An ASMT variant associated with bipolar disorder influences sleep and circadian rhythms: a pilot study

X-Chromosome Dependent Differences in the Neuronal Molecular Signatures and Their Implications in Sleep Patterns

Biological factors and mechanisms that drive sex differences observed in sleep disturbances are understudied and poorly understood. The extent to which sex chromosome constitution impacts on sex differences in circadian patterns is still a knowledge void in the sleep medicine field. Here we focus on the neurological consequences of X-chromosome functional imbalances between males and females and how this molecular inequality might affect sex divergencies on sleep. In light of the X-chromosome inactivation mechanism in females and its implications in gene regulation, we describe sleep-related neuronal circuits and brain regions impacted by sex-biased modulations of the transcriptome and the epigenome. Benefited from recent large-scale genetic studies on the interplay between X-chromosome and brain function, we list clinically relevant genes that might play a role in sex differences in neuronal pathways. Those molecular signatures are put into the context of sleep and sleep-associated neurological phenotypes, aiming to identify biological mechanisms that link X-chromosome gene regulation to sex-biased human traits. These findings are a significant step forward in understanding how X-linked genes manifest in sleep-associated transcriptional networks and point to future research opportunities to address female-specific clinical manifestations and therapeutic responses.

Bipolar Chronobiology in Men and Mice: A Narrative Review

In patients with bipolar disorder, we do not only see a cycling of mood episodes, but also a shift in circadian rhythm. In the present overview, the circadian rhythm, the "internal clock", and their disruptions are briefly described. In addition, influences on circadian rhythms such as sleep, genetics, and environment are discussed. This description is conducted with a translational focus covering human patients as well as animal models. Concluding the current knowledge on chronobiology and bipolar disorder, implications for specificity and the course of bipolar disorder and treatment options are given at the end of this article. Taken together, circadian rhythm disruption and bipolar disorder are strongly correlated; the exact causation, however, is still unclear.

Gene expression of circadian genes and CIART in bipolar disorder: A preliminary case-control study

Based on the observed circadian rhythms disruptions and sleep abnormalities in bipolar disorders (BD), a chronobiological model has been proposed suggesting that core clock genes play a central role in the vulnerability to the disorder. In this context, the analysis of circadian genes expression levels is particularly relevant, however studies focused on the whole set of core clock genes are scarce. We compared the levels of expression of 19 circadian genes (including the recently described circadian repressor (CIART)) in 37 euthymic individuals with BD and 20 healthy controls (HC), using data obtained by RNA sequencing of lymphoblastoid cell lines and validated the results using RT-qPCR. RNA sequencing data showed that CIART gene expression was correlated with those of ARNTL, ARNTL2, DBP, PER2 and TIMELESS. Data from RNA sequencing showed that the level of expression of four circadian genes (ARNTL, ARNTL2, BHLHE41 and CIART) discriminated individuals with BD from HC. We replicated this result using RT-qPCR for ARNTL and CIART. This study suggests that an imbalance between activation/repression of the transcription within the circadian system in individuals with BD as compared to HC and as such opens avenues for further research in larger independent samples combining both expression and epigenetic analyses.

Neurobiological and behavioral mechanisms of circadian rhythm disruption in bipolar disorder: A critical multi-disciplinary literature review and agenda for future research from the ISBD task force on chronobiology

AIM

Symptoms of bipolar disorder (BD) include changes in mood, activity, energy, sleep, and appetite. Since many of these processes are regulated by circadian function, circadian rhythm disturbance has been examined as a biological feature underlying BD. The International Society for Bipolar Disorders Chronobiology Task Force (CTF) was commissioned to review evidence for neurobiological and behavioral mechanisms pertinent to BD.

METHOD

Drawing upon expertise in animal models, biomarkers, physiology, and behavior, CTF analyzed the relevant cross-disciplinary literature to precisely frame the discussion around circadian rhythm disruption in BD, highlight key findings, and for the first time integrate findings across levels of analysis to develop an internally consistent, coherent theoretical framework.

RESULTS

Evidence from multiple sources implicates the circadian system in mood regulation, with corresponding associations with BD diagnoses and mood-related traits reported across genetic, cellular, physiological, and behavioral domains. However, circadian disruption does not appear to be specific to BD and is present across a variety of high-risk, prodromal, and syndromic psychiatric disorders. Substantial variability and ambiguity among the definitions, concepts and assumptions underlying the research have limited replication and the emergence of consensus findings.

CONCLUSIONS

Future research in circadian rhythms and its role in BD is warranted. Well-powered studies that carefully define associations between BD-related and chronobiologically-related constructs, and integrate across levels of analysis will be most illuminating.

Multi-Level Processes and Retina-Brain Pathways of Photic Regulation of Mood

Light exerts powerful biological effects on mood regulation. Whereas the source of photic information affecting mood is well established at least via intrinsically photosensitive retinal ganglion cells (ipRGCs) secreting the melanopsin photopigment, the precise circuits that mediate the impact of light on depressive behaviors are not well understood. This review proposes two distinct retina–brain pathways of light effects on mood: (i) a suprachiasmatic nucleus (SCN)-dependent pathway with light effect on mood via the synchronization of biological rhythms, and (ii) a SCN-independent pathway with light effects on mood through modulation of the homeostatic process of sleep, alertness and emotion regulation: (1) light directly inhibits brain areas promoting sleep such as the ventrolateral preoptic nucleus (VLPO), and activates numerous brain areas involved in alertness such as, monoaminergic areas, thalamic regions and hypothalamic regions including orexin areas; (2) moreover, light seems to modulate mood through orexin-, serotonin- and dopamine-dependent pathways; (3) in addition, light activates brain emotional processing areas including the amygdala, the nucleus accumbens, the perihabenular nucleus, the left hippocampus and pathways such as the retina–ventral lateral geniculate nucleus and intergeniculate leaflet–lateral habenula pathway. This work synthetizes new insights into the neural basis required for light influence mood

Association between the Arylalkylamine N-Acetyltransferase (AANAT) Gene and Seasonality in Patients with Bipolar Disorder

OBJECTIVE

Bipolar disorder (BD) is complex genetic disorder. Therefore, approaches using clinical phenotypes such as biological rhythm disruption could be an alternative. In this study, we explored the relationship between melatonin pathway genes with circadian and seasonal rhythms of BD.

METHODS

We recruited clinically stable patients with BD (n=324). We measured the seasonal variation of mood and behavior (seasonality), and circadian preference, on a lifetime basis. We analyzed 34 variants in four genes (MTNR1a, MTNR1b, AANAT, ASMT) involved in the melatonin pathway.

RESULTS

Four variants were nominally associated with seasonality and circadian preference. After multiple test corrections, the rs116879618 in AANAT remained significantly associated with seasonality (corrected p=0.0151). When analyzing additional variants of AANAT through imputation, the rs117849139, rs77121614 and rs28936679 (corrected p=0.0086, 0.0154, and 0.0092) also showed a significant association with seasonality.

CONCLUSION

This is the first study reporting the relationship between variants of AANAT and seasonality in patients with BD. Since AANAT controls the level of melatonin production in accordance with light and darkness, this study suggests that melatonin may be involved in the pathogenesis of BD, which frequently shows a seasonality of behaviors and symptom manifestations.

Molecular Regulation of the Melatonin Biosynthesis Pathway in Unipolar and Bipolar Depression

Melatonin is a neurohormone that maintains the circadian rhythms of the body. By regulating the secretion of other hormones and neurotransmitters, it acts as a pleiotropic modulator that affects, for example, reproductive, immune, cardiovascular, sleep, and wake systems and mood. Thus, synthetic melatonin has become an essential component in the treatment of depressive disorders. Although we know the pathway of melatonin action in the brain, we lack comprehensive cross-sectional studies on the periphery of depressed patients. This study aimed to comprehensively analyze the differences between healthy control subjects (n = 84) and unipolar and bipolar depression patients (n = 94), including an analysis of the melatonin pathway at the level of the genes and serum biomarkers. An innovative approach is a pilot study based on gene expression profiling carried out on clinical and cell culture models using agomelatine and melatonin. We confirmed the melatonin biosynthesis pathway's molecular regulation dysfunctions, with a specific pattern for unipolar and bipolar depression, at the AANAT gene, its polymorphisms (rs8150 and rs3760138), and examined the serum biomarkers (serotonin, AANAT, ASMT, and melatonin). The biological pathway analysis uncovered pathways and genes that were uniquely altered after agomelatine treatment in a clinical model and melatonin treatment in a cell culture model. In both models, we confirmed the immunomodulatory effect of melatonin agents in depression.

Biological rhythms and chronotherapeutics in depression

Depressive syndromes are frequent and heterogeneous brain conditions with more than 90% of patients suffering from sleep complaints. Better characterizing this "sleep" domain may allow to both better treat acute episodes with existing chronotherapeutics, but also to prevent the manifestation or recurrences of mood disorders. This work aims to i) review theoretical and fundamental data of chronotherapeutics, and ii) provide practical recommendations. Light therapy (LT) can be used as a first-line monotherapy of moderate to severe depression of all subtypes. LT can be also used as a combination with antidepressant to maximize patients' response rates, which has a clear superiority to antidepressant alone. Sleep deprivation (SD) is a rapid and powerful chronotherapeutic with antidepressant responses within hours in 45-60% of patients with unipolar or bipolar depression. Different strategies should be combined to stabilize the SD antidepressant effect, including concomitant medications, repeated SD, combination with sleep phase advance and/or LT (triple chronotherapy). Melatonin treatment is of interest in remitted patients with mood disorder to prevent relapses or recurrences, if a complaint of insomnia, poor sleep quality or phase delay syndrome is associated. During the acute phase, melatonin could be used as an adjuvant treatment for symptoms of insomnia associated with depression. The cognitive behavioral therapy for insomnia (CBT-I) can be recommend to treat insomnia during euthymic phases. The Interpersonal and social rhythm therapy (IPSRT) is indicated for the acute treatment of bipolar depression and for the prevention of mood episodes. Chronotherapeutics should always be associated with behavioral measures for healthy sleep.

Chronobiology Revisited in Psychiatric Disorders: From a Translational Perspective

OBJECTIVE

Several lines of evidence support a relationship between circadian rhythms disruption in the onset, course, and maintenance of mental disorders. Despite the study of circadian phenotypes promising a decent understanding of the pathophysiologic or etiologic mechanisms of psychiatric entities, several questions still need to be addressed. In this review, we aimed to synthesize the literature investigating chronobiologic theories and their associations with psychiatric entities.

METHODS

The Medline, Embase, PsycInfo, and Scopus databases were comprehensively and systematically searched and articles published between January 1990 and October 2019 were reviewed. Different combinations of the relevant keywords were polled. We first introduced molecular elements and mechanisms of the circadian system to promote a better understanding of the chronobiologic implications of mental disorders. Then, we comprehensively and systematically reviewed circadian system studies in mood disorders, schizophrenia, and anxiety disorders.

RESULTS

Although subject characteristics and study designs vary across studies, current research has demonstrated that circadian pathologies, including genetic and neurohumoral alterations, represent the neural substrates of the pathophysiology of many psychiatric disorders. Impaired HPA-axis function-related glucocorticoid rhythm and disrupted melatonin homeostasis have been prominently demonstrated in schizophrenia and other psychotic disorders, while alterations of molecular expressions of circadian rhythm genes including CLOCK, PER, and CRY have been reported to be involved in the pathogenesis of mood disorders.

CONCLUSION

Further translational work is needed to identify the causal relationship between circadian physiology abnormalities and mental disorders and related psychopathology, and to develop sound pharmacologic interventions.

Polymorphisms in the ASMT and ADAMTS1 gene may increase litter size in goats

Prolificacy of most local goat breeds in China is low. Jining Grey goat is one of the most prolific goat breeds in China, it is an important goat breed for the rural economy. ASMT (acetylserotonin O‐methyltransferase) and ADAMTS1 (ADAM metallopeptidase with thrombospondin type 1 motif) are essential for animal reproduction. Single nucleotide polymorphisms (SNPs) of ASMT and ADAMTS1 genes in the highly prolific breed (Jining Grey goats), medium prolific breed (Boer goats and Guizhou White goats) and low prolific breeds (Angora goats, Liaoning Cashmere goats and Inner Mongolia Cashmere goats) were detected by polymerase chain reaction‐restriction fragment length polymorphism and sequencing. Two SNPs (g.158122T>C, g.158700G>A) of ASMT gene and two SNPs (g.7979798A>G, g.7979477C>T) of ADAMTS1 gene were identified. For g.158122T>C of ASMT gene, further analysis revealed that genotype TC or CC had 0.66 (p < 0.05) or 0.75 (p < 0.05) kids more than those with genotype TT in Jining Grey goats. No significant difference (p > 0.05) was found in litter size between TC and CC genotypes. The SNP (g.158122T>C) caused a p.Tyr298His change and this SNP mutation resulted in changes in protein binding sites and macromolecule‐binding sites. The improvement in reproductive performance may be due to changes in the structure of ASMT protein. For g.7979477C>T of ADAMTS1 gene, Jining Grey does with genotype CT or TT had 0.82 (p < 0.05) or 0.86 (p < 0.05) more kids than those with genotype CC. No significant difference (p > 0.05) was found in litter size between CT or TT genotypes. These results preliminarily indicated that C allele (g.158122T>C) of ASMT gene and T allele (g.7979477C>T) of ADAMTS1 gene are potential molecular markers which could improve litter size of Jining Grey goats and be used in goat breeding.

Le trouble bipolaire : une maladie du sommeil et des rythmes circadiens ?

Le trouble bipolaire (TB) est une maladie psychiatrique multifactorielle à hérédité complexe faisant intervenir des facteurs de risque génétiques et environnementaux [1]. Parmi ces facteurs de risque, des anomalies des rythmes circadiens et du sommeil ont été mises en évidence dans les TB et témoignent de l’implication d’anomalies de l’horloge circadienne dans la physiopathologie du TB [2]. En effet, Il existe une littérature importante sur les anomalies circadiennes observées dans le TB (sommeil, rythmes veille/sommeil, chronotypes, perturbations circadiennes biologiques et comportementales, etc.). Ces anomalies sont présentes, non seulement en phase aiguë, mais aussi au cours des phases de stabilité de l’humeur (ou euthymiques) constituant ainsi des anomalies « trait » du TB [2]. Ainsi, l’exploration du sommeil et des rythmes circadiens chez des patients euthymiques avec TB par des mesures objectives (actigraphie) et subjectives (questionnaires) démontre que les patients présentent un sommeil plus long, de moins bonne qualité, avec retard important à l’endormissement, plus de réveils nocturnes et un retentissement diurne plus important que des témoins sains [3]. Par ailleurs, certains variants de gènes circadiens associés au TB peuvent s’associer chez les patients à des modifications particulières de ces rythmes circadiens. Ainsi, dans une étude pilote, il a été observé qu’un variant commun associé au TB du gène ASMT (codant pour l’une des deux enzymes de synthèse de la mélatonine) était associé à une modification des rythmes circadiens marquée par une période de sommeil allongée, une plus grande activité nocturne et une plus grande stabilité des rythmes [4]. Ces résultats intéressants soulignent l’intérêt de l’exploration des anomalies circadiennes du TB dans un but étiopathogénique et diagnostique, mais aussi possiblement thérapeutique.

Clinical characteristics of obstructive sleep apnea in bipolar disorders

BACKGROUND

Obstructive sleep apnea (OSA) is one of the leading non-psychiatric comorbidities in bipolar disorders (BD). We sought to explore associations between risk of OSA in BD, clinical characteristics alongside with both subjective sleep complaints and objective sleep abnormalities.

METHODS

Euthymic patients with BD (n = 144) were assessed over a three-week period, by actigraphy, clinical interviews and questionnaires.

RESULTS

Of the study sample, 32 (22%) individuals were at high risk of OSA (HR-OSA) and 112 (78%) had a low risk (LR-OSA), as assessed with the Berlin questionnaire. HR-OSA, compared to LR-OSA, were older (p = 0.031), had higher BMI (p < 0.0005), larger neck circumference (p = 0.002), and more residual depressive symptoms (p < 0.0005). HR-OSA was also associated with greater sleepiness (p = 0.003), poorer sleep quality (p = 0.003), insomnia complaints (p = 0.027), "languid" chronotype (p = 0.002), and higher actigraphy-derived fragmentation index (p = 0.015). Backward stepwise linear regression retained BMI and depressive symptoms (correct classification of 83% of participants). Classification increased up to 85.4% when adding sleepiness and languid-vigorous scales and up to 87.8% when adding fragmentation index. Combining ROC curve analysis and Youden Index provided best cut-offs (HR-OSA if cut-off greater than or equal to) of 29.84 for BMI (Sensibility(Se) = 0.47, Specificity(Spe) = 0.96) and 1.5 for MADRS total score (Se = 0.84, Spe = 0.58).

LIMITATIONS

No confirmation of OSA diagnosis with polysomnography.

CONCLUSIONS

Higher BMI and residual depressive symptoms are the two best independent predictors of OSA in BD. Such information contributes to improving the screening and management of OSA in BD.

TRIAL NUMBER

NCT02627404.

Sleep and circadian rhythms as possible trait markers of suicide attempt in bipolar disorders: An actigraphy study

BACKGROUND

The poor prognostic of Bipolar disorders (BD) is closely linked to deaths by suicide. Sleep and circadian abnormalities are observed during all phases of BD and are also associated with suicide attempt (SA). In this context, this study sought to identify specific sleep and circadian rhythms markers associated with suicidal attempt in euthymic patients with BD.

METHODS

The sample (N = 236) comprised 3 groups: 147 patients with BD including 57 with a history of SA and 90 without (NoSA), and 89 healthy controls (HC). All participants were recorded during 21 days with actigraphy.

RESULTS

SA was associated with women gender (p = 0.03), familial history of SA (p = 0.03), mixed episodes (p = 0.001), and benzodiazepines (p = 0.019). SA, compared to noSA, had a morning phase preference (p = 0.04), and were more vigorous on the circadian type inventory (p = 0.04), and tended to suffer more from insomnia (45% versus 25% respectively, p = 0.10). SA was also associated with an earlier onset of daily activity assessed with actigraphy (M10 onset: p = 0.01). Backward stepwise linear regression indicated that a combination of four variables (Gender, vigour, insomnia, M10onset) significantly differentiated patients with SA from NoSA (p = 0.03).

LIMITATIONS

Cross-sectional design, and no examination of suicidal behaviors' subgroups such as first attempters or repeaters, or violent suicide attempt.

CONCLUSIONS

Woman gender, vigorous circadian type, insomnia and an earlier daily activity appeared independently associated with SA in BD. If these biomarkers are confirmed in prospective studies, they should be screened and used to prevent suicide, with the development of personal and targeted chronobiological treatments.

Melatonin as a Hormone: New Physiological and Clinical Insights

Melatonin is a ubiquitous molecule present in almost every live being from bacteria to humans. In vertebrates, besides being produced in peripheral tissues and acting as an autocrine and paracrine signal, melatonin is centrally synthetized by a neuroendocrine organ, the pineal gland. Independently of the considered species, pineal hormone melatonin is always produced during the night and its production and secretory episode duration are directly dependent on the length of the night. As its production is tightly linked to the light/dark cycle, melatonin main hormonal systemic integrative action is to coordinate behavioral and physiological adaptations to the environmental geophysical day and season. The circadian signal is dependent on its daily production regularity, on the contrast between day and night concentrations, and on specially developed ways of action. During its daily secretory episode, melatonin coordinates the night adaptive physiology through immediate effects and primes the day adaptive responses through prospective effects that will only appear at daytime, when melatonin is absent. Similarly, the annual history of the daily melatonin secretory episode duration primes the central nervous/endocrine system to the seasons to come. Remarkably, maternal melatonin programs the fetuses' behavior and physiology to cope with the environmental light/dark cycle and season after birth. These unique ways of action turn melatonin into a biological time-domain-acting molecule. The present review focuses on the above considerations, proposes a putative classification of clinical melatonin dysfunctions, and discusses general guidelines to the therapeutic use of melatonin.

Lithium response in bipolar disorders and core clock genes expression

OBJECTIVES

We examine whether the lithium response is associated with changes in the expression of core clock genes.

METHODS

The effect of a therapeutic concentration of lithium (1 mM) on the expression levels of 17 circadian genes was examined in lymphoblastoid cell lines (LCLs) derived from two well-characterized groups of bipolar disorder patients, defined as lithium non-responders (NR, n = 20) or excellent responders (ER, n = 16). Quantitative real-time PCR (qRT-PCR) was conducted at 2, 4 and 8 days (d2, d4 and d8) with and without lithium exposure.

RESULTS

At d2, in ER only, BHLHE41, RORA, PER1, ARNTL, CRY2, BHLHE40 and CSNK1D were upregulated, whereas NR1D1 was downregulated. At d4, in ER only, CRY1 was downregulated. At d8, in NR only, GSK3β was upregulated and DBP, TIMELESS and CRY1 were downregulated. Significant Group × Lithium interactions existed for NR1D1 at d2 (P = 0.02), and CRY1 at d4 (P = 0.02). Longitudinal analyses showed differential temporal evolutions between NR and ER (significant Time × Group interaction) for PER3, NR1D1, DBP, RORA, CSNK1D and TIMELESS; and a significant Time × Lithium interaction for NR1D1. Coexpression data analyses suggested distinct groups of circadian genes concurrently modulated by lithium.

CONCLUSIONS

In LCLs, lithium influences expression of circadian genes with differences in amplitude and kinetics according to the patient's lithium response status.

[Diagnosis and comorbidities of Circadian Rhythm Sleep Disorders]

Circadian rhythm sleep disorders (CRSD) result from a disturbed endogenous clock (intrinsic CRSD) or from a misalignment between the biological clock and an imposed environment (extrinsic CRSD). Among intrinsic CRSD, one distinguishes the delayed sleep-wake phase disorder, the advanced sleep-wake phase disorder, the irregular sleep-wake rhythm disorder and the non-24-hour sleep-wake rhythm disorder. Shift work disorder, jet lag disorder and circadian sleep-wake disorder not otherwise specified are extrinsic CRSD. Prevalences of the different CRSD remain largely unknown. Some CRSD are particularly frequent such as sleep delayed phase syndrome in adolescents. Overall, CRSD are probably under-diagnosed. CRSD generate insomnia and excessive daytime somnolence. A biological clock dysfunction has to be evoked in case of insomnia or sleepiness. Furthermore, as CRSD can overlap with other sleep disorders, their diagnosis and treatment are essential. CRSD cause significant mental, physical or socio-professional sufferings. They are frequently associated with comorbidities, mainly neurodevelopmental, psychiatric and neurodegenerative disorders. Regarding neurodevelopmental comorbidities, therapy using a chronobiological approach is complementary to the usual clinical care. It helps to limit the significant impact of CRSD on quality of live, daytime functioning, social interactions and neurocognitive difficulties in the children. In psychiatry, sleep disorders and circadian rhythms sleep-wake disorders are a factor of vulnerability, of suicidal risk, of relapse and pharmacoresistance. Thus, diagnosis of CRSD associated with a psychiatric disorder is of major importance. Treatment using a chronobiological approach reinforcing the entrainment of the sleep-wake cycle is complementary to usual treatments. Sleep disorders and circadian sleep-wake rhythm disorders can be a preclinical sign of Alzheimer's and Parkinson's disease. In the elderly, a beginning neurodegenerative disorder can be associated with a CRSD and complaints of sleepiness, nocturnal awakenings and/or irregular sleep-wake cycles. Patients affected by neurogenerative disorders are particularly vulnerable for having CRSD. Data from different studies suggest that CRSD participate in pathophysiology of Alzheimer's disease. Even though treatment of CRSD associated with neurodegenerative disorders is entirely part of the treatment strategy, it remains uncertain to which extend this treatment may impact disease progression.

Pathophysiology of Depression: Molecular Regulation of Melatonin Homeostasis - Current Status

Circadian rhythm alterations resulting in disturbed sleep and disturbed melatonin secretion are flagship features of depression. Melatonin, known as a hormone of darkness, is secreted by the pineal gland located near to the center of the brain between the two hemispheres. Melatonin has an antidepressant effect by maintaining the body's circadian rhythm, by regulating the pattern of expression of the clock genes in the suprachiasmatic nucleus (SCN) and modifying the key genes of serotoninergic neurotransmission that are linked with a depressive mood. Melatonin is produced via the metabolism of serotonin in two steps which are catalyzed by serotonin N-acetyltransferase (SNAT) and acetylserotonin-O-methyltransferase (ASMT). Serotonin, SNAT, and ASMT are key melatonin level regulation factors. Melatonin acts mainly on the MT1 and MT2 receptors, which are present in the SCN, to regulate physiological and neuroendocrine functions including circadian entrainment, referred to as a chronobiotic effect. Although melatonin has been known about and refereed to for almost 50 years, the relationship between melatonin and depression is still not clear. In this review, we summarize current knowledge about the genetic and epigenetic regulation of enzymes involved in melatonin synthesis and metabolism as potential features of depression pathophysiology and treatment. Confirmation that melatonin metabolism in peripheral blood partially reflects a disorder in the brain could be a breakthrough in the standardization of measurements of melatonin level for the development of treatment standards, finding new therapeutic targets, and elaborating simple noninvasive clinical tests.

Genome-wide association study of 40,000 individuals identifies two novel loci associated with bipolar disorder

Bipolar disorder (BD) is a genetically complex mental illness characterized by severe oscillations of mood and behaviour. Genome-wide association studies (GWAS) have identified several risk loci that together account for a small portion of the heritability. To identify additional risk loci, we performed a two-stage meta-analysis of >9 million genetic variants in 9,784 bipolar disorder patients and 30,471 controls, the largest GWAS of BD to date. In this study, to increase power we used ∼2,000 lithium-treated cases with a long-term diagnosis of BD from the Consortium on Lithium Genetics, excess controls, and analytic methods optimized for markers on the X-chromosome. In addition to four known loci, results revealed genome-wide significant associations at two novel loci: an intergenic region on 9p21.3 (rs12553324, P =  5.87 × 10 -  9; odds ratio (OR) = 1.12) and markers within ERBB2 (rs2517959, P =  4.53 × 10 -  9; OR = 1.13). No significant X-chromosome associations were detected and X-linked markers explained very little BD heritability. The results add to a growing list of common autosomal variants involved in BD and illustrate the power of comparing well-characterized cases to an excess of controls in GWAS.

Differential melatonin alterations in cerebrospinal fluid and serum of patients with major depressive disorder and bipolar disorder

BACKGROUND

Melatonin, which plays an important role for regulation of circadian rhythms and the sleep/wake cycle has been linked to the pathophysiology of major depressive and bipolar disorder. Here we investigated melatonin levels in cerebrospinal fluid (CSF) and serum of depression and bipolar patients to elucidate potential differences and commonalities in melatonin alterations across the two disorders.

METHODS

Using enzyme-linked immunosorbent assays, CSF and serum melatonin levels were measured in 108 subjects (27 healthy volunteers, 44 depressed and 37 bipolar patients). Covariate adjusted multiple regression analysis was used to investigate group differences in melatonin levels.

RESULTS

In CSF, melatonin levels were significantly decreased in bipolar (P<0.001), but not major depressive disorder. In serum, we observed a significant melatonin decrease in major depressive (P=0.003), but not bipolar disorder. No associations were found between serum and CSF melatonin levels or between melatonin and measures of symptom severity or sleep disruptions in either condition.

CONCLUSION

This study suggests the presence of differential, body fluid specific alterations of melatonin levels in bipolar and major depressive disorder. Further, longitudinal studies are required to explore the disease phase dependency of melatonin alterations and to mechanistically explore the causes and consequences of site-specific alterations.

Genetic association study of circadian genes with seasonal pattern in bipolar disorders

About one fourth of patients with bipolar disorders (BD) have depressive episodes with a seasonal pattern (SP) coupled to a more severe disease. However, the underlying genetic influence on a SP in BD remains to be identified. We studied 269 BD Caucasian patients, with and without SP, recruited from university-affiliated psychiatric departments in France and performed a genetic single-marker analysis followed by a gene-based analysis on 349 single nucleotide polymorphisms (SNPs) spanning 21 circadian genes and 3 melatonin pathway genes. A SP in BD was nominally associated with 14 SNPs identified in 6 circadian genes: NPAS2, CRY2, ARNTL, ARNTL2, RORA and RORB. After correcting for multiple testing, using a false discovery rate approach, the associations remained significant for 5 SNPs in NPAS2 (chromosome 2:100793045–100989719): rs6738097 (p_c = 0.006), rs12622050 (p_c = 0.006), rs2305159 (p_c = 0.01), rs1542179 (p_c = 0.01), and rs1562313 (p_c = 0.02). The gene-based analysis of the 349 SNPs showed that rs6738097 (NPAS2) and rs1554338 (CRY2) were significantly associated with the SP phenotype (respective Empirical p-values of 0.0003 and 0.005). The associations remained significant for rs6738097 (NPAS2) after Bonferroni correction. The epistasis analysis between rs6738097 (NPAS2) and rs1554338 (CRY2) suggested an additive effect. Genetic variations in NPAS2 might be a biomarker for a seasonal pattern in BD.

Sleep- and circadian rhythm-associated pathways as therapeutic targets in bipolar disorder

INTRODUCTION

Disruptions in sleep and circadian rhythms are observed in individuals with bipolar disorders (BD), both during acute mood episodes and remission. Such abnormalities may relate to dysfunction of the molecular circadian clock and could offer a target for new drugs.

AREAS COVERED

This review focuses on clinical, actigraphic, biochemical and genetic biomarkers of BDs, as well as animal and cellular models, and highlights that sleep and circadian rhythm disturbances are closely linked to the susceptibility to BDs and vulnerability to mood relapses. As lithium is likely to act as a synchronizer and stabilizer of circadian rhythms, we will review pharmacogenetic studies testing circadian gene polymorphisms and prophylactic response to lithium. Interventions such as sleep deprivation, light therapy and psychological therapies may also target sleep and circadian disruptions in BDs efficiently for treatment and prevention of bipolar depression.

EXPERT OPINION

We suggest that future research should clarify the associations between sleep and circadian rhythm disturbances and alterations of the molecular clock in order to identify critical targets within the circadian pathway. The investigation of such targets using human cellular models or animal models combined with 'omics' approaches are crucial steps for new drug development.

Circadian biomarkers in patients with bipolar disorder: promising putative predictors of lithium response

Bipolar disorder (BD) is a common, severe mental disorder with a high recurrence rate. Lithium (Li) is the cornerstone of BD treatments to reduce recurrence, suicide, and mortality risks. However, only 30% of patients treated with Li achieve complete remission, and few markers of the response to treatment have yet been identified for application in routine practice. Circadian biomarkers may be relevant predictors of individual responses to Li because (1) Li has been shown to affect circadian rhythms, (2) disrupted circadian rhythms are a core expression of susceptibility to BD, and (3) circadian abnormalities during euthymia are associated with relapses.

Circadian rhythms and sleep in bipolar disorder: implications for pathophysiology and treatment

PURPOSE OF REVIEW

Multiple lines of evidence support the conceptualization of bipolar disorder as a disorder of circadian rhythms. Considering bipolar disorder in the framework of circadian disturbances also helps understand the clinical phenomenology pointing toward a multisystemic involvement.

RECENT FINDINGS

Patients with bipolar disorder show altered rhythmicity in body temperature and melatonin rhythms, high day-to-day variability in activity and sleep timing, persistent disturbances of sleep or wake cycles, including disturbances of sleep continuity. The internal clocks are, indeed, responsible for regulating a variety of physiologic functions, including appetitive behaviors, cognitive functions and metabolism.

SUMMARY

An underlying circadian pathology in bipolar disorder is a unifying explicatory model for the high psychiatric and medical comorbidity observed during the long-term course of the disorder. This model also provides a rationale for therapeutic interventions aimed at re-entraining the internal clock.