Circadian rhythm sleep disorders: part II, advanced sleep phase disorder, delayed sleep phase disorder, free-running disorder, and irregular sleep-wake rhythm. An American Academy of Sleep Medicine review

OBJECTIVE: This the second of two articles reviewing the scientific literature on the evaluation and treatment of circadian rhythm sleep disorders (CRSDs), employing the methodology of evidence-based medicine. We herein report on the accumulated evidence regarding the evaluation and treatment of Advamced Sleep Phase Disorder (ASPD), Delayed Sleep Phase Disorder (DSPD), Free-Running Disorder (FRD) and Irregular Sleep-Wake Rhythm ISWR). METHODS: A set of specific questions relevant to clinical practice were formulated, a systematic literature search was performed, and relevant articles were abstracted and graded. RESULTS: A substantial body of literature has accumulated that provides a rational basis the evaluation and treatment of CRSDs. Physiological assessment has involved determination of circadian phase using core body temperature and the timing of melatonin secretion. Behavioral assessment has involved sleep logs, actigraphy and the Morningness-Eveningness Questionnaire (MEQ). Treatment interventions fall into three broad categories: 1) prescribed sleep scheduling, 2) circadian phase shifting ("resetting the clock"), and 3) symptomatic treatment using hypnotic and stimulant medications. CONCLUSION: Circadian rhythm science has also pointed the way to rational interventions for CRSDs and these treatments have been introduced into the practice of sleep medicine with varying degrees of success. More translational research is needed using subjects who meet current diagnostic criteria.     

Circadian rhythm sleep disorders: part I, basic principles, shift work and jet lag disorders. An American Academy of Sleep Medicine review

OBJECTIVE: This the first of two articles reviewing the scientific literature on the evaluation and treatment of circadian rhythm sleep disorders (CRSDs), employing the methodology of evidence-based medicine. In this first part of this paper, the general principles of circadian biology that underlie clinical evaluation and treatment are reviewed. We then report on the accumulated evidence regarding the evaluation and treatment of shift work disorder (SWD) and jet lag disorder (JLD). METHODS: A set of specific questions relevant to clinical practice were formulated, a systematic literature search was performed, and relevant articles were abstracted and graded. RESULTS: A substantial body of literature has accumulated that provides a rational basis the evaluation and treatment of SWD and JLD. Physiological assessment has involved determination of circadian phase using core body temperature and the timing of melatonin secretion. Behavioral assessment has involved sleep logs, actigraphy and the Morningness-Eveningness Questionnaire (MEQ). Treatment interventions fall into three broad categories: 1) prescribed sleep scheduling, 2) circadian phase shifting ("resetting the clock"), and 3) symptomatic treatment using hypnotic and stimulant medications. CONCLUSION: Circadian rhythm science has also pointed the way to rational interventions for the SWD and JLD, and these treatments have been introduced into the practice of sleep medicine with varying degrees of success. More translational research is needed using subjects who meet current diagnostic criteria.     

Delayed sleep phase disorder in temporal isolation

STUDY OBJECTIVES: This study sought to characterize sleep and the circadian rhythm of body core temperature of an individual with delayed sleep phase disorder (DSPD) in the absence of temporal cues and social entrainment and to compare those measures to age-matched normal control subjects studied under identical conditions. DESIGN: Polysomnography and body temperature were recorded continuously for 4 days in entrained conditions, followed immediately by 17 days in a "free-running" environment. SETTING: Temporal isolation facility in the Laboratory of Human Chronobiology, Weill Cornell Medical College. PARTICIPANTS: One individual who met criteria for delayed sleep phase disorder according to the International Classification of Sleep Disorders Diagnostic and Coding Manual (ICSD-2) and 3 age-matched control subjects. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: The DSPD subject had a spontaneous period length (tau) of 25.38 hours compared to an average tau of 24.44 hours for the healthy controls. The DSPD subject also showed an altered phase relationship between sleep/wake and body temperature rhythms, as well as longer sleep latency, poorer sleep efficiency, and altered distribution of slow wave sleep (SWS) within sleep episodes, compared to control subjects. CONCLUSIONS: Delayed sleep phase disorder may be the reflection of an abnormal circadian timing system characterized not only by a long tau, but also by an altered internal phase relationship between the sleep/wake system and the circadian rhythm of body temperature. The latter results in significantly disturbed sleep, even when DSPD patients are permitted to sleep and wake at their preferred times.     

The endogenous circadian temperature period length (tau) in delayed sleep phase disorder compared to good sleepers

The currently assumed aetiology for delayed sleep phase disorder (DSPD) is a delay of the circadian system. Clinicians have sought to use bright light therapy, exogenous melatonin or chronotherapy to correct the disorder. However, these treatments have achieved unreliable outcomes for DSPD patients and, as such, one suggestion has been that the disorder may be caused by a longer than normal circadian rhythm period length (i.e. tau). The present study investigated this premise using a 78‐h ultradian, ultra‐short sleep–wake cycle. This constant bedrest routine was used to simulate a series of 1‐h long ‘days’ by alternating 20‐min sleep opportunities and 40 min of enforced wakefulness. Thirteen participants were recruited for the study including, six people diagnosed with DSPD according to the International Classification of Sleep Disorders—2 [mean age = 22.0, standard deviation (SD) = 3.3] and seven good sleepers (mean age = 23.1, SD = 3.9) with normal sleep timing. The DSPD participants' core temperature rhythm tau (mean = 24 h 54 min, SD = 23 min) was significantly longer (t = ?2.33, P = 0.04, Cohen's d = 1.91) than the good sleepers' (mean 24 h 29 min, SD = 16 min). The temperature rhythm of the DSPD participants delayed more rapidly (i.e. >25 min day^?1) than the good sleepers'. These findings provide an explanation for the difficulty that DSPD patients have in phase advancing to a more conventional sleep time and their frequent relapse following treatment. The outcomes of this study support a vigorous and continued application of chronobiological and behavioural therapies to entrain DSPD patients to their desired earlier sleep times.     

Practice parameters for the indications for polysomnography and related procedures: an update for 2005

These practice parameters are an update of the previously-published recommendations regarding the indications for polysomnography and related procedures in the diagnosis of sleep disorders. Diagnostic categories include the following: sleep related breathing disorders, other respiratory disorders, narcolepsy, parasomnias, sleep related seizure disorders, restless legs syndrome, periodic limb movement sleep disorder, depression with insomnia, and circadian rhythm sleep disorders. Polysomnography is routinely indicated for the diagnosis of sleep related breathing disorders; for continuous positive airway pressure (CPAP) titration in patients with sleep related breathing disorders; for the assessment of treatment results in some cases; with a multiple sleep latency test in the evaluation of suspected narcolepsy; in evaluating sleep related behaviors that are violent or otherwise potentially injurious to the patient or others; and in certain atypical or unusual parasomnias. Polysomnography may be indicated in patients with neuromuscular disorders and sleep related symptoms; to assist in the diagnosis of paroxysmal arousals or other sleep disruptions thought to be seizure related; in a presumed parasomnia or sleep related seizure disorder that does not respond to conventional therapy; or when there is a strong clinical suspicion of periodic limb movement sleep disorder. Polysomnography is not routinely indicated to diagnose chronic lung disease; in cases of typical, uncomplicated, and noninjurious parasomnias when the diagnosis is clearly delineated; for patients with seizures who have no specific complaints consistent with a sleep disorder; to diagnose or treat restless legs syndrome; for the diagnosis of circadian rhythm sleep disorders; or to establish a diagnosis of depression.     

Practice parameters for the use of actigraphy in the assessment of sleep and sleep disorders: an update for 2007

BACKGROUND: Actigraphy is increasingly used in sleep research and the clinical care of patients with sleep and circadian rhythm abnormalities. The following practice parameters update the previous practice parameters published in 2003 for the use of actigraphy in the study of sleep and circadian rhythms. METHODS: Based upon a systematic grading of evidence, members of the Standards of Practice Committee, including those with expertise in the use of actigraphy, developed these practice parameters as a guide to the appropriate use of actigraphy, both as a diagnostic tool in the evaluation of sleep disorders and as an outcome measure of treatment efficacy in clinical settings with appropriate patient populations. RECOMMENDATIONS: Actigraphy provides an acceptably accurate estimate of sleep patterns in normal, healthy adult populations and inpatients suspected of certain sleep disorders. More specifically, actigraphy is indicated to assist in the evaluation of patients with advanced sleep phase syndrome (ASPS), delayed sleep phase syndrome (DSPS), and shift work disorder. Additionally, there is some evidence to support the use of actigraphy in the evaluation of patients suspected of jet lag disorder and non-24hr sleep/wake syndrome (including that associated with blindness). When polysomnography is not available, actigraphy is indicated to estimate total sleep time in patients with obstructive sleep apnea. In patients with insomnia and hypersomnia, there is evidence to support the use of actigraphy in the characterization of circadian rhythms and sleep patterns/disturbances. In assessing response to therapy, actigraphy has proven useful as an outcome measure in patients with circadian rhythm disorders and insomnia. In older adults (including older nursing home residents), in whom traditional sleep monitoring can be difficult, actigraphy is indicated for characterizing sleep and circadian patterns and to document treatment responses. Similarly, in normal infants and children, as well as special pediatric populations, actigraphy has proven useful for delineating sleep patterns and documenting treatment responses. CONCLUSIONS: Recent research utilizing actigraphy in the assessment and management of sleep disorders has allowed the development of evidence-based recommendations for the use of actigraphy in the clinical setting. Additional research is warranted to further refine and broaden its clinical value.     

Improvement of a patient's circadian rhythm sleep disorders by aripiprazole was associated with stabilization of his bipolar illness

Splitting of the behavioural activity phase has been found in nocturnal rodents with suprachiasmatic nucleus (SCN) coupling disorder. A similar phenomenon was observed in the sleep phase in the diurnal human discussed here, suggesting that there are so‐called evening and morning oscillators in the SCN of humans. The present case suffered from bipolar disorder refractory to various treatments, and various circadian rhythm sleep disorders, such as delayed sleep phase, polyphasic sleep, separation of the sleep bout resembling splitting and circabidian rhythm (48 h), were found during prolonged depressive episodes with hypersomnia. Separation of sleep into evening and morning components and delayed sleep‐offset (24.69‐h cycle) developed when lowering and stopping the dose of aripiprazole (APZ). However, resumption of APZ improved these symptoms in 2 weeks, accompanied by improvement in the patient's depressive state. Administration of APZ may improve various circadian rhythm sleep disorders, as well as improve and prevent manic–depressive episodes, via augmentation of coupling in the SCN network.     

Bidirectional communication between sleep and circadian rhythms and its implications for depression: Lessons from agomelatine

Depression is a family of complex and multifactorial illnesses that are characterized by disruptions in the functioning of a number of physiological, neuroendocrine and behavioral processes. Of these, sleep disturbance and circadian rhythm abnormalities constitute the most prevalent signs of depressive illness. Difficulty in falling asleep, decreases in total sleep time and sleep efficiency, early morning awakenings, and rapid eye movement sleep alterations are all commonly seen in depressed patients. Advances or delays in the phase of circadian rhythms have been documented in patients with major depressive disorder (MDD), bipolar disorder and patients with seasonal affective disorder (SAD). The disturbances in the amplitude and rhythm of melatonin secretion that occur in patients with depression resemble those seen in subjects with chronobiological disorders. The finding that insomnia and circadian rhythm abnormalities are prominent features in depression suggests that a close link exists between melatonin secretion disturbance and depressed mood. This inference has been further strengthened by the finding that agomelatine, a recently introduced melatonergic agent with a novel mechanism of action, has beneficial effects in patients with MDD, bipolar disorder or SAD. Among agomelatine's characteristics are a rapid onset of action and a pronounced effectiveness for improving sleep efficiency and correcting circadian rhythm abnormalities. Disruptions in melatonin secretion or availability may be the common factor, which underlies depressive disorder and its prominent signs and symptoms such as sleep and circadian rhythm abnormalities.     

Influence of running wheel activity on free-running sleep/wake and drinking circadian rhythms in mice.

Previous studies have indicated that manipulation of activity levels can modify characteristics of sleep/wake and activity rhythms. The generality of these observations was evaluated by simultaneously measuring drinking and sleep/wake rhythms while mice had free or no access to a running wheel in constant conditions (DD). Robust circadian rhythms in all parameters were observed in the "wheel free" (unrestricted) condition. When wheels were locked, the peak amplitude of the sleep/wake circadian rhythm decreased by approximately 50% without affecting the amplitude of the drinking rhythm. Total wake time decreased 11% per circadian day when wheels were locked with increases in both NREM and REM sleep. Whereas the amplitude of the drinking waveform was unaffected, wheel restriction caused an equivalent increase in period length (tau) for both rhythms. These results indicate that, unlike the generalized effects of activity on tau, activity restriction influences on rhythm amplitude do not generalize to all behavioral and/or physiological variables. This work also supports the notion that activity influences on sleep/wake rhythm amplitude reflect behavioral "masking" rather than a fundamental change in the direct coupling mechanisms of the biological clock.     

Sleep and activity rhythms are related to circadian phase in the blind.

STUDY OBJECTIVES: Sleep is controlled by both circadian and homeostatic mechanisms. As the light-dark cycle is the most important time cue in humans, blind individuals may have circadian rhythm disorders including sleep. The aim of the study was to assess sleep with simultaneous measurement of an endogenous marker of the circadian clock, namely 6-sulphatoxymelatonin (aMT6s). SETTING AND PARTICIPANTS: 59 registered blind subjects were studied in their own homes. DESIGN: Subjects completed daily sleep and nap diaries for at least four weeks, wore activity monitors continuously, and collected urine samples over 48 hours each week for 3-5 weeks for assessment of aMT6s rhythms. RESULTS: The most sensitive indicator of a circadian rhythm disorder was day-time napping. Subjects with normally entrained (NE) aMT6s rhythms had fewer naps of a shorter duration than abnormally entrained (AE) or free-running (FR) subjects. The timing of these naps was not random; significantly more naps occurred within a five-hour range before and after the aMT6s acrophase (phi (phi)) than outside this range. Disorders in the timing and duration of night sleep in AE subjects manifested as either a permanent advance (advanced sleep phase syndrome, ASPS) or delay (delayed sleep phase syndrome, DSPS). In FR subjects there were transient advances and delays in sleep timing that paralleled aMT6s timing with increased night sleep duration and reduced number and duration of day-time naps associated with a normal aMT6s phase. CONCLUSIONS: Changes in sleep and activity rhythms reflect changes in circadian phase.     

Non-24: eine unterschätzte zirkadiane Schlafstörung bei Blinden

The non-24-hour sleep-wake disorder (Non-24) is a very rare circadian rhythm disorder but present in the majority of totally blind people due to the lack of the photic time cue to reset their circadian pacemaker, the master clock. Up to70?% of totally blind people have to live with their intrinsic circadian rhythm not aligned to the environmental 24-hour day. Due to social and professional demands, most of them attempt to live on a regular 24-hour schedule, although their intrinsic circadian rhythm of sleep and wakefulness follows a non-24-hour cycle. This may result in sleep disturbances and excessive sleepiness during the day. Since the phases of the environmental 24-hour day and of their endogenous circadian rhythm cyclically run in and out of synchrony with each other, symptoms also cyclically increase and decrease. The clinical picture is an intermittent sleep disorder. The characteristics of a cyclic sleep disorder, caused by a Non-24 rhythm, often are not even known to sleep specialists. Diagnosis of Non-24 includes a detailed sleep history, a specific questionnaire, a sleep diary kept over at least 2 weeks, preferably actigraphy and, possibly, polysomnography for differential diagnosis. Currently, symptomatic treatment of insomnia is often centered on prescribing hypnotics or psychopharmaceuticals while stimulants are used to address daytime sleepiness. Melatonin may be a treatment option but is not labelled for synchronization of the sleep-wake rhythm in Germany. Recently, tasimelteon, a melatonin receptor agonist, has received EU approval and provides a causal therapy for Non-24 in totally blind people. Treatment with tasimelteon is able to entrain the non-synchronized endogenous circadian sleep-wake rhythm to the 24-hour day.     

Cognitive Behavioral Therapy as an Adjunct Treatment to Light Therapy for Delayed Sleep Phase Disorder in Young Adults: A Randomized Controlled Feasibility Study

Delayed sleep phase disorder (DSPD) is common among young people, but there is still no evidence-based treatment available. In the present study, the feasibility of cognitive behavioral therapy (CBT) was evaluated as an additive treatment to light therapy (LT) in DSPD. A randomized controlled trial with participants aged 16 to 26 years received LT for two weeks followed by either four weeks of CBT or no treatment (NT). LT advanced sleep-wake rhythm in both groups. Comparing LT+CBT with LT+NT, no significant group differences were observed in the primary endpoints. Although anxiety and depression scores were low at pretreatment, they decreased significantly more in LT+CBT compared to LT+NT. The results are discussed and some suggestions are given for further studies.     

Workshop report. Circadian rhythm sleep–wake disorders: gaps and opportunities

This White Paper presents the results from a workshop cosponsored by the Sleep Research Society (SRS) and the Society for Research on Biological Rhythms (SRBR) whose goals were to bring together sleep clinicians and sleep and circadian rhythm researchers to identify existing gaps in diagnosis and treatment and areas of high-priority research in circadian rhythm sleep–wake disorders (CRSWD). CRSWD are a distinct class of sleep disorders caused by alterations of the circadian time-keeping system, its entrainment mechanisms, or a misalignment of the endogenous circadian rhythm and the external environment. In these disorders, the timing of the primary sleep episode is either earlier or later than desired, irregular from day-to-day, and/or sleep occurs at the wrong circadian time. While there are incomplete and insufficient prevalence data, CRSWD likely affect at least 800,000 and perhaps as many as 3 million individuals in the United States, and if Shift Work Disorder and Jet Lag are included, then many millions more are impacted. The SRS Advocacy Taskforce has identified CRSWD as a class of sleep disorders for which additional high-quality research could have a significant impact to improve patient care. Participants were selected for their expertise and were assigned to one of three working groups: Phase Disorders, Entrainment Disorders, and Other. Each working group presented a summary of the current state of the science for their specific CRSWD area, followed by discussion from all participants. The outcome of those presentations and discussions are presented here.     

Home dim light melatonin onsets with measures of compliance in delayed sleep phase disorder

The dim light melatonin onset (DLMO) assists with the diagnosis and treatment of circadian rhythm sleep disorders. Home DLMOs are attractive for cost savings and convenience, but can be confounded by home lighting and sample timing errors. We developed a home saliva collection kit with objective measures of light exposure and sample timing. We report on our first test of the kit in a clinical population. Thirty‐two participants with delayed sleep phase disorder (DSPD; 17 women, aged 18–52 years) participated in two back‐to‐back home and laboratory phase assessments. Most participants (66%) received at least one 30‐s epoch of light >50 lux during the home phase assessments, but for only 1.5% of the time. Most participants (56%) collected every saliva sample within 5 min of the scheduled time. Eighty‐three per cent of home DLMOs were not affected by light or sampling errors. The home DLMOs occurred, on average, 10.2 min before the laboratory DLMOs, and were correlated highly with the laboratory DLMOs (r = 0.93, P < 0.001). These results indicate that home saliva sampling with objective measures of light exposure and sample timing, can assist in identifying accurate home DLMOs.     

Endophenotypes in bipolar disorder

The search for genes in bipolar disorder has provided numerous genetic loci that have been linked to susceptibility to developing the disorder. However, because of the genetic heterogeneity inherent in bipolar disorder, additional strategies may need to be employed to fully dissect the genetic underpinnings. One such strategy involves reducing complex behaviors into their component parts (endophenotypes). Abnormal neurophysiological, biochemical, endocrinological, neuroanatomical, cognitive, and neuropsychological findings are characteristics that often accompany psychiatric illness. It is possible that some of these may eventually be useful in subdefining complex genetic disorders, allowing for improvements in diagnostic assessment, genetic linkage studies, and development of animal models. Findings in patients with bipolar disorder that may eventually be useful as endophenotypes include abnormal regulation of circadian rhythms (the sleep/wake cycle, hormonal rhythms, etc.), response to sleep deprivation, P300 event-related potentials, behavioral responses to psychostimulants and other medications, response to cholinergics, increase in white matter hyperintensities (WHIs), and biochemical observations in peripheral mononuclear cells. Targeting circadian rhythm abnormalities may be a particularly useful strategy because circadian cycles appear to be an inherent evolutionarily conserved function in all organisms and have been implicated in the pathophysiology of bipolar disorder. Furthermore, lithium has been shown to regulate circadian cycles in diverse species, including humans, possibly through inhibition of glycogen synthase kinase 3-beta (GSK-3beta), a known target of lithium.     

Clinical management of delayed sleep phase disorder

Delayed Sleep Phase Disorder is a circadian rhythm disorder that results in a late timed sleep pattern. Individuals have difficulty falling asleep at a conventional hour and difficulty waking in the morning. We discuss the contributing factors and consequences of a delayed sleep phase and describe treatment approaches. These include therapies to phase change the delayed sleep circadian rhythm such as morning bright light exposure, exogenous melatonin administration, and chronotherapy as well as some behavioral strategies.     

Frequency of narcolepsy symptoms and other sleep disorders in narcoleptic patients and their first-degree relatives

Narcolepsy is a rare neurological sleep disorder affecting around 0.05% of the general population. Genetic factors are known to have an important role in narcolepsy. However, because of its very low prevalence, it is difficult to have groups of comparison between first-degree relatives and general population subjects in order to identify a specific spectrum of disorders in these families. Consequently, from 157 Italian patients with narcolepsy, 263 first-degree relatives were recruited, two refused to participate. These family members were compared with a matched group of 1071 subjects selected from a sample of 3970 subjects representative of the general population of Italy (46 million inhabitants). Finally, 68 spouses of narcoleptic patients were used to assess for possible role of environmental factors. All subjects were interviewed by telephone using the Sleep-EVAL system. Nineteen cases of narcolepsy were discovered among the first-degree relatives of 17 probands (10.8%). Compared with the general population subjects, the relative risk of narcolepsy among female first-degree relatives was of 54.4 and of 105.1 among male first-degree relatives. First-degree relatives were also at higher risk for idiopatic hypersomnia (OR: 23.0), obstructive sleep apnea syndrome (OR: 6.8), adjustment sleep disorder (OR: 4.0), insufficient sleep syndrome (OR: 7.0), circadian rhythm disorders (OR: 2.5), REM behavior disorder (OR: 4.4), and sleep talking (OR: 2.0). The vulnerability to sleep disorders is very high in first-degree relatives and the link with different expressivity and severity of hypersomnia can be confirmed.     

Practice parameters for the role of actigraphy in the study of sleep and circadian rhythms: an update for 2002

Actigraphy is a method used to study sleep-wake patterns and circadian rhythms by assessing movement, most commonly of the wrist. These evidence-based practice parameters are an update to the Practice Parameters for the Use of Actigraphy in the Clinical Assessment of Sleep Disorders, published in 1995. These practice parameters were developed by the Standards of Practice Committee and reviewed and approved by the Board of Directors of the American Academy of Sleep Medicine. Recommendations are based on the accompanying comprehensive review of the medical literature regarding the role of actigraphy, which was developed by a task force commissioned by the American Academy of Sleep Medicine. The following recommendations serve as a guide to the appropriate use of actigraphy. Actigraphy is reliable and valid for detecting sleep in normal, healthy populations, but less reliable for detecting disturbed sleep. Although actigraphy is not indicated for the routine diagnosis, assessment, or management of any of the sleep disorders, it may serve as a useful adjunct to routine clinical evaluation of insomnia, circadian-rhythm disorders, and excessive sleepiness, and may be helpful in the assessment of specific aspects of some disorders, such as insomnia and restless legs syndrome/periodic limb movement disorder. The assessment of daytime sleepiness, the demonstration of multiday human-rest activity patterns, and the estimation of sleep-wake patterns are potential uses of actigraphy in clinical situations where other techniques cannot provide similar information (e.g., psychiatric ward patients). Superiority of actigraphy placement on different parts of the body is not currently established. Actigraphy may be useful in characterizing and monitoring circadian rhythm patterns or disturbances in certain special populations (e.g., children, demented individuals), and appears useful as an outcome measure in certain applications and populations. Although actigraphy may be a useful adjunct to portable sleep apnea testing, the use of actigraphy alone in the detection of sleep apnea is not currently established. Specific technical recommendations are discussed, such as using concomitant completion of a sleep log for artifact rejection and timing of lights out and on; conducting actigraphy studies for a minimum of three consecutive 24-hour periods; requiring raw data inspection; permitting some preprocessing of movement counts; stating that epoch lengths up to 1 minute are usually sufficient, except for circadian rhythm assessment; requiring interpretation to be performed manually by visual inspection; and allowing automatic scoring in addition to manual scoring methods.     

Endophenotypes in bipolar disorder†

The search for genes in bipolar disorder has provided numerous genetic loci that have been linked to susceptibility to developing the disorder. However, because of the genetic heterogeneity inherent in bipolar disorder, additional strategies may need to be employed to fully dissect the genetic underpinnings. One such strategy involves reducing complex behaviors into their component parts (endophenotypes). Abnormal neurophysiological, biochemical, endocrinological, neuroanatomical, cognitive, and neuropsychological findings are characteristics that often accompany psychiatric illness. It is possible that some of these may eventually be useful in subdefining complex genetic disorders, allowing for improvements in diagnostic assessment, genetic linkage studies, and development of animal models. Findings in patients with bipolar disorder that may eventually be useful as endophenotypes include abnormal regulation of circadian rhythms (the sleep/wake cycle, hormonal rhythms, etc.), response to sleep deprivation, P300 event‐related potentials, behavioral responses to psychostimulants and other medications, response to cholinergics, increase in white matter hyperintensities (WHIs), and biochemical observations in peripheral mononuclear cells. Targeting circadian rhythm abnormalities may be a particularly useful strategy because circadian cycles appear to be an inherent evolutionarily conserved function in all organisms and have been implicated in the pathophysiology of bipolar disorder. Furthermore, lithium has been shown to regulate circadian cycles in diverse species, including humans, possibly through inhibition of glycogen synthase kinase 3‐β (GSK‐3β), a known target of lithium. Published 2002 Wiley‐Liss, Inc.     

An evaluation of polymorphisms in casein kinase 1 delta and epsilon genes in major psychiatric disorders

Disturbances of the circadian rhythm are involved in the pathophysiology of bipolar disorder (BD), schizophrenia (SCZ) and major depressive disorder (MDD). Specifically, because clock gene dysfunction is good candidate for enhancing the susceptibility to these psychiatric disorders, we selected two circadian rhythm-related genes (CSNK1D and CSNK1E) and investigated genetic associations of the genes with these three disorders.