Fatal familial insomnia: a model disease in sleep physiopathology

Sleep architecture and sleep-disordered breathing in fatal insomnia

STUDY OBJECTIVES

Fatal insomnia (FI) is a rare prion disease severely affecting sleep architecture. Breathing during sleep has not been systematically assessed. Our aim was to characterize the sleep architecture, respiratory patterns, and neuropathologic findings in FI.

METHODS

Eleven consecutive FI patients (ten familial, one sporadic) were examined with video-polysomnography (vPSG) between 2002 and 2017. Wake/sleep stages and respiration were evaluated using a modified scoring system. Postmortem neuropathology was assessed in seven patients.

RESULTS

Median age at onset was 48 years and survival after vPSG was 1 year. All patients had different combinations of breathing disturbances including increased respiratory rate variability (RRV; n = 7), stridor (n = 9), central sleep apnea (CSA) (n = 5), hiccup (n = 6), catathrenia (n = 7), and other expiratory sounds (n = 10). RRV in NREM sleep correlated with ambiguous and solitary nuclei degeneration (r = 0.9, p = 0.008) and reduced survival (r = -0.7, p = 0.037). Two new stages, Subwake1 and Subwake2, present in all patients, were characterized. NREM sleep (conventional or undifferentiated) was identifiable in ten patients but reduced in duration in eight. REM sleep occurred in short segments in nine patients, and their reduced duration correlated with medullary raphe nuclei degeneration (r = -0.9, p = 0.005). Seven patients had REM without atonia. Three vPSG patterns were identified: agitated, with aperiodic, manipulative, and finalistic movements (n = 4); quiet-apneic, with CSA (n = 4); and quiet-non-apneic (n = 3).

CONCLUSIONS

FI patients show frequent breathing alterations, associated with respiratory nuclei damage, and, in addition to NREM sleep distortion, have severe impairment of REM sleep, related with raphe nuclei degeneration. Brainstem impairment is crucial in FI.

Clinical profile of fatal familial insomnia: phenotypic variation in 129 polymorphisms and geographical regions

OBJECTIVE

Elucidate the core clinical and genetic characteristics and identify the phenotypic variation between different regions and genotypes of fatal familial insomnia (FFI).

METHODS

A worldwide large sample of FFI patients from our case series and literature review diagnosed by genetic testing were collected. The prevalence of clinical symptoms and genetic profile were obtained, and then the phenotypic comparison between Asians versus non-Asians and 129Met/Met versus 129Met/Val were conducted.

RESULTS

In total, 131 cases were identified. The age of onset was 47.51±12.53 (range 17-76) years, 106 patients died and disease duration was 13.20±9.04 (range 2-48) months. Insomnia (87.0%) and rapidly progressive dementia (RPD; 83.2%) occurred with the highest frequency. Hypertension (33.6%) was considered to be an objective indicator of autonomic dysfunction. Genotype frequency at codon 129 was Met/Met (84.7%) and Met/Val (15.3%), and allele frequency was Met (92.4%) and Val (7.6%).129 Met was a risk factor (OR: 3.728, 95% CI: 2.194 to 6.333, p=0.000) for FFI in the non-Asian population. Comparison of Asians and non-Asians revealed clinical symptoms and genetic background to show some differences (p<0.05). In the comparison of 129 polymorphisms, a longer disease duration was found in the 129 MV group, with alleviation of some clinical symptoms (p<0.05). After considering survival probability, significant differences in survival time between genotypes remained (p<0.0001).

CONCLUSIONS

Insomnia, RPD and hypertension are representative key clinical presentations of FFI. Phenotypic variations in genotypes and geographic regions were documented. Prion protein gene 129 Met was considered to be a risk factor for FFI in the non-Asian population, and 129 polymorphisms could modify survival duration.

Differentiating Oneiric Stupor in Agrypnia Excitata From Dreaming Disorders

Oneiric Stupor (OS) in Agrypnia Excitata represents a peculiar condition characterized by the recurrence of stereotyped gestures such as mimicking daily-life activities associated with the reporting of a dream mentation consisting in a single oneiric scene. It arises in the context of a completely disorganized sleep structure lacking any physiological cyclic organization, thus, going beyond the concept of abnormal dream. However, a proper differential diagnosis of OS, in the complex world of the “disorders of dreaming” can become quite challenging. The aim of this review is to provide useful clinical and videopolygraphic data on OS to differentiate it from other dreaming disorders. Each entity will be clinically evaluated among the areas of dream mentation and abnormal sleep behaviors and its polygraphic features will be analyzed and distinguished from OS.

The eyes wake up: Screening for benign paroxysmal positional vertigo with polysomnography

OBJECTIVE

While positional nystagmus of benign paroxysmal positional vertigo (BPPV) has been shown to be detectable in electrooculography (EOG) tracings of polysomnography (PSG), the frequency of undiagnosed BPPV in patients referred for sleep-wake examination has never been investigated.

METHODS

Prospective evaluation of positional nystagmus in 129 patients, referred to a neurological sleep laboratory for sleep-wake examination with PSG. Both in the evening and morning, patients had diagnostic positioning maneuvers under ongoing EOG-PSG registration, followed by visual inspection of EOG for positional nystagmus.

RESULTS

In 19 patients (14.7%), we found patterns of positional nystagmus, typically appearing few seconds after changes in head position. In 9 of these patients (47%), the nystagmus was also provoked by the positioning maneuvers. Nystagmus only occurred during wakefulness, not during sleep. In a patient with severe cupulolithiasis, we observed disappearance of nystagmus while entering N1 sleep stage. Nocturnal positional nystagmus was independently associated with positive positioning maneuvers.

CONCLUSIONS

Inspection of EOG-PSG demonstrated that positional nystagmus is common, occurring only when wake, and independently associated with positive positioning maneuvers.

SIGNIFICANCE

By routinely searching for positional nystagmus in PSG, sleep physicians may substantially contribute to the identification of patients with so-far undiagnosed BPPV.

The cognitive neuroscience of lucid dreaming

Lucid dreaming refers to the phenomenon of becoming aware of the fact that one is dreaming during ongoing sleep. Despite having been physiologically validated for decades, the neurobiology of lucid dreaming is still incompletely characterized. Here we review the neuroscientific literature on lucid dreaming, including electroencephalographic, neuroimaging, brain lesion, pharmacological and brain stimulation studies. Electroencephalographic studies of lucid dreaming are mostly underpowered and show mixed results. Neuroimaging data is scant but preliminary results suggest that prefrontal and parietal regions are involved in lucid dreaming. A focus of research is also to develop methods to induce lucid dreams. Combining training in mental set with cholinergic stimulation has shown promising results, while it remains unclear whether electrical brain stimulation could be used to induce lucid dreams. Finally, we discuss strategies to measure lucid dreaming, including best-practice procedures for the sleep laboratory. Lucid dreaming has clinical and scientific applications, and shows emerging potential as a methodology in the cognitive neuroscience of consciousness. Further research with larger sample sizes and refined methodology is needed.

Fatal familial insomnia and Agrypnia Excitata: Autonomic dysfunctions and pathophysiological implications

Fatal Familial Insomnia (FFI) is a hereditary prion disease caused by a mutation at codon 178 of the prion-protein gene leading to a D178N substitution in the protein determining severe and selective atrophy of mediodorsal and anteroventral thalamic nuclei. FFI is characterized by physiological sleep loss, which polygraphically appears to be a slow wave sleep loss, autonomic and motor hyperactivation with peculiar episodes of oneiric stupor. Alteration of autonomic functions is a great burden for FFI patients consisting in sympathetic overactivation, dysregulation of its physiological responses and disruption of circadian rhythms. The cardiovascular system is the most frequently and severely affected confirming the increased sympathetic drive with preserved parasympathetic responses. Sleep loss, autonomic and motor hyperactivation define Agrypnia Excitata (AE), which is not exclusive to FFI, but it has been canonically described also in Morvan Syndrome and Delirium Tremens. These three conditions present different pathophysiological mechanisms but share the same thalamo-limbic impairment of which AE is one of the possible clinical presentations. FFI, and consequently also AE, is a model for the investigation of the essential role of the thalamus in the organization of body homeostasis, integrating both sleep and autonomic function control.

Association between abnormal thalamic metabolites and sleep disturbance in patients with end-stage renal disease

Sleep disturbances are common in end-stage renal disease (ESRD) patients. However, the underlying neuropathological mechanisms are largely unclear. Previous studies have revealed the important role of the thalamus in the potential mechanisms of sleep disorders. We hypothesized that the sleep disturbances in ESRD patients may correspond to metabolic changes of thalamus and the uremic factors may have a vital contribution on these changes. We performed multi-voxel ¹H-MRS of bilateral thalami in 27 ESRD patients who currently receiving hemodialysis treatment and 21 age-matched healthy volunteers. ESRD patients underwent Pittsburgh Sleep Quality Index (PSQI) scale and restless legs syndrome (RLS) rating scale assessment. Laboratory blood tests including serum creatinine, serum urea, cystatin-C, serum parathyroid hormone (PTH), calcium and phosphorus levels, hemoglobin and hematocrit were performed in all ESRD patients close to the time of the MR examination. We found correlations among elevated PTH, higher PSQI score and RLS rating score in ESRD patients. ESRD patients displayed decreased N-acetylaspartate and creatine ratio (NAA/Cr) of thalami compared with controls. There were significantly negative correlation between NAA/Cr and serum PTH level or PSQI score. The metabolic changes of thalami played an important role in the neuropathological mechanisms of lower sleep quality in ESRD patients. Secondary hyperparathyroidism as one of the main uremia-related factors was closely related to abnormal metabolites of the thalamus in patients with ESRD, revealing the crosstalk procedure between renal impairment and brain function.

Disorders of sleep and circadian rhythms

Sleep is fundamental to the survival of humans. However, knowledge regarding the role of sleep and its regulation is poorly understood. Genetics in flies, mice, and humans has led to a detailed understanding of some aspects of circadian regulation. Sleep homeostasis (the effect of increasing periods of wakefulness on our sleep propensity) is largely not understood. Sleep homeostasis is distinct from, but also linked to, the circadian clock. It is only in the last two decades that our understanding of some sleep disorders has been revealed. These breakthroughs were mostly fueled by intensive investigation using genetic tools. Although modern human genetics has revolutionized scientific research of neurologic disorders beginning ~35 years ago, studies of sleep and sleep disorders have lagged behind those of many neurologic diseases. This is due to the complexity in phenotyping behaviors like sleep and the fact that sleep is strongly influenced by environmental and other factors. We have long been aware that the amount of sleep required by individuals is normally distributed in the general population with small proportions of people being natural short or natural long sleepers. However, it has been less than a decade since Mendelian families of natural short sleepers have been recognized. Recent work has made significant advances and mechanistic insights of several sleep disorders as well as familial natural short sleepers by using ever-improving human genetic and cellular molecular tools. Given recent advances into genetic and biologic understanding of sleep, the hope of understanding this indispensable process is closer. Ultimately, our growing understanding will lead to more effective treatments of human sleep disorders.

A review of drug therapy for sporadic fatal insomnia

BACKGROUND

Sporadic fatal insomnia (sFI) is a rapid progressive neurodegenerative disease characterised by gradual to perpetual insomnia, followed by dysautonomia, coma and death. ¹ The cause of sFI was recently mapped to a mutation in a protein, the prion, found in the human brain. It is the unfolding of the prion that leads to the generation of toxic oligomers that destroy brain tissue and function. Recent studies have confirmed that a methionine mutation at codon 129 of the human Prion is characteristic of sFI. Current treatment slows down the progression of the disease, but no cure has been found, yet.

METHODS

We used Molecular Docking and Molecular Dynamics simulation methods, to study the toxic Fatal-Insomnia-prion conformations at local unfolding. The idea was to determine these sites and to stabilise these regions against unfolding and miss-folding, using a small ligand, based on a phenothiazine "moiety".

CONCLUSION

As a result we here discuss current fatal insomnia therapy and present seven novel possible compounds for in vitro and in vivo screening.

Clinical Features and Sleep Analysis of Chinese Patients with Fatal Familial Insomnia

This study aimed to examine clinical features, sleep, abnormal sleep-wake transition and non-sleep disturbances as well as lab tests in Chinese fatal familial insomnia (FFI) subjects. Patients with confirmed clinical and laboratory diagnosis of FFI have been retrospectively reviewed. The clinical features and the results of the complementary tests, including polysomnography (PSG), brain imaging and genetic analysis, were used. Two male and three female patients were recruited in this study. Three of the five patients had more comprehensive family medical records. The most typical clinical manifestations in all 5 patients were sleep disturbances, including insomnia, laryngeal stridor, sleep breath disturbance, and sleep-related involuntary movements. PSG of all these five cases showed reduction in total sleep time, sleep fragmentation, abnormal short non-rapid eye movement - rapid eye movement (REM) cycling, REM sleep reduction or loss, and REM sleep instruction in wakefulness. Patient 2's emission tomography scan demonstrated a reduction in glucose uptake in the left thalamus and bilateral inferior parietal lobe. In summary, Chinese FFI patients are typically characterized by organic sleep related symptoms, rapidly progressive dementia and sympathetic symptoms. We propose that structural damages in the thalamus and cortex are mostly responsible for clinical manifestations of FFI.

Fatal familial insomnia with abnormal signals on routine MRI: a case report and literature review

Background

Fatal familial insomnia (FFI) is a rare autosomal dominant disease caused by the PRNP D178N/129 M mutation. Routine brain CT and MRI usually reveal non-specific features. We report a patient with FFI presenting with diffuse abnormal signals on MRI, later confirmed as combined with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL).

Case presentation

The patient was a 58-year-old female, whose main clinical manifestations were insomnia, movement disorders, autonomic hyperactivity and mental deterioration. The patient also suffered a typical episode of transient global amnesia. MRI indicated a diffuse white matter abnormality and microbleeding on the susceptibility-weighted imaging. On biopsy, the brain tissue sections showed spongiform changes with gliosis, neuronal degeneration, and prion protein deposition in a portion of the neurons. In addition, arteriosclerosis was prominent. Transmission electron microscopy showed osmiophilic particle deposition in the matrix of medial smooth muscle cells. Gene sequencing confirmed a diagnosis of FFI with CADASIL.

Conclusions

This case is a compelling example that even with evidence of leukoencephalopathy, prion disease should be an important differential diagnosis of rapidly progressive dementia and related diseases. In cases of genetic diseases with atypical manifestations, the coexistence of two or even more diseases should be considered as a possible explanation.

Sleep spindle detection based on non-experts: A validation study

Accurate and efficient detection of sleep spindles is a methodological challenge. The present study describes a method of using non-experts for manual detection of sleep spindles. We recruited five experts and 168 non-experts to manually identify spindles in stage N2 and stage N3 sleep data using a MATLAB interface. Scorers classified each spindle into definite and indefinite spindle (with weights of 1 and 0.5, respectively). First, a method of optimizing the thresholds of the expert/non-expert group consensus according to the results of experts and non-experts themselves is described. Using this method, we established expert and non-expert group standards from expert and non-expert scorers, respectively, and evaluated the performance of the non-expert group standards by compared with the expert group standard (termed EGS). The results indicated that the highest performance was the non-expert group standard when definite spindles were only considered (termed nEGS-1; F1 score = 0.78 for N2; 0.68 for N3). Second, four automatic spindle detection methods were compared with the EGS. We found that the performance of nEGS-1 versus EGS was higher than that of the four automated methods. Our results also showed positive correlation between the mean F1 score of individual expert in EGS and the F1 score of nEGS-1 versus EGS across 30 segments of stage N2 data (r = 0.61, P < 0.001). Further, we found that six and nine non-experts were needed to manually identify spindles in stages N2 and N3, respectively, while maintaining acceptable performance of nEGS-1 versus EGS (F1 score = 0.79 for N2; 0.64 for N3). In conclusion, this study establishes a detailed process for detection of sleep spindles by non-experts in a crowdsourcing scheme.

Does selection for short sleep duration explain human vulnerability to Alzheimer's disease?

Compared with other primates, humans sleep less and have a much higher prevalence of Alzheimer 's disease (AD) pathology. This article reviews evidence relevant to the hypothesis that natural selection for shorter sleep time in humans has compromised the efficacy of physiological mechanisms that protect against AD during sleep. In particular, the glymphatic system drains interstitial fluid from the brain, removing extra-cellular amyloid beta (eAβ) twice as fast during sleep. In addition, melatonin - a peptide hormone that increases markedly during sleep - is an effective antioxidant that inhibits the polymerization of soluble eAβ into insoluble amyloid fibrils that are associated with AD. Sleep deprivation increases plaque formation and AD, which itself disrupts sleep, potentially creating a positive feedback cycle. These and other physiological benefits of sleep may be compromised by short sleep durations. Our hypothesis highlights possible long-term side effects of medications that reduce sleep, and may lead to potential new strategies for preventing and treating AD.

Lucid dreams, an atypical sleep disturbance in anterior and mediodorsal thalamic strokes

BACKGROUND

Cognitive, affective, and behavioural disturbances are commonly reported following thalamic strokes. Conversely, sleep disorders are rarely reported in this context.

OBSERVATIONS

Herein, we report the cases of two young patients admitted for an ischemic stroke located in the territories of the left pre-mammillary and paramedian arteries. Together with aphasia, memory complaint, impaired attention and executive functions, they reported lucid dreams with catastrophic content or conflicting situations.

CONCLUSION

Lucid dreams are an atypical presentation in thalamic strokes. These cases enlarge the clinical spectrum of sleep-wake disturbances potentially observed after an acute cerebrovascular event.

Solving the mystery of human sleep schedules one mutation at a time

Sleep behavior remains one of the most enigmatic areas of life. The unanswered questions range from "why do we sleep?" to "how we can improve sleep in today's society?" Identification of mutations responsible for altered circadian regulation of human sleep lead to unique opportunities for probing these territories. In this review, we summarize causative circadian mutations found from familial genetic studies to date. We also describe how these mutations mechanistically affect circadian function and lead to altered sleep behaviors, including shifted or shortening of sleep patterns. In addition, we discuss how the investigation of mutations can not only expand our understanding of the molecular mechanisms regulating the circadian clock and sleep duration, but also bridge the pathways between clock/sleep and other human physiological conditions and ailments such as metabolic regulation and migraine headaches.

Agrypnia excitata

Agrypnia (from the Greek: to chase sleep) excitata (AE) is a syndrome characterized by loss of sleep and permanent motor and autonomic hyperactivation (excitata). Disruption of the sleep-wake rhythm consists in the disappearance of spindle-delta activities, and the persistence of stage 1 non-rapid eye movement (NREM) sleep. Rapid eye movement (REM) sleep persists but fails to stabilize, appearing in short recurrent episodes, isolated, or mixed with stage 1 NREM sleep. Diurnal and nocturnal motor, autonomic and hormonal overactivity is the second hallmark of AE. Of particular interest is the finding that norepinephrine secretion is extremely elevated at all hours of the day and night whereas the nocturnal melatonin peak is lacking. Oneiric stupor is probably an exclusive sign of AE and consists in the recurrence of stereotyped gestures mimicking simple daily life activities. Agrypnia excitata aptly defines 3 different clinical conditions, fatal familial insomnia (FFI), an autosomal dominant prion disease, Morvan syndrome (MS), an autoimmune encephalitis, and delirium tremens (DT), the alcohol withdrawal syndrome. Agrypnia excitata is due to an intralimbic disconnection releasing the hypothalamus and brainstem reticular formation from cortico-limbic inhibitory control. This pathogenetic mechanism is visceral thalamus degeneration in FI, whereas it may depend on autoantibodies blocking voltage-gated potassium (VGK) channels within the limbic system in MS, and in the sudden changes in gabaergic synapses down-regulated by chronic alcohol abuse within the limbic system in DT.

Thalamic contribution to Sleep Slow Oscillation features in humans: a single case cross sectional EEG study in Fatal Familial Insomnia

OBJECTIVE

Studying the thalamic role in the cortical expression of the Sleep Slow Oscillation (SSO) in humans by comparing SSO features in a case of Fatal Familial Insomnia (FFI) and a group of controls.

METHODS

We characterize SSOs in a 51-year-old male with FFI carrying the D178N mutation and the methionine/methionine homozygosity at the polymorphic 129 codon of the PRNP gene and in eight gender and age-matched healthy controls. Polysomnographic (21 EEG electrodes, two consecutive nights) and volumetric- (Diffusion tensor imaging Magnetic Resonance Imaging DTI MRI) evaluations were carried out for the patient in the middle course of the disease (five months after the onset of insomnia; disease duration: 10 months). We measured a set of features describing each SSO event: the wave shape, the event-origin location, the number and the location of all waves belonging to the event, and the grouping of spindle activity as a function of the SSO phase.

RESULTS

We found that the FFI individual showed a marked reduction of SSO event rate and wave morphological alterations as well as a significant reduction in grouping spindle activity, especially in frontal areas. These alterations paralleled DTI changes in the thalamus and the cingulate cortex.

CONCLUSIONS

This work gives a quantitative picture of spontaneous SSO activity during the NREM sleep of a FFI individual. The results suggest that a thalamic neurodegeneration specifically alters the cortical expression of the SSO. This characterization also provides indications about cortico-thalamic interplays in SSO activity in humans.

Reduced γ-aminobutyric acid in occipital and anterior cingulate cortices in primary insomnia: a link to major depressive disorder?

Insomnia is closely related to major depressive disorder (MDD) both cross-sectionally and longitudinally, and as such, offers potential opportunities to refine our understanding of the neurobiology of both sleep and mood disorders. Clinical and basic science data suggest a role for reduced γ-aminobutyric acid (GABA) in both MDD and primary insomnia (PI). Here, we have utilized single-voxel proton magnetic spectroscopy (1H-MRS) at 4 Tesla to examine GABA relative to total creatine (GABA/Cr) in the occipital cortex (OC), anterior cingulate cortex (ACC), and thalamus in 20 non-medicated adults with PI (12 women) and 20 age- and sex-matched healthy sleeper comparison subjects. PI subjects had significantly lower GABA/Cr in the OC (p=0.0005) and ACC (p=0.03) compared with healthy sleepers. There was no significant difference in thalamic GABA/Cr between groups. After correction for multiple comparisons, GABA/Cr did not correlate significantly with insomnia severity measures among PI subjects. This study is the first to demonstrate regional reductions of GABA in PI in the OC and ACC. Reductions in GABA in similar brain regions in MDD using 1H-MRS suggest a common reduction in cortical GABA among PI and mood disorders.

Delta wave power: an independent sleep phenotype or epiphenomenon?

Electroencephalographic (EEG) δ waves during non-rapid eye movement sleep (NREMS) after sleep deprivation are enhanced. That observation eventually led to the use of EEG δ power as a parameter to model process S in the two-process model of sleep. It works remarkably well as a model parameter because it often co-varies with sleep duration and intensity. Nevertheless there is a large volume of literature indicating that EEG δ power is regulated independently of sleep duration. For example, high amplitude EEG δ waves occur in wakefulness after systemic atropine administration or after hyperventilation in children. Human neonates have periods of sleep with an almost flat EEG. Similarly, elderly people have reduced EEG δ power, yet retain substantial NREMS. Rats provided with a cafeteria diet have excess duration of NREMS but simultaneously decreased EEG δ power for days. Mice challenged with influenza virus have excessive EEG δ power and NREMS. In contrast, if mice lacking TNF receptors are infected, they still sleep more but have reduced EEG δ power. Sleep regulatory substances, e.g., IL1, TNF, and GHRH, directly injected unilaterally onto the cortex induce state-dependent ipsilateral enhancement of EEG δ power without changing duration of organism sleep. IL1 given systemically enhances duration of NREMS but reduces EEG δ power in mice. Benzodiazepines enhance NREMS but inhibit EEG δ power. If duration of NREMS is an indicator of prior sleepiness then simultaneous EEG δ power may or may not be a useful index of sleepiness. Finally, most sleep regulatory substances are cerebral vasodilators and blood flow affects EEG δ power. In conclusion, it seems unlikely that a single EEG measure will be reliable as a marker of sleepiness for all conditions.

Humoral sleep regulation; interleukin-1 and tumor necrosis factor

Two substances, the cytokines interleukin-1 beta (IL1β) and tumor necrosis factor alpha (TNFα), known for their many physiological roles, for example, cognition, synaptic plasticity, and immune function, are also well characterized in their actions of sleep regulation. These substances promote non-rapid eye movement sleep and can induce symptoms associated with sleep loss such as sleepiness, fatigue, and poor cognition. IL1β and TNFα are released from glia in response to extracellular ATP. They bind to their receptors on neurons resulting in neuromodulator and neurotransmitter receptor up/downregulation (e.g., adenosine and glutamate receptors) leading to altered neuronal excitability and function, that is, a state change in the local network. Synchronization of state between local networks leads to emergent whole brain oscillations, such as sleep/wake cycles.

Sleep disorders in cerebellar ataxias

Cerebellar ataxias comprise a wide range of etiologies leading to central nervous system-related motor and non-motor symptoms. Recently, a large body of evidence has demonstrated a high frequency of non-motor manifestations in cerebellar ataxias, specially in autosomal dominant spinocerebellar ataxias (SCA). Among these non-motor dysfunctions, sleep disorders have been recognized, although still under or even misdiagnosed. In this review, we highlight the main sleep disorders related to cerebellar ataxias focusing on REM sleep behavior disorder (RBD), restless legs syndrome (RLS), periodic limb movement in sleep (PLMS), excessive daytime sleepiness (EDS), insomnia and sleep apnea.

Sleep disorders in neurodegenerative diseases

The aim of this review is to provide data on sleep disturbances in three categories of neurodegenerative disorders: synucleinopathies, tauopathies, and other diseases (this heterogeneous group includes also spinocerebellar degeneration and amyotrophic lateral sclerosis). Analysing and knowing sleep disorders in neurodegenerative diseases may offer important insights into the pathomechanism of some of these diseases and calls attention to the still insufficiently known 'sleep neurology'. The identification of sleep disorders in some neurodegenerative conditions may make their diagnosis easier and earlier; for example, rapid eye movements sleep behaviour disorder may precede any other clinical manifestation of synucleinopathies by more than 10 years.

The role of cytokines in sleep regulation

Interleukin-1 beta (IL1) and tumor necrosis factor alpha (TNF) promote non-rapid eye movement sleep under physiological and inflammatory conditions. Additional cytokines are also likely involved but evidence is insufficient to conclude that they are sleep regulatory substances. Many of the symptoms induced by sleep loss, e.g. sleepiness, fatigue, poor cognition, enhanced sensitivity to pain, can be elicited by injection of exogenous IL1 or TNF. We propose that ATP, released during neurotransmission, acting via purine P2 receptors on glia releases IL1 and TNF. This mechanism may provide the means by which the brain keeps track of prior usage history. IL1 and TNF in turn act on neurons to change their intrinsic properties and thereby change input-output properties (i.e. state shift) of the local network involved. Direct evidence indicates that cortical columns oscillate between states, one of which shares properties with organism sleep. We conclude that sleep is a local use-dependent process influenced by cytokines and their effector molecules such as nitric oxide, prostaglandins and adenosine.

Identification of adjacent binding sites for the YY1 and E4BP4 transcription factors in the ovine PrP (Prion) gene promoter

The PrP gene encodes the cellular isoform of the prion protein (PrP(c)) which has been shown to be crucial to the development of transmissible spongiform encephalopathies (TSEs). PrP knock-out mice, which do not express endogenous PrP(c), exhibit resistance to TSE disease. The regulation of PrP gene expression represents, therefore, a crucial factor in the development of TSEs. Two sequence motifs in the PrP promoter (positions -287 to -263 from transcriptional start) were previously reported as being highly conserved, and it was suggested that they represent binding sites for as yet unidentified transcription factors. To test this hypothesis, binding of nuclear proteins was analyzed by electrophoretic mobility shift assays using ovine or murine cells and tissues with radiolabeled DNA probes containing the conserved motif sequences. Specific binding was observed to both motifs, and polymorphic variants of these motifs exhibited differential binding. Two proteins bound to these motifs were identified as the Yin Yang 1 (YY1) (motif 1) and E4BP4 (motif 2) transcription factors. Functional promoter analysis of four different promoter variants revealed that motif 1 (YY1) was associated with inhibitory activity in the context of the PrP promoter, whereas motif 2 (E4BP4) was linked to a slight enhancing activity. This represents the first demonstration of binding of nuclear factors to two highly conserved DNA sequence motifs within mammalian PrP promoters. The action of these factors on the PrP promoter is haplotype-specific, leading us to propose that the prion protein expression pattern and, with it, the distribution of TSE infectivity may be associated with PrP promoter genotype.

Sleep and temperature rhythms in two sisters with P102L Gerstmann-Sträussler-Scheinker (GSS) disease

BACKGROUND

Sleep disorders are increasingly recognized in the symptomatology of many neurodegenerative diseases. Gerstmann-Sträussler-Scheinker (GSS) disease is a hereditary prion disease featuring cerebellar ataxia, akinetic parkinsonism, pyramidal signs and cognitive decline.

METHODS

We performed a polysomnographic study (PSG) of sleep and body core temperature (BcT degrees ) in two sisters with GSS.

RESULTS

Our study showed protracted nocturnal awakenings, reduced sleep efficiency and brief daytime naps but also qualitatively preserved slow-wave and REM sleep and substantially normal arousal and periodic limb movements in sleep indices and BcT degrees rhythm.

CONCLUSIONS

These findings conflict with those in multiple system atrophy and other prion diseases such as fatal familial insomnia, which enter the differential diagnosis of GSS and are characterized by prominently disrupted sleep-wake and BcT degrees cycles.

Prion proteins: Physiological functions and role in neurological disorders

Stanley Prusiner was the first to promote the concept of misfolded proteins as a cause for neurological disease. It has since been shown by him and other investigators that the scrapie isoform of prion protein (PrP(Sc)) functions as an infectious agent in numerous human and non-human disorders of the central nervous system (CNS). Interestingly, other organ systems appear to be less affected, and do not appear to lead to major co-morbidities. The physiological function of the endogenous cellular form of the prion protein (PrP(C)) is much less clear. It is intriguing that PrP(c) is expressed on most tissues in mammals, suggesting not only biological functions outside the CNS, but also a role other than the propagation of its misfolded isotype. In this review, we summarize accumulating in vitro and in vivo evidence regarding the physiological functions of PrP(C) in the nervous system, as well as in lymphoid organs.