Effect of lithium on circadian rhythm in bipolar disorder: A systematic review and meta-analysis

Bipolar disorder is characterized by chronotype instability: A longitudinal investigation of circadian typology and mood

BACKGROUND

Chronotype is associated with circadian rhythmicity, a core etiological factor underlying bipolar disorder (BD). Given converging evidence linking late chronotype with poor mental health, the goal of the present study was to examine chronotype (in)stability and its relation to mood symptoms over time.

METHODS

Participants with BD I (n = 271), BD II (n = 88), and healthy controls (n = 217) were included (follow-upM=10 years, Range=5-15) from the Prechter Longitudinal Study. Chronotype category and midpoint of sleep, corrected for weekend sleep-debt (MSFsc), were measured with the Munich Chronotype Questionnaire administered every 12 months alongside clinician-rated mood and medication usage. Self-reported mood was measured bi-monthly. Mixed effects models tested whether mood was associated with (in)stability of chronotype category and MSFsc covarying for age, sex, age, and medication.

RESULTS

Compared to HC, individuals with BD self-reported having a later chronotype that significantly fluctuated over time. Individuals with BDI showed significantly less stability in MSFsc than HC. Anticonvulsant use was associated with more stability in MSFsc whereas antidepressant use was associated with less stability in MSFsc.

CONCLUSIONS

In a large longitudinal cohort, individuals with BD displayed significant instability in circadian typology. Psychopharmacology in BD may have differential impacts on circadian timing that is important to monitor.

Exploring the genetics of lithium response in bipolar disorders

BACKGROUND

Lithium (Li) remains the treatment of choice for bipolar disorders (BP). Its mood-stabilizing effects help reduce the long-term burden of mania, depression and suicide risk in patients with BP. It also has been shown to have beneficial effects on disease-associated conditions, including sleep and cardiovascular disorders. However, the individual responses to Li treatment vary within and between diagnostic subtypes of BP (e.g. BP-I and BP-II) according to the clinical presentation. Moreover, long-term Li treatment has been linked to adverse side-effects that are a cause of concern and non-adherence, including the risk of developing chronic medical conditions such as thyroid and renal disease. In recent years, studies by the Consortium on Lithium Genetics (ConLiGen) have uncovered a number of genetic factors that contribute to the variability in Li treatment response in patients with BP. Here, we leveraged the ConLiGen cohort (N = 2064) to investigate the genetic basis of Li effects in BP. For this, we studied how Li response and linked genes associate with the psychiatric symptoms and polygenic load for medical comorbidities, placing particular emphasis on identifying differences between BP-I and BP-II.

RESULTS

We found that clinical response to Li treatment, measured with the Alda scale, was associated with a diminished burden of mania, depression, substance and alcohol abuse, psychosis and suicidal ideation in patients with BP-I and, in patients with BP-II, of depression only. Our genetic analyses showed that a stronger clinical response to Li was modestly related to lower polygenic load for diabetes and hypertension in BP-I but not BP-II. Moreover, our results suggested that a number of genes that have been previously linked to Li response variability in BP differentially relate to the psychiatric symptomatology, particularly to the numbers of manic and depressive episodes, and to the polygenic load for comorbid conditions, including diabetes, hypertension and hypothyroidism.

CONCLUSIONS

Taken together, our findings suggest that the effects of Li on symptomatology and comorbidity in BP are partially modulated by common genetic factors, with differential effects between BP-I and BP-II.

Special Issue "Pathophysiology and Treatment of Alzheimer's Disease"

The majority of clinical trials, whose primary aims were to moderate Alzheimer's dementia (AD), have been based upon the prevailing paradigm, i [...].

Causal dynamics of sleep, circadian rhythm, and mood symptoms in patients with major depression and bipolar disorder: insights from longitudinal wearable device data

BACKGROUND

Sleep and circadian rhythm disruptions are common in patients with mood disorders. The intricate relationship between these disruptions and mood has been investigated, but their causal dynamics remain unknown.

METHODS

We analysed data from 139 patients (76 female, mean age = 23.5 ± 3.64 years) with mood disorders who participated in a prospective observational study in South Korea. The patients wore wearable devices to monitor sleep and engaged in smartphone-delivered ecological momentary assessment of mood symptoms. Using a mathematical model, we estimated their daily circadian phase based on sleep data. Subsequently, we obtained daily time series for sleep/circadian phase estimates and mood symptoms spanning >40,000 days. We analysed the causal relationship between the time series using transfer entropy, a non-linear causal inference method.

FINDINGS

The transfer entropy analysis suggested causality from circadian phase disturbance to mood symptoms in both patients with MDD (n = 45) and BD type I (n = 35), as 66.7% and 85.7% of the patients with a large dataset (>600 days) showed causality, but not in patients with BD type II (n = 59). Surprisingly, no causal relationship was suggested between sleep phase disturbances and mood symptoms.

INTERPRETATION

Our findings suggest that in patients with mood disorders, circadian phase disturbances directly precede mood symptoms. This underscores the potential of targeting circadian rhythms in digital medicine, such as sleep or light exposure interventions, to restore circadian phase and thereby manage mood disorders effectively.

FUNDING

Institute for Basic Science, the Human Frontiers Science Program Organization, the National Research Foundation of Korea, and the Ministry of Health & Welfare of South Korea.

Dietary lithium stimulates female fecundity in Drosophila melanogaster

The trace element lithium exerts a versatile bioactivity in humans, to some extend overlapping with in vivo findings in the model organism Drosophila melanogaster. A potentially essential function of lithium in reproduction has been suggested since the 1980s and multiple studies have since been published postulating a regulatory role of lithium in female gametogenesis. However, the impact of lithium on fruit fly egg production has not been at the center of attention to date. In the present study, we report that dietary lithium (0.1-5.0 mM LiCl) substantially improved life time egg production in D. melanogaster w1118 females, with a maximum increase of plus 45% when supplementing 1.0 mM LiCl. This phenomenon was not observed in the insulin receptor mutant InRE19, indicating a potential involvement of insulin-like signaling in the lithium-mediated fecundity boost. Analysis of the whole-body and ovarian transcriptome revealed that dietary lithium affects the mRNA levels of genes encoding proteins related to processes of follicular maturation. To the best of our knowledge, this is the first report on dietary lithium acting as an in vivo fecundity stimulant in D. melanogaster, further supporting the suggested benefit of the trace element in female reproduction.

Associations between actigraphy estimates of sleep and circadian rhythmicity and psychotropic medications in bipolar disorders: An exploratory study

INTRODUCTION

Disturbances in sleep and circadian rhythmicity (CR) are frequent in individuals with bipolar disorders (BD). Very few studies explored the associations between psychotropic medications and these disturbances in euthymic BD. Therefore, we aimed at exploring the associations between several classes of medications (lithium, sedative/non-sedative Atypical Antipsychotics (AAP), anticonvulsants, antidepressants, benzodiazepines) and sleep disturbances and CR dimensions in a sample of euthymic individuals with BD.

METHODS

We included euthymic adults with BD type 1 or 2 assessed with 21 days of actimetry. We used a Principal Component Analysis (PCA) of sleep and CR estimates to generate dimensions to be studied in association with the current use of psychotropic medications, with adjustments for potential confounding factors.

RESULTS

We included individuals with BD-1 (n = 116) or BD-2 (n = 37). The PCA led to four dimensions of sleep and CR estimates. Benzodiazepines were associated with better sleep quality (pcorrected = 0.032). Aripiprazole was associated with less robust CR (pcorrected = 0.016), but with earlier peak of activity patterns (pcorrected = 0.020). Sedative AAPs were associated with better sleep quality, which was no longer significant after correction. We found no association between lithium or anticonvulsants and CR.

LIMITATIONS

The cross-sectional design and the possible non-representativeness of the sample were limitations of our study.

CONCLUSIONS

In euthymic individuals with BD, benzodiazepines may have a positive effect on sleep quality, while aripiprazole may have mixed effects on CR (less robust but with earlier peak of activity patterns). No association with lithium or anticonvulsants observed. Further studies are warranted to replicate and extend these results.

The Relationship Among Seasonality, Night Eating, and Chronotype in Bipolar Disorder: Exploring the Mediating Role of Sleep Quality

ABSTRACT

The purpose of the study was to explore the association among chronotype, seasonality, sleep quality, and night eating syndrome (NES) among patients with bipolar disorder (BD) and the mediating role of sleep quality in this relationship. Ninety-two individuals with BD type 1 who had been euthymic for at least 8 weeks and 87 healthy controls were included. In addition to sociodemographic/clinical data, chronotype, seasonality, sleep quality, and NES were evaluated using the Morningness-Eveningness Questionnaire (MEQ), Seasonal Pattern Assessment Questionnaire, Pittsburgh Sleep Quality Index, and Night Eating Questionnaire. The prevalence of NES (17.4%) was higher among BD than the controls. BD patients with NES had poorer sleep quality, greater seasonality, and lower MEQ scores. Chronotype had an indirect effect that was partially mediated by sleep quality on night eating symptoms in BD patients, in addition to a direct effect. Seasonality was found to have a direct effect on night eating symptoms. Therapeutic interventions that target both sleep and circadian disruption should be implemented when addressing NES in patients with BD.

Dopamine pathways mediating affective state transitions after sleep loss

The pathophysiology of affective disorders-particularly circuit-level mechanisms underlying bidirectional, periodic affective state transitions-remains poorly understood. In patients, disruptions of sleep and circadian rhythm can trigger transitions to manic episodes, whereas depressive states are reversed. Here, we introduce a hybrid automated sleep deprivation platform to induce transitions of affective states in mice. Acute sleep loss causes mixed behavioral states, featuring hyperactivity, elevated social and sexual behaviors, and diminished depressive-like behaviors, where transitions depend on dopamine (DA). Using DA sensor photometry and projection-targeted chemogenetics, we reveal that elevated DA release in specific brain regions mediates distinct behavioral changes in affective state transitions. Acute sleep loss induces DA-dependent enhancement in dendritic spine density and uncaging-evoked dendritic spinogenesis in the medial prefrontal cortex, whereas optically mediated disassembly of enhanced plasticity reverses the antidepressant effects of sleep deprivation on learned helplessness. These findings demonstrate that brain-wide dopaminergic pathways control sleep-loss-induced polymodal affective state transitions.

The circadian clock time tunes axonal regeneration

Nerve injuries cause permanent neurological disability due to limited axonal regeneration. Injury-dependent and -independent mechanisms have provided important insight into neuronal regeneration, however, common denominators underpinning regeneration remain elusive. A comparative analysis of transcriptomic datasets associated with neuronal regenerative ability revealed circadian rhythms as the most significantly enriched pathway. Subsequently, we demonstrated that sensory neurons possess an endogenous clock and that their regenerative ability displays diurnal oscillations in a murine model of sciatic nerve injury. Consistently, transcriptomic analysis showed a time-of-day-dependent enrichment for processes associated with axonal regeneration and the circadian clock. Conditional deletion experiments demonstrated that Bmal1 is required for neuronal intrinsic circadian regeneration and target re-innervation. Lastly, lithium enhanced nerve regeneration in wild-type but not in clock-deficient mice. Together, these findings demonstrate that the molecular clock fine-tunes the regenerative ability of sensory neurons and propose compounds affecting clock pathways as a novel approach to nerve repair.

Exploring the genetics of lithium response in bipolar disorders

Background

Lithium (Li) remains the treatment of choice for bipolar disorders (BP). Its mood-stabilizing effects help reduce the long-term burden of mania, depression and suicide risk in patients with BP. It also has been shown to have beneficial effects on disease-associated conditions, including sleep and cardiovascular disorders. However, the individual responses to Li treatment vary within and between diagnostic subtypes of BP (e.g. BP-I and BP-II) according to the clinical presentation. Moreover, long-term Li treatment has been linked to adverse side-effects that are a cause of concern and non-adherence, including the risk of developing chronic medical conditions such as thyroid and renal disease. In recent years, studies by the Consortium on Lithium Genetics (ConLiGen) have uncovered a number of genetic factors that contribute to the variability in Li treatment response in patients with BP. Here, we leveraged the ConLiGen cohort (N=2,064) to investigate the genetic basis of Li effects in BP. For this, we studied how Li response and linked genes associate with the psychiatric symptoms and polygenic load for medical comorbidities, placing particular emphasis on identifying differences between BP-I and BP-II.

Results

We found that clinical response to Li treatment, measured with the Alda scale, was associated with a diminished burden of mania, depression, substance and alcohol abuse, psychosis and suicidal ideation in patients with BP-I and, in patients with BP-II, of depression only. Our genetic analyses showed that a stronger clinical response to Li was modestly related to lower polygenic load for diabetes and hypertension in BP-I but not BP-II. Moreover, our results suggested that a number of genes that have been previously linked to Li response variability in BP differentially relate to the psychiatric symptomatology, particularly to the numbers of manic and depressive episodes, and to the polygenic load for comorbid conditions, including diabetes, hypertension and hypothyroidism.

Conclusions

Taken together, our findings suggest that the effects of Li on symptomatology and comorbidity in BP are partially modulated by common genetic factors, with differential effects between BP-I and BP-II.

Chronotype is associated with affective temperaments, clinical severity and worse treatment outcomes in bipolar disorders: results from a two-center, cross-sectional study

OBJECTIVE

The present study was aimed at investigating the clinical correlates of evening chronotype in a population of subjects suffering from bipolar disorders (BD).

METHODS

We assessed chronotype using the Morningness-Eveningness Questionnaire. We administered the brief Temperament Evaluation of Memphis, Pisa, and San Diego, the Barratt Impulsiveness Scale, and the Alda Scale to evaluate affective temperaments, impulsiveness, and response to mood stabilisers. We performed bivariate analyses and ran a logistic regression model to analyse clinical variables associated with evening chronotype.

RESULTS

In our sample (n = 178), subjects with an evening chronotype (n = 56, 31.5%) more often suffered from BD type I and reported higher prevalence of seasonality, antidepressant-induced mood switches, psychotic, aggressive, mixed, and anxiety features, and substance use disorders. The number of lifetime suicide attempts and mood episodes was higher in this subgroup. Depressive, cyclothymic, irritable, and anxious temperament scores were higher among evening-chronotype subjects, who also displayed greater levels of impulsiveness and worse treatment response. At the logistic regression, evening chronotype was associated with depressive and irritable temperaments.

CONCLUSIONS

Subjects with evening chronotype display higher clinical severity and worse BD course. Clinicians should evaluate the presence of evening chronotype in BD subjects, especially in those with irritable or depressive temperament.Key pointsEvening chronotype is a frequent clinical feature in subjects suffering from bipolar disorders (BD);Affective temperaments, particularly depressive and irritable, are associated with evening chronotype in BD;Evening chronotype underpins higher severity of the clinical picture in BD, as well as a worse response to mood stabiliser treatment;Circadian preferences should be systematically assessed in subjects suffering from BD, with particular attention to evening preference.

Effects of exogenous melatonin on sleep and circadian rhythm parameters in bipolar disorder with comorbid delayed sleep-wake phase disorder: An actigraphic study

The present study evaluates the effect of exogenous melatonin (exo-MEL) on sleep and circadian parameters in patients with bipolar disorder (BD) and delayed sleep-wake phase disorder (DSWPD). BD euthymic patients (n = 83, mean age = 45.13 ± 13.68, males 56%) were evaluated for chronotype (reduced Morningness-Eveningness Questionnaire [rMEQ]), sleep quality (Pittsburgh Sleep Quality Index), sleep and circadian parameters (actigraphic monitoring). Patients that fulfilled criteria for DSWPD (n = 25) were treated for three months with exo-MEL 2 mg administered approximately 4 h before the sleep onset time (SOT) actigraphically-determined at baseline. Sleep and circadian parameters at baseline (T0) and after the exo-MEL treatment (T1) were compared using paired Wilcoxon test. In patients that completed the treatment (n = 19), the rMEQ score increased between T0 (median = 8.0 [IQR = 7.0, 11.0]) and T1 (median = 13.5 [IQR = 9.3, 15.0], p-value = 0.006), the SOT was advanced between T0 (median = 00:55 [IQR = 00:25, 01:39] and T1 (median = 00:09 [IQR = 23:41, 01:04], p-value = 0.039), the sleep efficiency and total sleep time increased (T0: median = 84.4 [IQR = 81.3, 89.4]; T1 (median = 90.3 [IQR = 85.5, 92.9] %, p-value = 0.01, and T0: median = 7.20 [IQR = 6.15, 8.15]; T1: median = 7.7 [IQR = 7.0, 9.3] hours, p-value = 0.04, respectively). These results indicate that in BD with comorbid DSWPD, the self-reported chronotype, the sleep onset time, and sleep efficiency and duration were modified after a personalized treatment with exo-MEL, suggesting its potential efficacy in improving sleep patterns in BD. The absence of proper control groups and of treatment randomization constitute limitations of our study and further randomized controlled trials are required to confirm our results.

Habitual light exposure and circadian activity rhythms in bipolar disorder: A cross-sectional analysis of the APPLE cohort

BACKGROUND

Circadian activity rhythm disruption is a core feature in bipolar disorder. We investigated whether light exposure in daily life is associated with circadian activity rhythms in patients with bipolar disorder.

METHODS

In a cross-sectional study, we enrolled 194 outpatients with bipolar disorder who were participants of the Association between Pathology of Bipolar Disorder and Light Exposure in Daily Life (APPLE) cohort study. The participants' physical activity and daytime illuminance were measured using an actigraph over 7 consecutive days. Nighttime illuminance in the bedroom was measured using a portable photometer. Circadian activity rhythm parameters were calculated using cosinor analysis and a nonparametric circadian rhythm analysis.

RESULTS

The median daytime illuminance and nighttime illuminance were 224.5 lx (interquartile range, 154.5-307.5 lx) and 2.3 lx (0.3-9.4 lx), respectively. Multivariable linear regression analysis, adjusted for potential confounding factors, showed that higher daytime illuminance was significantly associated with higher amplitude and most active continuous 10-hour period, advanced acrophase, higher interdaily stability, and lower intradaily variability. Higher nighttime illuminance was significantly associated with lower relative amplitude, delayed onset of the least active continuous 5-hour period, and higher intradaily variability.

LIMITATIONS

As this was a cross-sectional study, the results do not necessarily imply that light exposure alters circadian activity rhythms.

CONCLUSIONS

Daytime light exposure was associated with a positive effect and nighttime light exposure with a negative effect on circadian activity rhythms in bipolar disorder.

The impact of lithium on circadian rhythms and implications for bipolar disorder pharmacotherapy

Bipolar disorder (BD) is characterized by disrupted circadian rhythms affecting sleep, arousal, and mood. Lithium is among the most effective mood stabilizer treatments for BD, and in addition to improving mood symptoms, stabilizes sleep and activity rhythms in treatment responsive patients. Across a variety of experimental models, lithium has effects on circadian rhythms. However, uncertainty exists as to whether these actions directly pertain to lithium's therapeutic effects. Here, we consider evidence from mechanistic studies in animals and cells and clinical trials in BD patients that identify associations between circadian rhythms and the therapeutic effects of lithium. Most evidence indicates that lithium has effects on cellular circadian rhythms and increases morningness behaviors in BD patients, changes that may contribute to the therapeutic effects of lithium. However, much of this evidence is limited by cross-sectional analyses and/or imprecise proxy markers of clinical outcomes and circadian rhythms in BD patients, while mechanistic studies rely on inference from animals or small numbers of patients . Further study may clarify the essential mechanisms underlying lithium responsive BD, better characterize the longitudinal changes in circadian rhythms in BD patients, and inform the development of therapeutic interventions targeting circadian rhythms.

Chronotype, circadian rhythm, and psychiatric disorders: Recent evidence and potential mechanisms

The circadian rhythm is crucial for physiological and behavioral functions. Chronotype, which represents individual preferences for activity and performance, is associated with human health issues, particularly psychiatric disorders. This narrative review, which focuses on the relationship between chronotype and mental disorders, provides an insight into the potential mechanism. Recent evidence indicates that (1) the evening chronotype is a risk factor for depressive disorders and substance use disorders, whereas the morning chronotype is a protective factor. (2) Evening chronotype individuals with bipolar disorder tend to have more severe symptoms and comorbidities. (3) The evening chronotype is only related to anxiety symptoms. (4) The relationship between chronotype and schizophrenia remains unclear, despite increasing evidence on their link. (5) The evening chronotype is significantly associated with eating disorders, with the majority of studies have focused on binge eating disorders. Furthermore, the underlying mechanisms or influence factors are described in detail, including clock genes, brain characteristics, neuroendocrinology, the light/dark cycle, social factors, psychological factors, and sleep disorders. These findings provide the latest evidence on chronotypes and psychiatric disorders and serve as a valuable reference for researchers.

Magnetic field effects in biology from the perspective of the radical pair mechanism

Hundreds of studies have found that weak magnetic fields can significantly influence various biological systems. However, the underlying mechanisms behind these phenomena remain elusive. Remarkably, the magnetic energies implicated in these effects are much smaller than thermal energies. Here, we review these observations, and we suggest an explanation based on the radical pair mechanism, which involves the quantum dynamics of the electron and nuclear spins of transient radical molecules. While the radical pair mechanism has been studied in detail in the context of avian magnetoreception, the studies reviewed here show that magnetosensitivity is widespread throughout biology. We review magnetic field effects on various physiological functions, discussing static, hypomagnetic and oscillating magnetic fields, as well as isotope effects. We then review the radical pair mechanism as a potential unifying model for the described magnetic field effects, and we discuss plausible candidate molecules for the radical pairs. We review recent studies proposing that the radical pair mechanism provides explanations for isotope effects in xenon anaesthesia and lithium treatment of hyperactivity, magnetic field effects on the circadian clock, and hypomagnetic field effects on neurogenesis and microtubule assembly. We conclude by discussing future lines of investigation in this exciting new area of quantum biology.

Circulating miRNAs as Potential Biomarkers for Patient Stratification in Bipolar Disorder: A Combined Review and Data Mining Approach

Bipolar disorder is a debilitating psychiatric condition that is shaped in a concerted interplay between hereditary and triggering risk factors. Profound depression and mania define the disorder, but high clinical heterogeneity among patients complicates diagnosis as well as pharmacological intervention. Identification of peripheral biomarkers that capture the genomic response to the exposome may thus progress the development of personalized treatment. MicroRNAs (miRNAs) play a prominent role in of post-transcriptional gene regulation in the context of brain development and mental health. They are coordinately modulated by multifarious effectors, and alteration in their expression profile has been reported in a variety of psychiatric conditions. Intriguingly, miRNAs can be released from CNS cells and enter circulatory bio-fluids where they remain remarkably stable. Hence, peripheral circulatory miRNAs may act as bio-indicators for the combination of genetic risk, environmental exposure, and/or treatment response. Here we provide a comprehensive literature search and data mining approach that summarize current experimental evidence supporting the applicability of miRNAs for patient stratification in bipolar disorder.

Associations between circadian misalignment and telomere length in BD: an actigraphy study

BACKGROUND

Life expectancy is significantly decreased in bipolar disorder (BD). This is associated with accelerated cellular aging which can be estimated by telomere length (TL). However, specific determinants of shorter TL in BD are under-explored. This study examines whether circadian misalignment (i.e. mismatch between preferred and actual phase of circadian activity rhythms) is associated with shorter TL in BD.

METHODS

Euthymic individuals with BD (n = 101) undertook 21 consecutive days of actigraphy recording and completed the Composite Scale of Morningness (CSM) to assess phase preference for activities (chronotype). Polymerase chain reaction was used to measure TL in blood. Cluster analysis identified circadian aligned/misaligned subgroups as defined by preferred (CSM score) and actual phases of activity (actigraphically determined onset of active and inactive periods). We tested for any associations between TL and clusters, with adjustments for between-cluster differences in socio-demographic and illness factors.

RESULTS

We identified three clusters: an "Aligned Morning" cluster (n = 31) with preferred and actual timing of activity in the morning, an "Aligned Evening" cluster (n = 37) with preferred and actual timing of activity in the evening and a "Misaligned" cluster (n = 32) with an evening chronotype, but an earlier objective onset of active periods. After adjustment for confounders, we found that TL was significantly associated with circadian misalignment and older age.

CONCLUSIONS

Circadian misalignment may partly explain shorter TL in BD and could contribute to accelerated aging in these individuals.

Which Actigraphy Dimensions Predict Longitudinal Outcomes in Bipolar Disorders?

Bipolar disorder (BD) is characterized by recurrent mood episodes. It is increasingly suggested that disturbances in sleep–wake cycles and/or circadian rhythms could represent valuable predictors of recurrence, but few studies have addressed this question. Euthymic individuals with BD (n = 69) undertook 3 weeks of actigraphy recording and were then followed up for a median duration of 3.5 years. Principal component analyses were used to identify core dimensions of sleep quantity/variability and circadian rhythmicity. Associations between clinical variables and actigraphy dimensions and time to first recurrence were explored using survival analyses, and then using area under the curve (AUC) analyses (early vs. late recurrence). Most participants (64%) experienced a recurrence during follow-up (median survival time: 18 months). After adjusting for potential confounding factors, an actigraphy dimension comprising amplitude and variability/stability of circadian rhythms was a significant predictor of time to recurrence (p = 0.009). The AUC for correct classification of early vs. late recurrence subgroups was only 0.64 for clinical predictors, but combining these variables with objectively measured intra-day variability improved the AUC to 0.82 (p = 0.04). Actigraphy estimates of circadian rhythms, particularly variability/stability and amplitude, may represent valid predictive markers of future BD recurrences and could be putative targets for future psychosocial interventions.

A Comparison of Different Approaches to Clinical Phenotyping of Lithium Response: A Proof of Principle Study Employing Genetic Variants of Three Candidate Circadian Genes

Optimal classification of the response to lithium (Li) is crucial in genetic and biomarker research. This proof of concept study aims at exploring whether different approaches to phenotyping the response to Li may influence the likelihood of detecting associations between the response and genetic markers. We operationalized Li response phenotypes using the Retrospective Assessment of Response to Lithium Scale (i.e., the Alda scale) in a sample of 164 cases with bipolar disorder (BD). Three phenotypes were defined using the established approaches, whilst two phenotypes were generated by machine learning algorithms. We examined whether these five different Li response phenotypes showed different levels of statistically significant associations with polymorphisms of three candidate circadian genes (RORA, TIMELESS and PPARGC1A), which were selected for this study because they were plausibly linked with the response to Li. The three original and two revised Alda ratings showed low levels of discordance (misclassification rates: 8–12%). However, the significance of associations with circadian genes differed when examining previously recommended categorical and continuous phenotypes versus machine-learning derived phenotypes. Findings using machine learning approaches identified more putative signals of the Li response. Established approaches to Li response phenotyping are easy to use but may lead to a significant loss of data (excluding partial responders) due to recent attempts to improve the reliability of the original rating system. While machine learning approaches require additional modeling to generate Li response phenotypes, they may offer a more nuanced approach, which, in turn, would enhance the probability of identifying significant signals in genetic studies.

Association between circadian activity rhythms and mood episode relapse in bipolar disorder: a 12-month prospective cohort study

A significant proportion of patients with bipolar disorder experience mood episode relapses. We examined whether circadian activity rhythms were associated with mood episode relapses in patients with bipolar disorder. This prospective cohort study included outpatients with bipolar disorder who participated in a study titled "Association between the Pathology of Bipolar Disorder and Light Exposure in Daily Life (APPLE) cohort study." The participants' physical activity was objectively assessed using a wrist-worn accelerometer over 7 consecutive days for the baseline assessment and then at the 12-month follow-up for mood episode relapses. The levels and timing of the circadian activity rhythms were estimated using a cosinor analysis and a nonparametric circadian rhythm analysis. Of the 189 participants, 88 (46%) experienced mood episodes during follow-up. The Cox proportional hazards model adjusting for potential confounders showed that a robust circadian activity rhythm, including midline-estimating statistic of rhythm (MESOR) and amplitude by cosinor analysis and 10 consecutive hours with the highest amplitude values (M10) by the nonparametric circadian rhythm analysis, was significantly associated with a decrease in mood episode relapses (per counts/min, hazard ratio [95% confidence interval]: MESOR, 0.993 [0.988-0.997]; amplitude, 0.994 [0.988-0.999]; and M10, 0.996 [0.993-0.999]). A later timing of the circadian activity rhythm (M10 onset time) was significantly associated with an increase in the depressive episode relapses (per hour; 1.109 [1.001-1.215]). We observed significant associations between circadian activity rhythms and mood episode relapses in bipolar disorder.