Advanced sleep phase disorder
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Advanced Sleep Phase Disorder (ASPD), also known as the advanced sleep-phase type (ASPT) of circadian rhythm sleep disorder, is a condition that is characterized by a recurrent pattern of early evening (e.g. 7-9 PM) sleepiness and very early morning awakening (e.g. 2-4 AM). This sleep phase advancement can interfere with daily social and work schedules, and results in shortened sleep duration and excessive daytime sleepiness. The timing of sleep and melatonin levels are regulated by the body's central
circadian clock A circadian clock, or circadian oscillator, is a biochemical oscillator that cycles with a stable phase (waves), phase and is synchronized with solar time. Such a clock's ''in vivo'' period is necessarily almost exactly 24 hours (the earth's curre ...
, which is located in the
suprachiasmatic nucleus The suprachiasmatic nucleus or nuclei (SCN) is a tiny region of the brain in the hypothalamus, situated directly above the optic chiasm. It is responsible for controlling circadian rhythms. The neuronal and hormonal activities it generates regula ...
in the
hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamu ...
.


Symptoms

Individuals with ASPD report being unable to stay awake until conventional bedtime, falling asleep early in the evening, and being unable to stay asleep until their desired waking time, experiencing early morning
insomnia Insomnia, also known as sleeplessness, is a sleep disorder in which people have trouble sleeping. They may have difficulty falling asleep, or staying asleep as long as desired. Insomnia is typically followed by daytime sleepiness, low energy, ...
. When someone has advanced sleep phase disorder their
melatonin Melatonin is a natural product found in plants and animals. It is primarily known in animals as a hormone released by the pineal gland in the brain at night, and has long been associated with control of the sleep–wake cycle. In vertebrates ...
levels and core body temperature cycle hours earlier than an average person. These symptoms must be present and stable for a substantial period of time to be correctly diagnosed.


Diagnosis

Individuals expressing the above symptoms may be diagnosed with ASPD using a variety of methods and tests. Sleep specialists measure the patient's sleep onset and offset, dim light melatonin onset, and evaluate Horne-Ostberg morningness-eveningness questionnaire results. Sleep specialists may also conduct a
polysomnography Polysomnography (PSG), a type of sleep study, is a multi-parameter study of sleep and a diagnostic tool in sleep medicine. The test result is called a polysomnogram, also abbreviated PSG. The name is derived from Greek and Latin roots: the Gree ...
test to rule out other sleep disorders like
narcolepsy Narcolepsy is a long-term neurological disorder that involves a decreased ability to regulate sleep–wake cycles. Symptoms often include periods of excessive daytime sleepiness and brief involuntary sleep episodes. About 70% of those affec ...
. Age and family history of the patient is also taken into consideration.


Treatment

Once diagnosed, ASPD may be treated with bright
light therapy Light therapy, also called phototherapy or bright light therapy is intentional daily exposure to direct sunlight or similar-intensity artificial light in order to treat medical disorders, especially seasonal affective disorder (SAD) and circadi ...
in the evenings, or behaviorally with
chronotherapy Chronotherapy, also called chronotherapeutics or chronotherapeutic drug delivery, refers to the coordination of therapeutic treatments with an individual's circadian or other rhythmic cycles. This may be done to maximize effectiveness of a sp ...
, in order to delay sleep onset and offset. The use of pharmacological approaches to treatment are less successful due to the risks of administering sleep-promoting agents early in the morning. Additional methods of treatment, like timed
melatonin Melatonin is a natural product found in plants and animals. It is primarily known in animals as a hormone released by the pineal gland in the brain at night, and has long been associated with control of the sleep–wake cycle. In vertebrates ...
administration or
hypnotic Hypnotic (from Greek ''Hypnos'', sleep), or soporific drugs, commonly known as sleeping pills, are a class of (and umbrella term for) psychoactive drugs whose primary function is to induce sleep (or surgical anesthesiaWhen used in anesthesia ...
s have been proposed, but determining their safety and efficacy will require further research. Unlike other sleep disorders, ASPD does not necessarily disrupt normal functioning at work during the day and some patients may not complain of excessive daytime sleepiness. Social obligations may cause an individual to stay up later than their circadian rhythm requires, however, they will still wake up very early. If this cycle continues, it can lead to chronic sleep deprivation and other
sleep disorders A sleep disorder, or somnipathy, is a medical disorder of an individual's sleep patterns. Some sleep disorders are severe enough to interfere with normal physical, mental, social and emotional functioning. Polysomnography and actigraphy are tests ...
.


Epidemiology

ASPD is more common among middle and older adults. The estimated prevalence of ASPD is about 1% in middle-age adults, and is believed to affect men and women equally.  The disorder has a strong familial tendency, with 40-50% of affected individuals having relatives with ASPD. A genetic basis has been demonstrated in one form of ASPD, familial advanced sleep phase disorder (FASPS), which implicates missense mutations in genes hPER2 and CKIdelta in producing the advanced sleep phase phenotype. The identification of two different genetic mutations suggests that there is heterogeneity of this disorder.  


Familial advanced sleep phase syndrome


FASPS symptoms

While advanced sleep and wake times are relatively common, especially among older adults, the extreme phase advance characteristic of familial advanced sleep phase syndrome (also known as familial advanced sleep phase disorder) is rare. Individuals with FASPS fall asleep and wake up 4–6 hours earlier than the average population, generally sleeping from 7:30pm to 4:30am. They also have a free running circadian period of 22 hours, which is significantly shorter than the average human period of slightly over 24 hours. The shortened period associated with FASPS results in a shortened period of activity, causing earlier sleep onset and offset. This means that individuals with FASPS must delay their sleep onset and offset each day in order to entrain to the 24-hour day. On holidays and weekends, when the average person's sleep phase is delayed relative to their workday sleep phase, individuals with FASPS experience further advance in their sleep phase. Aside from the unusual timing of sleep, FASPS patients experience normal quality and quantity of sleep. Like general ASPD, this syndrome does not inherently cause negative impacts, however,
sleep deprivation Sleep deprivation, also known as sleep insufficiency or sleeplessness, is the condition of not having adequate duration and/or quality of sleep to support decent alertness, performance, and health. It can be either chronic or acute and may vary ...
may be imposed by social norms causing individuals to delay sleep until a more socially acceptable time, causing them to losing sleep due to earlier-than-usual wakeup time. Another factor that distinguishes FASPS from other advanced sleep phase disorders is its strong familial tendency and life-long expression. Studies of affected lineages have found that approximately 50% of directly related family members experience the symptoms of FASPS, which is an autosomal dominant trait. Diagnosis of FASPS can be confirmed through genetic sequencing analysis by locating genetic mutations known to cause the disorder. Treatment with sleep and wake scheduling and bright light therapy can be used to try to delay sleep phase to a more conventional time frame, however treatment of FASPS has proven largely unsuccessful. Bright light exposure in the evening (between 7:00 and 9:00), during the delay zone as indicated by the
phase response curve A phase response curve (PRC) illustrates the transient change (phase response) in the cycle period of an oscillation induced by a perturbation as a function of the phase at which it is received. PRCs are used in various fields; examples of biolog ...
to light, has been shown to delay circadian rhythms, resulting in later sleep onset and offset in patients with FASPS or other advanced sleep phase disorders.


Discovery

In 1999,
Louis Ptáček Louis Ptáček (Czech origin, Ptáček means a Little Bird) is an American neurologist and professor who contributed greatly to the field of genetics and neuroscience. He was also an HHMI investigator from 1997 to 2018. His chief areas of research ...
conducted a study at the University of Utah in which he coined the term ''familial advanced sleep phase disorder'' after identifying individuals with a genetic basis for an advanced sleep phase. The first patient evaluated during the study reported "disabling early evening sleepiness" and "early morning awakening"; similar symptoms were also reported in her family members. Consenting relatives of the initial patient were evaluated, as well as those from two additional families. The clinical histories, sleep logs and actigraphy patterns of subject families were used to define a hereditary circadian rhythm variant associated with a short endogenous (i.e. internally-derived) period. The subjects demonstrated a phase advance of sleep-wake rhythms that was distinct not only from control subjects, but also to sleep-wake schedules widely considered to be conventional. The subjects were also evaluated using the Horne-Östberg questionnaire, a structured self-assessment questionnaire used to determine morningness-eveningness in human circadian rhythms. The Horne-Östberg scores of first-degree relatives of affected individuals were higher than those of 'marry-in' spouses and unrelated control subjects. While much of morning and evening preference is heritable, the allele causing FASPS was hypothesized to have a quantitatively larger effect on clock function than the more common genetic variations that influence these preferences. Additionally, the circadian phase of subjects was determined using plasma
melatonin Melatonin is a natural product found in plants and animals. It is primarily known in animals as a hormone released by the pineal gland in the brain at night, and has long been associated with control of the sleep–wake cycle. In vertebrates ...
and body core temperature measurements; these rhythms were both phase-advanced by 3–4 hours in FASPS subjects compared with control subjects. The Ptáček group also constructed a pedigree of the three FASPS kindreds which indicated a clear
autosomal dominant In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...
transmission of the sleep phase advance. In 2001, the research group of Phyllis C. Zee phenotypically characterized an additional family affected with ASPS. This study involved an analysis of sleep/wake patterns, diurnal preferences (using a Horne-Östberg questionnaire), and the construction of a pedigree for the affected family. Consistent with established ASPS criteria, the evaluation of subject sleep architecture indicated that the advanced sleep phase was due to an alteration of circadian timing rather than an exogenous (i.e. externally-derived) disruption of sleep homeostasis, a mechanism of
sleep regulation A circadian rhythm (), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism (i.e., endogenous) and responds to ...
. Furthermore, the identified family was one in which an ASPS-affected member was present in every generation; consistent with earlier work done by the Ptáček group, this pattern suggests that the phenotype segregates as a single gene with an autosomal dominant mode of inheritance. In 2001, the research groups of Ptáček and
Ying-Hui Fu Ying-Hui Fu () is a Taiwanese-American biologist and human geneticist who has made important contributions to understanding the genetics of many neurological disorders. Her chief discoveries include describing Mendelian sleep phenotypes, identif ...
published a genetic analysis of subjects experiencing the advanced sleep phase, implicating a mutation in the CK1-binding region of
PER2 PER2 is a protein in mammals encoded by the ''PER2'' gene. ''PER2'' is noted for its major role in circadian rhythms. Discovery The ''per ''gene'' ''was first discovered using forward genetics in '' Drosophilla melanogaster'' in 1971. Mammalia ...
in producing the FASPS behavioral phenotype. FASPS is the first disorder to link known core clock genes directly with human circadian sleep disorders. As the PER2 mutation is not exclusively responsible for causing FASPS, current research has continued to evaluate cases in order to identify new mutations that contribute to the disorder.


Mechanisms (Per2 and CK1)

Two years after reporting the finding of FASPS, Ptáček's and Fu's groups published results of genetic sequencing analysis on a family with FASPS. They genetically mapped the FASPS locus to
chromosome 2 Chromosome 2 is one of the twenty-three pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 2 is the second-largest human chromosome, spanning more than 242 million base pairs and representing almost e ...
q where very little human genome sequencing was then available. Thus, they identified and sequenced all the genes in the critical interval. One of these was ''Period2'' (''Per2'') which is a mammalian gene sufficient for the maintenance of circadian rhythms. Sequencing of the ''hPer2'' gene ('h' denoting a human strain, as opposed to Drosophila or mouse strains) revealed a serine-to-glycine
point mutation A point mutation is a genetic mutation where a single nucleotide base is changed, inserted or deleted from a DNA or RNA sequence of an organism's genome. Point mutations have a variety of effects on the downstream protein product—consequences ...
in the Casein Kinase I (CK1)
binding domain In molecular biology, binding domain is a protein domain which binds to a specific atom or molecule, such as calcium or DNA. A protein domain is a part of a protein sequence and a tertiary structure that can change or evolve, function, and live ...
of the hPER2 protein that resulted in hypophosphorylation of hPER2 in vitro. The hypophosphorylation of hPER2 disrupts the transcription-translation (negative) feedback loop (TTFL) required for regulating the stable production of hPER2 protein. In a wildtype individual, ''Per2'' mRNA is transcribed and translated to form a PER2 protein. Large concentrations of PER2 protein inhibits further transcription of ''Per2'' mRNA. CK1 regulates PER2 levels by binding to a CK1 binding site on the protein, allowing for phosphorylation which marks the protein for degradation, reducing protein levels. Once proteins become phosphorylated, PER2 levels decrease again, and ''Per2'' mRNA transcription can resume. This negative feedback regulates the levels and expression of these circadian clock components. Without proper phosphorylation of hPER2 in the instance of a mutation in the CK1 binding site, less ''Per2'' mRNA is transcribed and the period is shortened to less than 24 hours. Individuals with a shortened period due to this phosphorylation disruption entrain to a 24h light-dark cycle, which may lead to a phase advance, causing earlier sleep and wake patterns. However, a 22h period does not necessitate a phase shift, but a shift can be predicted depending on the time the subject is exposed to the stimulus, visualized on a Phase Response Curve (PRC). This is consistent with studies of the role of CK1ɛ (a unique member of the CK1 family) in the TTFL in mammals and more studies have been conducted looking at specific regions of the Per2 transcript. In 2005, Fu's and Ptáček's labs reported discovery of a mutation in CKIδ (a functionally redundant form of CK1ɛ in the phosphorylation process of PER2) also causing FASPS. An A-to-G
missense mutation In genetics, a missense mutation is a point mutation in which a single nucleotide change results in a codon that codes for a different amino acid. It is a type of nonsynonymous substitution. Substitution of protein from DNA mutations Missense m ...
resulted in a threonine-to-alanine alteration in the protein. This mutation prevented the proper phosphorylation of PER2. The evidence for both a mutation in the binding domain of PER2 and a mutation in CKIδ as causes of FASPS is strengthened by the lack of the FASPS phenotype in wild type individuals and by the observed change in the circadian phenotype of these mutant individuals in vitro and an absence of said mutations in all tested control subjects. Fruit flies and mice engineered to carry the human mutation also demonstrated abnormal circadian phenotypes, although the mutant flies had a long circadian period while the mutant mice had a shorter period. The genetic differences between flies and mammals that account for this difference circadian phenotypes are not known. Most recently, Ptáček and Fu reported additional studies of the human ''Per2'' S662G mutation and generation of mice carrying the human mutation. These mice had a circadian period almost 2 hours shorter than wild-type animals under constant darkness. Genetic dosage studies of CKIδ on the ''Per2'' S662G mutation revealed that depending on the binding site on ''Per2'' that CK1δ interacts with, CK1δ may lead to hypo- or hyperphosphorylation of the ''Per2'' gene.


See also

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Delayed sleep phase disorder Delayed sleep phase disorder (DSPD), more often known as delayed sleep phase syndrome and also as delayed sleep–wake phase disorder, is a delaying of a person's circadian rhythm (biological clock) compared to those of societal norms. The diso ...
*
Irregular sleep–wake rhythm Irregular sleep–wake rhythm (ISWD) is a rare form of circadian rhythm sleep disorder. It is characterized by numerous naps throughout the 24-hour period, no main nighttime sleep episode, and irregularity from day to day. Affected individuals ha ...
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Non-24-hour sleep–wake disorder Non-24-hour sleep–wake disorder (non-24 or N24SWD) is one of several chronic circadian rhythm sleep disorders (CRSDs). It is defined as a "chronic steady pattern comprising ..daily delays in sleep onset and wake times in an individual livin ...


References


External links

{{DEFAULTSORT:Advanced Sleep Phase Syndrome Sleep disorders Circadian rhythm Syndromes Sleep physiology