Advanced Sleep Phase Syndrome Research Articles

Role of Phosphorylation in the Mammalian Circadian Clock

Circadian clocks regulate a wide variety of processes ranging from gene expression to behavior. At the molecular level, circadian rhythms are thought to be produced by a set of clock genes and proteins interconnected to form transcriptional-translational feedback loops. Rhythmic gene expression was formerly regarded as the major drive for rhythms in clock protein abundance, but recent findings underline the crucial importance of posttranslational mechanisms for both the generation and dynamics of circadian rhythms. In particular, the reversible phosphorylation of PER proteins-essential components within the negative feedback loop in Drosophila and mammals-seems to have a key role for the correct timing of nuclear repression. To understand how PER protein phosphorylation regulates the dynamics of the circadian oscillator, we have mapped endogenous phosphorylation sites in mPER2. Detailed investigation of the functional role of one particular phosphorylation site (Ser-659, which is mutated in the familial advanced sleep phase syndrome [FASPS]) led us propose a model of functionally different phosphorylation sites in PER2. This concept explains not only the FASPS phenotype, but also the effect of the tau mutation in hamster.

Circadian Rhythms in the CNS and Peripheral Clock Disorders: Human Sleep Disorders and Clock Genes

Genetic analyses of circadian rhythm sleep disorders (CRSD), such as familial advanced sleep phase syndrome (ASPS) and delayed sleep phase syndrome (DSPS), and morningness-eveningness revealed the relationship between variations in clock genes and diurnal change in human behaviors. Variations such as T3111C in the Clock gene are reportedly associated with morningness-eveningness. Two of the pedigrees of familial ASPS (FASPS) are caused by mutations in clock genes: the S662G mutation in the Per2 gene or the T44A mutation in the casein kinase 1 delta (CK1δ) gene, although these mutations are not found in other pedigrees of FASPS. As for DSPS, a missense variation in the Per3 gene is identified as a risk factor, while the one in the CK1ε gene is thought to be protective. These findings suggest that further, as yet unidentified, gene variations are involved in human circadian activity. Many of the CRSD-relevant variations reported to date seem to affect the phosphorylation status of the clock proteins. A recent study using mathematical models of circadian rhythm generation has provided a new insight into the role of phosphorylation in the molecular mechanisms of these disorders.

Modeling of a Human Circadian Mutation Yields Insights into Clock Regulation by PER2

Circadian rhythms are endogenous oscillations of physiological and behavioral phenomena with period length of approximately 24 hr. A mutation in human Period 2 (hPER2), a gene crucial for resetting the central clock in response to light, is associated with familial advanced sleep phase syndrome (FASPS), an autosomal dominant condition with early morning awakening and early sleep times. The FASPS hPER2 S662G mutation resulted in PER2 being hypophosphorylated by casein kinase I (CKI) in vitro. We generated transgenic mice carrying the FASPS hPER2 S662G mutation and faithfully recapitulate the human phenotype. We show that phosphorylation at S662 leads to increased PER2 transcription and suggest that phosphorylation at another site leads to PER2 degradation. Altering CKIdelta dosage modulates the S662 phenotype demonstrating that CKIdelta can regulate period through PER2 in vivo. Modeling a naturally occurring human variant in mice has yielded novel insights into PER2 regulation.

A Circadian Sleep Disorder Reveals a Complex Clock

Circadian rhythms are established by transcription of clock genes and autoregulatory transcriptional feedback loops. In this issue, Xu et al. (2007) characterize mice expressing a human Per2 mutation identified in patients with familial advanced sleep phase syndrome. Their results reveal that PER2 phosphorylation, by CK1delta and other kinases, is surprisingly complex and has opposite effects on PER2 levels and period length.

Genetic Basis for Sleep Regulation and Sleep Disorders

Sleep disorders arise by an interaction between the environment and the genetic makeup of the individual but the relative contribution of nature and nurture varies with diseases. At one extreme are the disorders with simple Mendelian patterns of inheritance such as familial advanced sleep phase syndrome, and at the other extreme are diseases such as insomnia, which can be associated with a multitude of medical and psychiatric conditions. In this article, we review data on the relative contribution of genetic and environmental factors in the pathogenesis of various sleep disorders. The understanding of many of these disorders has been advanced by the study of sleep and circadian rhythms in model laboratory organisms. We summarize this model system research and how it relates to human sleep disorders. The current challenge in this field is the identification of susceptibility genetic loci for complex diseases such as obstructive sleep apnea. We anticipate such identification will increase our ability to assess risk for disease before symptom onset and by doing so will shift the focus from treatment to prevention of disease.

Differential effects of PER2 phosphorylation: molecular basis for the human familial advanced sleep phase syndrome (FASPS)

PERIOD (PER) proteins are central components within the mammalian circadian oscillator, and are believed to form a negative feedback complex that inhibits their own transcription at a particular circadian phase. Phosphorylation of PER proteins regulates their stability as well as their subcellular localization. In a systematic screen, we have identified 21 phosphorylated residues of mPER2 including Ser 659, which is mutated in patients suffering from familial advanced sleep phase syndrome (FASPS). When expressing FASPS-mutated mPER2 in oscillating fibroblasts, we can phenocopy the short period and advanced phase of FASPS patients' behavior. We show that phosphorylation at Ser 659 results in nuclear retention and stabilization of mPER2, whereas phosphorylation at other sites leads to mPER2 degradation. To conceptualize our findings, we use mathematical modeling and predict that differential PER phosphorylation events can result in opposite period phenotypes. Indeed, interference with specific aspects of mPER2 phosphorylation leads to either short or long periods in oscillating fibroblasts. This concept explains not only the FASPS phenotype, but also the effect of the tau mutation in hamster as well as the doubletime mutants (dbtS and dbtL ) in Drosophila.

睡眠障害の理解

The most frequent sleep problems are sleep-related breathing disorders, insomnia, excessive daytime sleepiness, and circadian rhythm disorder. In 2004, we treated 468 sleep disorder patients, at the Sleep Disorder Center, Shiga University of Medical Science Hospital. Forty-nine percent of the subjects were diagnosed as having sleep related breathing disorders, 22% as insomnia, 10% as rhythm disorders and 5% as having excessive daytime sleepiness. Insomnia is a common sleep-wake-related complaint, and sleeping pills are among the most commonly prescribed drugs in clinical practice. However, insomnia is a symptom that can be caused by various disorder's, many of which require specific therapies. One specific cause of insomnia in older adults is restless legs syndrome. This condition, characterized by an urge to move the legs, which is usually accompanied by sensations of discomfort and aggravations of symptoms by rest. Daytime sleepiness is a common complaint. Snoring, the use of hypnotic agents, sleep difficulties, irregular sleep-wake schedule and sleep deprivation are related to daytime sleepiness. Circadian rhythm sleep disorders have intrinsic and extrinsic subtypes: delayed sleep phase syndrome, advanced sleep phase syndrome and non-24-h sleep-wake syndrome. The underlying problem of circadian rhythm sleep disorders is that the patient cannot sleep when sleep is desired. Waking episodes may occur at inappropriate times; therefore, the patient may complain of insomnia or excessive sleepiness.

Treatment of sleep disorders in elderly patients

Sleep disorders are common among the elderly and are associated with diminished quality of life, increased risk for development of psychiatric disorders, inappropriate use of sleep aids, and decreased daytime functioning. The most common and important sleep disorders in the elderly include insomnia, obstructive sleep apnea syndrome, restless legs syndrome, rapid eye movement sleep behavior disorder, and the advanced sleep phase syndrome. In this article, we summarize the current treatment strategies for each of these sleep-related disorders. Before contemplating specific treatments, the authors recommend that more conservative and nonpharmacologic therapies be attempted first because the elderly are more likely to have medication side effects or complications related to surgery. Many sleep problems can be treated by simple sleep hygiene modifications that can be implemented and adopted easily. For others, therapies that specifically consider older adults may be required. For each of the sleep disorders we provide an updated discussion of therapies beginning with diet and lifestyle, pharmacologic treatment, interventional procedures, surgery, assistive devices, physical and speech therapy, exercise, and emerging therapies with specific considerations for older adults.

A single‐nucleotide polymorphism in the 5′‐untranslated region of the hPER2 gene is associated with diurnal preference

The PERIOD2 (PER2) gene is a key component of the molecular mechanism that generates circadian rhythms in mammals. A missense mutation in the human PER2 gene has previously been linked to advanced sleep phase syndrome (ASPS). We have investigated three other single-nucleotide polymorphisms in the hPER2 gene, one downstream of the transcription start site (C-1228T), one in exon 2 in the 5'-untranslated region (5'-UTR) (C111G), and one missense mutation (G3853A) causing a glycine to glutamine substitution in the predicted protein. Subjects selected from a group of 484 volunteers for extreme morning or evening preference, or intermediate diurnal preference were genotyped with regard to the three polymorphisms (n=35 for each group). Whereas allele frequencies for the other two polymorphisms did not differ significantly between any of the groups, the 111G allele frequency was significantly higher in subjects with extreme morning preference (0.14) than in subjects with extreme evening preference (0.03) (Fisher's exact test, two-sided P value=0.031, odds ratio=5.67). No significant difference in 111G allele frequency was observed between either of these groups and subjects with intermediate diurnal preference. Computer prediction indicated that the C111G polymorphism, which occurs 12 bases upstream from the translation start codon, might alter the secondary structure of the transcript. The PER2 111G allele associates with morning preference and is a potential candidate allele for ASPS.

Hey, That Clock Is Fast

If you like to "burn the midnight oil," you'll find it hard to imagine the behavior of humans who have a defect in signaling by CKI (casein kinase I), a protein kinase that participates in the biochemical machinery that establishes circadian rhythms. Affected individuals go to sleep early and awaken early in the morning. To explore the molecular mechanisms behind this sleep syndrome, known as FASPS (familial advanced sleep phase syndrome), Xu et al. characterized a mutation in the CKI δ gene from a family afflicted with FASPS. The encoded kinase had decreased catalytic activity in vitro. Transgenic mice engineered to express the mutation had a circadian period that was shorter than normal, as do the human patients noted above. Thus, the authors conclude that CKIδ is an important component of the mammalian clock. The components of the clock are generally evolutionarily conserved between mammals and fruit flies and are controlled by similar phosphorylation mechanisms, but when transgenic flies were created that expressed the mutant CKI, they actually had a lengthened circadian period. Thus, although the "parts list" is similar, clock assembly in flies and mammals appears to differ. Nevertheless, both mechanisms provide the animals with similar timing functions. Y. Xu, Q. S. Padiath, R. E. Shapiro, C. R. Jones, S. C. Wu, N. Saigoh, K. Saigoh, L. J. Ptáček, Y.-H. Fu, Functional consequences of a CKI δ mutation causing familial advanced sleep phase syndrome. Nature 434 , 640-644 (2005). [PubMed]

Importin α/β Mediates Nuclear Transport of a Mammalian Circadian Clock Component, mCRY2, Together with mPER2, through a Bipartite Nuclear Localization Signal

Circadian rhythms, which period is approximately one day, are generated by endogenous biological clocks. These clocks are found throughout the animal kingdom, as well as in plants and even in prokaryotes. Molecular mechanisms for circadian rhythms are based on transcriptional oscillation of clock component genes, consisting of interwoven autoregulatory feedback loops. Among the loops, the nuclear transport of clock proteins is a crucial step for transcriptional regulation. In the present study, we showed that the nuclear entry of mCRY2, a mammalian clock component, is mediated by the importin alpha/beta system through a bipartite nuclear localization signal in its carboxyl end. In vitro transport assay using digitonin-permeabilized cells demonstrated that all three importin alphas, alpha1 (Rch1), alpha3 (Qip-1), and alpha7 (NPI-2), can mediate mCRY2 import. mCRY2 with the mutant nuclear localization signal failed to transport mPER2 into the nucleus of mammalian cultured cells, indicating that the nuclear localization signal identified in mCRY2 is physiologically significant. These results suggest that the importin alpha/beta system is involved in nuclear entry of mammalian clock components, which is indispensable to transcriptional oscillation of clock genes.

Functional consequences of a CKIδ mutation causing familial advanced sleep phase syndrome

Familial advanced sleep phase syndrome (FASPS) is a human behavioural phenotype characterized by early sleep times and early-morning awakening. It was the first human, mendelian circadian rhythm variant to be well-characterized, and was shown to result from a mutation in a phosphorylation site within the casein kinase I (CKI)-binding domain of the human PER2 gene. To gain a deeper understanding of the mechanisms of circadian rhythm regulation in humans, we set out to identify mutations in human subjects leading to FASPS. We report here the identification of a missense mutation (T44A) in the human CKIdelta gene, which results in FASPS. This mutant kinase has decreased enzymatic activity in vitro. Transgenic Drosophila carrying the human CKIdelta-T44A gene showed a phenotype with lengthened circadian period. In contrast, transgenic mice carrying the same mutation have a shorter circadian period, a phenotype mimicking human FASPS. These results show that CKIdelta is a central component in the mammalian clock, and suggest that mammalian and fly clocks might have different regulatory mechanisms despite the highly conserved nature of their individual components.

Sleep in the Geriatric Patient Population

Older patients often suffer from sleep disturbances caused by age-related physiological changes, polypharmacy, changes in circadian rhythm, retirement, and loss of spouse. Many seniors have readily diagnosed sleep disorders that can be treated to achieve improvement in daytime somnolence or cognitive impairments. After a discussion of normal age-related changes in sleep, specific sleep pathologies common in the elderly will be reviewed, including sleep apnea, restless legs syndrome, advanced sleep phase syndrome, and rapid eye movement sleep behavior disorder.

Modeling the mammalian circadian clock: Sensitivity analysis and multiplicity of oscillatory mechanisms

We extend the study of a computational model recently proposed for the mammalian circadian clock (Proc. Natl Acad. Sci. USA 100 (2003) 7051). The model, based on the intertwined positive and negative regulatory loops involving the Per, Cry, Bmal1, and Clock genes, can give rise to sustained circadian oscillations in conditions of continuous darkness. These limit cycle oscillations correspond to circadian rhythms autonomously generated by suprachiasmatic nuclei and by some peripheral tissues. By using different sets of parameter values producing circadian oscillations, we compare the effect of the various parameters and show that both the occurrence and the period of the oscillations are generally most sensitive to parameters related to synthesis or degradation of Bmal1 mRNA and BMAL1 protein. The mechanism of circadian oscillations relies on the formation of an inactive complex between PER and CRY and the activators CLOCK and BMAL1 that enhance Per and Cry expression. Bifurcation diagrams and computer simulations nevertheless indicate the possible existence of a second source of oscillatory behavior. Thus, sustained oscillations might arise from the sole negative autoregulation of Bmal1 expression. This second oscillatory mechanism may not be functional in physiological conditions, and its period need not necessarily be circadian. When incorporating the light-induced expression of the Per gene, the model accounts for entrainment of the oscillations by light–dark (LD) cycles. Long-term suppression of circadian oscillations by a single light pulse can occur in the model when a stable steady state coexists with a stable limit cycle. The phase of the oscillations upon entrainment in LD critically depends on the parameters that govern the level of CRY protein. Small changes in the parameters governing CRY levels can shift the peak in Per mRNA from the L to the D phase, or can prevent entrainment. The results are discussed in relation to physiological disorders of the sleep–wake cycle linked to perturbations of the human circadian clock, such as the familial advanced sleep phase syndrome or the non-24h sleep–wake syndrome.

Approach to the patient with a sleep complaint.

There have always been sleep disorders, many of which have been recognized for centuries, and some of our treatments have even been dated from the past. However, there has been a dramatic increase in knowledge about sleep disorders and their treatments in the past 20 years. It is now possible to objectively diagnose most sleep disorders and new, specific treatments can be instituted. The recent recognition of chronobiology has resulted in an understanding of the alterations in the sleep-wake pattern of humans. Genetic causes of sleep disorders, such as advanced sleep phase syndrome, have shed new light on disorders that were previously believed to be largely behaviorally produced. Neurochemical changes have led to a better understanding of the pathophysiology of some disorders such as narcolepsy. However, despite advances in our understanding of sleep disorders, accurate diagnosis and treatment always requires a detailed understanding of the patient's sleep-wake cycle and medical history. The art of good sleep medicine still lies in the ability of the clinician to take a thorough history, develop a differential diagnosis, and formulate a treatment plan. This article details the important elements of the clinical evaluation.

Circadian rhythm disorders.

Circadian rhythm sleep disorders occur when individuals attempt to sleep at the wrong circadian time. The misalignment between the internal circadian timing system and the external environment is typically due to either an alteration in the functioning of the circadian timing system (e.g., delayed or advanced sleep phase syndrome) or to changes in the external environment (e.g., jet lag). However, the clinical presentation of most of the circadian rhythm sleep disorders is influenced by a combination of physiological, behavioral, and environmental factors. These disorders lead to complaints of insomnia and excessive daytime sleepiness, with impairment in important areas of functioning and quality of life. Current treatments primarily involve the use of circadian synchronizing agents, such as light, to realign the internal and external environment. These treatments are limited by the availability of adequate diagnostic tools and well-controlled clinical trials. A better understanding of the pathophysiology of these disorders is required to develop more effective treatments.

Efficacy of Enhanced Evening Light for Advanced Sleep Phase Syndrome

This study tested whether a newly designed enhanced evening light therapy was well tolerated and effective in relieving symptoms of Advanced Sleep Phase Syndrome (ASPS). Participants with self-reported ASPS symptoms were 47 older adults (21 men and 26 women, age 60-86). After baseline, participants underwent 28 consecutive days of either dim or enhanced intensity light treatment for 2-3 hr in the evening. Enhanced evening light (~265 lux) exposure was no more effective than a placebo dim light (~2 lux) at alleviating advanced sleep phase as measured by actigraphically recorded sleep and urinary 6-sulphatoxymelatonin (aMT6s) excretion patterns. Participants receiving the enhanced light reported subjective benefit and a significant delay in sleep onset as compared to the placebo. Although compliance was good and the new enhanced evening light therapy design was well tolerated, the benefits were statistically equivocal.

Two pedigrees of familial advanced sleep phase syndrome in Japan.

To determine whether a known missense mutation (bp2106 A/G) in hPer2 (a human homolog of the Drosophila period gene) for familial advanced sleep phase syndrome in a Caucasian family is involved in Japanese familial advanced sleep phase syndrome pedigrees. We identified 2 new Japanese families with advanced sleep phase syndrome, and a systematic survey was carried out in 28 relatives of theses 2 families. A total of 9 affected subjects were identified. The affected members showed significantly strong morningness tendencies compared with the unaffected members in various circadian parameters including the Horne-Ostberg Morningness-Eveningness Questionnaire score (77.3 +/- 4.8 vs 57.5 +/- 7.6, p < 0.001), average sleep-onset time (20:45 +/- 75 min vs 23:16 +/- 64 min, p < 0.02), and average wake time (4:55 +/- 38 min vs 6:13 +/- 25 min, p < 0.01), as well as saliva dim-light melatonin-onset time (20:15 +/- 21 min vs 22:25 +/- 65 min, p < 0.02). DNA samples were obtained from 7 affected and 7 unaffected subjects. None of the tested subjects possessed the missense mutation (bp2106 A/G) in hPer2. Furthermore, there is no significant linkage between affected subjects with hPer2 region by 2-point mapping and by direct sequencing of 23 exons of hPer2. These findings support the notion of genetic heterogeneity of familial advanced sleep phase syndrome cases in humans. The search for more familial advanced sleep phase syndrome cases and for loci other than hPer2 are necessary to further examine the roles of circadian-related genes in genetically determined human circadian rhythm disorders.

Mutation screening of the human period 2 gene in bipolar disorder

We tested whether the human period 2 gene (h per2), one of the essential components of the circadian oscillator, might have influence on bipolar disorder. We screened 88 bipolar disorder patients and 127 controls, all of Japanese origin. Screening in the casein kinase I epsilon (CKIϵ) binding region of h per2, which was previously reported in familial advanced sleep-phase syndrome patients, with polymerase chain reaction amplification revealed four polymorphisms. One of the four polymorphisms had an amino acid substitution of a serine at 662 with a glycine (S662G). The frequencies of the S662G allele and genotypes on patients with bipolar disorder were very low and had no difference from those in controls. Polymorphism on the CKIϵ binding region of h per2 gene which was previously reported, is unlikely to play an important role in the development of bipolar disorder.

Big Ben Rings in a Lesson on Biological Clocks

There is a long history of experimental work seeking a connection between circadian clocks and the cell cycle. For some eukaryotic, unicellular systems, the evidence is quite good—photocycles that entrain circadian rhythms reset ∼24 hr rhythms of cell division that persist for many days in constant darkness or constant light (reviewed by Edmunds, 1988xEdmunds, L.N. Jr. See all ReferencesEdmunds, 1988). Are there comparable interactions in multicellular organisms, even mammals?Cheng Chi Lee produced a list of novel phenotypes in Per 2 mutant mice that indicate action of PER as a tumor suppressor, as a regulator of cell growth, and as a component of the DNA damage response (Fu et al., 2002xThe circadian gene Period2 plays an important role in tumor suppression and DNA damage response in vivo. Fu, L., Pelicano, H., Liu, J., Huang, P., and Lee, C. Cell. 2002; 111: 41–50Abstract | Full Text | Full Text PDF | PubMed | Scopus (690)See all References(Fu et al., 2002). First, there is a highly significant difference in the frequency of spontaneous and γ irradiation-induced tumors and hyperplasia in Per2 mice. In fact, all Per2 mice develop an otherwise rarely encountered, salivary gland hyperplasia by the age of 8 months. Per2 mice were also found to be unusually resistant to irradiation-induced apoptosis. This deficiency appears to be linked to reduced induction of p53 and associated cytochrome c regulation. Even more surprising, Lee's laboratory reports that genes composing the clock are induced by γ irradiation in wild-type but not Per2 mice, suggesting a possible role for the clock itself in the apoptotic response.Timed expression of several genes central to cell cycle control is altered in Per2 mice. For example, both cyclin A and cyclin D1 mRNAs accumulate in hepatocytes from wild-type mice with a circadian rhythm. The phase and amplitude of both rhythms appear to be substantially altered in Per2 mice (Fu et al., 2002xThe circadian gene Period2 plays an important role in tumor suppression and DNA damage response in vivo. Fu, L., Pelicano, H., Liu, J., Huang, P., and Lee, C. Cell. 2002; 111: 41–50Abstract | Full Text | Full Text PDF | PubMed | Scopus (690)See all References(Fu et al., 2002). Since cyclin D1 is a target for c-myc, the latter gene's regulation was also examined; c-myc too oscillates with a circadian rhythm that is significantly altered in Per2 mutants. Lee suggested that, in particular, strong upward swings in c-myc expression may underlie the salivary gland hyperplasia his laboratory sees in Per2 mice.Testing a focused proposal of this sort will be challenging because circadian clocks command such broad programs of timed gene expression. Recall that in the mouse, 24 hr clocks not only determine the sequential expression of hundreds of genes, but the list of clock-controlled targets is tissue specific, amplifying the complexity of the temporal code. Presumably, a Per2 mutant response ripples through the entire program of rhythmic expression in each tissue. Surely connections between individual clock-controlled genes and elements of the Per2 phenotype will remain speculative for awhile. These difficulties aside, the mouse Per2 study does remind us that a dominant mutation of this gene has been associated with FASPS, a familial sleep disorder in humans (Toh et al., 2001xAn hPer2 phosphorylation site mutation in familial advanced sleep phase syndrome. Toh, K.L., Jones, C.R., He, Y., Eide, E.J., Hinz, W.A., Virshup, D.M., Ptacek, L.J., and Fu, Y.H. Science. 2001; 291: 1040–1043Crossref | PubMed | Scopus (824)See all References(Toh et al., 2001). It would be fascinating to study the range of phenotypic effects associated with this Per2 mutation in transgenic mice.