Decreased cerebrospinal fluid hypocretin-1 levels near the onset of narcolepsy in 2 prepubertal children

Design and synthesis of novel orexin 2 receptor agonists with a 1,3,5‑trioxazatriquinane skeleton

A novel series of 1,3,5‑trioxazatriquinane with multiple effective residues (TriMER) derivatives with amino-methylene side chains was designed and synthesized based on the docking-simulation results between orexin receptors (OXRs) and TriMER-type OXR antagonists. In vitro screening against orexin receptors identified six TriMER derivatives with a cis side-chain configuration, and, among these, 20d and 28d showed full agonist activity against OX₂R at a concentration of 10 µM. To determine the absolute stereochemistry of these hit compounds, we also conducted the first asymmetric synthesis of a 1,3,5‑trioxazatriquinane skeleton using a Katsuki-Sharpless asymmetric epoxidation as the key reaction and obtained a set of the individual stereoisomers. After evaluating their activity, (+)-20d (EC₅₀ = 3.87 μM for OX₂R) and (+)-28d (EC₅₀ = 1.62 μM for OX₂R) were determined as eutomers for OX₂R agonist activity. Our results provide a new class of skeleton consisting of an (R)-1,3,5‑trioxazatriquinane core with flexible methylene linkers and hydrophobic substituents at the terminals of the side chains via carbamates/sulfonamides as OX₂R agonists.

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.

Reviewing the Clinical Implications of Treating Narcolepsy as an Autoimmune Disorder

Narcolepsy type 1 (NT1) is a lifelong sleep disorder, primarily characterized clinically by excessive daytime sleepiness and cataplexy and pathologically by the loss of hypocretinergic neurons in the lateral hypothalamus. Despite being a rare disorder, the NT1-related burden for patients and society is relevant due to the early onset and chronic nature of this condition. Although the etiology of narcolepsy is still unknown, mounting evidence supports a central role of autoimmunity. To date, no cure is available for this disorder and current treatment is symptomatic. Based on the hypothesis of the autoimmune etiology of this disease, immunotherapy could possibly represent a valid therapeutic option. However, contrasting and limited results have been provided so far. This review discusses the evidence supporting the use of immunotherapy in narcolepsy, the outcomes obtained so far, current issues and future directions.

Design and Synthesis of Non-Peptide, Selective Orexin Receptor 2 Agonists

Orexins are a family of neuropeptides that regulate sleep/wakefulness, acting on two G-protein-coupled receptors, orexin receptors 1 (OX1R) and 2 (OX2R). Genetic and pharmacologic evidence suggests that orexin receptor agonists, especially OX2R agonist, will be useful for mechanistic therapy of the sleep disorder narcolepsy/cataplexy. We herein report the discovery of a potent (EC50 on OX2R is 0.023 μM) and OX2R-selective (OX1R/OX2R EC50 ratio is 70) agonist, 4'-methoxy-N,N-dimethyl-3'-[N-(3-{[2-(3-methylbenzamido)ethyl]amino}phenyl)sulfamoyl]-(1,1'-biphenyl)-3-carboxamide 26.

The hypocretin/orexin system: an increasingly important role in neuropsychiatry

Hypocretins, also named as orexins, are excitatory neuropeptides secreted by neurons specifically located in lateral hypothalamus and perifornical areas. Orexinergic fibers are extensively distributed in various brain regions and involved in a number of physiological functions, such as arousal, cognition, stress, appetite, and metabolism. Arousal is the most important function of orexin system as dysfunction of orexin signaling leads to narcolepsy. In addition to narcolepsy, orexin dysfunction is associated with serious neural disorders, including addiction, depression, and anxiety. However, some results linking orexin with these disorders are still contradictory, which may result from differences of detection methods or the precision of tools used in measurements; strategies targeted to orexin system (e.g., antagonists to orexin receptors, gene delivery, and cell transplantation) are promising new tools for treatment of neuropsychiatric disorders, though studies are still in a stage of preclinical or clinical research.

Hypocretin-1 deficiency in a girl with ROHHAD syndrome

Rapid-onset obesity with hypothalamic dysfunction, hypoventilation, and autonomic dysregulation (ROHHAD) is a rare and complex pediatric syndrome, essentially caused by dysfunction of 3 vital systems regulating endocrine, respiratory, and autonomic nervous system functioning. The clinical spectrum of ROHHAD is broad, but sleep/wake disorders have received relatively little attention so far, although the central hypothalamic dysfunction would make the occurrence of sleep symptoms likely. In this case report, we expand the phenotype of ROHHAD with a number of striking sleep symptoms that together can be classified as a secondary form of narcolepsy. We present a 7-year-old girl with ROHHAD who displayed the classic features of narcolepsy with cataplexy: excessive daytime sleepiness with daytime naps, visual hallucinations, and partial cataplexy reflected in intermittent loss of facial muscle tone. Nocturnal polysomnography revealed sleep fragmentation and a sleep-onset REM period characteristic for narcolepsy. The diagnosis was confirmed by showing an absence of hypocretin-1 in the cerebrospinal fluid. We discuss potential pathophysiological implications as well as symptomatic treatment options.

Validation of the ICSD-2 criteria for CSF hypocretin-1 measurements in the diagnosis of narcolepsy in the Danish population

STUDY OBJECTIVES

The International Classification of Sleep Disorders (ICSD-2) criteria for low CSF hypocretin-1 levels (CSF hcrt-1) still need validation as a diagnostic tool for narcolepsy in different populations because inter-assay variability and different definitions of hypocretin deficiency complicate direct comparisons of study results.

DESIGN AND PARTICIPANTS

Interviews, polysomnography, multiple sleep latency test, HLA-typing, and CSF hcrt-1 measurements in Danish patients with narcolepsy with cataplexy (NC) and narcolepsy without cataplexy (NwC), CSF hcrt-1 measurements in other hypersomnias, neurological and normal controls. Comparisons of hypocretin deficiency and frequency of HLA-DQB1*0602-positivity in the Danish and eligible NC and NwC populations (included via MEDLINE search), by (re)calculation of study results using the ICSD-2 criterion for low CSF hcrt-1 (< 30% of normal mean).

MEASUREMENTS AND RESULTS

In Danes, low CSF hcrt-1 was present in 40/46 NC, 3/14 NwC and 0/106 controls (P < 0.0001). Thirty-nine of 41 NC and 4/13 NwC patients were HLA-DQB1*0602-positive (P < 0.01). Hypocretin-deficient NC patients had higher frequency of cataplexy, shorter mean sleep latency, more sleep onset REM periods (P < 0.05) and more awakenings (NS) than did NC patients with normal CSF hcrt-1. Across populations, low CSF hcrt-1 and HLA-DQB1*0602-positivity characterized the majority of NC (80% to 100%, P = 0.53; 80% to 100%, P = 0.11) but a minority of NwC patients (11% to 29%, P = 0.75; 29% to 89%, P = 0.043).

CONCLUSION

The study provides evidence that hypocretin deficiency causes a more severe NC phenotype. The ICSD-2 criterion for low CSF hcrt-1 (< 30% of normal mean) is valid for diagnosing NC, but not NwC. HLA-typing should precede CSF hcrt-1 measurements because hypocretin deficiency is rare in HLA-DQB1*0602-negative patients.

Childhood narcolepsy with partial facial cataplexy: a diagnostic dilemma

Sixteen percent of adults ultimately diagnosed with having narcolepsy/cataplexy experienced symptoms before the age of ten years, 4.5% even before the age of five years. The symptomatology in childhood narcolepsy/cataplexy can differ significantly from adults and can lead to misinterpretations and misdiagnosis. Standard diagnostic tools (polysomnography and multiple sleep latency test) can give false negative results and do not exclude the disorder. The decision to determine hypocretins in cerebrospinal fluid (CSF) should be made as early as possible in children. Here, we present a case of a five-year-old girl with acute onset of narcolepsy/cataplexy after a closed head trauma. The first symptoms were excessive daytime sleepiness, partial facial cataplexy and a serious behavioral disorder. Hypocretin-1 level (Hrt-1) in CSF was undetectable.

Pediatric narcolepsy

Narcolepsy is a disabling disease with a prevalence of 0.05%. It is characterized by excessive daytime sleepiness, cataplexy, sleep paralysis, hypnogogic hallucinations, automatic behavior, and disrupted nocturnal sleep. The presentation can be very variable, making diagnosis difficult. Loss of hypocretin containing neurons in the lateral hypothalamus has been noted in autopsy studies, and the cerebrospinal fluid level of hypocretin is reduced in patients with narcolepsy with cataplexy. New treatment options are available for the many symptoms of this disease. Early recognition and treatment can greatly improve the quality of life of patients with narcolepsy. A detail review of the epidemiology, pathophysiology, and management of narcolepsy in children is presented.

Narcolepsy: immunological aspects

Narcolepsy with cataplexy is a debilitating sleep disorder with an estimated prevalence of about 0.05%. Narcolepsy is caused by a selective loss of hypocretin (orexin) producing neurons in the perifornical hypothalamus. Based on the very strong association with the HLA subtype DQB1*0602, it is currently hypothesized narcolepsy is caused by an autoimmune-mediated process directed at the hypocretin neurons. So far however, studies focusing on general markers of (auto)immune activation, as well as humoral immunity against the hypocretin system have not yielded consistent results supporting this hypothesis.

Hypocretins (orexins) and sleep–wake disorders

Since their discovery in 1998, the hypocretins (orexins)-peptides that are produced by a group of neurons situated in the posterolateral hypothalamus--have been shown to excite many CNS areas including many neuronal systems that regulate sleep and wakefulness. Animal studies indicate that hypocretins play a part in the regulation of various functions including arousal, muscle tone, locomotion, regulation of feeding behaviour, and neuroendocrine and autonomic functions. A link between hypocretin deficiency and narcoleptic symptoms was first shown in canine and rodent models of narcolepsy. Hypocretin deficiency, as shown by low or absent concentrations in CSF, was subsequently found in 90% of patients with sporadic narcolepsy-cataplexy, and less commonly in familial narcolepsy. In most other sleep-wake and neurological disorders, hypocretin concentrations are normal. Low concentrations were also found in hypothalamic disorders, acute traumatic brain injury, and a few other disorders. The exact function of the hypocretin system in sleep-wake regulation and its pathophysiological role in hypocretin-deficient and non-deficient narcolepsy as well as in non-narcoleptic, hypocretin-deficiency syndromes remain unclear.

Hypocretins (orexins): clinical impact of the discovery of a neurotransmitter

Hypothalamic excitatory hypocretin (orexin) neurons have been discovered in 1998 and found to have widespread projections to basal forebrain, monoaminergic and cholinergic brainstem, and spinal cord regions. The hypocretin system is influenced both neuronally (e.g. suprachiasmatic nucleus, GABAergic, cholinergic and aminergic brainstem nuclei) as well as metabolically (e.g. glucose, ghrelin, and leptin). Physiologically the hypocretin system has been implicated in the regulation of behaviours that are associated with wakefulness, locomotion, and feeding. A role in REM sleep, neuroendocrine, autonomic and metabolic functions has also been suggested. Pathophysiologically a deficient hypocretin neurotransmission has been found in human narcolepsy and (engineered) animal models of the disorder. Different mechanisms are involved including (1) degeneration of hypocretin neurons (mice), (2) hypocretin ligand deficiency (humans, mice, dogs), (3) hypocretin receptor deficiency (mice, dogs). Reports of low hypocretin-1 cerebrospinal fluid levels in neurologic conditions (e.g. Guillain-Barré syndrome, traumatic brain injury, hypothalamic lesions) with and without sleep-wake disturbances and, on the other hand, observations of normal levels in about 11% of narcoleptics raise questions about the exact nature and pathophysiological base of the link between hypocretin deficiency and clinical manifestations in human narcolepsy.

Symptomatic narcolepsy, cataplexy and hypersomnia, and their implications in the hypothalamic hypocretin/orexin system

Human narcolepsy is a chronic sleep disorder affecting 1:2000 individuals. The disease is characterized by excessive daytime sleepiness, cataplexy and other abnormal manifestations of REM sleep, such as sleep paralysis and hypnagogic hallucinations. Recently, it was discovered that the pathophysiology of (idiopathic) narcolepsy-cataplexy is linked to hypocretin ligand deficiency in the brain and cerebrospinal fluid (CSF), as well as the positivity of the human leukocyte antigen (HLA) DR2/DQ6 (DQB1*0602). The symptoms of narcolepsy can also occur during the course of other neurological conditions (i.e. symptomatic narcolepsy). We define symptomatic narcolepsy as those cases that meet the International Sleep Disorders Narcolepsy Criteria, and which are also associated with a significant underlying neurological disorder that accounts for excessive daytime sleepiness (EDS) and temporal associations. To date, we have counted 116 symptomatic cases of narcolepsy reported in literature. As, several authors previously reported, inherited disorders (n=38), tumors (n=33), and head trauma (n=19) are the three most frequent causes for symptomatic narcolepsy. Of the 116 cases, 10 are associated with multiple sclerosis, one case of acute disseminated encephalomyelitis, and relatively rare cases were reported with vascular disorders (n=6), encephalitis (n=4) and degeneration (n=1), and hererodegenerative disorder (three cases in a family). EDS without cataplexy or any REM sleep abnormalities is also often associated with these neurological conditions, and defined as symptomatic cases of EDS. Although it is difficult to rule out the comorbidity of idiopathic narcolepsy in some cases, review of the literature reveals numerous unquestionable cases of symptomatic narcolepsy. These include cases with HLA negative and/or late onset, and cases in which the occurrences of the narcoleptic symptoms are parallel with the rise and fall of the causative disease. A review of these cases (especially those with brain tumors), illustrates a clear picture that the hypothalamus is most often involved. Several cases of symptomatic cataplexy (without EDS) were also reported and in contrast, these cases appear to be often associated with non-hypothalamic structures. CSF hypocretin-1 measurement were also carried out in a limited number of symptomatic cases of narcolepsy/EDS, including narcolepsy/EDS associated with tumors (n=5), head trauma (n=3), vascular disorders (n=5), encephalopathies (n=3), degeneration (n=30), demyelinating disorder (n=7), genetic/congenital disorders (n=11) and others (n=2). Reduced CSF hypocretin-1 levels were seen in most symptomatic narcolepsy cases of EDS with various etiologies and EDS in these cases is sometimes reversible with an improvement of the causative neurological disorder and an improvement of the hypocretin status. It is also noted that some symptomatic EDS cases (with Parkinson diseases and the thalamic infarction) appeared, but they are not linked with hypocretin ligand deficiency. In contrast to idiopathic narcolepsy cases, an occurrence of cataplexy is not tightly associated with hypocretin ligand deficiency in symptomatic cases. Since CSF hypocretin measures are still experimental, cases with sleep abnormalities/cataplexy are habitually selected for CSF hypocretin measures. Therefore, it is still not known whether all or a large majority of cases with low CSF hypocretin-1 levels with CNS interventions, exhibit EDS/cataplexy. It appears that further studies of the involvement of the hypocretin system in symptomatic narcolepsy and EDS are helpful to understand the pathophysiological mechanisms for the occurrence of EDS and cataplexy.

Successful management of cataplexy with intravenous immunoglobulins at narcolepsy onset

Hypocretin/orexin deficiency appears to be a consistent feature of narcolepsy with a putative autoimmune mechanism involved. We treated four hypocretin/orexin-deficient narcolepsy patients with intravenous immunoglobulins and assessed the efficacy by repeated polysomnographies and questionnaires. Three patients received the treatment within a few months after acute onset of narcolepsy. A clear improvement in the frequency and severity of cataplexy was obtained with a benefic effect up to 7 months without any anticataplectics drugs at follow-up. Our findings point to the importance of early diagnosis of narcolepsy, which once treated quickly may modify its long-term outlook.