Circadian polymorphisms in night owls, in bipolars, and in non-24-hour sleep cycles

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.

Genetic Associations of Chronotype in the Finnish General Population

Individuals with a later chronotype (evening types) tend to have unhealthier behaviors and increased morbidity and mortality as compared with those with an earlier chronotype (morning types). However, the role of genetics in explaining evening types' adverse health and health behavior is unclear. Our aim was to study genetic associations of chronotype among 8433 Finns from the cross-sectional National FINRISK 2007 and 2012 studies. First, we studied associations between chronotype and 20 key clock genes with a candidate-gene approach and then performed a full genome-wide association study (GWAS) of chronotype. We also developed a genetic risk score (GRS) for chronotype based on 313 single nucleotide polymorphisms (SNPs) that have previously been associated with chronotype. Chronotype was assessed with a shortened version of Horne and Östberg's Morningness-Eveningness Questionnaire (sMEQ), and for comparison, we also used the single self-evaluation question on chronotype from the questionnaire. Linear and logistic regression was used for statistical analysis assuming additive effects. The clock gene analysis revealed 1 independent association signal within NR1D2 (lead SNP rs4131403) that was associated with chronotype (p < 0.05; as based on both chronotype assessment methods). The GWAS analysis did not yield any genome-wide significant associations (p > 5 × 10^-8). However, higher GRS was associated with evening chronotype (p < 0.001; as based on both chronotype assessment methods). In conclusion, our findings indicated novel genetic associations between chronotype and the NR1D2 clock gene, which has previously been associated with carbohydrate and lipid metabolism. Furthermore, the GRS was able to capture the genetic aspect of chronotype in our study population. These findings expand our knowledge of the genetic basis of chronotype.

Rhythms of life: circadian disruption and brain disorders across the lifespan

Many processes in the human body - including brain function - are regulated over the 24-hour cycle, and there are strong associations between disrupted circadian rhythms (for example, sleep-wake cycles) and disorders of the CNS. Brain disorders such as autism, depression and Parkinson disease typically develop at certain stages of life, and circadian rhythms are important during each stage of life for the regulation of processes that may influence the development of these disorders. Here, we describe circadian disruptions observed in various brain disorders throughout the human lifespan and highlight emerging evidence suggesting these disruptions affect the brain. Currently, much of the evidence linking brain disorders and circadian dysfunction is correlational, and so whether and what kind of causal relationships might exist are unclear. We therefore identify remaining questions that may direct future research towards a better understanding of the links between circadian disruption and CNS disorders.

Circadian Rhythm Disturbances in the Blind

PURPOSE OF REVIEW

Sleep timing, quantity, and quality are controlled by homeostatic and circadian systems. Circadian clock systems are present in all cells and organs and their timing is determined by a transcriptional-translational feedback loop of circadian genes. Individual cellular clocks are synchronized by the central body clock, situated in the suprachiasmatic nucleus, which communicates with them through humoral and neural signals including melatonin. The circadian system controls both the circadian period: (i.e., the length of the intrinsic clock), but also the circadian phase (i.e., the clock timing). An important determinant of the circadian system is light exposure. In most humans, the circadian period is slightly longer than 24 h and without regular resetting it tends to drift, leading to progressively later bedtimes and wake times and a tendency to cycle though periods of normal and abnormal sleep. Blind patients are thus at an increased risk of abnormal circadian function. The purpose of this article is to review recent research and clinical management of circadian rhythm disorders in blind patients.

RECENT FINDINGS

Blind patients can present delayed and advanced sleep phase disorders but the most common abnormality in totally blind patients without light perception is non-24-hour sleep-wake disorder (N24SWD). This is rare in the general population but may affect up to 50% of blind patients without light perception. The diagnosis of a circadian rhythm disorder in the blind is complex. New screening tools have been developed but actigraphy and repeated melatonin profiles over 24 h remain essential. Circadian disorders in the blind are frequent, especially in the patients without light perception. They require accurate diagnosis in order to target treatment. Determining the precise nature of a sleep disorder in blind patients with a suspected circadian rhythm abnormality is complex and requires a detailed clinical history with sleep diaries and the use of actigraphy and melatonin profiles.

ARNTL, CLOCK and PER3 polymorphisms - links with chronotype and affective dimensions

Recently, seven single nucleotide polymorphisms (SNPs) of ARNTL, TIM and PER3 genes were found associated with affective temperaments in bipolar disorder patients. This study aimed to test whether a) the same associations appear in a non-clinical sample; b) the SNPs are related to other affective dimensions; c) the SNPs underpin the associations between chronotype and affective temperaments/dimensions. Three hundred thirty-eight university students completed the Temperament Scale of Memphis, Pisa, Paris and San Diego Auto-questionnaire, the Centre for Epidemiological Studies Depression Scale, the Perceived Stress Scale, the General Health Questionnaire, the Seasonal Pattern Assessment Questionnaire and the Composite Scale of Morningness. Seven SNPs of the ARNTL, TIM and PER3 genes were genotyped. According to nominal significance, ARNTL rs7107287 was associated with a cyclothymic temperament, depressive and stress symptoms, general mental health and perceived negative impact of seasonality, while TIM rs10876890 was associated with a hyperthymic temperament, and the TIM rs2291738 was associated with chronotype. Different SNPs were related to chronotype and affective temperaments/dimensions, and therefore, they seem to not underpin relationships between chronotype and affective dysfunction, that is, in the present study, eveningness was related to dysthymic, cyclothymic and irritable temperaments, more symptoms of depression, stress, worse mental health and a negative impact of seasonality, while morningness was related to hyperthymic temperament. The SNPs associations need further replication given that they did not achieve Bonferroni criteria of significance accounting for the number of polymorphisms considered and tests conducted.

Mutation of the Human Circadian Clock Gene CRY1 in Familial Delayed Sleep Phase Disorder

Patterns of daily human activity are controlled by an intrinsic circadian clock that promotes ∼24 hr rhythms in many behavioral and physiological processes. This system is altered in delayed sleep phase disorder (DSPD), a common form of insomnia in which sleep episodes are shifted to later times misaligned with the societal norm. Here, we report a hereditary form of DSPD associated with a dominant coding variation in the core circadian clock gene CRY1, which creates a transcriptional inhibitor with enhanced affinity for circadian activator proteins Clock and Bmal1. This gain-of-function CRY1 variant causes reduced expression of key transcriptional targets and lengthens the period of circadian molecular rhythms, providing a mechanistic link to DSPD symptoms. The allele has a frequency of up to 0.6%, and reverse phenotyping of unrelated families corroborates late and/or fragmented sleep patterns in carriers, suggesting that it affects sleep behavior in a sizeable portion of the human population.

Circadian Rhythm Dysregulation in Bipolar Spectrum Disorders

PURPOSE OF REVIEW

We review recent evidence for circadian rhythm dysregulation in bipolar spectrum disorders (BSDs). We examine evidence for endogenous abnormalities in the biological clock and disruptions in the external entrainment of circadian rhythms in BSDs. We also address whether circadian dysregulation provides vulnerability to onset of BSD and evidence for a new integration of reward and circadian dysregulation in BSD.

RECENT FINDINGS

Relative circadian phase delay (e.g., later melatonin peak, evening chronotype) is associated with BSD, particularly in the depressive phase. More consistent evidence supports irregularity of social rhythms, sleep/wake and activity patterns, and disruptions of social rhythms by life events, as stable trait markers of BSD and potential vulnerabilities for BSD onset. Growing research supports an integrative reward/circadian model. Both endogenous abnormalities in the biological clock pacemaking function and disruptions in the external entrainment of circadian rhythms by physical and social cues are involved in BSDs. Circadian dysregulation may provide vulnerability to BSD onset.

Prevalence of Circadian Rhythm Sleep-Wake Disorders and Associated Factors in Euthymic Patients with Bipolar Disorder

Recent studies have suggested that there are certain pathophysiological relationships between bipolar disorder (BD) and circadian rhythm dysfunction. However, apparently no studies have clarified the prevalence of circadian rhythm sleep-wake disorders (CRSWD) in patients with BD. This study was set out to investigate the prevalence of CRSWD and associated factors in patients with BD. One hundred four euthymic BD outpatients participated in this study. The subjects were asked to answer questionnaires including demographic variables, clinical course of BD, and family history of psychiatric disorders and suicide. Severity of BD was assessed by the Montgomery-Åsberg Depression Rating Scale and Young Mania Rating Scale. CRSWD was diagnosed by clinical interview, together with sleep logs, according to the International Classification of Sleep Disorders, third edition (ICSD-3). Thirty-five subjects (32.4%) met the criteria for CRSWD. The age at the time of investigation and that at the onset of BD were both lower in the CRSWD group than in the non-CRSWD group. The rates of family history of psychiatric disorders and suicide in the CRSWD group were higher than those in the non-CRSWD group. Multiple logistic regression analysis revealed that the presence of CRSWD was significantly associated with younger onset age of BD and family history of suicide. The prevalence of CRSWD could be quite high in BD patients. Younger onset age of BD and family history of suicide were associated with presence of CRSWD in BD patients.

Circadian Melatonin and Temperature Taus in Delayed Sleep-wake Phase Disorder and Non-24-hour Sleep-wake Rhythm Disorder Patients: An Ultradian Constant Routine Study

Our objectives were to investigate the period lengths (i.e., taus) of the endogenous core body temperature rhythm and melatonin rhythm in delayed sleep-wake phase disorder patients (DSWPD) and non-24-h sleep-wake rhythm disorder patients (N24SWD) compared with normally entrained individuals. Circadian rhythms were measured during an 80-h ultradian modified constant routine consisting of 80 ultrashort 1-h "days" in which participants had 20-min sleep opportunities alternating with 40 min of enforced wakefulness. We recruited a community-based sample of 26 DSWPD patients who met diagnostic criteria (17 males, 9 females; age, 21.85 ± 4.97 years) and 18 healthy controls (10 males, 8 females; age, 23.72 ± 5.10 years). Additionally, 4 full-sighted patients (3 males, 1 female; age, 25.75 ± 4.99 years) were diagnosed with N24SWD and included as a discrete study group. Ingestible core temperature capsules were used to record minute temperatures that were averaged to obtain 80 hourly data points. Salivary melatonin concentration was assessed every half-hour to determine time of dim light melatonin onset at the beginning and end of the 80-h protocol. DSWPD patients had significantly longer melatonin rhythm taus (24 h 34 min ± 17 min) than controls (24 h 22 min ± 15 min, p = 0.03, d = 0.70). These results were further supported by longer temperature rhythm taus in DSWPD patients (24 h 34 min ± 26 min) relative to controls (24 h 13 min ± 15 min, p = 0.01, d = 0.80). N24SWD patients had even longer melatonin (25 h ± 19 min) and temperature (24 h 52 min ± 17 min) taus than both DSWPD (p = 0.007, p = 0.06) and control participants (p < 0.001, p = 0.02, respectively). Between 12% and 19% of the variance in DSWPD patients' sleep timing could be explained by longer taus. This indicates that longer taus of circadian rhythms may contribute to the DSWPD patients' persistent tendency to delay, their frequent failure to respond to treatment, and their relapse following treatment. Additionally, other factors can contribute to misalignments in DSWPD and N24SWD disorders.

Photoperiodic and circadian bifurcation theories of depression and mania

Seasonal effects on mood have been observed throughout much of human history.  Seasonal changes in animals and plants are largely mediated through the changing photoperiod (i.e., the photophase or duration of daylight).  We review that in mammals, daylight specifically regulates SCN (suprachiasmatic nucleus) circadian organization and its control of melatonin secretion.  The timing of melatonin secretion interacts with gene transcription in the pituitary pars tuberalis to modulate production of TSH (thyrotropin), hypothalamic T3 (triiodothyronine), and tuberalin peptides which modulate pituitary production of regulatory gonadotropins and other hormones.  Pituitary hormones largely mediate seasonal physiologic and behavioral variations.  As a result of long winter nights or inadequate illumination, we propose that delayed morning offset of nocturnal melatonin secretion, suppressing pars tuberalis function, could be the main cause for winter depression and even cause depressions at other times of year.  Irregularities of circadian sleep timing and thyroid homeostasis contribute to depression.  Bright light and sleep restriction are antidepressant and conversely, sometimes trigger mania.  We propose that internal desynchronization or bifurcation of SCN circadian rhythms may underlie rapid-cycling manic-depressive disorders and perhaps most mania.  Much further research will be needed to add substance to these theories.

Wake up time, light, and mood in a population sample age 40-64 years

OBJECTIVE

Concern that disturbances of sleep and light exposures at night might increase cancer risks have been expressed, but little actual exposure data has been collected. Measurements from a representative population sample were examined to understand the magnitude of in-bed light exposure at night and possible correlates.

METHODS

From 1990 to 1994, a home survey of sleep disorders among adults ages 40-64 was conducted in the City of San Diego California, using stratified representative sampling techniques. Along with questionnaires, sleep logs, and 3-night wrist activity and pulse oximetry measures, bedside illumination was measured with a computer recording system. Questionnaires included the CESD depression scale and a scale of symptoms typical of winter depression.

RESULTS

Complete data were available from 286 men and women, whose mean in-bed intervals averaged 7 hours and 42 minutes. The mean room illumination during the first part of the night was mean 12.7 lux (median 3.2 lux) and during the last 2 hours in bed averaged 28.7 lux (median 18.9 lux). Nocturnal light exposure was positively correlated with age, male gender, summer season, time in bed, wake-up time, and depressive symptoms.

CONCLUSION

Complex bi-directional interactions may take place between sleep disturbances, depression, time in bed, wake-up-time, and in-bed illumination. The most crucial light exposures appear to occur in the last 2 hours in bed, largely after dawn, so daylight exposure may be an important factor.

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.

Genetic variants associated with sleep disorders

OBJECTIVE

The diagnostic boundaries of sleep disorders are under considerable debate. The main sleep disorders are partly heritable; therefore, defining heritable pathophysiologic mechanisms could delineate diagnoses and suggest treatment. We collected clinical data and DNA from consenting patients scheduled to undergo clinical polysomnograms, to expand our understanding of the polymorphisms associated with the phenotypes of particular sleep disorders.

METHODS

Patients at least 21 years of age were recruited to contribute research questionnaires, and to provide access to their medical records, saliva for deoxyribonucleic acid (DNA), and polysomnographic data. From these complex data, 38 partly overlapping phenotypes were derived indicating complaints, subjective and objective sleep timing, and polysomnographic disturbances. A custom chip was used to genotype 768 single-nucleotide polymorphisms (SNPs). Additional assays derived ancestry-informative markers (eg, 751 participants of European ancestry). Linear regressions controlling for age, gender, and ancestry were used to assess the associations of each phenotype with each of the SNPs, highlighting those with Bonferroni-corrected significance.

RESULTS

In peroxisome proliferator-activated receptor gamma, coactivator 1 beta (PPARGC1B), rs6888451 was associated with several markers of obstructive sleep apnea. In aryl hydrocarbon receptor nuclear translocator-like (ARNTL), rs10766071 was associated with decreased polysomnographic sleep duration. The association of rs3923809 in BTBD9 with periodic limb movements in sleep was confirmed. SNPs in casein kinase 1 delta (CSNK1D rs11552085), cryptochrome 1 (CRY1 rs4964515), and retinoic acid receptor-related orphan receptor A (RORA rs11071547) were less persuasively associated with sleep latency and time of falling asleep.

CONCLUSIONS

SNPs associated with several sleep phenotypes were suggested, but due to risks of false discovery, independent replications are needed before the importance of these associations can be assessed, followed by investigation of molecular mechanisms.