Narcolepsy: clinical features, new pathophysiologic insights, and future perspectives

Interim analysis of a post-authorization safety study of pitolisant in treating narcolepsy: A real-world European study

BACKGROUND

Narcolepsy is a chronic sleep disorder characterized mainly by excessive daytime sleepiness (EDS) and cataplexy in the case of narcolepsy type 1 (NT1). Pitolisant is a histamine 3 receptor antagonist/inverse agonist that reduces EDS and cataplexy in patients with narcolepsy.

METHODS

We performed a prospective 5-year follow-up, non-interventional study of adults with NT1 and NT2 receiving pitolisant. The primary objectives were to collect information on the long-term safety of pitolisant and analyze the utilization patterns of pitolisant. The secondary objectives were to assess clinical benefit, adherence, impact on patients' quality of life, disease burden, and patient satisfaction. We reported the results of an interim analysis after 42.6 months.

RESULTS

The population comprised 370 patients (mean age, 40 ± 15 years; 51.4 % women; NT1, 71.4 %; NT2, 28.6 %); 364 received ≥1 dose of pitolisant. Data were available for 356 patients (97.8 %). Most patients (68.4 %) had ≥1 comorbidity (obesity [BMI≥30], 31.9 %; neuropsychiatric, 31 %; and cardiovascular, 22.8 %). Forty-eight patients (13.2 %) had received no prior narcoleptic treatment, while 98 (31 %) were taking a previous therapy, which was switched to pitolisant. Treatment was combined with pitolisant in 218 (69 %) patients. Pitolisant was discontinued by 131 patients (35.4 %), mainly for safety reasons (14.3 %), lack of response (8.7 %), and patient decision (7.6 %). Overall, 355 treatment-emergent adverse events (3 serious) were reported by 156 patients (42.9 % of safety population), with 218 possibly treatment-related (61.4 %) in 109 patients (29.9 %). Improvements were observed in EDS, cataplexy, and quality of life.

CONCLUSIONS

Pitolisant was generally safe and well tolerated in patients with NT1 and NT2 and can be used in both types. Improvements were found in EDS, cataplexy, and quality of life, with good adherence and satisfaction.

Out-of-body experiences in relation to lucid dreaming and sleep paralysis: A theoretical review and conceptual model

Out-of-body experiences (OBEs) are characterized by the subjective experience of being located outside the physical body. Little is known about the neurophysiology of spontaneous OBEs, which are often reported by healthy individuals as occurring during states of reduced vigilance, particularly in proximity to or during sleep (sleep-related OBEs). In this paper, we review the current state of research on sleep-related OBEs and hypothesize that maintaining consciousness during transitions from wakefulness to REM sleep (sleep-onset REM periods) may facilitate sleep-related OBEs. Based on this hypothesis, we propose a new conceptual model that potentially describes the relationship between OBEs and sleep states. The model sheds light on the phenomenological differences between sleep-related OBEs and similar states of consciousness, such as lucid dreaming (the realization of being in a dream state) and sleep paralysis (feeling paralyzed while falling asleep or waking up), and explores the potential polysomnographic features underlying sleep-related OBEs. Additionally, we apply the predictive coding framework and suggest a connecting link between sleep-related OBEs and OBEs reported during wakefulness.

Multiple Sleep Latency Test/Maintenance of Wakefulness Test and Central Hypersomnias: Evolving Diagnostic and Therapeutic Approaches

SUMMARY

Central disorders of hypersomnolence include a spectrum of conditions, such as narcolepsy, idiopathic hypersomnia, and Kleine-Levin syndrome, in which excessive daytime sleepiness is the primary feature. Subjective testing with tools, such as sleep logs and sleepiness scales, are often helpful in the evaluation of these disorders but do not necessarily correlate well with objective testing, such as polysomnography and multiple sleep latency test and maintenance of wakefulness test. The most recent International Classification of Sleep Disorders-Third Edition has incorporated biomarkers, such as cerebrospinal fluid hypocretin level, into the diagnostic criteria and have restructured the classification of conditions based on our evolved understanding of their underlying pathophysiologic mechanisms. Therapeutic approaches largely consist of behavioral therapy, with a focus on optimizing sleep hygiene, optimizing opportunity for sleep, and strategic napping, along with judicious use of analeptic and anticataleptic agents when necessary. Emerging therapy has revolved around hypocretin-replacement therapy, immunotherapy, and nonhypocretin agents, with the goal of better targeting the underlying pathophysiology of these disorders rather than addressing symptoms. The most novel treatments have targeted the histaminergic system (pitolisant), dopamine reuptake transmission (solriamfetol), and gamma-aminobutyric acid modulation (flumazenil and clarithromycin) to promote wakefulness. Continued research is required for a more solid understanding of the biology of these conditions to develop a more robust armamentarium of therapeutic options.

Narcolepsy and emotions: Is there a place for a theory of mind approach?

Narcolepsy type 1 is a central disorder of hypersomnolence characterized by excessive daytime sleepiness, rapid eye movement sleep-related manifestations, and cataplexy. In the current literature there is general agreement regarding neural correlates of Narcolepsy type 1 that appear to be related to anatomical and functional abnormalities in the hypothalamic region. In the last two decades, researchers shed light on the neurological bases of cataplexy by focusing on the neurobiological correlates of emotions. Although the results of these studies differ, they all point to an impairment in the amygdala and hypothalamus functions that are known to be involved in emotional processing, suggesting an impairment in this domain in narcoleptic patients. Indeed, despite heterogeneous results, several studies showed that narcoleptic patients differed from healthy controls in processing emotional stimuli. From a behavioral point of view, these findings suggest that alterations in emotional processing may be driven, at least in part, by compensatory strategies to avoid or reduce the frequency of cataplexy attacks. Surprisingly, the only study exploring in NT1 the behavioural performances in emotional facial recognition found no differences between NT1 adults and controls. We hypothesize that narcoleptic patients may present an alteration in a more complex socio-cognitive ability that is related to emotional processing, namely Theory of Mind. This review aims to investigate the literature supporting this hypothesis and to propose possible future developments on this topic.

Narcolepsy in Children: Sleep disorders in children, A rapidly evolving field seeking consensus

Narcolepsy is a life-long sleep disorder with two distinct subtypes, narcolepsy type I and narcolepsy type II. It is now well recognized that the loss of hypocretin neurons underlies the pathogenesis of narcolepsy type I, however, the pathogenesis of narcolepsy type II is currently unknown. Both genetic and environmental factors play an important role in the pathogenesis of narcolepsy. There is increasing evidence that autoimmune processes may play a critical role in the loss of hypocretin neurons. Infections especially streptococcus and influenza have been proposed as a potential trigger for the autoimmune-mediated mechanism. Several recent studies have shown increased cases of pediatric narcolepsy following the 2009 H1N1 pandemic. The increased cases in Europe seem to be related to a specific type of H1N1 influenza vaccination (Pandemrix), while the increased cases in China are related to influenza infection. Children with narcolepsy can have an unusual presentation at disease onset including complex motor movements which may lead to delayed diagnosis. All classic narcolepsy tetrads are present in only a small proportion of children. The diagnosis of narcolepsy is confirmed by either obtaining cerebrospinal fluid hypocretin or overnight sleep study with the multiple sleep latency test (MSLT). There are limitations of using MSLT in young children such that a negative MSLT test cannot exclude narcolepsy. HLA markers have limited utility in narcolepsy, but it may be useful in young children with clinical suspicion of narcolepsy. For management, both pharmacologic and non-pharmacologic treatments are important in the management of narcolepsy. Pharmacotherapy is primarily aimed to address excessive daytime sleepiness and REM-related symptoms such as cataplexy. In addition to pharmacotherapy, routine screening of behavioral and psychosocial issues is warranted to identify patients who would benefit from bio-behavior intervention.

Changed Cerebral White Matter Structural Network Topological Characters and Its Correlation with Cognitive Behavioral Abnormalities in Narcolepsy Type 1

OBJECTIVE

In the current study we investigated topological abnormalities of the cerebral white matter networks in narcolepsy type 1 (NT1) patients and its relationship with their cognitive abnormalities using diffusion tensor imaging (DTI) technology.

METHODS

DTI and the Beijing version of the Montreal Cognitive Assessment (MoCA-BJ) were applied to 30 NT1 patients and 30 age-matched healthy controls. DTI studies were also carried using the 3T MRI system. Next, DTI data was used to establish a cerebral white matter network for all subjects and graph theory was applied to analyze the topological characteristics of the white matter structural network. Topographical parameters (such as local efficiency (Eloc), global efficiency (Eglob) and small-world (σ)) between NT1 patients and controls were then compared. The correlation between MoCA-BJ scores and topological parameters was also analyzed.

RESULTS

MoCA-BJ scores in NT1 patients were lower than those in the healthy controls. Compared with healthy controls, the global efficiency of the white matter network and attributes of the small world network were significantly reduced in NT1 patients. Finally, the global efficiency of the white matter structural network was related to the MoCA-BJ score of NT1 patients.

CONCLUSION

The abnormal topological characteristics of the white matter structural network in NT1 patients may be associated with their cognitive impairment.

Abnormal Brain Network Topology During Non-rapid Eye Movement Sleep and Its Correlation With Cognitive Behavioral Abnormalities in Narcolepsy Type 1

Objective: Simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) were applied to investigate the abnormalities in the topological characteristics of functional brain networks during non-rapid eye movement(NREM)sleep. And we investigated its relationship with cognitive abnormalities in patients with narcolepsy type 1 (NT1) disorder in the current study. Methods: The Beijing version of the Montreal Cognitive Assessment (MoCA-BJ) and EEG-fMRI were applied in 25 patients with NT1 and 25 age-matched healthy controls. All subjects participated in a nocturnal video polysomnography(PSG)study, and total sleep time (TST), percentage of TST (%TST) for each sleep stage and arousal index were calculated. The Epworth Sleepiness Score (ESS) was used to measure the degree of daytime sleepiness. The EEG-fMRI study was performed simultaneously using a 3T MRI system and a 32-channel MRI-compatible EEG system during sleep. Visual scoring of EEG data was used for sleep staging. Cognitive function was assessed for all subjects using the MoCA-BJ. The fMRI data were applied to establish a whole-brain functional connectivity network for all subjects, and the topological characteristics of the whole-brain functional network were analyzed using a graph-theoretic approach. The topological parameters were compared between groups. Lastly, the correlation between topological parameters and the assessment scale using Montreal Cognition was analyzed. Results: The MoCA-BJ scores were lower in patients with NT1 than in normal controls. Whole-brain global efficiency during stage N2 sleep in patients with NT1 displayed significantly lower small-world properties than in normal controls. Whole-brain functional network global efficiency in patients with NT1 was significantly correlated with MoCA-BJ scores. Conclusion: The global efficiency of the functional brain network during stage N2 sleep in patients with NT1 and the correspondingly reduced small-world attributes were associated with cognitive impairment.

Polygenic risk score analysis revealed shared genetic background in attention deficit hyperactivity disorder and narcolepsy

Attention deficit hyperactive disorder (ADHD) is a highly heritable neurodevelopmental disorder, and excessive daytime sleepiness is frequently observed in ADHD patients. Excessive daytime sleepiness is also a core symptom of narcolepsy and essential hypersomnia (EHS), which are also heritable conditions. Psychostimulants are effective for the symptomatic control of ADHD (primary recommended intervention) and the two sleep disorders (frequent off-label use). However, the common biological mechanism for these disorders has not been well understood. Using a previously collected genome-wide association study of narcolepsy and EHS, we calculated polygenic risk scores (PRS) for each individual. We investigated a possible genetic association between ADHD and narcolepsy traits in the Hamamatsu Birth Cohort for mothers and children (HBC study) (n = 876). Gene-set enrichment analyses were used to identify common pathways underlying these disorders. Narcolepsy PRS were significantly associated with ADHD traits both in the hyperactivity domain (e.g., P-value threshold < 0.05, β [SE], 5.815 [1.774]; P = 0.002) and inattention domain (e.g., P-value threshold < 0.05, β [SE], 5.734 [1.761]; P = 0.004). However, EHS PRS was not significantly associated with either domain of ADHD traits. Gene-set enrichment analyses revealed that pathways related to dopaminergic signaling, immune systems, iron metabolism, and glial cell function involved in both ADHD and narcolepsy. Findings indicate that ADHD and narcolepsy are genetically related, and there are possible common underlying biological mechanisms for this relationship. Future studies replicating these findings would be warranted to elucidate the genetic vulnerability for daytime sleepiness in individuals with ADHD.

Hypothalamic MCH Neuron Activity Dynamics during Cataplexy of Narcolepsy

Hypothalamic orexin (hypocretin, HCRT) deficiency causes sleep disorder narcolepsy with cataplexy in humans and murine. As another integral group of sleep/wake-regulating neurons in the same brain area, the melanin-concentrating hormone (MCH) neurons' involvement in cataplexy remains ambiguous. Here we used the live animal deep-brain calcium (Ca2+) imaging tool to record MCH neuron dynamics during cataplexy by expressing calcium sensor GCaMP6s into genetically defined MCH neurons in orexin knock-out mice, which are a model of human narcolepsy. Similar to wild-type mice, MCH neurons of the narcoleptic mice displayed significantly higher Ca2+ transient fluorescent intensity during rapid eye movement (REM) sleep and active waking (AW) episodes compared with non-REM (NREM) sleep. Moreover, MCH neurons displayed significantly lower Ca2+ signals during cataplexy. Importantly, a pre-cataplexy elevation of Ca2+ signals from MCH neurons was not a prerequisite for cataplexy initiation. Our results demonstrated the inactivation status of MCH neurons during cataplexy and suggested that MCH neurons are not involved in the initiation and maintenance of cataplexy in orexin knock-out mice.

Evaluation of the validity of psychological preparation for children undergoing polysomnography

STUDY OBJECTIVES

Nocturnal polysomnography (PSG) is an essential diagnostic technique to assess sleep abnormalities, including sleep-disordered breathing (SDB). Although low in invasiveness, it is extremely difficult to conduct PSG with children who are not cooperative with wearing electrodes and sensors. Particularly, it is difficult to conduct PSG on children with autism spectrum disorder (ASD) because they have poor predictive ability, exhibit extreme anxiety about novel and unfamiliar things, and have difficulty understanding verbal instructions. Recently, the usefulness of psychological preparation was reported. The primary aim of this study was to assess the usefulness of psychological preparation for PSG.

METHODS

The goal of our study was to assess the usefulness of psychological preparation for PSG. A total of 253 children were enrolled in the study: 131 in the control group (19 with ASD) and 122 selected for psychological preparation (51 with ASD).

RESULTS

In the preparation group, 110 of 122 (90.2%) could undergo regular PSG, a significantly higher percentage than the control group at 104 of 131 (79.4%), P = .018. Regarding hypnotic drugs, in the preparation group 111 of 122 (91.0%) underwent PSG without hypnotic drugs, which was a significantly higher percentage than in the control group at 107 of 131 (81.7%), P = .032. Additionally, 45 of 51 children with ASD in the preparation group (88.2%) could undergo PSG without hypnotic drugs.

CONCLUSIONS

This study indicated that psychological preparation was effective in facilitating PSG without hypnotic drugs in children who have difficulty cooperating with PSG, including those with ASD.

Comorbidity of Narcolepsy and Psychotic Disorders: A Nationwide Population-Based Study in Taiwan

BACKGROUND

Narcolepsy is a chronic sleep disorder that is likely to have neuropsychiatric comorbidities. Psychotic disorders are characterized by delusion, hallucination, and reality impairments. This study investigates the relationship between narcolepsy and psychotic disorders.

DESIGN AND METHODS

This study involves patients who were diagnosed with narcolepsy between January 2002 and December 2011 (n = 258) and age- and gender-matched controls (n = 2580) from Taiwan's National Health Insurance database. Both the patients and the controls were monitored from January 1, 2002 to December 31, 2011 to identify any occurrence of a psychotic disorder. Drugs that have been approved for treating narcolepsy: immediate-release methylphenidate (IR-MPH), osmotic controlled-release formulations of methylphenidate (OROS-MPH), and modafinil, were analyzed. A multivariate logistic regression model was used to evaluate the potential comorbidity of narcolepsy with psychotic disorders.

RESULTS

During the study period, 8.1% of the narcoleptic patients exhibited comorbidity with a psychotic disorder, whereas only 1.5% of the control subjects (1.5%) had psychotic disorders (aOR, 4.07; 95% CI, 2.21-7.47). Of the narcolepsy patients, 41.5, 5.4, and 13.2% were treated with MPH-IR, MPH-OROS, and modafinil, accordingly. Pharmacotherapy for narcolepsy did not significantly affect the risk of exhibiting a psychotic disorder.

CONCLUSIONS

This nationwide study revealed that narcolepsy and psychotic disorders commonly co-occur. Pharmacotherapy for narcolepsy was not associated with the risk of psychotic disorders. Our findings serve as a reminder that clinicians must consider the comorbidity of narcolepsy and psychosis.

Sleep disorders in NiemannPick disease type C, beyond cataplexy

PURPOSE

The aim of this study was to clinically characterize sleep disorders in a cohort of Niemann-Pick type C (NPC) patients, correlating these findings with disease features and polysomnographic (PSG) results.

METHODS

We evaluated eight consecutive patients with molecular confirmation of NPC followed at the Hospital Geral de Fortaleza. Patients underwent a comprehensive neurological and sleep evaluation. Four participants underwent polysomnography and then performed the multiple sleep latency test.

RESULTS

All eight patients evaluated had sleep disorders. Four participants performed polysomnography followed by multiple sleep latency test. Chronic insomnia and Obstructive Sleep Apnea (OSA) were the most frequent sleep disorders (62,5%). Two patients were diagnosed with Restless Legs Syndrome (RLS) (25%) and two with probable REM sleep behavior disorder (RBD) (25%). All the patients who did polysomnography had reduced and/or disorganized sleep, with reduction on sleep efficiency, total sleep time and REM sleep time.

CONCLUSION

Our results suggest that sleep abnormalities in Niemann-Pick type C patients may be more prevalent than previously thought.

Oral L-Carnitine used to treat narcoleptic type 1 patient during pregnancy - A case report

Narcolepsy type 1 is a sleep disorder characterized by excessive daytime sleepiness (EDS), sleep fragmentation, hypnagogic hallucinations, sleep paralysis, and cataplexy. Stimulant medications such as modafinil and amphetamines are the first-line medications for treating sleepiness. However, the management of narcolepsy during special circumstances of life such as pregnancy is complex. MMDM is a 34-year-old female with Narcolepsy type 1 treated with modafinil (400mg/d) and citalopram (20mg/d). Before she become pregnant, modafinil and citalopram were replaced for L-Carnitine 510mg/d with good outcome. She underwent an usual pregnancy and was submitted to a term cesarean delivery without child-birth complications. This is the first description of oral L-Carnitine such an alternative to treatment narcolepsy type 1 during pregnancy. Treat these patients is not easy but care narcolepsy pregnant is a challenging even bigger. In a disease without many treatment options, L-Carnitine can be used to treat daytime sleepiness during pregnancy in narcolepsy.

Narcolepsy and emotional experience: a review of the literature

Narcolepsy is a chronic sleep disorder characterized by excessive daytime sleepiness, cataplexy, hypnagogic hallucinations, and sleep paralysis. This disease affects significantly the overall patient functioning, interfering with social, work, and affective life. Some symptoms of narcolepsy depend on emotional stimuli; for instance, cataplectic attacks can be triggered by emotional inputs such as laughing, joking, a pleasant surprise, and also anger. Neurophysiological and neurochemical findings suggest the involvement of emotional brain circuits in the physiopathology of cataplexy, which seems to depending on the dysfunctional interplay between the hypothalamus and the amygdala associated with an alteration of hypocretin levels. Furthermore, behavioral studies suggest an impairment of emotions processing in narcolepsy-cataplexy (NC), like a probable coping strategy to avoid or reduce the frequency of cataplexy attacks. Consistently, NC patients seem to use coping strategies even during their sleep, avoiding unpleasant mental sleep activity through lucid dreaming. Interestingly, NC patients, even during sleep, have a different emotional experience than healthy subjects, with more vivid, bizarre, and frightening dreams. Notwithstanding this evidence, the relationship between emotion and narcolepsy is poorly investigated. This review aims to provide a synthesis of behavioral, neurophysiological, and neurochemical evidence to discuss the complex relationship between NC and emotional experience and to direct future research.

Drugs Used in Narcolepsy and Other Hypersomnias

Narcolepsy and idiopathic hypersomnia cannot be cured; all available treatments are symptomatic. It is of paramount importance for patients, and their relatives, to be informed about the consequences of these chronic diseases and to become ready to accept the consequences of the diagnosis before starting any treatment. This facilitates the implementation of behavioral modifications and the proper use of medication to decrease the disease burden. A supportive social environment (eg, family members, friends, employer, colleagues, and patient support groups) is instrumental. Current treatment options are discussed with a focus on pharmacologic treatment, including future directions.

Orexin/hypocretin and dysregulated eating: Promotion of foraging behavior

At its discovery, orexin/hypocretin (OX) was hypothesized to promote food intake. Subsequently, with the identification of the participation of OX in numerous other phenomena, including arousal and drug seeking, this neuropeptide was proposed to be involved in highly motivated behaviors. The present review develops the hypothesis that the primary evolutionary function of OX is to promote foraging behavior, seeking for food under conditions of limited availability. Thus, it will first describe published literature on OX and homeostatic food intake, which shows that OX neurons are activated by conditions of food deprivation and in turn stimulate food intake. Next, it will present literature on excessive and binge-like food intake, which demonstrates that OX stimulates both intake and willingness to work for palatable food. Importantly, studies show that binge-like eating can be inhibited by OX antagonists at doses far lower than those required to suppress homeostatic intake (3 mg/kg vs. 30 mg/kg), suggesting that an OX-based pharmacotherapy, at the right dose, could specifically control dysregulated eating. Finally, the review will discuss the role of OX in foraging behavior, citing literature which shows that OX neurons, which are activated during the anticipation of food reward, can promote a number of phenomena involved in successful foraging, including food-anticipatory locomotor behavior, olfactory sensitivity, visual attention, spatial memory, and mastication. Thus, OX may promote homeostatic eating, as well as binge eating of palatable food, due to its ability to stimulate and coordinate the activities involved in foraging behavior.

Narcolepsy type 1 and hypersomnia associated with a psychiatric disorder show different slow wave activity dynamics

The aim of the study was to compare electrophysiological parameters of night sleep in narcolepsy type 1 and hypersomnia associated with a psychiatric disorder. Fortyfour patients: 15 with narcolepsy type 1, 14 with hypersomnia associated with a psychiatric disorder and 15 age- and sex-matched controls participated in the study. The study subjects filled in the Athens Insomnia Scale (AIS) and the Beck Depression Inventory (BDI). The severity of daytime sleepiness was quantified subjectively using the Epworth Sleepiness Scale (ESS) and the Stanford Sleepiness Scale (SSS), and objectively using the Multiple Sleep Latency Test (MSLT). All subjects underwent polysomnography (PSG) on the two consecutive nights. The data from the second night was analysed. The slow wave activity (SWA, 1-4 Hz) was calculated for the three consecutive sleep cycles, and topographic delta power maps were plotted. In contrast to narcoleptics, psychiatric hypersomniacs had undisturbed nocturnal sleep, high sleep efficiency, normal non-rapid eye movement (NREM) and rapid eye movement (REM) sleep proportions, normal REM latency and sleep latencies on MSLT and PSG. The subjective and objective sleepiness was significantly higher in narcolepsy group than in psychiatric hypersomnia group. In all the study groups SWA was the most prominent in frontal areas, while the greatest between-group differences were found in the central areas. There were significant differences between the groups in SWA in the second NREM episode. The highest SWA was observed in the hypersomnia group, while the lowest in the narcolepsy group. Psychiatric hypersomniacs and controls did not differ in the SWA exponential decline over consecutive NREM episodes, whereas narcoleptics exhibited a steeper dissipation of sleep pressure from the first to the second NREM episode. In conclusion, narcolepsy type1 and hypersomnia associated with psychiatric disorder differ in the SWA dynamics. Narcoleptics presented with the altered dynamics of sleep homeostasis, whereas psychiatric hypersomniacs showed normal nocturnal sleep and normal sleep homeostasis.

Comorbidity of narcolepsy and depressive disorders: a nationwide population-based study in Taiwan

OBJECTIVE

Narcolepsy is a chronic sleep disorder that is likely to have neuropsychiatric comorbidities. Depression is a serious mood disorder that affects individuals' daily activities and functions. The current study aimed to investigate the relationship between narcolepsy and depressive disorders.

METHODS

The study consisted of patients diagnosed with narcolepsy between January 2002, and December 2011 (n = 258), and age-matched and gender-matched controls (n = 2580) from Taiwan's National Health Insurance database. Both the patients and the controls were monitored through December 31, 2011, to identify the occurrence of a depressive disorder. A multivariate logistic regression model was used to assess the narcolepsy's potential influence on the comorbidity of a depressive disorder.

RESULTS

During the study period, 32.7%, 24.8%, and 10.9% of the narcoleptic patients were comorbid with any depressive disorder, dysthymic disorder, and major depressive disorder, respectively. When compared to the control subjects, the patients with narcolepsy were at greater risks of having any depressive disorder (aOR 6.77; 95% CI 4.90-9.37), dysthymic disorder (aOR 6.62; 95% CI 4.61-9.57), and major depressive disorder (aOR 6.83; 95% CI 4.06-11.48). Of the narcoleptic patients that were comorbid with depression, >50% had been diagnosed with depression prior to being diagnosed with narcolepsy.

CONCLUSIONS

This nationwide data study revealed that narcolepsy and depression commonly co-occurred. Since some symptoms of narcolepsy overlapped with those of depressive disorders, the findings serve as a reminder that clinicians must pay attention to the comorbidity of narcolepsy and depression.

Pleiotropic genetic effects influencing sleep and neurological disorders

Research evidence increasingly points to the large impact of sleep disturbances on public health. Many aspects of sleep are heritable and genes influencing traits such as timing, EEG characteristics, sleep duration, and response to sleep loss have been identified. Notably, large-scale genome-wide analyses have implicated numerous genes with small effects on sleep timing. Additionally, there has been considerable progress in the identification of genes influencing risk for some neurological sleep disorders. For restless legs syndrome, implicated variants are typically in genes associated with neuronal development. By contrast, genes conferring risk for narcolepsy function in the immune system. Many genetic variants associated with sleep disorders are also implicated in neurological disorders in which sleep abnormalities are common; for example, variation in genes involved in synaptic homoeostasis are implicated in autism spectrum disorder and sleep-wake control. Further investigation into pleiotropic roles of genes influencing both sleep and neurological disorders could lead to new treatment strategies for a variety of sleep disturbances.

Listening to the Patient Voice in Narcolepsy: Diagnostic Delay, Disease Burden, and Treatment Efficacy

STUDY OBJECTIVES

Describe common symptoms, comorbidities, functional limitations, and treatment responsiveness among patients with narcolepsy. Investigate the effect of pediatric onset of narcolepsy symptoms on time to diagnosis of narcolepsy and presence of comorbid depression.

METHODS

Cross-sectional survey of 1,699 people in the United States with self-reported diagnosis of narcolepsy. We utilized mixed-methods data analyses to report study findings.

RESULTS

Most participants reported receiving a diagnosis of narcolepsy more than 1 y after symptom onset. We found that the strongest predictor of this delayed diagnosis was pediatric onset of symptoms (odds ratio = 2.4, p < 0.0005). Depression was the most common comorbidity but we detected no association with pediatric onset of narcolepsy symptoms. Overall, participants reported that fatigue and cognitive difficulties were their most burdensome symptoms in addition to sleepiness and cataplexy. The majority of participants reported residual daytime fatigue and/or sleepiness despite treatment. Most participants reported they could not perform at work or school as well as they would like because of narcolepsy symptoms.

CONCLUSIONS

This study provides unique insight into the narcolepsy disease experience. The study quantifies the problem of diagnostic delay for narcolepsy patients in the United States and highlights that symptoms are more likely to be missed if they develop before 18 y of age. These results suggest that narcolepsy awareness efforts should be aimed at parents, pediatric health care providers, school professionals, and children/adolescents themselves. Disease burden is high because of problems with fatigue, cognition, and persistence of residual symptoms despite treatment.

GABA Cells in the Central Nucleus of the Amygdala Promote Cataplexy

Cataplexy is a hallmark of narcolepsy characterized by the sudden uncontrollable onset of muscle weakness or paralysis during wakefulness. It can occur spontaneously, but is typically triggered by positive emotions such as laughter. Although cataplexy was identified >130 years ago, its neural mechanism remains unclear. Here, we show that a newly identified GABA circuit within the central nucleus of the amygdala (CeA) promotes cataplexy. We used behavioral, electrophysiological, immunohistochemical, and chemogenetic strategies to target and manipulate CeA activity selectively in narcoleptic (orexin^-/-) mice to determine its functional role in controlling cataplexy. First, we show that chemogenetic activation of the entire CeA produces a marked increase in cataplexy attacks. Then, we show that GABA cells within the CeA are responsible for mediating this effect. To manipulate GABA cells specifically, we developed a new mouse line that enables genetic targeting of GABA cells in orexin^-/- mice. We found that chemogenetic activation of GABA CeA cells triggered a 253% increase in the number of cataplexy attacks without affecting their duration, suggesting that GABA cells play a functional role in initiating but not maintaining cataplexy. We show that GABA cell activation only promotes cataplexy attacks associated with emotionally rewarding stimuli, not those occurring spontaneously. However, we found that chemogenetic inhibition of GABA CeA cells does not prevent cataplexy, suggesting these cells are not required for initiating cataplexy attacks. Our results indicate that the CeA promotes cataplexy onset and that emotionally rewarding stimuli may trigger cataplexy by activating GABA cells in the CeA.SIGNIFICANCE STATEMENT Although cataplexy has been closely linked to positive emotions for >130 years, the neural circuitry that underlies this relationship is poorly understood. Recent work suggests that the amygdala, a brain area important for processing emotion, may be part of this circuit. This study provides the first functional evidence to implicate GABA cells in the amygdala as regulators of cataplexy triggered by positive emotions and identifies the amygdala as the brain region important more for gating the entrance into rather than the exit from cataplexy. We also generated a new mouse model for studying GABA neurons in narcoleptic mice, which could serve as a useful tool for studying the neurobiological underpinnings of narcolepsy.

Changes in Histidine Decarboxylase, Histamine N-Methyltransferase and Histamine Receptors in Neuropsychiatric Disorders

Compared to other monoamine neurotransmitters, information on the association between the histaminergic system and neuropsychiatric disorders is scarce, resulting in a lack of histamine-related treatment for these disorders. The current chapter tries to combine information obtained from genetic studies, neuroimaging, post-mortem human brain studies and cerebrospinal fluid measurements with data from recent clinical trials on histamine receptor agonists and antagonists, with a view to determining the possible role of the histaminergic system in neuropsychiatric disorders and to pave the way for novel histamine-related therapeutic strategies.

Brain imaging and cognition in young narcoleptic patients

The relationship between functional brain images and performances in narcoleptic patients and controls is a new field of investigation. We studied 71 young, type 1 narcoleptic patients and 20 sex- and age-matched control individuals using brain positron emission tomography (PET) images and neurocognitive testing. Clinical investigation was carried out using sleep-wake evaluation questionnaires; a sleep-wake study was conducted with actigraphy, polysomnography, multiple sleep latency test (MSLT), and blood tests (with human leukocyte antigen typing). The continuous performance test (CPT) and Wisconsin card sorting test (WCST) were administered on the same day as the PET study. PET data were analyzed using Statistical Parametric Mapping (version 8) software. Correlation of brain imaging and neurocognitive function was performed by Pearson's correlation. Statistical analyses (Student's t-test) were conducted with SPSS version-18. Seventy-one narcoleptic patients (mean age: 16.15 years, 41 boys (57.7%)) and 20 controls (mean age: 15.1 years, 12 boys (60%)) were studied. Results from the CPT and WCST showed significantly worse scores in narcoleptic patients than in controls (P < 0.05). Compared to controls, narcoleptic patients presented with hypometabolism in the right mid-frontal lobe and angular gyrus (P < 0.05) and significant hypermetabolism in the olfactory lobe, hippocampus, parahippocampus, amygdala, fusiform, left inferior parietal lobe, left superior temporal lobe, striatum, basal ganglia and thalamus, right hypothalamus, and pons (P < 0.05) in the PET study. Changes in brain metabolic activity in narcoleptic patients were positively correlated with results from the sleepiness scales and performance tests. Young, type 1 narcoleptic patients face a continuous cognitive handicap. Our imaging cognitive test protocol can be useful for investigating the effects of treatment trials in these patients.

Emerging drugs for common conditions of sleepiness: obstructive sleep apnea and narcolepsy

INTRODUCTION

Obstructive sleep apnea (OSA) and narcolepsy are sleep disorders associated with high prevalence and high symptomatic burden including prominent sleepiness, daytime dysfunction and poor nocturnal sleep. Both have elevated risk of poor health outcomes. Current therapies are often underutilized, cumbersome, costly or associated with residual symptoms.

AREAS COVERED

This review covers current available therapies for OSA and narcolepsy as well as discusses areas for potential drug development, and agents in the therapeutic pipeline, including the cannabinoid dronabinol (OSA), the histamine inverse agonist/ antagonist pitolisant (narcolepsy), and stimulants with uncertain and/or multiple activities such as JZP-110 and JZP-386 (narcolepsy, possibly OSA). Finally it addresses new approaches and uses for therapies currently on the market such as the carbonic anhydrase inhibitor acetazolamide (OSA).

EXPERT OPINION

Both OSA and narcolepsy are conditions of sleepiness for which lifelong treatments are likely to be required. In OSA, while continuous positive airway pressure will likely remain the gold standard therapy for the foreseeable future, there is plenty of room for integrating phenotypes and variants of OSA into therapeutic strategies to lead to better, more personalized disease modification. In narcolepsy, unlike OSA, drug therapy is the current mainstay of treatment. Advances using novel mechanisms to treat targeted symptoms such as sleepiness and/or novel agents that can treat more than one symptom of narcolepsy, hold promise. However, cost, convenience and side effects remain challenges.

Narcolepsy in African Americans

STUDY OBJECTIVES

Although narcolepsy affects 0.02-0.05% of individuals in various ethnic groups, clinical presentation in different ethnicities has never been fully characterized. Our goal was to study phenotypic expression across ethnicities in the United States.

DESIGN/SETTING

Cases of narcolepsy from 1992 to 2013 were identified from searches of the Stanford Center for Narcolepsy Research database. International Classification of Sleep Disorders, Third Edition diagnosis criteria for type 1 and type 2 narcolepsy were used for inclusion, but subjects were separated as with and without cataplexy for the purpose of data presentation. Information extracted included demographics, ethnicity and clinical data, HLA-DQB1*06:02, polysomnography (PSG), multiple sleep latency test (MSLT) data, and cerebrospinal fluid (CSF) hypocretin-1 level.

PATIENTS

182 African-Americans, 839 Caucasians, 35 Asians, and 41 Latinos with narcolepsy.

RESULTS

Sex ratio, PSG, and MSLT findings did not differ across ethnicities. Epworth Sleepiness Scale (ESS) score was higher and age of onset of sleepiness earlier in African Americans compared with other ethnicities. HLA-DQB1*06:02 positivity was higher in African Americans (91.0%) versus others (76.6% in Caucasians, 80.0% in Asians, and 65.0% in Latinos). CSF hypocretin-1 level, obtained in 222 patients, was more frequently low (≤ 110 pg/ml) in African Americans (93.9%) versus Caucasians (61.5%), Asians (85.7%) and Latinos (75.0%). In subjects with low CSF hypocretin-1, African Americans (28.3%) were 4.5 fold more likely to be without cataplexy when compared with Caucasians (8.1%).

CONCLUSIONS

Narcolepsy in African Americans is characterized by earlier symptom onset, higher Epworth Sleepiness Scale score, higher HLA-DQB1*06:02 positivity, and low cerebrospinal fluid hypocretin-1 level in the absence of cataplexy. In African Americans, more subjects without cataplexy have type 1 narcolepsy.

Sleep disorders, obesity, and aging: the role of orexin

The hypothalamic neuropeptides orexin A and B (hypocretin 1 and 2) are important homeostatic mediators of central control of energy metabolism and maintenance of sleep/wake states. Dysregulation or loss of orexin signaling has been linked to narcolepsy, obesity, and age-related disorders. In this review, we present an overview of our current understanding of orexin function, focusing on sleep disorders, energy balance, and aging, in both rodents and humans. We first discuss animal models used in studies of obesity and sleep, including loss of function using transgenic or viral-mediated approaches, gain of function models using exogenous delivery of orexin receptor agonist, and naturally-occurring models in which orexin responsiveness varies by individual. We next explore rodent models of orexin in aging, presenting evidence that orexin loss contributes to age-related changes in sleep and energy balance. In the next section, we focus on clinical importance of orexin in human obesity, sleep, and aging. We include discussion of orexin loss in narcolepsy and potential importance of orexin in insomnia, correlations between animal and human studies of age-related decline, and evidence for orexin involvement in age-related changes in cognitive performance. Finally, we present a summary of recent studies of orexin in neurodegenerative disease. We conclude that orexin acts as an integrative homeostatic signal influencing numerous brain regions, and that this pivotal role results in potential dysregulation of multiple physiological processes when orexin signaling is disrupted or lost.

Unmet needs of patients with narcolepsy: perspectives on emerging treatment options

The treatment options currently available for narcolepsy are often unsatisfactory due to suboptimal efficacy, troublesome side effects, development of drug tolerance, and inconvenience. Our understanding of the neurobiology of narcolepsy has greatly improved over the last decade. This knowledge has not yet translated into additional therapeutic options for patients, but progress is being made. Some compounds, such as histaminergic H3 receptor antagonists, may prove useful in symptom control of narcolepsy. The prospect of finding a cure still seems distant, but hypocretin replacement therapy offers some promise. In this narrative review, we describe these developments and others which may yield more effective narcolepsy treatments in the future.

miRNA profiles in plasma from patients with sleep disorders reveal dysregulation of miRNAs in narcolepsy and other central hypersomnias

STUDY OBJECTIVES

MicroRNAs (miRNAs) have been implicated in the pathogenesis of human diseases including neurological disorders. The aim is to address the involvement of miRNAs in the pathophysiology of central hypersomnias including autoimmune narcolepsy with cataplexy and hypocretin deficiency (type 1 narcolepsy), narcolepsy without cataplexy (type 2 narcolepsy), and idiopathic hypersomnia.

DESIGN

We conducted high-throughput analysis of miRNA in plasma from three groups of patients-with type 1 narcolepsy, type 2 narcolepsy, and idiopathic hypersomnia, respectively-in comparison with healthy controls using quantitative real-time polymerase chain reaction (qPCR) panels.

SETTING

University hospital based sleep clinic and research laboratories.

PATIENTS

Twelve patients with type 1 narcolepsy, 12 patients with type 2 narcolepsy, 12 patients with idiopathic hypersomnia, and 12 healthy controls.

MEASUREMENTS AND RESULTS

By analyzing miRNA in plasma with qPCR we identified 50, 24, and 6 miRNAs that were different in patients with type 1 narcolepsy, type 2 narcolepsy, and idiopathic hypersomnia, respectively, compared with healthy controls. Twenty miRNA candidates who fulfilled the criteria of at least two-fold difference and p-value < 0.05 were selected to validate the miRNA changes in an independent cohort of patients. Four miRNAs differed significantly between type 1 narcolepsy patients and healthy controls. Levels of miR-30c, let-7f, and miR-26a were higher, whereas the level of miR-130a was lower in type 1 narcolepsy than healthy controls. The miRNA differences were not specific for type 1 narcolepsy, since the levels of the four miRNAs were also altered in patients with type 2 narcolepsy and idiopathic hypersomnia compared with healthy controls.

CONCLUSION

The levels of four miRNAs differed in plasma from patients with type 1 narcolepsy, type 2 narcolepsy and idiopathic hypersomnia suggesting that alterations of miRNAs may be involved in the pathophysiology of central hypersomnias.

Genome-wide analysis of CNV (copy number variation) and their associations with narcolepsy in a Japanese population

In humans, narcolepsy with cataplexy (narcolepsy) is a sleep disorder that is characterized by sleepiness, cataplexy and rapid eye movement (REM) sleep abnormalities. Narcolepsy is caused by a reduction in the number of neurons that produce hypocretin (orexin) neuropeptide. Both genetic and environmental factors contribute to the development of narcolepsy.Rare and large copy number variations (CNVs) reportedly play a role in the etiology of a number of neuropsychiatric disorders. Narcolepsy is considered a neurological disorder; therefore, we sought to investigate any possible association between rare and large CNVs and human narcolepsy. We used DNA microarray data and a CNV detection software application, PennCNV-Affy, to detect CNVs in 426 Japanese narcoleptic patients and 562 healthy individuals. Overall, we found a significant enrichment of rare and large CNVs (frequency ≤1%, size ≥100 kb) in the patients (case-control ratio of CNV count=1.54, P=5.00 × 10(-4)). Next, we extended a region-based association analysis by including CNVs with its size ≥30 kb. Rare and large CNVs in PARK2 region showed a significant association with narcolepsy. Four patients were assessed to carry duplications of the gene region, whereas no controls carried the duplication, which was further confirmed by quantitative PCR assay. This duplication was also found in 2 essential hypersomnia (EHS) patients out of 171 patients. Furthermore, a pathway analysis revealed enrichments of gene disruptions by rare and large CNVs in immune response, acetyltransferase activity, cell cycle regulation and regulation of cell development. This study constitutes the first report on the risk association between multiple rare and large CNVs and the pathogenesis of narcolepsy. In the future, replication studies are needed to confirm the associations.

Glucose and fat metabolism in narcolepsy and the effect of sodium oxybate: a hyperinsulinemic-euglycemic clamp study

INTRODUCTION

Narcolepsy is associated with obesity though it is uncertain whether this is caused by changes in glucose and fat metabolism. Therefore, we performed a detailed analysis of systemic energy homeostasis in narcolepsy patients, and additionally, investigated whether it was affected by three months of sodium oxybate (SXB) treatment.

METHODS

Nine hypocretin deficient patients with narcolepsy-cataplexy, and nine healthy sex, age, and BMI matched controls were enrolled. A hyperinsulinemic-euglycemic clamp combined with stable isotopes ([6,6-(2)H2]-glucose and [(2)H5]- glycerol) was performed at baseline. In seven patients a second study was performed after three months of SXB treatment.

RESULTS

Glucose disposal rate (GDR) per unit serum insulin was significantly higher in narcolepsy patients compared to matched controls (1.6 ± 0.2 vs. 1.1 ± 0.3 μmol/kgFFM/min/mU×L; P = 0.024), whereas β-cell function was similar (P = 0.50). Basal steady state glycerol appearance rate tended to be lower in narcolepsy patients (5.2 ± 0.4 vs. 7.5 ± 1.3 μmol/kgFM/min; P = 0.058), suggesting a lower rate of lipolysis. SXB treatment induced a trend in reduction of the GDR (1.4 ± 0.1 vs. 1.1 ± 0.2 μmol/kgFFM/min/mU×L; P = 0.063) and a reduction in endogenous glucose production (0.24 ± 0.03 vs. 0.16 ± 0.03 μmol/kgFFM/min/mU×L: P = 0.028) per unit serum insulin. After SXB treatment lipolysis increased (4.9 ± 0.4 vs. 6.5 ± 0.6 μmol/kgFM/min; P = 0.018), and body weight decreased in narcolepsy patients (99.2 ± 6.0 vs. 94.0 ± 5.4 kg; P = 0.044).

CONCLUSION

We show that narcolepsy patients are more insulin sensitive and may have a lower rate of lipolysis than matched controls. SXB stimulated lipolysis in narcolepsy patients, possibly accounting for the weight loss after treatment. While sodium oxybate tended to decrease systemic insulin sensitivity, it increased hepatic insulin sensitivity, suggesting tissue-specific effects.

Identification of the variations in the CPT1B and CHKB genes along with the HLA-DQB1*06:02 allele in Turkish narcolepsy patients and healthy persons

BACKGROUND

The HLA-DQB1*06:02 allele across all ethnic groups and the rs5770917 variation between CPT1B and CHKB genes in Japanese and Koreans are common genetic susceptibility factors for narcolepsy. This comprehensive genetic study sought to assess variations in CHKB and CPT1B susceptibility genes and HLA-DQB1*06:02 allele status in Turkish patients with narcolepsy and healthy persons.

METHODS

CHKB/CPT1B genes were sequenced in patients with narcolepsy (n=37) and healthy persons (n=100) to detect variations. The HLA-DQB1*06:02 allele status was determined by sequence specific polymerase chain reaction.

RESULTS

The HLA-DQB1*06:02 allele was significantly more frequent in narcoleptic patients than in healthy persons (p=2×10(-7)) and in patients with narcolepsy and cataplexy than in those without (p=0.018). The mean of the multiple sleep latency test, sleep-onset rapid eye movement periods, and frequency of sleep paralysis significantly differed in the HLA-DQB1*06:02-positive patients. rs5770917, rs5770911, rs2269381, and rs2269382 were detected together as a haplotype in three patients and 11 healthy persons. In addition to this haplotype, the indel variation (rs144647670) was detected in the 5' upstream region of the human CHKB gene in the patients and healthy persons carrying four variants together.

CONCLUSION

This study identified a novel haplotype consisting of the indel variation, which had not been detected in previous studies in Japanese and Korean populations, and observed four single-nucleotide polymorphisms in CHKB/CPT1B. The study confirmed the association of the HLA-DQB1*06:02 allele with narcolepsy and cataplexy susceptibility. The findings suggest that the presence of HLA-DQB1*06:02 may be a predictor of cataplexy in narcoleptic patients and could therefore be used as an additional diagnostic marker alongside hypocretin.

Etiopathogenesis and neurobiology of narcolepsy: a review

Narcolepsy is a chronic lifelong sleep disorder and it often leaves a debilitating effect on the quality of life of the sufferer. This disorder is characterized by a tetrad of excessive daytime sleepiness, cataplexy (brief loss of muscle tone following strong emotion), hypnogogic hallucinations and sleep paralysis. There are two distinct subgroups of Narcolepsy: Narcolepsy with cataplexy and Narcolepsy without cataplexy. For over 100 years, clinicians have recognised narcolepsy, but only in the last few decades have scientists been able to shed light on the true cause and pathogenesis of narcolepsy. Recent studies have shown that a loss of the hypothalamic neuropeptide Hypocretin/Orexincauses Narcolepsy with cataplexy and that an autoimmune mechanism may be responsible for this loss. Our understanding of the neurophysiologic aspect of narcolepsy has also significantly improved. The basic neural mechanisms behind sleepiness and cataplexy, the two defining symptoms of narcolepsy have started to become clearer. In this review, we have provided a detailed account of the key aspects of etiopathogenesis and neurobiology of narcolepsy, along with a critical appraisal of the more recent and interesting causal associations.We have also looked at the contributions of neuroimaging to the etiopathogenesis of Narcolepsy.

Thyrotropin secretion patterns in health and disease

Thyroid hormones are extremely important for metabolism, development, and growth during the lifetime. The hypothalamo-pituitary-thyroid axis is precisely regulated for these purposes. Much of our knowledge of this hormonal axis is derived from experiments in animals and mutations in man. This review examines the hypothalamo-pituitary-thyroid axis particularly in relation to the regulated 24-hour serum TSH concentration profiles in physiological and pathophysiological conditions, including obesity, primary hypothyroidism, pituitary diseases, psychiatric disorders, and selected neurological diseases. Diurnal TSH rhythms can be analyzed with novel and precise techniques, eg, operator-independent deconvolution and approximate entropy. These approaches provide indirect insight in the regulatory components in pathophysiological conditions.

Transcranial magnetic stimulation and sleep disorders: pathophysiologic insights

The neural mechanisms underlying the development of the most common intrinsic sleep disorders are not completely known. Therefore, there is a great need for noninvasive tools which can be used to better understand the pathophysiology of these diseases. Transcranial magnetic stimulation (TMS) offers a method to noninvasively investigate the functional integrity of the motor cortex and its corticospinal projections in neurologic and psychiatric diseases. To date, TMS studies have revealed cortical and corticospinal dysfunction in several sleep disorders, with cortical hyperexcitability being a characteristic feature in some disorders (i.e., the restless legs syndrome) and cortical hypoexcitability being a well-established finding in others (i.e., obstructive sleep apnea syndrome narcolepsy). Several research groups also have applied TMS to evaluate the effects of pharmacologic agents, such as dopaminergic agent or wake-promoting substances. Our review will focus on the mechanisms underlying the generation of abnormal TMS measures in the different types of sleep disorders, the contribution of TMS in enhancing the understanding of their pathophysiology, and the potential diagnostic utility of TMS techniques. We also briefly discussed the possible future implications for improving therapeutic approaches.

Plasma obestatin and autonomic function are altered in orexin-deficient narcolepsy, but ghrelin is unchanged

Narcolepsy-cataplexy is characterised by orexin deficiency, sleep disturbance, obesity and dysautonomia. Ghrelin and obestatin affect both energy intake and sleep. Our aim was to investigate ghrelin, obestatin and metabolic/autonomic function in narcolepsy-cataplexy. Eight narcolepsy-cataplexy patients (seven CSF orexin-deficient) and eight matched controls were studied. The subjects had a fixed energy meal with serial blood samples and measurement of heart rate variability (HRV). Fasting plasma obestatin was more than threefold higher in narcolepsy subjects (narcolepsy 89.6 ± 16 pg/ml vs. control 24.9 ± 3 pg/ml, p < 0.001). There was no change in HRV total power, but post-prandial low-frequency (LF) power and high-frequency (HF) power were lower in the narcolepsy group [area under the curve (AUC): HF power narcolepsy 1.4 × 10(5) ± 0.2 × 10(5) vs. control 3.3 × 10(5) ± 0.6 × 10(5 )ms(2)/h, p < 0.001]. On multiple regression analyses, the only significant predictor of plasma obestatin was HF power, which was inversely correlated with obestatin (β = -0.65 R (2) = 38 %, p = 0.009). Fasting and post-prandial plasma ghrelin were similar in both groups (narcolepsy 589.5 ± 88 pg/ml vs. control 686.9 ± 81 pg/ml, p = 0.5; post-prandial AUC-narcolepsy 161.3 ± 22 ng/ml/min vs. control 188.6 ± 62 ng/ml/min, p = 0.4). Only the narcolepsy group had significant suppression of plasma ghrelin after the meal (ANOVA, p = 0.004). In orexin-deficient narcolepsy, fasting plasma ghrelin is unaltered, and post-prandial suppression is preserved. Fasting plasma obestatin is increased and correlates with autonomic dysfunction. As obestatin affects NREM sleep, we suggest that increased plasma levels contribute to the disrupted sleep-state control in narcolepsy.

Genetic association, seasonal infections and autoimmune basis of narcolepsy

In recent years, a growing number of potential autoimmune disorders affecting neurons in the central nervous system have been identified, including narcolepsy. Narcolepsy is a lifelong sleep disorder characterized by excessive daytime sleepiness with irresistible sleep attacks, cataplexy (sudden bilateral loss of muscle tone), hypnagogic hallucinations, and abnormalities of Rapid Eye Movement sleep. Narcolepsy is generally a sporadic disorder and is caused by the loss of hypocretin (orexin)-producing neurons in the hypothalamus region of the brain. Studies have established that more than 90% of patients have a genetic association with HLA DQB1*06:02. Genome-wide association analysis shows a strong association between narcolepsy and polymorphisms in the TCRα locus and weaker associations within TNFSF4 (also called OX40L), Cathepsin H and the P2RY11-DNMT1 (purinergic receptor subtype P2Y11 to DNMT1, a DNA methytransferase) loci, suggesting an autoimmune basis. Mutations in DNMT1 have also been reported to cause narcolepsy in association with a complex neurological syndrome, suggesting the importance of DNA methylation in the pathology. More recently, narcolepsy was identified in association with seasonal streptococcus, H1N1 infections and following AS03-adjuvanted pH1N1 influenza vaccination in Northern Europe. Potential immunological pathways responsible for the loss of hypocretin producing neurons in these cases may be molecular mimicry or bystander activation. Specific autoantibodies or T cells cross-reactive with hypocretin neurons have not yet been identified, however, thus narcolepsy does not meet Witebsky's criteria for an autoimmune disease. As the brain is not an easily accessible organ, mechanisms of disease initiation and progression remain a challenge to researchers.

Effects of orexin gene transfer in the dorsolateral pons in orexin knockout mice

STUDY OBJECTIVES

Narcolepsy is a sleep disorder characterized by loss of orexin neurons. Previously, our group demonstrated that transfer of the orexin gene into surrogate neurons in the lateral hypothalamus and the zona incerta significantly reduced cataplexy bouts in the orexin-ataxin-3 mice model of narcolepsy. The current study determined the effects of orexin gene transfer into the dorsolateral pontine neurons in the orexin knockout (KO) mice model of narcolepsy. The dorsolateral pons was chosen because it plays a critical role in regulating muscle tone and thus it is conceivable to be involved in cataplexy as well. Cataplexy is the pathognomonic symptom in narcolepsy.

DESIGN

Independent groups of orexin KO mice were given bilateral microinjections (0.75 μL each side) of either recombinant adenoassociated virus-orexin (rAAV-orexin; n = 7), or rAAV-green fluorescent protein (rAAV-GFP; n = 7) into the dorsolateral pons. A group of orexin KO mice that did not receive rAAV (n = 7) and a group of wild-type mice (C57BL/J6; n = 5) were used as controls. Three weeks after rAAV-mediated gene transfer narcolepsy symptoms were examined using sleep and behavioral recordings. Number, location of the orexin-immunoreactive neurons, and relative density of orexin immunoreactive fibers were determined.

MEASUREMENTS AND RESULTS

Orexin gene transfer into the dorsolateral pons significantly decreased cataplexy and modestly improved wake maintenance compared to the orexin KO mice that did not receive rAAV. In contrast, GFP gene transfer worsened narcoleptic symptoms compared to the no-rAAV orexin KO group.

CONCLUSION

Orexin gene transfer into the dorsolateral pontine neurons can control cataplexy attacks and modestly improve wake maintenance.