[Hypocretin system and narcolepsy]

Narcolepsy is a sleep disorder characterized by excessive daytime sleepiness, cataplexy, hypnagogic hallucinations, and sleep-onset rapid eye movement (REM) sleep periods. It is now identified as a neurodegenerative disease because there is a massive loss of specific neurons in the brain. These neurons contain the neuropeptides hypocretin-1 and hypocretin-2, which are also known as orexin-A and orexin-B. Cerebrospinal fluid hypocretin-1 measurements are diagnostic for primary narcolepsy. The cause of neural loss could be autoimmune since most patients have the HLA DQB1 0602 allele that predisposes to the disorders. The discovery of hypocretin deficiency is redefining the clinical entity of narcolepsy and offering novel diagnostic procedures. This article reviews the current understanding of narcolepsy and discusses the implications of hypocretin discovery.

The link between childhood trauma and depression: insights from HPA axis studies in humans

Childhood trauma is a potent risk factor for developing depression in adulthood, particularly in response to additional stress. We here summarize results from a series of clinical studies suggesting that childhood trauma in humans is associated with sensitization of the neuroendocrine stress response, glucocorticoid resistance, increased central corticotropin-releasing factor (CRF) activity, immune activation, and reduced hippocampal volume, closely paralleling several of the neuroendocrine features of depression. Neuroendocrine changes secondary to early-life stress likely reflect risk to develop depression in response to stress, potentially due to failure of a connected neural circuitry implicated in emotional, neuroendocrine and autonomic control to compensate in response to challenge. However, not all of depression is related to childhood trauma and our results suggest the existence of biologically distinguishable subtypes of depression as a function of childhood trauma that are also responsive to differential treatment. Other risk factors, such as female gender and genetic dispositions, interfere with components of the stress response and further increase vulnerability for depression. Similar associations apply to a spectrum of other psychiatric and medical disorders that frequently coincide with depression and are aggravated by stress. Taken together, this line of evidence demonstrates that psychoneuroendocrine research may ultimately promote optimized clinical care and help prevent the adverse outcomes of childhood trauma.

Detection of elastin derived peptides in cerebrospinal fluid of patients with first ever ischaemic stroke

OBJECTIVE

We have previously reported the optimized methods for the detection of elastin derived peptides (EDP) in the serum, synovial fluid, and bronchoalveolar lavage. The aim of the present study was to investigate whether EDP are detectable in cerebrospinal fluid (CSF) of patients with acute brain ischaemia.

PATIENTS AND METHODS

Twenty-seven first ever ischaemic stroke patients (mean age 61.5+/-10.8 years; age range 47-70 years; 12 women) were studied in acute phase (1-15 days after the onset) with clinical evaluations, radiological assessments, and the analysis of serum and CSF based on Western blot and ELISA for the detection and quantification of EDP.

RESULTS

None of the serum EDP concentrations are significantly higher in stroke patients compared with 25 healthy control individuals. However, EDP levels in CSF are strongly (p<0.0001) elevated compared with healthy subjects. They correlated with total cholesterol (r=0.53; p=0.02), triglycerides (r=0.67; p=0.004) and retinopathy (r=0.24; p=0.03), and with the interval between the stroke onset and the time of lumbar puncture (r=0.35; p=0.02).

CONCLUSION

EDPs are detectable in CSF of healthy subjects and patients with ischaemic stroke. Acute brain infarction is followed by increased levels of EDP in CSF.

Plasma and CSF serpins in Alzheimer disease and dementia with Lewy bodies

OBJECTIVE

Serine protease inhibitors (serpins), the acute phase reactants and regulators of the proteolytic processing of proteins, have been recognized as potential contributors to the pathogenesis of Alzheimer disease (AD). We measured plasma and CSF levels of serpins in controls and patients with dementia.

METHODS

Using rocket immunoelectrophoresis, ELISA, and Luminex xMAP technology, we analyzed plasma levels of alpha(1)-antichymotrypsin and alpha(1)-antitrypsin, and CSF levels of alpha(1)-antichymotrypsin, alpha(1)-antitrypsin, and neuroserpin along with three standard biomarkers (total tau, tau phosphorylated at threonine-181, and the A beta(1-42)) in patients with AD (n = 258), patients with dementia with Lewy bodies (DLB; n = 38), and age-matched controls (n = 37).

RESULTS

The level of CSF neuroserpin was significantly higher in AD compared with controls and DLB, whereas CSF alpha(1)-antichymotrypsin and alpha(1)-antitrypsin were significantly higher in both AD and DLB groups than in controls. Results from logistic regression analyses demonstrate a relationship between higher CSF levels of alpha(1)-antichymotrypsin and neuroserpin and increased predicted probability and odds ratios (ORs) of AD (OR 5.3, 95% CI 1.3 to 20.8 and OR 3.3, CI 1.3 to 8.8). Furthermore, a logistic regression model based on CSF alpha(1)-antichymotrypsin, neuroserpin, and A beta(1-42) enabled us to discriminate between AD patients and controls with a sensitivity of 94.7% and a specificity of 77.8%.

CONCLUSIONS

Higher CSF levels of neuroserpin and alpha(1)-antichymotrypsin were associated with the clinical diagnosis of Alzheimer disease (AD) and facilitated the diagnostic classification of AD vs controls. CSF serpin levels did not improve the diagnostic classification of AD vs dementia with Lewy bodies.

Reduced orexin levels in the cerebrospinal fluid of suicidal patients with major depressive disorder

Orexins are neuropeptides selectively expressed in a small number of neurons in the lateral-posterior hypothalamus. We measured orexin-A in the cerebrospinal fluid (CSF) of 66 patients with major depressive disorder (MDD), dysthymia and adjustment disorder after a suicide attempt. Blood samples confirmed that the patients were free from antidepressive and neuroleptic medication at the time of the lumbar punctures. CSF levels of orexin-A were significantly lower in patients with MDD than in patients with adjustment disorder and dysthymia. Orexin correlated significantly with CSF levels of somatostatin, delta sleep inducing peptide-like immunoreactivity (DSIP-LI) and corticotrophin releasing factor (CRF), but not with leptin or vasopressin. Plasma levels of thyroid-stimulating hormone (TSH) were not reduced in MDD patients, and did not correlate with CSF-orexin. Our results suggest that suicidal patients with MDD have distinct neurobiological features, involving compromised levels of hypothalamic peptides regulating the state of arousal.

CSF orexin-A/hypocretin-1 concentrations in patients with intracerebral hemorrhage (ICH)

Orexins/hypocretins are neuropeptides that have various physiological effects, including the regulation of both the feeding behavior neuroendocrine functions and sleep-wakefulness cycle. Recent studies have suggested that the orexin system may also be involved in neuronal damage in the clinical setting and animal experiments. The aim of this study was to examine the role of the hypothalamic orexin-A/hypocretin-1 system in patients with intracerebral hemorrhage (ICH). The CSF orexin-A/hypocretin-1 levels were measured in 11 ICH patients. CSF orexin-A/hypocretin-1 levels were low in ICH patients during the 13 days following the ICH event. The mean CSF orexin-A/hypocretin-1 levels were 61.1+/-22.3 (S.D.) pg/ml (range 27.5-106.9 pg/ml). The decreasing in the CSF orexin-A/hypocretin-1 levels was not related to the severity of ICH. The CSF orexin-A/hypocretin-1 levels were lower in the thalamic hemorrhage patients than those in other patients (48.5+/-23.3 pg/ml vs. 65.2+/-21.2 pg/ml; p=0.03.) These data indicate that orexin-A/hypocretin-1 may therefore play an important role in the various physiological responses including sleep, feeding, and the overall metabolism in ICH patients.

CSF metabolic and proteomic profiles in patients prodromal for psychosis

BACKGROUND

The initial prodromal state of psychosis (IPS) is defined as an early disease stage prior to the onset of overt psychosis characterized by sub-threshold or more unspecific psychiatric symptoms. Little is known regarding the biochemical changes during this period.

METHODOLOGY/PRINCIPAL FINDINGS

We investigated the metabolic/proteomic profiles of cerebrospinal fluid (CSF) of first-onset drug naïve paranoid schizophrenia patients (n = 54) and individuals presenting with initial prodromal symptoms (n = 24), alongside healthy volunteers (n = 70) using proton nuclear magnetic resonance ((1)H-NMR) spectroscopy and surface enhanced laser desorption ionization (SELDI) mass spectrometry, respectively. Partial least square discriminant analysis (PLS-DA) showed that 36%/29% of IPS patients displayed proteomic/metabolic profiles characteristic of first-onset, drug naïve schizophrenia, i.e., changes in levels of glucose and lactate as well as changes in a VGF-derived peptide (VGF23-62) and transthyretin protein concentrations. However, only 29% (n = 7) of the investigated IPS patients (who to date have been followed up for up to three years) have so far received a diagnosis of schizophrenia. The presence of biochemical alterations in the IPS group did not correlate with the risk to develop schizophrenia.

CONCLUSIONS/SIGNIFICANCE

Our results imply that schizophrenia-related biochemical disease processes can be traced in CSF of prodromal patients. However, the biochemical disturbances identified in IPS patients, at least when measured at a single time point, may not be sufficient to predict clinical outcome.

Increasing length of wakefulness and modulation of hypocretin-1 in the wake-consolidated squirrel monkey

The neuropeptides hypocretins (orexins), the loss of which results in the sleep disorder narcolepsy, are hypothesized to be involved in the consolidation of wakefulness and have been proposed to be part of the circadian-driven alertness signal. To elucidate the role of hypocretins in the consolidation of human wakefulness we examined the effect of wake extension on hypocretin-1 in squirrel monkeys, primates that consolidate wakefulness during the daytime as do humans. Wake was extended up to 7 h with hypocretin-1, cortisol, ghrelin, leptin, locomotion, and feeding, all being assayed. Hypocretin-1 (P < 0.01), cortisol (P < 0.001), and locomotion (P < 0.005) all increased with sleep deprivation, while ghrelin (P = 0.79) and leptin (P = 1.00) did not change with sleep deprivation. Using cross-correlation and multivariate modeling of these potential covariates along with homeostatic pressure (a measure of time awake/asleep), we found that time of day and homeostatic pressure together explained 44% of the variance in the hypocretin-1 data (P < 0.001), while cortisol did not significantly contribute to the overall hypocretin-1 variance. Locomotion during the daytime, but not during the nighttime, helped explain < 5% of the hypocretin-1 variance (P < 0.05). These data are consistent with earlier evidence indicating that in the squirrel monkey hypocretin-1 is mainly regulated by circadian inputs and homeostatic sleep pressure. Concomitants of wakefulness that affect hypocretin-1 in polyphasic species, such as locomotion, food intake, and food deprivation, likely have a more minor role in monophasic species, such as humans.

CSF hypocretin-1 levels and clinical profiles in narcolepsy and idiopathic CNS hypersomnia in Norway

OBJECTIVE

To evaluate the relationship between CSF hypocretin-1 levels and clinical profiles in narcolepsy and CNS hypersomnia in Norwegian patients.

METHOD

CSF hypocretin-1 was measured by a sensitive radioimmunoassay in 47 patients with narcolepsy with cataplexy, 7 with narcolepsy without cataplexy, 10 with idiopathic CNS hypersomnia, and a control group.

RESULTS

Low hypocretin-1 values were found in 72% of the HLA DQB1*0602 positive patients with narcolepsy and cataplexy. Patients with low CSF hypocretin-1 levels reported more extensive muscular involvement during cataplectic attacks than patients with normal levels. Hypnagogic hallucinations and sleep paralysis occurred more frequently in patients with cataplexy than in the other patient groups, but with no correlation to hypocretin-1 levels.

CONCLUSION

About three quarters of the HLA DQB1*0602 positive patients with narcolepsy and cataplexy had low CSF hypocretin-1 values, and appear to form a distinct clinical entity. Narcolepsy without cataplexy could not be distinguished from idiopathic CNS hypersomnia by clinical symptoms or biochemical findings.

HLA-DQB1 genotyping in a family with narcolepsy-cataplexy

Narcolepsy is a unique model for dysfunction in mechanisms that regulate sleep and wakefulness. The narcolepsy syndrome is characterized by excessive daytime sleepiness with recurrent episodes of irresistible sleep, cataplexy, hypnagogic and/or hypnopompic hallucinations and sleep paralysis. The current hypothesis for the etiology of narcolepsy is that it is an autoimmune disorder because of its strong association with the human leukocyte antigen (HLA) system. HLA-DQ alleles are not particularly mutated in narcoleptic patients but they directly influence susceptibility to the disease. DQB10602 homozygote carriers have a two to four times higher risk of developing the disease than heterozygote carriers. In the present study we report a rare multiplex familial case of narcolepsy-cataplexy and show the strong effect of the HLA-DQB10602 allele upon the disease phenotype. In the family studied herein, both the proband and his brother are severely affected and homozygous DQB10602, whereas their sister does not carry the allele and is not affected at all. These data corroborate previous findings proposing DQB10602 homozygous subjects to be far more susceptible to narcolepsy. Insights into the DQB10602 positive family that include homozygous subjects may prove to be an important asset in the investigation of genetic vs. environmental factors predisposing to narcolepsy.

Sleep-wake disturbances 6 months after traumatic brain injury: a prospective study

Sleep-wake disturbances (SWD) are common after traumatic brain injury (TBI). In acute TBI, we recently found decreased CSF levels of hypocretin-1, a wake-promoting neurotransmitter. In the present study, we aimed to delineate the frequency and clinical characteristics of post-traumatic SWD, to assess CSF hypocretin-1 levels 6 months after TBI, and to identify risk factors for posttraumatic SWD. A total of 96 consecutive patients were enrolled within the first 4 days after TBI. Six months later, out of 76 TBI patients, who did not die and who did not move to foreign countries, we included 65 patients (86%, 53 males, mean age 39 years) in our study. Patients were examined using interviews, questionnaires, clinical examinations, computed tomography of the brain, laboratory tests (including CSF hypocretin-1 levels, and HLA typing), conventional polysomnography, maintenance of wakefulness and multiple sleep latency tests (MSLT) and actigraphy. Potential causes of post-traumatic SWD were assessed according to international criteria. New-onset sleep-wake disturbances following TBI were found in 47 patients (72%): subjective excessive daytime sleepiness (EDS; defined by the Epworth Sleepiness Scale > or = 10) was found in 18 (28%), objective EDS (as defined by mean sleep latency < 5 min on MSLT) in 16 (25%), fatigue (daytime tiredness without signs of subjective or objective EDS) in 11 (17%), post-traumatic hypersomnia 'sensu strictu' (increased sleep need of > or = 2 h per 24 h compared to pre-TBI) in 14 (22%) patients and insomnia in 3 patients (5%). In 28 patients (43% of the study population), we could not identify a specific cause of the post-traumatic SWD other than TBI. Low CSF hypocretin-1 levels were found in 4 of 21 patients 6 months after TBI, as compared to 25 of 27 patients in the first days after TBI. Hypocretin levels 6 months after TBI were significantly lower in patients with post-traumatic EDS. There were no associations between post-traumatic SWD and severity or localization of TBI, general clinical outcome, gender, pathological neurological findings and HLA typing. However, post-traumatic SWD correlated with impaired quality of life. These results suggest that sleep-wake disturbances, particularly EDS, fatigue and hypersomnia are common after TBI, and significantly impair quality of life. In almost one out of two patients, post-traumatic SWD appear to be directly related to the TBI. An involvement of the hypocretin system in the pathophysiology of post-traumatic SWD appears possible. Other risk factors predisposing towards the development of post-traumatic SWD were not identified.

The development of hypocretin (orexin) deficiency in hypocretin/ataxin-3 transgenic rats

Narcolepsy is linked to a widespread loss of neurons containing the neuropeptide hypocretin (HCRT), also named orexin. A transgenic (TG) rat model has been developed to mimic the neuronal loss found in narcoleptic humans. In these rats, HCRT neurons gradually die as a result of the expression of a poly-glutamine repeat under the control of the HCRT promoter. To better characterize the changes in HCRT-1 levels in response to the gradual HCRT neuronal loss cerebrospinal fluid (CSF) HCRT-1 levels were measured in various age groups (2-82 weeks) of wild-type (WT) and TG Sprague-Dawley rats. TG rats showed a sharp decline in CSF HCRT-1 level at week 4 with levels remaining consistently low (26%+/-9%, mean+/-S.D.) thereafter compared with WT rats. In TG rats, HCRT-1 levels were dramatically lower in target regions such as the cortex and brainstem (100-fold), indicating decreased HCRT-1 levels at terminals. In TG rats, CSF HCRT-1 levels significantly increased in response to 6 h of prolonged waking, indicating that the remaining HCRT neurons can be stimulated to release more neuropeptide. Rapid eye movement (REM) sleep in TG rats (n=5) was consistent with a HCRT deficiency. In TG rats HCRT immunoreactive (HCRT-ir) neurons were present in the lateral hypothalamus (LH), even in old rats (24 months) but some HCRT-ir somata were in various stages of disintegration. The low output of these neurons is consistent with a widespread dysfunction of these neurons, and establishes this model as a tool to investigate the consequences of partial hypocretin deficiency.

[Comparative analysis of patients with narcolepsy-cataplexy, narcolepsy without cataplexy and idiopathic hypersomnia]

BACKGROUND AND OBJECTIVE

To evaluate the distribution of clinical, electrophysiological and biological variables, and their relationship with the CSF hypocretin-1 levels, in patients with central hypersomnias diagnosed as narcolepsy-cataplexy (NC), narcolepsy without cataplexy (NnC) and idiopathic hypersomnia (IH) based on the ICSD-2 criteria.

PATIENTS AND METHOD

We performed in all patients a clinical interview, a nocturnal polysomnogram and a multiple sleep latency test (MSLT), HLA analysis and measurement of CSF Hcrt-1 levels (low < or = 110 pg/mL).

RESULTS

Out of 51 patients, 31 were classified as NC, 11 as NnC and 8 as IH. 34 patients (66.7%) had low CSF Hcrt-1 levels (29 NC, 3 NnC and 1 IH). In the NC group, 96.1% were HLA DQB1*0602 positive and 91% had low CSF Hcrt-1 levels. The most frequent variables found in NC patients and in those with a low CSF Hcrt-1 levels were cataplexy, fragmented nocturnal sleep, short refreshing naps, automatic behavior, HLA DQB1*0602, and, in the MSLT, a short mean sleep latency, a higher number of REM sleep episodes and a short mean latency of REM sleep episodes. A long nocturnal sleep time and morning sleep drunkenness, 2 variables used in the ICSD-2 for the diagnosis of IH, were not different among the three groups of hypersomnias.

CONCLUSIONS

Central hypersomnias have a superposition of several clinical, electrophysiological and biological variables that makes sometimes difficult the differential diagnosis. The measurement of CSF Hcrt-1 levels may help in the diagnosis of those patients with unclear clinical or electrophysiological forms.

Orexin and psychiatric symptoms in suicide attempters

BACKGROUND

The orexins (hypocretins) are recently discovered hypothalamic peptides that are involved in the regulation of sleep, appetite and state of arousal. In the present study, we investigated the relationship between cerebrospinal fluid (CSF) orexin and specific psychiatric symptoms in suicidal patients.

METHODS

A total of 101 patients were enrolled in the study shortly after a suicide attempt. All patients underwent a lumbar puncture after a wash-out period during which they did not receive any antipsychotic or antidepressive medication. Structured interviews were performed using the Comprehensive Psychopathological Rating Scale (CPRS). CSF-orexin-A was measured and correlated with ratings of psychiatric symptoms.

RESULTS

There were significant and negative correlations between CSF-orexin and the symptoms lassitude (difficulty to initiate activities) and slowness of movement, as well as the ratings of global illness (p<0.005 for all three items, Spearman's rho).

LIMITATIONS

Correlation analysis is an indirect method of investigation and does not demonstrate causal relationships.

CONCLUSION

Low CSF-orexin levels are related to pronounced symptoms of inertia and reduced motor activity in suicidal patients. Interestingly, the lower the orexin levels, the higher were ratings of overall illness, as observed by a specialist in psychiatry. Our results suggest that reduced orexin levels are involved in the etiology of specific psychiatric symptoms.

Hypocretin (orexin) loss in Parkinson's disease

The hypothalamic hypocretin (orexin) system plays a central role in the regulation of various functions, including sleep/wake regulation and metabolism. There is a growing interest in hypocretin function in Parkinson's disease (PD), given the high prevalence of non-motor symptoms such as sleep disturbances in this disorder. However, studies measuring CSF hypocretin levels have yielded contradictory results. In PD patients and matched controls, we (i) estimated the number of hypocretin neurons in post-mortem hypothalami using immunocytochemistry and an image analysis system (ii) quantified hypocretin levels in post-mortem ventricular CSF and (iii) prefrontal cortex using a radioimmunoassay. Furthermore, presence of Lewy bodies was verified in the hypothalamic hypocretin cell area. Data are presented as median (25th-75th percentile). We showed a significant decrease between PD patients and controls in (i) the number of hypocretin neurons (PD: 20 276 (13 821-31 229); controls: 36 842 (32 546-50 938); P = 0.016); (ii) the hypocretin-1 concentration in post-mortem ventricular CSF (PD: 365.5 pg/ml (328.0-448.3); controls: 483.5 (433.5-512.3); P = 0.012) and (iii) the hypocretin-1 concentrations in prefrontal cortex (PD: 389.6 pg/g (249.2-652.2); controls: 676.6 (467.5-883.9); P = 0.043). Hypocretin neurotransmission is affected in PD. The hypocretin-1 concentration in the prefrontal cortex was almost 40% lower in PD patients, while ventricular CSF levels were almost 25% reduced. The total number of hypocretin neurons was almost half compared to controls.

Normal cerebrospinal fluid levels of hypocretin-1 (orexin A) in patients with fibromyalgia syndrome

BACKGROUND

The hypothalamic neuropeptide hypocretin (orexin) modulates sleep-wake, feeding and endocrine functions. Cerebrospinal fluid (CSF) hypocretin-1 (Hcrt-1) concentrations are low in patients with narcolepsy-cataplexy, a sleep disorder characterized by hypersomnolence and rapid eye movement (REM) sleep abnormalities.

METHODS

We determined CSF Hcrt-1 concentrations of patients with the fibromyalgia syndrome (FMS), a condition characterized by fatigue, insomnia and in some cases daytime hypersomnolence.

RESULTS

Basal CSF levels of Hcrt-1 in FMS did not differ from those in healthy normal controls.

CONCLUSIONS

These findings suggest that abnormally low Hcrt-1 is not a likely cause of fatigue in FMS.

Isolated mediotegmental lesion causing narcolepsy and rapid eye movement sleep behaviour disorder: a case evidencing a common pathway in narcolepsy and rapid eye movement sleep behaviour disorder

Narcolepsy is usually an idiopathic disorder, often with a genetic predisposition. Symptomatic cases have been described repeatedly, often as a consequence of hypothalamic lesions. Conversely, REM (rapid eye movement) sleep behaviour disorder (RBD) is usually a secondary disorder, often due to degenerative brain stem disorders or narcolepsy. The case of a hitherto healthy man is presented, who simultaneously developed narcolepsy and RBD as the result of an acute focal inflammatory lesion in the dorsomedial pontine tegmentum in the presence of normal cerebrospinal fluid hypocretin-1 levels and in the absence of human lymphocyte antigen haplotypes typically associated with narcolepsy and RBD (DQB1*0602, DQB1*05). This first observation of symptomatic narcolepsy with RBD underlines the importance of the mediotegmental pontine area in the pathophysiology of both disorders, even in the absence of a detectable hypocretin deficiency and a genetic predisposition.

Narcolepsy without cataplexy: 2 subtypes based on CSF hypocretin-1/orexin-A findings

STUDY OBJECTIVES

Cerebrospinal fluid (CSF) hypocretin-1 levels and their relationship with the clinical characteristics of narcolepsy without cataplexy have not been well elucidated. Our aim was to examine whether clinical characteristics vary with CSF hypocretin-1 levels among narcoleptic patients without cataplexy.

DESIGN

Clinical features, variables on the multiple sleep latency test, and results of HLA typing were correlated with CSF hypocretin-1 levels.

SETTING

University-based sleep laboratories and a sleep disorders center.

PATIENTS

Seventeen patients (5 male, 12 female) who fulfilled the diagnostic criteria of narcolepsy without cataplexy according to the International Classification of Sleep Disorders. INERVENTIONS: Patients underwent lumbar puncture for CSF sampling.

MEASUREMENTS AND RESULTS

Five patients showed a markedly decreased CSF hypocretin-1 level, whereas the remaining 12 patients showed almost normal levels. The mean rapid eye movement (REM) latency was significantly shorter and the age at onset was significantly earlier in the low CSF hypocretin-1 group compared with the normal CSF hypocretin-1 group. HLA-DR2 was positive in all of the patients with low CSF hypocretin-1, whereas only 33.3% of patients with normal CSF hypocretin-1 were DR2 positive.

CONCLUSIONS

Some narcoleptic patients without cataplexy have low CSF hypocretin-1 levels. In patients who have narcolepsy without cataplexy, short mean REM latency, younger age at onset, and HLA-DR2 are associated with CSF hypocretin-1 deficiency. Markedly decreased CSF hypocretin-1 levels could be a significant marker for identifying subgroups of narcolepsy patients without cataplexy.

Narcolepsy with cataplexy

Narcolepsy with cataplexy is a disabling sleep disorder affecting 0.02% of adults worldwide. It is characterised by severe, irresistible daytime sleepiness and sudden loss of muscle tone (cataplexy), and can be associated with sleep-onset or sleep-offset paralysis and hallucinations, frequent movement and awakening during sleep, and weight gain. Sleep monitoring during night and day shows rapid sleep onset and abnormal, shortened rapid-eye-movement sleep latencies. The onset of narcolepsy with cataplexy is usually during teenage and young adulthood and persists throughout the lifetime. Pathophysiological studies have shown that the disease is caused by the early loss of neurons in the hypothalamus that produce hypocretin, a wakefulness-associated neurotransmitter present in cerebrospinal fluid. The cause of neural loss could be autoimmune since most patients have the HLA DQB1*0602 allele that predisposes individuals to the disorder. Treatment is with stimulant drugs to suppress daytime sleepiness, antidepressants for cataplexy, and gamma hydroxybutyrate for both symptoms. Because narcolepsy is an under-recognised disease, it is important that general practitioners and other primary health-care workers identify abnormal daytime sleepiness early.

HLA-DQB1 allele and hypocretin in Korean narcoleptics with cataplexy

Cataplexy is one of the most pathognomonic symptoms in narcolepsy. This study was designed to investigate the frequency of the HLA-DQB1 allele and cerebrospinal fluid (CSF) hypocretin levels in Korean narcoleptics with cataplexy as compared with those who do not have cataplexy. Seventy-two narcoleptics were selected based on polysomnography and multiple sleep latency test as well as their history and clinical symptoms at Sleep Disorders Clinic. The patients were divided into a narcolepsy with cataplexy group (n=56) and a narcolepsy without cataplexy group (n=16). All patients were subjected to HLA typing to determine the frequency of DQB1 allele and to spinal tapping to measure the level of CSF hypocretin. In cataplexy-positive patients, as compared with cataplexy-negative patients, the frequency of HLA-DQB1*0602 was found to be significantly high (89.3% vs. 50.0%) (p=0.003). On the other hand, the frequency of HLA-DQB1*0601 was found to be significantly low (0% vs. 43.8%) (p<0.001). In 48 of 56 cataplexy-positive patients (85.7 %), hypocretin levels were decreased (<or=110 pg/mL). However, only 6 of 16 cataplexy-negative patients (37.5%) exhibited a decreased hyopcretin level (p<0.001). The high frequency of HLA-DQB1*0602, low frequency of HLA-DQB1*0601 and low hypocretin levels in cataplexy-positive groups suggest that cataplexy-positive narcolepsy might be an etiologically different disease entity from the cataplexy-negative.