depression, (3) time of onset-based subtypes, as illustrated by early and late onset depression, as well as seasonal affective disorder, (4) gender-based (e.g. female) depression, and (5) treatment resistant depression. An overview considering definition, bio-psycho-social correlates and the evidence base of treatment options for each subtype is provided.

LIMITATIONS

Despite the large data base, this meta-review is nevertheless narrative focused.

CONCLUSIONS

Subtyping depression is a promising attempt to overcome the non-specificity of many diagnostic constructs such as major depression, both in relation to their intrinsic non-specificity and failure to provide treatment-specific information. If a subtyping model is to be advanced it would need, however, to demonstrate differential impacts of causes and treatments.

Childhood adversity and allostatic overload of the hypothalamic-pituitary-adrenal axis: a vulnerability model for depressive disorders

Childhood adversity is associated with increased risk for onset of depressive episodes. This review will present evidence that allostatic overload of the hypothalamic-pituitary-adrenal axis (HPAA) partially mediates this association. The HPAA is the physiological system that regulates levels of the stress hormone cortisol. First, data from animals and humans has shown that early environmental adversity is associated with long-term dysregulation of the HPAA. This may occur due to permanent epigenetic modification of the glucocorticoid receptor. Second, data from humans has demonstrated that HPAA dysregulation is associated with increased risk of future depression onset in healthy individuals, and pharmacological correction of HPAA dysregulation reduces depressive symptoms. HPAA dysregulation may result in corticoid-mediated abnormalities in neurogenesis in early life and/or neurotoxicity on neural systems that subserve emotion and cognition.

Chronic family stress interacts with 5-HTTLPR to predict prospective depressive symptoms among youth

BACKGROUND

Previous research, predominantly with adults, has shown that the serotonin transporter gene (5-HTTLPR) interacts with stress (G × E) to predict depressive symptoms; however, few G × E studies have been conducted with youth using rigorous methods, particularly a prospective design and contextual interview to assess stress. This study examined the interaction between 5-HTTLPR and stress, both chronic and episodic, to predict longitudinal change in depressive symptoms among children and adolescents.

METHODS

A general community sample of youth (N = 200; 57% girls; mean age: 12.09 years old) was genotyped for 5-HTTLPR (rs 25531) at baseline. They were interviewed via contextual stress procedures to ascertain chronic family stress and episodic stressors and completed depressive symptoms questionnaires at baseline and 6 months later.

RESULTS

A significant G × E showed that chronic family stress predicted prospective increases in depressive symptoms over 6 months among youth possessing the high-risk S allele. This G × E was not found for episodic stressors occurring in the last 6 months. There was no moderation by sex or pubertal status.

CONCLUSIONS

These findings advance knowledge on G × E effects in depression among youth. This is the first study to show that chronic family stress, but not episodic stressors, when ascertained by rigorous stress interview, interacts with 5-HTTLPR to prospectively predict depressive symptoms among children and adolescents.

Hypocortisolism as a potential marker of allostatic load in children: associations with family risk and internalizing disorders

Although the majority of research attention to the hypothalamic-pituitary-adrenal (HPA) axis in stress-related disorders and as a marker of allostatic load has focused on overactivation of this stress system, theory and data clearly indicate that underactivation is also an important type of dysregulation. In the current study we focused on low cortisol, exploring a constellation of risk factors including stress exposure, maternal depression, and attenuated basal and stress reactive cortisol in two samples of children. The first sample was comprised of 110 preschoolers living in high-stress environments. Cortisol was assessed across the day at home and at child care as well as across two stress paradigms. These data were used to classify whether children's HPA axis activity was attenuated. Serious family financial strain, maternal depression, and attenuated cortisol all made unique contributions in models predicting current clinical levels of internalizing symptoms as rated by mothers and teachers. The second sample was 166 third, sixth, and ninth graders studied five times across a 1-year period. Maternal and child depression were determined through structured clinical interviews, and stress exposure was assessed via checklist and interview techniques with the child and parent. Cortisol was assessed multiple times across a lab visit at Time 1, and these data were combined into a single continuous measure. Cortisol concentrations across the lab visit interacted with stress exposure across the year such that children with lower average cortisol at Time 1 and increased stress across the 12 months showed elevated levels of internalizing symptoms. Based on these and related data we propose that prior to puberty low cortisol may be an important marker of allostatic load, particularly for risk of depression and anxiety.

The hippocampus, neurotrophic factors and depression: possible implications for the pharmacotherapy of depression

Depression is a prevalent, highly debilitating mental disorder affecting up to 15% of the population at least once in their lifetime, with huge costs for society. Neurobiological mechanisms of depression are still not well known, although there is consensus about interplay between genetic and environmental factors. Antidepressant medications are frequently used in depression, but at least 50% of patients are poor responders, even to more recently discovered medications. Furthermore, clinical response only occurs following weeks to months of treatment and only chronic treatment is effective, suggesting that actions beyond the rapidly occurring effect of enhancing monoaminergic systems, such as adaptation of these systems, are responsible for the effects of antidepressants. Recent studies indicate that an impairment of synaptic plasticity (neurogenesis, axon branching, dendritogenesis and synaptogenesis) in specific areas of the CNS, particularly the hippocampus, may be a core factor in the pathophysiology of depression. The abnormal neural plasticity may be related to alterations in the levels of neurotrophic factors, namely brain-derived neurotrophic factor (BDNF), which play a central role in plasticity. As BDNF is repressed by stress, epigenetic regulation of the BDNF gene may play an important role in depression. The hippocampus is smaller in depressed patients, although it is unclear whether smaller size is a consequence of depression or a pre-existing, vulnerability marker for depression. Environmental stressors triggering activation of the hypothalamic-pituitary-adrenal axis cause the brain to be exposed to corticosteroids, affecting neurobehavioural functions with a strong downregulation of hippocampal neurogenesis, and are a major risk factor for depression. Antidepressant treatment increases BDNF levels, stimulates neurogenesis and reverses the inhibitory effects of stress, but this effect is evident only after 3-4 weeks of administration, the time course for maturation of new neurons. The ablation of hippocampal neurogenesis blocks the behavioural effects of antidepressants in animal models. The above findings suggest new possible targets for the pharmacotherapy of depression such as neurotrophic factors, their receptors and related intracellular signalling cascades; agents counteracting the effects of stress on hippocampal neurogenesis (including antagonists of corticosteroids, inflammatory cytokines and their receptors); and agents facilitating the activation of gene expression and increasing the transcription of neurotrophins in the brain.

Antidepressants and adolescent brain development

Despite being a first-line treatment for adolescent depression and anxiety, antidepressant drugs appear to have questionable efficacy and carry an increased risk of adverse effects in this population. The neural mechanisms underlying this phenomenon are currently unknown. Recent research into the neural effects of alcohol and recreational drugs suggests that the developmental trajectory of the adolescent brain may be particularly vulnerable to pharmacological disturbance. It is therefore important to consider whether prescription psychotropic drugs may have analogous effects. This article reviews the contribution of recent preclinical, clinical and pharmacogenetic literature to current knowledge on the short-term and enduring neural effects of antidepressants on the adolescent brain, with a particular focus on the major neurotransmitter systems and neuroplasticity.

Maternal postnatal depression and the development of depression in offspring up to 16 years of age

OBJECTIVE

The aim of this study was to determine the developmental risk pathway to depression by 16 years in offspring of postnatally depressed mothers.

METHOD

This was a prospective longitudinal study of offspring of postnatally depressed and nondepressed mothers; child and family assessments were made from infancy to 16 years. A total of 702 mothers were screened, and probable cases interviewed. In all, 58 depressed mothers (95% of identified cases) and 42 nondepressed controls were recruited. A total of 93% were assessed through to 16-year follow-up. The main study outcome was offspring lifetime clinical depression (major depression episode and dysthymia) by 16 years, assessed via interview at 8, 13, and 16 years. It was analysed in relation to postnatal depression, repeated measures of child vulnerability (insecure infant attachment and lower childhood resilience), and family adversity.

RESULTS

Children of index mothers were more likely than controls to experience depression by 16 years (41.5% versus 12.5%; odds ratio = 4.99; 95% confidence interval = 1.68-14.70). Lower childhood resilience predicted adolescent depression, and insecure infant attachment influenced adolescent depression via lower resilience (model R(2) = 31%). Family adversity added further to offspring risk (expanded model R(2) = 43%).

CONCLUSIONS

Offspring of postnatally depressed mothers are at increased risk for depression by 16 years of age. This may be partially explained by within child vulnerability established in infancy and the early years, and by exposure to family adversity. Routine screening for postnatal depression, and parenting support for postnatally depressed mothers, might reduce offspring developmental risks for clinical depression in childhood and adolescence.

Association of the brain-derived neurotrophic factor Val66Met polymorphism with hippocampus volumes in drug-free depressed patients

OBJECTIVES

Val66Met BDNF gene polymorphism is shown to affect the function of mature BDNF and mature BDNF plays an important role in the hippocampal neurogenesis and neuronal survival.

METHODS

A relationship of Val66Met BDNF gene polymorphism and hippocampal volumes in 33 MDD patients and 40 healthy controls is investigated. Region of interest analysis was conducted on the images acquired via MRI.

RESULTS

Depressed patients had smaller left hippocampal volumes compared to healthy controls. The diagnosis of MDD was not significantly related to hippocampal volumes among Met carriers; however, among Val homozygotes depressed patients had significantly smaller left hippocampal volumes compared to controls. Although both right and left hippocampal volumes showed nearly significant correlation with the duration of illness, this correlation reached (negative) significant levels only in the right hippocampal volume of the Val homozygotes.

CONCLUSIONS

Val homozygote genotype may serve as a vulnerability factor in MDD regarding hippocampal volume loss. This finding can be considered as a supportive evidence for the neurotrophic factor hypothesis of depression.

Polymorphisms in BDNF (Val66Met) and 5-HTTLPR, morning cortisol and subsequent depression in at-risk adolescents

BACKGROUND

There is increasing evidence for genetic effects on the hypothalamic-pituitary axis system. More than one gene is likely to moderate corticoid-mediated activity.

AIMS

To investigate whether the brain-derived neurotrophic factor (BDNF) polymorphism (rs6265, Val66Met) is associated with morning waking salivary cortisol and moderates the corticoid-mediated risk for subsequent depressive episode onset independently of the known effects of 5-HTTLPR (the serotonin transporter gene promoter).

METHOD

High-risk adolescents (n = 401) were genotyped for Val66Met BDNF and 5-HTTLPR. Salivary samples were obtained on four consecutive school days within 1 h of waking. There were 365 (91%) remaining participants reassessed at 12 months for episodes of psychiatric disorder in the follow-up period. Of these, 357 (89%) had complete data for multivariate modelling.

RESULTS

There were 41 (11.2%) individuals who reported a new episode of clinical depression over the follow-up period. Increased risk for subsequent depression was found in carriers of the Val66Val genotype in BDNF with higher morning waking cortisol. This remained present when the known interaction between carriers of a short allele of 5-HTTLPR with higher morning salivary cortisol was taken into account.

CONCLUSIONS

Both BDNF and 5-HTTLPR genes show evidence of modifying the risk of a subsequent new depressive episode associated with elevated morning salivary cortisol. In adolescents morning salivary cortisol levels may constitute a biomarker for some forms of unipolar depression.

Paediatric major depressive disorder: neurobiology and implications for early intervention

AIM

Paediatric major depressive disorder (MDD) is associated with chronicity and poor outcomes. The goals of this review are (i) to integrate how developing biological systems contribute to the pathophysiology of paediatric MDD, and (ii) to consider the role of early intervention for depressed youth.

METHODS

A developmental perspective is applied herein to review and integrate key neurobiological systems that are implicated in paediatric MDD. We also review recent treatment research for adolescents with MDD.

RESULTS

Available evidence in paediatric and adult populations support an integrative model for the pathophysiology of MDD that involves fronto-limbic neural circuitry and the neuroendocrine stress response system. Evidence from treatment research supports the efficacy of available treatments modalities, including antidepressant medications, cognitive behavioral therapy, and their combination, for the majority of adolescents with moderate to severe MDD.

CONCLUSIONS

Since the biological systems implicated in MDD mature through adolescence, adolescents may be more susceptible to developing depression but also may be more amenable to treatment interventions. Early identification and treatment of paediatric MDD may be able to divert negative trajectories and lead to improved outcomes.