[Autoimmune mechanisms and new opportunities for treatment narcolepsy]. / Autoimmunnye mekhanizmy i novye vozmozhnosti lecheniia narkolepsii.

Narcolepsy is a disease related to hypersomnia type-sleep disorders and characterized by the following manifestations: excessive daytime sleepiness, cataplexy, hypnagogic hallucinations, sleep paralysis and disturbed night sleep. There are several models of the disease pathogenesis each of them assumes the autoimmune nature of the disease. In this regard, it is necessary to develop etiological approaches to the treatment of the disease.

Narcolepsy-Associated HLA Class I Alleles Implicate Cell-Mediated Cytotoxicity.

STUDY OBJECTIVES: Narcolepsy with cataplexy is tightly associated with the HLA class II allele DQB1*06:02. Evidence indicates a complex contribution of HLA class II genes to narcolepsy susceptibility with a recent independent association with HLA-DPB1. The cause of narcolepsy is supposed be an autoimmune attack against hypocretin-producing neurons. Despite the strong association with HLA class II, there is no evidence for CD4+ T-cell-mediated mechanism in narcolepsy. Since neurons express class I and not class II molecules, the final effector immune cells involved might include class I-restricted CD8+ T-cells. METHODS: HLA class I (A, B, and C) and II (DQB1) genotypes were analyzed in 944 European narcolepsy with cataplexy patients and in 4,043 control subjects matched by country of origin. All patients and controls were DQB1*06:02 positive and class I associations were conditioned on DQB1 alleles. RESULTS: HLA-A*11:01 (OR = 1.49 [1.18-1.87] P = 7.0*10(-4)), C*04:01 (OR = 1.34 [1.10-1.63] P = 3.23*10(-3)), and B*35:01 (OR = 1.46 [1.13-1.89] P = 3.64*10(-3)) were associated with susceptibility to narcolepsy. Analysis of polymorphic class I amino-acids revealed even stronger associations with key antigen-binding residues HLA-A-Tyr(9) (OR = 1.32 [1.15-1.52] P = 6.95*10(-5)) and HLA-C-Ser(11) (OR = 1.34 [1.15-1.57] P = 2.43*10(-4)). CONCLUSIONS: Our findings provide a genetic basis for increased susceptibility to infectious factors or an immune cytotoxic mechanism in narcolepsy, potentially targeting hypocretin neurons.

Allergies and Disease Severity in Childhood Narcolepsy: Preliminary Findings.

INTRODUCTION: Narcolepsy frequently begins in childhood, and is characterized by excessive daytime sleepiness, with the presence of cataplexy reflecting a more severe phenotype. Narcolepsy may result from genetic predisposition involving deregulation of immune pathways, particularly involving T helper 2 cells (Th2). Increased activation of Th2 cells is usually manifested as allergic conditions such as rhinitis, atopic dermatitis, and asthma. We hypothesized that the presence of allergic conditions indicative of increased Th2 balance may dampen the severity of the phenotype in children with narcolepsy. METHODS: A retrospective chart review of childhood narcolepsy patients was conducted at three major pediatric sleep centers. Patients were divided into those with narcolepsy without cataplexy (NC-) and narcolepsy with cataplexy (NC+). Demographics, polysomnographic and multiple sleep latency test data, and extraction of information on the presence of allergic diseases such allergic rhinitis, atopic dermatitis, and asthma was performed. RESULTS: There were 468 children identified, with 193 children in NC- group and 275 patients in the NC+ group. Overall, NC+ children were significantly younger, had higher body mass index, and had shorter mean sleep latencies and increased sleep onset rapid eye movement events. The frequency of allergic conditions, particularly asthma and allergic rhinitis, was markedly lower in NC+ (58/275) compared to NC- patients (94/193; P < 0.0001). CONCLUSION: Involvement of the immune system plays an important role in the pathophysiology of narcolepsy. Current findings further suggest that an increased shift toward T helper 2 cells, as indicated by the presence of allergic conditions, may modulate the severity of the phenotype in childhood narcolepsy, and reduce the prevalence of cataplexy in these patients.

Narcolepsia-cataplejía, una enfermedad de etiología autoinmune / Narcolepsy-cataplexy, a disease of autoimmune origin

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Hypocretin (orexin) biology and the pathophysiology of narcolepsy with cataplexy.

The discovery of hypocretins (orexins) and their causal implication in narcolepsy is the most important advance in sleep research and sleep medicine since the discovery of rapid eye movement sleep. Narcolepsy with cataplexy is caused by hypocretin deficiency owing to destruction of most of the hypocretin-producing neurons in the hypothalamus. Ablation of hypocretin or hypocretin receptors also leads to narcolepsy phenotypes in animal models. Although the exact mechanism of hypocretin deficiency is unknown, evidence from the past 20 years strongly favours an immune-mediated or autoimmune attack, targeting specifically hypocretin neurons in genetically predisposed individuals. These neurons form an extensive network of projections throughout the brain and show activity linked to motivational behaviours. The hypothesis that a targeted immune-mediated or autoimmune attack causes the specific degeneration of hypocretin neurons arose mainly through the discovery of genetic associations, first with the HLA-DQB1*06:02 allele and then with the T-cell receptor α locus. Guided by these genetic findings and now awaiting experimental testing are models of the possible immune mechanisms by which a specific and localised brain cell population could become targeted by T-cell subsets. Great hopes for the identification of new targets for therapeutic intervention in narcolepsy also reside in the development of patient-derived induced pluripotent stem cell systems.

Increased plasma IL-6, IL-8, TNF-alpha, and G-CSF in Japanese narcolepsy.

Narcolepsy is a chronic hypersomnia involving excessive daytime sleepiness and cataplexy. Some susceptibility genes and environmental factors suggest that post-infectious immunological alterations underlie its pathophysiology. To investigate the immunological alterations in narcolepsy patients, we examined cytokines. Nine healthy controls and twenty-one narcolepsy patients with cataplexy were studied. All subjects were positive for the HLA-DRB1(∗)1501-DQB1(∗)0602 allele. Age-, sex-, and body mass index -matched healthy controls were selected. Plasma samples were separated using EDTA-2K-coated blood collection tubes. Bioplex Pro Human Cytokine 17-Plex Assays were used to measure plasma cytokines. Elevations of interleukin (IL)-6, IL-8, granulocyte- colony stimulating factor (G-CSF), and tumor necrosis factor-alpha were found in the narcolepsy group compared with healthy controls (p<0.05). G-CSF values were significantly correlated with the disease duration in narcolepsy patients (r=0.426, p<0.05). IL-8 and G-CSF play major roles in neutrophil activation in respiratory diseases. Since environmental factors including infection are reportedly associated with narcolepsy onset, elevated IL-8 and G-CSF may be involved in the pathophysiology of narcolepsy.

Narcolepsy and H1N1 vaccination: a link?

PURPOSE OF REVIEW: A number of European countries have reported a dramatic increase in the rates of childhood narcolepsy with cataplexy in children immunized with a split-virion adjuvanted swine flu vaccine. Here, we review the strengths and weaknesses of these epidemiological studies and possible neuroimmunological mechanisms. RECENT FINDINGS: Initial concerns of a 13-fold increased relative risk of narcolepsy were raised by the Scandinavian health protection agencies in 2010. Subsequent retrospective studies support these findings in Canada, France, Ireland, England and Denmark. The cases are predominantly young children who present with severe and rapid onset of cataplexy as well as narcolepsy often within a few weeks of vaccination. The proposed mechanism for postvaccination narcolepsy is one in which an environmental trigger causes or enhances an antibody-mediated autoimmune response in patients with a preexisting genetic susceptibility. However, there have not yet been any reports of specific autoimmunity, either antibody or T-cell-mediated. SUMMARY: There is a strong association between narcolepsy and H1N1 vaccination. However, whether this reflects a true increase in affected individuals or a hastening of disease onset in individuals who would otherwise have developed narcolepsy later will become clear in the coming years. The pathological explanation of this association and narcolepsy is likely to be autoimmune, although supportive evidence is lacking.Video abstract available: See the Video Supplementary Digital Content 1 (http://links.lww.com/COPM/A9).

Passive transfer of narcolepsy: anti-TRIB2 autoantibody positive patient IgG causes hypothalamic orexin neuron loss and sleep attacks in mice.

Narcolepsy is a sleep disorder characterized by excessive daytime sleepiness and cataplexy (a sudden weakening of posture muscle tone usually triggered by emotion) caused by the loss of orexin neurons in the hypothalamus. Autoimmune mechanisms are implicated in narcolepsy by increased frequency of specific HLA alleles and the presence of specific autoantibody (anti-Tribbles homolog 2 (TRIB2) antibodies) in the sera of patients with narcolepsy. Presently, we passively transferred narcolepsy to naïve mice by injecting intra-cerebra-ventricularly (ICV) pooled IgG positive for anti-TRIB2 antibodies. Narcolepsy-IgG-injected mice had a loss of the NeuN (neuronal marker), synaptophysin (synaptic marker) and orexin-positive neurons in the lateral hypothalamus area in narcolepsy compared to control-IgG-injected mice and these changes were associated with narcolepsy-like immobility attacks at four weeks post injection and with hyperactivity and long term memory deficits in the staircase and novel object recognition tests. Similar behavioral and cognitive deficits are observed in narcoleptic patients. This is the first report of passive transfer of experimental narcolepsy to naïve mice induced by autoantibodies and supports the autoimmune pathogenesis in narcolepsy.

Analysis of cortical thickness in narcolepsy patients with cataplexy.

STUDY OBJECTIVES: To investigate differences in cortical thickness in narcolepsy patients with cataplexy and control subjects. DESIGN: Cortical thickness was measured using a 3-D surface-based method that enables more accurate measurement in deep sulci and localized regional mapping. SETTING: University hospital. PATIENTS AND PARTICIPANTS: We enrolled 28 patients with narcolepsy and cataplexy and 33 age-and sex-matched control subjects. INTERVENTIONS: Cortical thickness was measured using a direct method for calculating the distance between corresponding vertices from inner and outer cortical surfaces. MEASUREMENTS AND RESULTS: We normalized cortical surfaces using 2-D surface registration and performed diffusion smoothing to reduce the variability of folding patterns and to increase the power of the statistical analysis. Localized cortical thinning in narcolepsy patients with cataplexy was found in orbitofrontal gyri, dorsolateral and medial prefrontal cortexes, insula, cingulate gyri, middle and inferior temporal gyri, and inferior parietal lobule of the right and left hemispheres at the level of a false discovery rate P<0.05. No significant local increases in cortical thickness were observed in narcolepsy patients. A significant negative correlation was observed between the narcolepsy patients' scores on the Epworth Sleepiness Scale and the cortical thickness of the left supramarginal gyrus. CONCLUSIONS: Cortical thinning in narcolepsy patients with cataplexy in localized anatomic brain regions may serve as a possible neuroanatomic mechanism of the disturbances in attention, memory, emotion, and sleepiness.

Ventilatory chemoresponsiveness, narcolepsy-cataplexy and human leukocyte antigen DQB1*0602 status.

We hypothesised that hypocretin (orexin) plays a role in the determination of ventilatory chemosensitivity. 130 patients with narcolepsy-cataplexy (mean ± SD age 20 ± 10 yrs, 69% male) and 117 controls (22 ± 6.9 yrs, 62% male) were recruited and tested for human leukocyte antigen (HLA)-DQB1*0602 status, hyperoxia hypercapnic (change in minute ventilation (δV'(E))/carbon dioxide tension (δP(CO(2))) L·min(-1)·mmHg(-1)) and hypoxic (δV'(E) /change in arterial oxygen saturation measured by probe oximetry (δS(p,O(2))) L·min(-1) per %S(p,O(2))) responsiveness, and by spirometry. Hypocretin deficiency was determined either by measures of cerebrospinal fluid hypocretin-1 (37 patients) or by positive HLA-DQB1*0602 status. All patients and 49% of controls underwent polysomnography and multiple sleep latency testing. Despite similar spirometric values, patients had a higher apnoea/hypopnoea index (AHI) (2.8 ± 5.4 versus 0.8 ± 1.6 h(-1); p = 0.03) and lower minimal oxygen saturation during sleep (87% ± 7 versus 91 ± 4%; p = 0.0002), independent of age, sex and body mass index. Patients had depressed hypoxic responsiveness (0.13 ± 0.09 versus 0.19 ± 0.13 L·min(-1) per %S(p,O(2)); p<0.0001), independent of AHI, but hypercapnic responsiveness did not differ. Examined by HLA status, positive (26 out of 117) controls had lower hypoxic but similar hypercapnic responsiveness than those marker-negative (0.13 ± 0.08 versus 0.20 ± 0.14 L·min(-1) per %S(p,O(2)); p<0.0001). Thus, a lower hypoxic responsiveness in the narcolepsy-cataplexy group is a result of DQB1*0602 status rather than the clinical features of disease.

Body mass index-independent metabolic alterations in narcolepsy with cataplexy.

STUDY OBJECTIVES: To contribute to the anthropometric and metabolic phenotyping of orexin-A-deficient narcoleptic patients, and to explore a possible risk of their developing a metabolic syndrome. DESIGN: We performed a cross-sectional study comparing metabolic alterations in patients with narcolepsy with cataplexy (NC) and patients with idiopathic hypersomnia without long sleep time. SETTING: University hospital. PATIENTS: Fourteen patients with narcolepsy with cataplexy and 14 sex and age-matched patients with idiopathic hypersomnia without long sleep time. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: Metabolic parameters were evaluated by measuring body mass index (BMI), waist circumference (also with abdominal computed tomography), blood pressure, and daily calorie intake (3-day diary). Chronotypes were assessed through the morningness-eveningness questionnaire. Lumbar puncture for cerebrospinal fluid orexin-A determination and HLA typing were performed. Patients with narcolepsy with cataplexy (all HLA DQB1*0602 positive and with cerebrospinal fluid orexin-A levels < 110 pg/mL) had a higher BMI and BMI-independent metabolic alterations, namely waist circumference, high-density lipoprotein cholesterol, and glucose/insulin ratio (an insulin resistance index), with respect to patients with idiopathic hypersomnia without long sleep time (cerebrospinal fluid orexin-A levels > 300 pg/mL). Despite lower daily food intake, patients with narcolepsy with cataplexy displayed significant alterations in metabolic parameters resulting in a diagnosis of metabolic syndrome in more than half the cases. CONCLUSIONS: BMI-independent metabolic alterations and the relative hypophagia of patients with narcolepsy with cataplexy, as compared with patients with idiopathic hypersomnia without long sleep time, suggest that orexin-A influences the etiology of this phenotype. Moreover, considering that these dysmetabolic alterations are present from a young age, a careful metabolic follow-up of patients diagnosed with narcolepsy with cataplexy is mandatory.

Elevated anti-streptococcal antibodies in patients with recent narcolepsy onset.

STUDY OBJECTIVES: Narcolepsy-cataplexy has long been thought to have an autoimmune origin. Although susceptibility to narcolepsy, like many autoimmune conditions, is largely genetically determined, environmental factors are involved based on the high discordance rate (approximately 75%) of monozygotic twins. This study evaluated whether Streptococcus pyogenes and Helicobacter pylori infections are triggers for narcolepsy. DESIGN: Retrospective, case-control. SETTING: Sleep centers of general hospitals. PARTICIPANTS: 200 patients with narcolepsy/hypocretin deficiency, with a primary focus on recent onset cases and 200 age-matched healthy controls. All patients were DQB1*0602 positive with low CSF hypocretin-1 or had clear-cut cataplexy. MEASUREMENTS AND RESULTS: Participants were tested for markers of immune response to beta hemolytic streptococcus (anti-streptolysin O [ASO]; anti DNAse B [ADB]) and Helicobacter pylori [Anti Hp IgG], two bacterial infections known to trigger autoimmunity. A general inflammatory marker, C-reactive protein (CRP), was also studied. When compared to controls, ASO and ADB titers were highest close to narcolepsy onset, and decreased with disease duration. For example, ASO > or = 200 IU (ADB > or = 480 IU) were found in 51% (45%) of 67 patients within 3 years of onset, compared to 19% (17%) of 67 age matched controls (OR = 4.3 [OR = 4.1], P < 0.0005) or 20% (15%) of 69 patients with long-standing disease (OR = 4.0 [OR = 4.8], P < 0.0005]. CRP (mean values) and Anti Hp IgG (% positive) did not differ from controls. CONCLUSIONS: Streptococcal infections are probably a significant environmental trigger for narcolepsy.

Comparison of clinical characteristics among narcolepsy with and without cataplexy and idiopathic hypersomnia without long sleep time, focusing on HLA-DRB1( *)1501/DQB1( *)0602 finding.

BACKGROUND: Clinical characteristics of narcolepsy without cataplexy (NA w/o CA) and its relation to positivity of HLA-DRB1( *)1501/DQB1( *)0602 remain unclarified. We investigated clinical features of NA w/o CA, particularly addressing HLA-DRB1( *)1501/DQB1( *)0602. METHODS: Comparisons of the Epworth Sleepiness Scale (ESS), multiple sleep latency test (MSLT) variables, rapid eye movement (REM)-related symptoms, and treatment response to psychostimulant medication were made for four patient groups (narcolepsy with cataplexy; NA-CA, NA w/o CA HLA-positive, NA w/o CA HLA-negative, and idiopathic hypersomnia without long sleep time; IHS w/o LST). RESULTS: Mean sleep latency was significantly shorter and the rate of reduction of ESS after medication was lower in both NA-CA and NA w/o CA HLA-positive groups than those in the IHS w/o LST group. Among the three narcoleptic groups, the NA w/o CA HLA-negative group showed the lowest REM latency and the highest reduction rate of ESS after treatment. Neither these subjective and objective sleepiness measures nor the treatment response measure was significantly different between this group and the IHS w/o LST group. CONCLUSIONS: In NA w/o CA, HLA-positivity might affect hypersomnia severity and REM propensity. The NA w/o CA HLA-negative group and the IHS w/o LST group exhibit equivalent hypersomnia severity.

Identification of differentially expressed genes in blood cells of narcolepsy patients.

STUDY OBJECTIVE: A close association between the human leukocyte antigen (HLA)-DRB1*1501/DQB1*0602 and abnormalities in some inflammatory cytokines have been demonstrated in narcolepsy. Specific alterations in the immune system have been suggested to occur in this disorder. We attempted to identify alterations in gene expression underlying the abnormalities in the blood cells of narcoleptic patients. DESIGNS: Total RNA from 12 narcolepsy-cataplexy patients and from 12 age- and sex-matched healthy controls were pooled. The pooled samples were initially screened for candidate genes for narcolepsy by differential display analysis using annealing control primers (ACP). The second screening of the samples was carried out by semiquantitative PCR using gene-specific primers. Finally, the expression levels of the candidate genes were further confirmed by quantitative real-time PCR using a new set of samples (20 narcolepsy-cataplexy patients and 20 healthy controls). RESULTS: The second screening revealed differential expression of 4 candidate genes. Among them, MX2 was confirmed as a significantly down-regulated gene in the white blood cells of narcoleptic patients by quantitative real-time PCR. CONCLUSION: We found the MX2 gene to be significantly less expressed in comparison with normal subjects in the white blood cells of narcoleptic patients. This gene is relevant to the immune system. Although differential display analysis using ACP technology has a limitation in that it does not help in determining the functional mechanism underlying sleep/wakefulness dysregulation, it is useful for identifying novel genetic factors related to narcolepsy, such as HLA molecules. Further studies are required to explore the functional relationship between the MX2 gene and narcolepsy pathophysiology.

Evaluation of hypothalamic-specific autoimmunity in patients with narcolepsy.

An autoimmune-mediated mechanism is considered the most probable etiology for narcolepsy. However, this hypothesis remains unproven. Since narcolepsy is characterized by dysfunction of the hypothalamic hypocretinergic (orexinergic) system, we evaluated the presence of hypothalamic-specific antibodies in sera and CSF of 25 hypocretin-deficient and 6 non-deficient narcoleptic patients by immunohistochemistry and analyzing a screening of a rat cDNA expression hypothalamic library. There was no hypothalamic-specific reactivity in serum or CSF by inmmunohistochemistry. The screening of the hypothalmic library detected some reactive clones but not a common reactivity. Our study did not find any evidence of hypothalamic-specific autoimmunity in narcolepsy.

Narcolepsy: a review of evidence for autoimmune diathesis.

Sporadic narcolepsy with cataplexy is a disabling disease that is strongly associated with the major histocompatibility class II allele HLA DQB1*0602 and is characterized by profound reduction in the cerebrospinal fluid (CSF) concentration of hypocretin 1 levels. This article provides a comprehensive review of the evidence that neurologic autoimmunity is the pathogenic basis of narcolepsy with cataplexy. Despite this evidence, specific antibody markers for narcolepsy have been elusive. Clinical trials using intravenous immunoglobulin infusions in recent onset narcolepsy with cataplexy have led to improvement in cataplexy in some patients. Future research must focus on elucidation of immune markers and early ameliorative treatments for narcolepsy.