The role of cerebrospinal fluid hypocretin measurement in the diagnosis of narcolepsy and other hypersomnias

REM sleep behavior disorder in Parkinson's disease and dementia with Lewy bodies

Rapid eye movement (REM) sleep behavior disorder (RBD) is a parasomnia manifested by vivid, often frightening dreams associated with simple or complex motor behavior during REM sleep. Patients appear to "act out their dreams," in which the exhibited behaviors mirror the content of the dreams. Management of RBD involves counseling about safety measures in the sleep environment; in those at risk for injury, clonazepam and/or melatonin is usually effective. In this article, the authors present a detailed review of the clinical and polysomnographic features, differential diagnosis, diagnostic criteria, management strategies, and pathophysiologic mechanisms of RBD. They then review the literature and their institutional experience of RBD associated with neurodegenerative disease, particularly Parkinson's disease and dementia with Lewy bodies. The evolving data suggests that RBD may have clinical diagnostic and pathophysiologic significance in isolation and when associated with neurodegenerative disease.

The roles of midbrain and diencephalic dopamine cell groups in the regulation of cataplexy in narcoleptic Dobermans

Cataplexy, an emotion-triggered sudden loss of muscle tone specific to narcolepsy, is tightly associated with hypocretin deficiency. Using hypocretin receptor 2 gene (hcrtr 2)-mutated narcoleptic Dobermans, we have previously demonstrated that altered dopamine (DA) D(2/3) receptor mechanisms in mesencephalic DA nuclei are important for the induction of cataplexy. In the current study, we also found that the administration of D(2/3) agonists into diencephalic dopaminergic cell groups, including the area dorsal to the ventral tegmental area (DRVTA) and the periventricular gray (PVG) matter of the caudal thalamus (corresponding to area A11), significantly aggravated cataplexy in hcrtr 2-mutated narcoleptic Dobermans. A D(1) agonist and antagonist and a DA uptake inhibitor perfused into the DRVTA had no effect on cataplexy, suggesting an involvement of D(2/3) receptors located on DA cell bodies (i.e., autoreceptors) for the regulation of cataplexy. Because the A11 cell group projects to the spinal ventral horn, the A11 D(2/3) receptive mechanisms may directly modulate the activity of spinal motoneurons and modulate cataplexy.

Exploring the cytokine and endocrine involvement in narcolepsy

Narcolepsy is a disabling neurological sleep disorder characterized by excessive daytime sleepiness and abnormal REM sleep manifestations. Recently, the role of cytokines and growth hormone in the regulation of sleep and narcolepsy has been considered, and data suggest that proinflammatory cytokines may be involved in sleep and narcoleptic symptoms. Serum and clinical data were obtained from the Stanford Center for Narcolepsy Research for 39 Narcoleptics (22 Females, 17 Males, age 39+/-14.9) and 40 controls (13 Females, 27 Males, age 46+/-17.9). Plasma levels of TNF-alpha, IL-6, and human growth hormone (hGH) were measured by ELISA. TNF-alpha and IL-6 were significantly increased in narcoleptic subjects compared to controls (p=.001). Interestingly, hGH was significantly increased in narcoleptic subjects (p <.0001). There was also a significant difference in the epworth sleepiness scale (ESS) (17.7+/-4.6 vs. 5.5+/-3.2, p <.0001). These data indicate that narcoleptics, relative to controls, had higher serum levels of TNF-alpha, IL-6, and hGH. These data suggest that the dysregulation of sleep observed in narcoleptics correlates with the immune and endocrine dysregulation seen in these subjects, and the observed changes may in fact contribute to the higher likelihood of disturbed sleep and/or increased incidence of infection. Additional work is required to fully characterize connections between cytokines and narcoleptic symptomatology.

Monozygotic twins concordant for narcolepsy-cataplexy without any detectable abnormality in the hypocretin (orexin) pathway

Narcolepsy with cataplexy is thought to be a hypocretin ligand or hypocretin receptor deficiency syndrome caused by genetic and environmental factors. We looked for an abnormality of the hypocretin pathway in HLA-DQB1*0602-positive monozygotic twins who were concordant for narcolepsy-cataplexy. They had normal cerebrospinal fluid concentrations of hypocretin-1, and we found no mutation in the prepro-hypocretin gene or either hypocretin receptor gene. Our finding points to the existence of presumably genetic forms of narcolepsy with cataplexy without any demonstrable defect in the hypocretin pathway.

Mistaken diagnosis of psychogenic gait disorder in a man with status cataplecticus ("Limp Man Syndrome")

We report on a 45-year-old man with a history of multiple psychiatric admissions for a gait disorder and episodic weakness thought to be psychogenic who was subsequently diagnosed with status cataplecticus due to narcolepsy. The gait difficulties resolved with venlafaxine. This case demonstrates that status cataplecticus can be misdiagnosed as a psychogenic gait disorder.

Orexin peptides prevent cataplexy and improve wakefulness in an orexin neuron-ablated model of narcolepsy in mice

Narcolepsy-cataplexy is a neurological disorder associated with the inability to maintain wakefulness and abnormal intrusions of rapid eye movement sleep-related phenomena into wakefulness such as cataplexy. The vast majority of narcoleptic-cataplectic individuals have low or undetectable levels of orexin (hypocretin) neuropeptides in the cerebrospinal fluid, likely due to specific loss of the hypothalamic orexin-producing neurons. Currently available treatments for narcolepsy are only palliative, symptom-oriented pharmacotherapies. Here, we demonstrate rescue of the narcolepsy-cataplexy phenotype of orexin neuron-ablated mice by genetic and pharmacological means. Ectopic expression of a prepro-orexin transgene in the brain completely prevented cataplectic arrests and other abnormalities of rapid eye movement sleep in the absence of endogenous orexin neurons. Central administration of orexin-A acutely suppressed cataplectic behavioral arrests and increased wakefulness for 3 h. These results indicate that orexin neuron-ablated mice retain the ability to respond to orexin neuropeptides and that a temporally regulated and spatially targeted secretion of orexins is not necessary to prevent narcoleptic symptoms. Orexin receptor agonists would be of potential value for treating human narcolepsy.

Hypocretin-1 CSF levels in anti-Ma2 associated encephalitis

Idiopathic narcolepsy is associated with deficient hypocretin transmission. Narcoleptic symptoms have recently been described in paraneoplastic encephalitis with anti-Ma2 antibodies. The authors measured CSF hypocretin-1 levels in six patients with anti-Ma2 encephalitis, and screened for anti-Ma antibodies in patients with idiopathic narcolepsy. Anti-Ma autoantibodies were not detected in patients with idiopathic narcolepsy. Four patients with anti-Ma2 encephalitis had excessive daytime sleepiness; hypocretin-1 was not detectable in their cerebrospinal fluid, suggesting an immune-mediated hypocretin dysfunction.

Narcolepsy in the older adult: epidemiology, diagnosis and management

Narcolepsy is a disorder of impaired expression of wakefulness and rapid-eye-movement (REM) sleep. This manifests as excessive daytime sleepiness and expression of individual physiological correlates of REM sleep that include cataplexy and sleep paralysis (REM sleep atonia intruding into wakefulness), impaired maintenance of REM sleep atonia (e.g. REM sleep behaviour disorder [RBD]), and dream imagery intruding into wakefulness (e.g. hypnagogic and hypnopompic hallucinations). Excessive sleepiness typically begins in the second or third decade followed by expression of auxiliary symptoms. Only cataplexy exhibits a high specificity for diagnosis of narcolepsy. While the natural history is poorly defined, narcolepsy appears to be lifelong but not progressive. Mild disease severity, misdiagnoses or long delays in cataplexy expression often cause long intervals between symptom onset, presentation and diagnosis. Only 15-30% of narcoleptic individuals are ever diagnosed or treated, and nearly half first present for diagnosis after the age of 40 years. Attention to periodic leg movements (PLM), sleep apnoea and RBD is particularly important in the management of the older narcoleptic patient, in whom these conditions are more likely to occur. Diagnosis requires nocturnal polysomnography (NPSG) followed by multiple sleep latency testing (MSLT). The NPSG of a narcoleptic patient may be totally normal, or demonstrate the patient has a short nocturnal REM sleep latency, exhibits unexplained arousals or PLM. The MSLT diagnostic criteria for narcolepsy include short sleep latencies (<8 minutes) and at least two naps with sleep-onset REM sleep. Treatment includes counselling as to the chronic nature of narcolepsy, the potential for developing further symptoms reflective of REM sleep dyscontrol, and the hazards associated with driving and operating machinery. Elderly narcoleptic patients, despite age-related decrements in sleep quality, are generally less sleepy and less likely to evidence REM sleep dyscontrol. Nonpharmacological management also includes maintenance of a strict wake-sleep schedule, good sleep hygiene, the benefits of afternoon naps and a programme of regular exercise. Thereafter, treatment is highly individualised, depending on the severity of daytime sleepiness, cataplexy and sleep disruption. Wake-promoting agents include the traditional psychostimulants. More recently, treatment with the 'activating' antidepressants and the novel wake-promoting agent modafinil has been advocated. Cataplexy is especially responsive to antidepressants which enhance synaptic levels of noradrenaline (norepinephrine) and/or serotonin. Obstructive sleep apnoea and PLMs are more common in narcolepsy and should be suspected when previously well controlled older narcolepsy patients exhibit a worsening of symptoms. The discovery that narcolepsy/cataplexy results from the absence of neuroexcitatory properties of the hypothalamic hypocretin-peptidergic system will significantly advance understanding and treatment of the symptom complex in the future.

Pediatric sleep pharmacology: you want to give my kid sleeping pills?

There is a need for greater information about the pharmacologic management of sleep disorders in children. Pharmacologic guidelines must be developed specifically for sleep disorders in children. Ideally, these guidelines should be approved by the Food and Drug Administration for a specific sleep disorder or for the pediatric age range. This approval prevents physicians from being forced to prescribe medications as an "off label" indication. Development of easy-to-swallow, chewable, or liquid forms of these medications would be well received by parents everywhere. When these are not available, instructions for compounding these medications into a suspension by pharmacists are needed. Integration of behavioral and pharmacologic treatments may yield better patient outcomes. This approach requires pediatricians to have a comprehensive understanding of clinical sleep disorders in children. Training programs should play the lead role in enhancing pediatricians' knowledge of the pharmacologic treatment of sleep disorders in children.

Clinical aspects and pathophysiology of narcolepsy

Narcolepsy is a chronic debilitating sleep disorder first described in the late 19th century. It is characterized by two major symptoms, excessive daytime sleepiness and cataplexy, and two so-called auxiliary symptoms, hypnagogic hallucinations and sleep paralysis. The final diagnosis relies on polysomnography showing the presence of sleep onset rapid eye movement periods (SOREMPs) during the multiple sleep latency test. The presence of HLA DQA1*0102-DQB1*0602 is supportive of the diagnosis. The pathophysiology of the disorder is still unknown but an imbalance between monoamines and acetylcholine is generally accepted. Recent findings in narcoleptic dogs, a natural model of narcolepsy, and in knockout mice revealed that a mutation of type 2 hypocretin receptor plays a major role in the etiology of narcolepsy. Up to now, no mutation has been found in humans except a case of early onset and atypical narcolepsy. However, a marked reduction of hypocretin type 1 has been found in the cerebrospinal fluid (CSF) of a majority of patients and a global loss of hypocretins was noted in post-mortem brain tissue of narcoleptic subjects. Conversely, no hypocretin neuron degeneration has been observed in the genetic form of narcolepsy in dogs but no trace of hypocretin was seen in the brain or the CSF in cases of sporadic canine narcolepsy. This suggests that different hypocretinergic mechanisms are involved in sporadic and genetic forms of canine narcolepsy. Treatment has not evolved significantly over the last few years. However, new drugs, such as hypocretin agonists, are currently being developed.

SIGNIFICANCE

After the discovery of the type 2 hypocretin receptor mutation in canine narcolepsy and the finding of a CSF hypocretin-1 deficiency in human narcolepsy, the major stream of research has involved the hypocretinergic system. However, other lines of research deserve to be pursued simultaneously, in view of comprehensive advancements in the understanding of narcolepsy.

Prader-Willi syndrome: advances in genetics, pathophysiology and treatment

Prader-Willi syndrome (PWS) is a complex human genetic disease that arises from lack of expression of paternally inherited imprinted genes on chromosome 15q11-q13. Identification of the imprinting control centre, novel imprinted genes and distinct phenotypes in PWS patients and mouse models has increased interest in this human obesity syndrome. In this review I focus on: (i) the chromosomal region and candidate genes associated with PWS, and the possible links with individual PWS phenotypes identified using mouse models; (ii) the metabolic and hormonal phenotypes in PWS; (iii) postmortem studies of human PWS hypothalami; and (iv) current and potential advances in the management of PWS and its complications. This could have benefits for a wide spectrum of endocrine, paediatric and neuropsychiatric diseases.

Increased hypocretin-1 levels in cerebrospinal fluid after REM sleep deprivation

Rat cisternal (CSF) hypocretin-1 in cerebrospinal fluid was measured after 6 or 96 h of REM sleep deprivation and following 24 h of REM sleep rebound. REM deprivation was found to increase CSF hypocretin-1 collected at zeitgeber time (ZT) 8 but not ZT0. Decreased CSF hypocretin levels were also observed at ZT8 after 24 h of REM sleep rebound. These results suggest that REM sleep deprivation activates and REM sleep rebound inhibits the hypocretin system. Increased hypocretin tone during REM deprivation may be important in mediating some of the effects of REM sleep deprivation such as antidepressant effects, hyperphagia and increased sympathetic activity.

Neuropeptides in hypothalamic neuronal disorders

A few examples of hypothalamic, peptidergic disorders leading to clinical signs and symptoms are presented in this review. Increased activity of corticotropin-releasing hormone (CRH) neurons in the paraventricular nucleus (PVN) and decreased activity of the vasopressin neurons in the biological clock and of the thyroxine-releasing hormone (TRH) neurons in the PVN contribute to the signs and symptoms of depression. In men, the central nucleus of the bed nucleus of the stria terminalis (BSTc) is about twice as large and contains twice as many somatostatin neurons as in women. In transsexuals this sex difference is reversed, pointing to a role of this structure in gender. Luteinizing hormone-releasing hormone (LHRH) neurons are formed in the fetal olfactory placade and migrate along the terminal nerve fibers into the hypothalamus. In Kallmann's syndrome the migration process of the LHRH (gonadotropin-releasing hormone) neurons is aborted, which explains the joint occurrence of hypogonadotropic hypogonadism and anosmia in this syndrome. In postmenopausal women, the neurons of the infundibular nucleus hypertrophy and become hyperactive because of the disappearance of the estrogen feedback and contain hyperactive peptidergic neurons. Climacteric flushes may be caused by hyperactivity of the neurokinin-B or LHRH neurons in this nucleus. The hypocretin (orexin) neurons in the perifornical area are involved in sleep. In narcolepsy with cataplexy, a loss of these neurons, probably due to an autoimmune process, is found. Obese subjects with a mutation in the gene that encodes for leptin, the preproghrelin gene, or the alpha-melanocyte-stimulating hormone (alpha-MSH) gene have been described. Decreased numbers and activity of the oxytocin neurons in the PVN may be responsible for the absence of satiety in Prader-Willi syndrome. Moreover, a glucocorticoid receptor polymorphism is associated with obesitas and dysregulation of the hypothalamus-pituitary-adrenal axis. In contrast, two single nucleotide polymorphisms (SNPs) of the AGRP gene have been associated with anorexia nervosa.

Relationship between CSF hypocretin levels and hypocretin neuronal loss

The sleep disorder narcolepsy may now be considered a neurodegenerative disease, as there is a massive reduction in the number of neurons containing the neuropeptide, hypocretin (HCRT). Most narcoleptic patients have low to negligible levels of HCRT in the cerebrospinal fluid (CSF), and such measurements serve as an important diagnostic tool. However, the relationship between HCRT neurons and HCRT levels in CSF in human narcoleptics is not known and cannot be directly assessed. To identify this relationship in the present study, the neurotoxin, hypocretin-2-saporin (HCRT2-SAP), was administered to the lateral hypothalamus (LH) to lesion HCRT neurons. CSF was extracted at circadian times (ZT) 0 (time of lights-on) or ZT8 at various intervals (2, 4, 6, 12, 21, 36, 60 days) after neurotoxin administration. Compared to animals given saline in the LH, rats with an average loss of 73% of HCRT neurons had a 50% decline in CSF HCRT levels on day 60. The decline in HCRT levels was evident by day 6 and there was no recovery or further decrease. The decline in HCRT was correlated with increased REM sleep. Lesioned rats that were kept awake for 6 h were not able to release HCRT to match the output of saline rats. As most human narcoleptics have more than 80% reduction of CSF HCRT, the results from this study lead us to conclude that in these patients, virtually all of the HCRT neurons might be lost. In those narcoleptics where CSF levels are within the normal range, it is possible that not all of the HCRT neurons are lost and that the surviving HCRT neurons might be increasing output of CSF HCRT.

CSF hypocretin-1 levels in narcolepsy, Kleine-Levin syndrome, and other hypersomnias and neurological conditions

OBJECTIVE

To determine the role of CSF hypocretin-1 in narcolepsy with and without cataplexy, Kleine-Levin syndrome (KLS), idiopathic and other hypersomnias, and several neurological conditions.

PATIENTS

26 narcoleptic patients with cataplexy, 9 narcoleptic patients without cataplexy, 2 patients with abnormal REM-sleep-associated hypersomnia, 7 patients with idiopathic hypersomnia, 2 patients with post-traumatic hypersomnia, 4 patients with KLS, and 88 patients with other neurological disorders.

RESULTS

23 patients with narcolepsy-cataplexy had low CSF hypocretin-1 levels, while one patient had a normal hypocretin level (HLA-DQB1*0602 negative) and the other two had intermediate levels (familial forms). One narcoleptic patient without cataplexy had a low hypocretin level. One patient affected with post-traumatic hypersomnia had intermediate hypocretin levels. The KLS patients had normal hypocretin levels while asymptomatic, but one KLS patient (also affected with Prader-Willi syndrome) showed a twofold decrease in hypocretin levels during a symptomatic episode. Among the patients without hypersomnia, two patients with normal pressure hydrocephalus and one with unclear central vertigo had intermediate levels.

CONCLUSION

Low CSF hypocretin-1 is highly specific (99.1%) and sensitive (88.5%) for narcolepsy with cataplexy. Hypocretin ligand deficiency appears not to be the major cause for other hypersomnias, with a possible continuum in the pathophysiology of narcolepsy without cataplexy and idiopathic hypersomnia. However, partial hypocretin lesions without low CSF hypocretin-1 consequences cannot be definitely excluded in those disorders. The existence of normal hypocretin levels in narcoleptic patients and intermediate levels in other rare aetiologies needs further investigation, especially for KLS, to establish the functional significance of hypocretin neurotransmission alterations.

CSF hypocretin measures in patients with obstructive sleep apnea

The majority of patients with narcolepsy-cataplexy were reported to have very low cerebrospinal fluid (CSF) hypocretin-1 (orexin-A) levels. The hypocretin-1 levels of secondary excessive daytime sleepiness (EDS) disorders are not known. In this study, we found that CSF hypocretin levels in the patients with obstructive sleep apnea syndrome were within the control range. The low hypocretin levels seem to reflect only the presence of cataplexy and DR2 positive in narcoleptics but not EDS itself.

CSF hypocretin-1 levels in restless legs syndrome

CSF hypocretin-1 levels at 6 pm did not significantly differ between patients with restless legs syndrome (RLS) and control subjects as measured by direct radioimmunoassay and after acid extraction. The authors did not observe significant differences between early onset and late onset RLS. Hypocretin-1 levels did not correlate with RLS severity or polysomnographic measures. These results contrast with previous findings reporting significantly increased CSF hypocretin-1 in the late evening and mostly in early onset RLS.

Pharmacological management of narcolepsy

Narcolepsy is a disabling disorder characterised by excessive daytime sleepiness, cataplexy, hypnagogic hallucinations, sleep paralysis and disturbed nocturnal sleep. Traditionally, a wide variety of substances are used in the symptomatic pharmacological treatment of narcolepsy. Several generally more-tolerated substances have been added to the therapeutic repertoire after extensive testing in large patient populations during recent years. This review addresses the state-of-the-art knowledge about the pharmacological treatment of narcolepsy along with the personal view of the authors. The recent discovery that narcolepsy is caused by deficient hypocretin (orexin) transmission opens a perspective on causal therapy.

THEGENETICS OFNARCOLEPSY

Human narcolepsy is a genetically complex disorder. Family studies indicate a 20-40 times increased risk of narcolepsy in first-degree relatives and twin studies suggest that nongenetic factors also play a role. The tight association between narcolepsy-cataplexy and the HLA allele DQB1*0602 suggests that narcolepsy has an autoimmune etiology. In recent years, extensive genetic studies in animals, using positional cloning in dogs and gene knockouts in mice, have identified abnormalities in hypothalamic hypocretin (orexin) neurotransmission as key to narcolepsy pathophysiology. Though most patients with narcolepsy-cataplexy are hypocretin deficient, mutations or polymorphisms in hypocretin-related genes are extremely rare. It is anticipated that susceptibility genes that are independent of HLA and impinge on the hypocretin neurotransmitter system are isolated in human narcolepsy.

Hypocretin deficiency in narcoleptic humans is associated with abdominal obesity

OBJECTIVE

To determine the prevalence of obesity among patients with narcolepsy, to estimate associated long-term health risks on the basis of waist circumference, and to distinguish the impact of hypocretin deficiency from that of increased daytime sleepiness (i.e., reduced physical activity) on these anthropometric measures.

RESEARCH METHODS AND PROCEDURES

A cross-sectional, case-control study was conducted. Patients with narcolepsy (n = 138) or idiopathic hypersomnia (IH) (n = 33) were included. Age-matched, healthy members of the Dutch population (Monitoring Project on Risk Factors for Chronic Diseases and Doetinchem Project; n = 10,526) were used as controls. BMI and waist circumference were determined.

RESULTS

Obesity (BMI > or = 30 kg/m(2)) and overweight (BMI 25 to 30 kg/m(2)) occurred more often among narcolepsy patients [prevalence: 33% (narcoleptics) vs. 12.5% (controls) and 43% (narcoleptics) vs. 36% (controls), respectively; both p < 0.05]. Narcoleptics had a larger waist circumference (mean difference 5 +/- 1.4 cm, p < 0.001). The BMI of patients with IH was significantly lower than that of narcolepsy patients (25.6 +/- 3.6 vs. 28.5 +/- 5.4 kg/m(2); p = 0.004).

DISCUSSION

Overweight and obesity occur frequently in patients with narcolepsy. Moreover, these patients have an increased waist circumference, indicating excess fat storage in abdominal depots. The fact that patients with IH had a lower BMI than narcoleptics supports the notion that excessive daytime sleepiness (i.e., inactivity) cannot account for excess body fat in narcoleptic patients.

The hypocretin/orexin system in health and disease

Using positional cloning in a canine model of narcolepsy and mouse gene knockouts, genes involved in the pathogenesis of narcolepsy in animals have been identified. Hypocretin/orexin ligand and hypocretin/orexin receptor genes are key to the pathogenesis of narcolepsy in animals. Mutations in hypocretin-related genes are rare in humans, but hypocretin-ligand deficiency is found in many cases. Hypocretins/orexins are novel hypothalamic neuropeptides involved in various hypothalamic mechanisms, such as energy homeostasis and neuroendocrine function. Hypocretin-deficient human narcolepsy appears to be a more complex condition than a simple sleep disorder, and it may serve as an important disease model for studying hypothalamic function in health and disease.

Diurnal variation of cerebrospinal fluid hypocretin-1 (Orexin-A) levels in control and depressed subjects

BACKGROUND

Hypocretins, excitatory neuropeptides at monoaminergic synapses, appear to regulate human sleep-wake cycles. Undetectable cerebrospinal fluid hypocretin-1 levels are seen in narcolepsy, which is frequently associated with secondary depression. Shortened rapid eye movement latency is observed in both narcolepsy and depression. Cerebrospinal fluid hypocretin-1 levels have not been reported in mood disorders.

METHODS

We examined hypocretin-1 levels in 14 control and 15 depressed subjects. Cerebrospinal fluid was drawn continuously in supine subjects for 24 hours with an indwelling intrathecal catheter under entrained light-dark conditions. Depressed subjects were studied before and after 5 weeks of sertraline (n=10, three nonresponders) or bupropion (n=5, two nonresponders).

RESULTS

Hypocretin-1 levels varied slightly (amplitude 10%) but significantly across the diurnal cycle in control subjects, with amplitude significantly reduced in depression (3%). Levels were lowest at midday, surprising for a hypothetically wake-promoting peptide. Mean hypocretin levels trended higher in depressive than in control subjects. Hypocretin-1 levels decreased modestly but significantly after sertraline (-14%) but not bupropion.

CONCLUSIONS

Our results are consistent with previous physiologic findings in depression indicating dampened diurnal variations in hypocretin-1. The finding that sertraline but not bupropion slightly decreased cerebrospinal fluid hypocretin-1 indicates a serotoninergic influence on hypocretin tone.

Narcolepsy in a hypocretin/orexin-deficient chihuahua

A two-year-old male chihuahua suffered attacks of muscle weakness and immobility, although it had no family history of paroxysmal attacks. No neurological or blood biochemical abnormalities were recorded when it was first examined. The attacks were typically elicited by stimulation, such as feeding, and a case of sporadic narcolepsy-cataplexy was therefore suspected. Treatment orally three times a day with 1 mg/kg imipramine, was effective in reducing the attacks. The concentration of hypocretin-1/orexin A in the dog's cerebrospinal fluid was less than 80 pg/ml (22.5 pmol/litre), compared with normal canine levels of 250 to 350 pg/ml (70.0 to 98.3 pmol/litre), supporting a diagnosis of hypocretin-deficient narcolepsy.

Distinct narcolepsy syndromes in Orexin receptor-2 and Orexin null mice: molecular genetic dissection of Non-REM and REM sleep regulatory processes

Narcolepsy-cataplexy, a neurological disorder associated with the absence of hypothalamic orexin (hypocretin) neuropeptides, consists of two underlying problems: inability to maintain wakefulness and intrusion of rapid eye movement (REM) sleep into wakefulness. Here we document, using behavioral, electrophysiological, and pharmacological criteria, two distinct classes of behavioral arrests exhibited by mice deficient in orexin-mediated signaling. Both OX2R(-/-) and orexin(-/-) mice are similarly affected with behaviorally abnormal attacks of non-REM sleep ("sleep attacks") and show similar degrees of disrupted wakefulness. In contrast, OX2R(-/-) mice are only mildly affected with cataplexy-like attacks of REM sleep, whereas orexin(-/-) mice are severely affected. Absence of OX2Rs eliminates orexin-evoked excitation of histaminergic neurons in the hypothalamus, which gate non-REM sleep onset. While normal regulation of wake/non-REM sleep transitions depends critically upon OX2R activation, the profound dysregulation of REM sleep control unique to the narcolepsy-cataplexy syndrome emerges from loss of signaling through both OX2R-dependent and OX2R-independent pathways.

Screening for anti-ganglioside antibodies in hypocretin-deficient human narcolepsy

Narcolepsy is a sleep disorder caused by defective hypocretin (orexin) neurotransmission. It is thought to result from an autoimmune destruction of hypocretin producing neurons. Recently, low hypocretin levels were found in patients with Guillain-Barré syndrome, a post-infectious immune-mediated disorder in which a variety of circulating antibodies against neuronal gangliosides are found. We therefore considered gangliosides to be candidate antigens in narcolepsy as well, and screened for the presence of a panel of serum anti-ganglioside antibodies in a group of 28 well-characterized narcoleptic patients. We did not find a correlation between increased titers of anti-ganglioside antibodies and hypocretin-deficient narcolepsy. This study does not support the hypothesis that an autoimmune response is involved in narcolepsy. However, as an autoimmune attack may be selective and/or transient, future studies are needed to ultimately refute or confirm the autoimmune hypothesis.

The neurobiology, diagnosis, and treatment of narcolepsy

Narcolepsy is a common cause of chronic sleepiness distinguished by intrusions into wakefulness of physiological aspects of rapid eye movement sleep such as cataplexy and hallucinations. Recent advances provide compelling evidence that narcolepsy may be a neurodegenerative or autoimmune disorder resulting in a loss of hypothalamic neurons containing the neuropeptide orexin (also known as hypocretin). Because orexin promotes wakefulness and inhibits rapid eye movement sleep, its absence may permit inappropriate transitions between wakefulness and sleep. These discoveries have considerably improved our understanding of the neurobiology of sleep and should foster the development of rational treatments for a variety of sleep disorders.

The narcoleptic borderland: a multimodal diagnostic approach including cerebrospinal fluid levels of hypocretin-1 (orexin A)

OBJECTIVES

Biological markers of narcolepsy with cataplexy (classical narcolepsy) include sleep-onset REM periods (SOREM) on multiple sleep latency tests (MSLT), HLA-DQB1*0602 positivity, low levels of cerebrospinal fluid (CSF) hypocretin-1 (orexin A), increased body mass index (BMI), and high levels of CSF leptin. The clinical borderland of narcolepsy and the diagnostic value of different markers of narcolepsy remain controversial and were assessed in a consecutive series of 27 patients with hypersomnia of (mainly) neurological origin.

METHODS

Diagnoses included classical narcolepsy (n=3), symptomatic narcolepsy (n=1), narcolepsy without cataplexy (n=4), idiopathic hypersomnia (n=5), hypersomnia associated with psychiatric disorders (n=5), and hypersomnia secondary to neurological disorders or of undetermined origin (n=9). Clinical assessment included BMI, Epworth Sleepiness Scale (ESS), Ullanlinna Narcolepsy Scale (UNS), and history of REM-symptoms (sleep paralysis, hallucinations). HLA-typing, electrophysiological studies (conventional polysomnography, MSLT, 1-week actigraphy), and measurements of CSF levels of hypocretin and leptin were also performed.

RESULTS

Hypocretin-1 was undetectable in three patients with classic narcolepsy and detectable in the remaining 24 patients. Other narcoleptic markers also frequently found in patients without narcolepsy included ESS>14 (78% of 27 patients), UNS>14 (75%), REM symptoms (30%), sleep latencies on MSLT<5 min (41%), >/=2 SOREM (30%), DQB1*0602 positivity (52%), BMI>25 (52%), and increased CSF leptin (48%). Hypersomnia was documented by an increased time 'asleep' in 41% of patients. Overlapping clinical and electrophysiological findings were seen mostly in patients with narcolepsy without cataplexy, idiopathic hypersomnia, and psychiatric hypersomnia.

CONCLUSIONS

(1) Hypocretin dysfunction is not the 'final common pathway' in the pathophysiology of most hypersomnolent syndromes that fall on the borderline for a diagnosis of narcolepsy. (2) The observed overlap among these hypersomnolent syndromes implies that current diagnostic categories are not entirely unambiguous. (3) A common hypothalamic, hypocretin-independent dysfunction may be present in some of these syndromes.