Extensive HLA class II studies in 58 non-DRB1*15 (DR2) narcoleptic patients with cataplexy

Connecting the dots: An updated review of the role of autoimmunity in narcolepsy and emerging immunotherapeutic approaches

BACKGROUND

Narcolepsy type 1 (NT1) is a chronic disorder characterized by pathological daytime sleepiness and cataplexy due to the disappearance of orexin immunoreactive neurons in the hypothalamus. Genetic and environmental factors point towards a potential role for inflammation and autoimmunity in the pathogenesis of the disease. This study aims to comprehensively review the latest evidence on the autoinflammatory mechanisms and immunomodulatory treatments aimed at suspected autoimmune pathways in NT1.

METHODS

Recent relevant literature in the field of narcolepsy, its autoimmune hypothesis, and purposed immunomodulatory treatments were reviewed.

RESULTS

Narcolepsy is strongly linked to specific HLA alleles and T-cell receptor polymorphisms. Furthermore, animal studies and autopsies have found infiltration of T cells in the hypothalamus, supporting T cell-mediated immunity. However, the role of autoantibodies has yet to be definitively established. Increased risk of NT1 after H1N1 infection and vaccination supports the autoimmune hypothesis, and the potential role of coronavirus disease 2019 and vaccination in triggering autoimmune neurodegeneration is a recent finding. Alterations in cytokine levels, gut microbiota, and microglial activation indicate a potential role for inflammation in the disease's development. Reports of using immunotherapies in NT1 patients are limited and inconsistent. Early treatment with IVIg, corticosteroids, plasmapheresis, and monoclonal antibodies has seldomly shown some potential benefits in some studies.

CONCLUSION

The current body of literature supports that narcolepsy is an autoimmune disorder most likely caused by T-cell involvement. However, the potential for immunomodulatory treatments to reverse the autoinflammatory process remains understudied. Further clinical controlled trials may provide valuable insights into this area.

Origins and immunopathogenesis of autoimmune central nervous system disorders

The field of autoimmune neurology is rapidly evolving, and recent discoveries have advanced our understanding of disease aetiologies. In this article, we review the key pathogenic mechanisms underlying the development of CNS autoimmunity. First, we review non-modifiable risk factors, such as age, sex and ethnicity, as well as genetic factors such as monogenic variants, common variants in vulnerability genes and emerging HLA associations. Second, we highlight how interactions between environmental factors and epigenetics can modify disease onset and severity. Third, we review possible disease mechanisms underlying triggers that are associated with the loss of immune tolerance with consequent recognition of self-antigens; these triggers include infections, tumours and immune-checkpoint inhibitor therapies. Fourth, we outline how advances in our understanding of the anatomy of lymphatic drainage and neuroimmune interfaces are challenging long-held notions of CNS immune privilege, with direct relevance to CNS autoimmunity, and how disruption of B cell and T cell tolerance and the passage of immune cells between the peripheral and intrathecal compartments have key roles in initiating disease activity. Last, we consider novel therapeutic approaches based on our knowledge of the immunopathogenesis of autoimmune CNS disorders.

Animal models of narcolepsy and the hypocretin/orexin system: Past, present, and future

Animal models have advanced not only our understanding of the etiology and phenotype of the sleep disorder narcolepsy but have also informed sleep/wake regulation more generally. The identification of an inheritable narcolepsy phenotype in dogs in the 1970s allowed the establishment of a breeding colony at Stanford University, resulting in studies that provided the first insights into the genetics and neurotransmitter systems that underlie cataplexy and rapid-eye movement sleep atonia. Although the discovery of the hypocretin/orexin neuropeptides in 1998 initially seemed unrelated to sleep/wake control, the description of the phenotype of the prepro-orexin knockout (KO) mouse as strongly resembling cataplexy, the pathognomonic symptom of narcolepsy, along with identification of a mutation in hypocretin receptor-2 gene as the source of canine narcolepsy, unequivocally established the relationship between this system and narcolepsy. The subsequent discovery of hypocretin neuron degeneration in human narcolepsy demystified a disorder whose etiology had been unknown since its initial description 120 years earlier. These breakthroughs prompted the development of numerous other animal models that have allowed manipulation of the hypocretin/orexin system, thereby advancing our understanding of sleep/wake circuitry. While animal models have greatly informed understanding of this fascinating disorder and the role of the hypocretin/orexin system in sleep/wake control, the question of why these neurons degenerate in human narcolepsy is only beginning to be understood. The development of new immune-mediated narcolepsy models are likely to further inform the etiology of this sleep disorder and animal models will undoubtedly play a critical role in the development of novel narcolepsy therapeutics.

Dream Activity in Narcoleptic Patients During the COVID-19 Lockdown in Italy

Some studies highlighted that patients with narcolepsy type-1 (NT1) experience high lucid dream frequency, and this phenomenon has been associated with a creative personality. Starting from the well-known “pandemic effect” on sleep and dreaming, we presented a picture of dream activity in pharmacologically treated NT1 patients during the Italian lockdown. Forty-three NT1 patients completed a web-survey during Spring 2021 and were compared with 86 matched-controls. Statistical comparisons revealed that: (a) NT1 patients showed greater sleepiness than controls; (b) controls showed higher sleep disturbances than NT1 patients, and this result disappeared when the medication effect in NT1 was controlled; (c) NT1 patients reported higher lucid dream frequency than controls. Focusing on dreaming in NT1 patients, we found that (a) nightmare frequency was correlated with female gender, longer sleep duration, higher intrasleep wakefulness; (b) dream recall, nightmare and lucid dream frequency were positively correlated with sleepiness. Comparisons between low and high NT1 lucid dreamers showed that patients more frequently experiencing lucid dreams reported a greater influence of dreaming during wakefulness, especially concerning problem-solving and creativity. Overall, our results are consistent with previous studies on pandemic dreaming carried out on healthy subjects. Moreover, we confirmed a link between lucidity and creativity in NT1 patients. Considering the small sample size and the cross-sectional design, our findings cannot provide a causal relationship between lucid dreams and the COVID-19 lockdown. Nevertheless, they represent a first contribution to address future studies on this issue, suggesting that some stable characteristics could interact with changes provoked by the pandemic.

T cell reactivity to regulatory factor X4 in type 1 narcolepsy

Type 1 narcolepsy is strongly (98%) associated with human leukocyte antigen (HLA) class II DQA1*01:02/DQB1*06:02 (DQ0602) and highly associated with T cell receptor (TCR) alpha locus polymorphism as well as other immune regulatory loci. Increased incidence of narcolepsy was detected following the 2009 H1N1 pandemic and linked to Pandemrix vaccination, strongly supporting that narcolepsy is an autoimmune disorder. Although recent results suggest CD4+ T cell reactivity to neuropeptide hypocretin/orexin and cross-reactive flu peptide is involved, identification of other autoantigens has remained elusive. Here we study whether autoimmunity directed against Regulatory Factor X4 (RFX4), a protein co-localized with hypocretin, is involved in some cases of narcolepsy. Studying human serum, we found that autoantibodies against RFX4 were rare. Using RFX4 peptides bound to DQ0602 tetramers, antigen RFX4-86, -95, and -60 specific human CD4+ T cells were detected in 4/10 patients and 2 unaffected siblings, but not in others. Following culture with each cognate peptide, enriched autoreactive TCRαβ clones were isolated by single-cell sorting and TCR sequenced. Homologous clones bearing TRBV4-2 and recognizing RFX4-86 in patients and one twin control of patient were identified. These results suggest the involvement of RFX4 CD4+ T cell autoreactivity in some cases of narcolepsy, but also in healthy donors.

Narcolepsy Type I as an autoimmune disorder

Narcolepsy Type 1 (NT1) is hypothesized to be an autoimmune disease targeting the hypocretin/orexin neurons in the lateral hypothalamus. Ample genetic and epidemiologic evidence point in the direction of a pathogenesis involving the immune system. Many autoantibodies have been detected in blood samples from NT1 patients, but none in a consistent manner. Importantly, T cells directed toward hypocretin/orexin neurons have been detected in samples from NT1 patients. However, it remains to be seen if these potentially autoreactive T cells are also present in the hypothalamus and if they are pathogenic. For this reason, NT1 does still not fully meet the criteria for being classified as a genuine autoimmune disease, even though more and more results are pointing in that direction as will be described in this chapter. The autoimmune hypothesis has led to many attempts at slowing or stopping disease progression with immunomodulatory treatment, but so far the overall results have not been very encouraging. It is clear that more research into the pathogenesis of NT1 is needed to establish the precise role of the immune system in disease development.

Treatment of Isolated Cataplexy With Low-dose Aripiprazole in an Adolescent Patient

BACKGROUND

Cataplexy is a clinical entity that is characterized by transient muscle tone loss that mostly occurring as a part of narcolepsy. On the other hand, isolated cataplexy (IC) (hereditary cataplexy) is defined as loss of muscle tone that is not accompanied by narcolepsy. Emotional reactions may trigger IC episodes. Additionally, human leukocyte antigen (HLA) DQB1 alleles were shown to be related to IC. Various antidepressants are useful in the treatment of IC; however, there is limited knowledge on the use of antipsychotics in the treatment of IC.

CASE REPORT

A 16-year-old adolescent girl was consulted child and adolescent psychiatry outpatient clinic with complaint of sudden episodes of loss of muscle tone. Her HLA typing showed HLA DQB1*03 haplotype. She was diagnosed with IC and was prescribed aripiprazole 2.5 mg/d and her IC symptoms disappeared and never recurred over 6 months of follow-up.

CONCLUSIONS

In this case report, we present an adolescent girl with IC that is successfully treated with aripiprazole, an antipsychotic. This case report suggests that aripiprazole may be safely used in some adolescents who diagnosed with IC.

Giving a voice to cataplectic experience: recollections from patients with narcolepsy type 1

STUDY OBJECTIVES

The objective of this study was to assess the narratives from the recalled accounts of cataplexy attacks of patients with narcolepsy type 1 (NT1).

METHODS

Twenty-two drug-naive adult patients meeting the International Classification of Sleep Disorders criteria for the diagnosis of NT1 referring to the Narcolepsy Center of the University of Bologna in the year 2017 underwent a semistructured interview focusing on their personal experiences during the cataplectic attacks. Verbatim transcripts were analyzed by thematic analysis of elementary contexts using T-LAB software.

RESULTS

The thematic analysis performed on the entire body text showed 3 clusters that explained 36.2%, 34.1%, and 29.7% of the variance, respectively: a cluster related to situations that trigger attacks of cataplexy, a cluster to bodily sensations, and another control strategies during episodes. The thematic content highlighted a tendency to disregard emotional experiences, thus affecting the ability to name, recognize, and regulate critical emotions.

CONCLUSIONS

The study showed that patients with NT1 spoke of their cataplectic attacks in terms of self-reported bodily experiences, trigger situations, and their management. Therefore, patients may have developed strategies of symptom management focused on emotion avoidance and/or inhibition.

[Narcolepsy: From the discovery of a wake promoting peptide to autoimmune T cell biology and molecular mimicry with flu epitopes]

Narcolepsy-cataplexy was first described in the late 19th century in Germany and France. Prevalence was established to be 0.05 % and a canine model was discovered in the 1970s. In 1983, a Japanese study found that all patients carried HLA-DR2, suggesting autoimmunity as the cause of the disease. Studies in the canine model established that dopaminergic stimulation underlies anti-narcoleptic action of psychostimulants, while antidepressants were found to suppress cataplexy through adrenergic reuptake inhibition. No HLA association was found in canines. A linkage study initiated in 1988 revealed in hypocretin (orexin) receptor two mutations as the cause of canine narcolepsy in 1999. In 1992, studies on African Americans showed that DQ0602 was a better marker than DR2 across all ethnic groups. In 2000, hypocretin-1/orexin A levels were measured in the cerebrospinal fluid (CSF) and found to be undetectable in most patients, establishing hypocretin deficiency as the cause of narcolepsy. Decreased CSF hypocretin-1 was then found to be secondary to the loss of the 70,000 neurons producing hypocretin in the hypothalamus, suggesting immune destruction of these cells as the cause of the disease. Additional genetic studies, notably genome wide associations (GWAS), found multiple genetic predisposing factors for narcolepsy. These were almost all involved in other autoimmune diseases, although a strong and unique association with T cell receptor (TCR) alpha and beta loci were observed. Nonetheless, all attempts to demonstrate presence of autoantibodies against hypocretin cells in narcolepsy failed, and the presumed autoimmune cause remained unproven. In 2009, association with strep throat infections were found, and narcolepsy onsets were found to occur more frequently in spring and summer, suggesting upper away infections as triggers. Following reports that narcolepsy cases were triggered by vaccinations and infections against influenza A 2009 pH1N1, a new pandemic strain that erupted in 2009, molecular mimicry with influenza A virus was suggested in 2010. This hypothesis was later confirmed by peptide screening showing higher activity of CD4⁺ T cell reactivity to a specific post-translationally amidated segment of hypocretin (HCRT-_NH2) and cross-reactivity of specific TCRs with a pH1N1-specific segment of hemagglutinin that shares homology with HCRT-_NH2. Strikingly, the most frequent TCR recognizing these antigens was found to carry sequences containing TRAJ24 or TRVB4-2, segments modulated by narcolepsy-associated genetic polymorphisms. Cross-reactive CD4⁺ T cells with these cross-reactive TCRs likely subsequently recruit CD8⁺ T cells that are then involved in hypocretin cell destruction. Additional flu mimics are also likely to be discovered since narcolepsy existed prior to 2009. The work that has been conducted over the years on narcolepsy offers a unique perspective on the conduct of research on the etiopathogeny of a specific disease.

Sleep modulating agents

Sleep and wake are two fundamental states of human existence. Conditions such as insomnia and hypersomnia can have profound negative effects on human health. Many pharmacological interventions impacting sleep and wake are available or are under development. This brief digest surveys early approaches to sleep modulation and highlights recent developments in sleep modulating agents.

De novo ATP1A3 and compound heterozygous NLRP3 mutations in a child with autism spectrum disorder, episodic fatigue and somnolence, and muckle-wells syndrome

Complex phenotypes may represent novel syndromes that are the composite interaction of several genetic and environmental factors. We describe an 9-year old male with high functioning autism spectrum disorder and Muckle-Wells syndrome who at age 5  years of age manifested perseverations that interfered with his functioning at home and at school. After age 6, he developed intermittent episodes of fatigue and somnolence lasting from hours to weeks that evolved over the course of months to more chronic hypersomnia. Whole exome sequencing showed three mutations in genes potentially involved in his clinical phenotype. The patient has a predicted pathogenic de novo heterozygous p.Ala681Thr mutation in the ATP1A3 gene (chr19:42480621C>T, GRCh37/hg19). Mutations in this gene are known to cause Alternating Hemiplegia of Childhood, Rapid Onset Dystonia Parkinsonism, and CAPOS syndrome, sometimes accompanied by autistic features. The patient also has compound heterozygosity for p.Arg490Lys/p.Val200Met mutations in the NLRP3 gene (chr1:247588214G>A and chr1:247587343G>A, respectively). NLRP3 mutations are associated in an autosomal dominant manner with clinically overlapping auto-inflammatory conditions including Muckle-Wells syndrome. The p.Arg490Lys is a known pathogenic mutation inherited from the patient's father. The p.Val200Met mutation, inherited from his mother, is a variant of unknown significance (VUS). Whether the de novoATP1A3mutation is responsible for or plays a role in the patient's episodes of fatigue and somnolence remains to be determined. The unprecedented combination of two NLRP3 mutations may be responsible for other aspects of his complex phenotype.

Genetic Ancestry for Sleep Research: Leveraging Health Inequalities to Identify Causal Genetic Variants

Recent evidence has highlighted the health inequalities in sleep behaviors and sleep disorders that adversely affect outcomes in select populations, including African-American and Hispanic-American subjects. Race-related sleep health inequalities are ascribed to differences in multilevel and interlinked health determinants, such as sociodemographic factors, health behaviors, and biology. African-American and Hispanic-American subjects are admixed populations whose genetic inheritance combines two or more ancestral populations originating from different continents. Racial inequalities in admixed populations can be parsed into relevant groups of mediating factors (environmental vs genetic) with the use of measures of genetic ancestry, including the proportion of an individual's genetic makeup that comes from each of the major ancestral continental populations. This review describes sleep health inequalities in African-American and Hispanic-American subjects and considers the potential utility of ancestry studies to exploit these differences to gain insight into the genetic underpinnings of these phenotypes. The inclusion of genetic approaches in future studies of admixed populations will allow greater understanding of the potential biological basis of race-related sleep health inequalities.

Genetic Association in the HLA Region

The MHC/HLA region has been consistently associated with a large number of complex traits, including but not limited to, most immune-mediated ones. Efforts to pinpoint drivers of this commonly encountered association peak at the short arm of chromosome 6, however, have been challenging, owing to the high density of genes and the long and extended linkage disequilibrium that are characteristic of this region.The development of methods to impute classical HLA alleles and amino acids from SNP genotyping data has offered an important additional layer of information to the investigators seeking to fine map the signal in the region. As a result, imputation-aided association analyses are now typically employed to shed light on the relationship of this locus with disease susceptibility and response to drugs.In this chapter we discuss how the signal in the HLA region can be interrogated in practice, from performing the imputation to understanding its output and to incorporating it into downstream analysis. In addition, we recount some of the analytical approaches that are commonly used and suggest ways in which the findings from such imputation-aided analyses can be interpreted.

Comparison of Pandemrix and Arepanrix, two pH1N1 AS03-adjuvanted vaccines differentially associated with narcolepsy development

Narcolepsy onset in children has been associated with the 2009 influenza A H1N1 pandemic and vaccination with Pandemrix. However it was not clearly observed with other adjuvanted pH1N1 vaccines such as Arepanrix or Focetria. Our aim was to characterize the differences between Pandemrix and Arepanrix that might explain the risk for narcolepsy after Pandemrix vaccination using 2D-DIGE and mass spectrometry (MS). We found that Pandemrix (2009 batch) and Arepanrix (2010 batch) showed 5 main viral proteins: hemagglutinin HA1 and HA2 subunits, neuraminidase NA, nucleoprotein NP, and matrix protein MA1 and non-viral proteins from the Gallus gallus growth matrix used in the manufacturing of the vaccines. Latticed patterns of HA1, HA2 and NA indicated charge and molecular weight heterogeneity, a phenomenon likely caused by glycosylation and sulfation. Overall, Pandemrix contained more NP and NA, while Arepanrix displayed a larger diversity of viral and chicken proteins, with the exception of five chicken proteins (PDCD6IP, TSPAN8, H-FABP, HSP and TUB proteins) that were relatively more abundant in Pandemrix. Glycosylation patterns were similar in both vaccines. A higher degree of deamidation and dioxidation was found in Pandemrix, probably reflecting differential degradation across batches. Interestingly, HA1 146N (residue 129N in the mature protein) displayed a 10-fold higher deamidation in Arepanrix versus Pandemrix. In recent vaccine strains and Focetria, 146N is mutated to D which is associated with increased production yields suggesting that 146N deamidation may have also occurred during the manufacturing of Arepanrix. The presence of 146N in large relative amounts in Pandemrix and the wild type virus and in lower relative quantities in Arepanrix or other H1N1 vaccines may have affected predisposition to narcolepsy.

HLA dosage effect in narcolepsy with cataplexy

Narcolepsy with cataplexy is a sleep disorder caused by the loss of hypocretin-producing neurons in the hypothalamus. It is tightly associated with a specific human leukocyte antigen (HLA)-allele: HLA-DQB1*06:02. Based on this, an autoimmune process has been hypothesized. A functional HLA-DQ molecule consists of a DQα and a DQβ chain. HLA-DQB1*06:02 (DQβ) has a strong preference for binding to HLA-DQA1*01:02 (DQα), and together they form the functional DQ0602 dimer. A dosage effect would be expected if the HLA-DQ0602 dimer itself is directly involved in the aetiology. An increased expression of the HLA-DQ0602 dimer is expected in individuals homozygous for HLA-DQB1*06:02-DQA1*01:02, but is also hypothesized in individuals heterozygous for HLA-DQB1*06:02 and homozygous for HLA-DQA1*01:02. To study the impact of the expression of the HLA-DQ0602 dimer on narcolepsy susceptibility, 248 Dutch narcolepsy patients and 1272 Dutch control subjects, all of them positive for DQB1*06:02 (heterozygous and homozygous), were HLA-genotyped with attention not only to DQB1 but also to DQA1*01:02. DQB1*06:02-DQA1*01:02 homozygosity was significantly more often seen in patients compared to controls (O.R. 2.29) confirming previous observations. More importantly, a significantly higher prevalence of homozygosity for DQA1*01:02 was found in HLA-DQB1*06:02 heterozygous patients compared to controls (O.R. 2.37, p < 0.001). The latter finding clearly supports a direct role of the HLA-DQ molecule in the development of disease.

Risk of narcolepsy associated with inactivated adjuvanted (AS03) A/H1N1 (2009) pandemic influenza vaccine in Quebec

Context

An association between an adjuvanted (AS03) A/H1N1 pandemic vaccine and narcolepsy has been reported in Europe.

Objective

To assess narcolepsy risk following administration of a similar vaccine in Quebec.

Design

Retrospective population-based study.

Setting

Neurologists and lung specialists in the province were invited to report narcolepsy cases to a single reference centre.

Population

Patients were interviewed by two sleep experts and standard diagnostic tests were performed. Immunization status was verified in the provincial pandemic influenza vaccination registry.

Main Outcome Measures

Confirmed narcolepsy with or without cataplexy with onset of excessive daytime sleepiness between January 1^st, 2009, and December 31^st, 2010. Relative risks (RRs) were calculated using a Poisson model in a cohort analysis, by a self-controlled case series (SCCS) and a case-control method.

Results

A total of 24 cases were included and overall incidence rate was 1.5 per million person-years. A cluster of 7 cases was observed among vaccinated persons in the winter 2009–2010. In the primary cohort analysis, 16-week post-vaccination RR was 4.32 (95% CI: 1.50–11.12). RR was 2.07 (0.70–6.17) in the SCCS, and 1.48 (0.37–7.03) using the case-control method. Estimates were lower when observation was restricted to the period of pandemic influenza circulation, and tended to be higher in persons <20 years old and for cataplexy cases.

Conclusions

Results are compatible with an excess risk of approximately one case per million vaccine doses, mainly in persons less than 20 years of age. However, a confounding effect of the influenza infection cannot be ruled out.

History of narcolepsy at Stanford University

Although narcolepsy was first described in the late nineteenth century in Germany and France, much of the research on this disorder has been conducted at Stanford University, starting with Drs. William C. Dement and Christian Guilleminault in the 1970s. The prevalence of narcolepsy was established, and a canine model discovered. Following the finding in Japan that almost all patients with narcolepsy carry a specific HLA subtype, HLA-DR2, Hugh Mac Devitt, F. Carl Grumet, and Larry Steinman initiated immunological studies, but results were generally negative. Using the narcoleptic canines, Dr. Nishino and I established that stimulants increased wakefulness by stimulating dopaminergic transmission while antidepressants suppress cataplexy via adrenergic reuptake inhibition. A linkage study was initiated with Dr. Grumet in 1988, and after 10 years of work, the canine narcolepsy gene was cloned by in 1999 and identified as the hypocretin (orexin) receptor 2. In 1992, studying African Americans, we also found that DQ0602 rather than DR2 was a better marker for narcolepsy across all ethnic groups. In 2000, Dr. Nishino and I, in collaboration with Dr. Lammers in the Netherlands, found that hypocretin 1 levels in the cerebrospinal fluid (CSF) were undetectable in most cases, establishing hypocretin deficiency as the cause of narcolepsy. Pursuing this research, our and Dr. Siegel's group, examining postmortem brains, found that the decreased CSF hypocretin 1 was secondary to the loss the 70,000 neurons producing hypocretin in the hypothalamus. This finding revived the autoimmune hypothesis but attempts at demonstrating immune targeting of hypocretin cells failed until 2013. At this date, Dr. Elisabeth Mellins and I discovered that narcolepsy is characterized by the presence of autoreactive CD4(+) T cells to hypocretin fragments when presented by DQ0602. Following reports that narcolepsy cases were triggered by vaccinations and infections against influenza A 2009 pH1N1, a new pandemic strain that erupted in 2009, our groups also established that a small epitope of pH1N1 resembles hypocretin and is likely involved in molecular mimicry. Although much remains to be done, these achievements, establishing hypocretin deficiency as the cause of narcolepsy, demonstrating its autoimmune basis, and showing molecular mimicry between hypocretin and sequences derived from a pandemic strain of influenza, are likely to remain classics in human immunology.

Sodium oxybate for narcolepsy

Sodium oxybate (Xyrem), also known as gamma-hydroxybutyric acid, is the only therapeutic specifically approved in the USA for the treatment of cataplexy in narcolepsy. The US FDA has recently expanded its indication to include excessive daytime sleepiness associated with narcolepsy. In contrast to the antidepressants and stimulants commonly used to treat the disorder, sodium oxybate is the only compound that addresses both sets of symptoms and, when used properly, is less likely to lead to the development of tolerance and other undesirable side effects. In this review, the results of clinical trials and the place of sodium oxybate in narcolepsy treatment are discussed.

DQB1 locus alone explains most of the risk and protection in narcolepsy with cataplexy in Europe

STUDY OBJECTIVE

Prior research has identified five common genetic variants associated with narcolepsy with cataplexy in Caucasian patients. To replicate and/or extend these findings, we have tested HLA-DQB1, the previously identified 5 variants, and 10 other potential variants in a large European sample of narcolepsy with cataplexy subjects.

DESIGN

Retrospective case-control study.

SETTING

A recent study showed that over 76% of significant genome-wide association variants lie within DNase I hypersensitive sites (DHSs). From our previous GWAS, we identified 30 single nucleotide polymorphisms (SNPs) with P < 10(-4) mapping to DHSs. Ten SNPs tagging these sites, HLADQB1, and all previously reported SNPs significantly associated with narcolepsy were tested for replication.

PATIENTS AND PARTICIPANTS

For GWAS, 1,261 narcolepsy patients and 1,422 HLA-DQB1*06:02-matched controls were included. For HLA study, 1,218 patients and 3,541 controls were included.

MEASUREMENTS AND RESULTS

None of the top variants within DHSs were replicated. Out of the five previously reported SNPs, only rs2858884 within the HLA region (P < 2x10(-9)) and rs1154155 within the TRA locus (P < 2x10(-8)) replicated. DQB1 typing confirmed that DQB1*06:02 confers an extraordinary risk (odds ratio 251). Four protective alleles (DQB1*06:03, odds ratio 0.17, DQB1*05:01, odds ratio 0.56, DQB1*06:09 odds ratio 0.21, DQB1*02 odds ratio 0.76) were also identified.

CONCLUSION

An overwhelming portion of genetic risk for narcolepsy with cataplexy is found at DQB1 locus. Since DQB1*06:02 positive subjects are at 251-fold increase in risk for narcolepsy, and all recent cases of narcolepsy after H1N1 vaccination are positive for this allele, DQB1 genotyping may be relevant to public health policy.

Major histocompatibility complex genomics and human disease

Over several decades, various forms of genomic analysis of the human major histocompatibility complex (MHC) have been extremely successful in picking up many disease associations. This is to be expected, as the MHC region is one of the most gene-dense and polymorphic stretches of human DNA. It also encodes proteins critical to immunity, including several controlling antigen processing and presentation. Single-nucleotide polymorphism genotyping and human leukocyte antigen (HLA) imputation now permit the screening of large sample sets, a technique further facilitated by high-throughput sequencing. These methods promise to yield more precise contributions of MHC variants to disease. However, interpretation of MHC-disease associations in terms of the functions of variants has been problematic. Most studies confirm the paramount importance of class I and class II molecules, which are key to resistance to infection. Infection is likely driving the extreme variation of these genes across the human population, but this has been difficult to demonstrate. In contrast, many associations with autoimmune conditions have been shown to be specific to certain class I and class II alleles. Interestingly, conditions other than infections and autoimmunity are also associated with the MHC, including some cancers and neuropathies. These associations could be indirect, owing, for example, to the infectious history of a particular individual and selective pressures operating at the population level.

HLA-DQ association and allele competition in Chinese narcolepsy

In Japanese, Koreans and Caucasians, narcolepsy/hypocretin deficiency is tightly associated with the DRB1*15:01-DQA1*01:02-DQB1*06:02 haplotype. Studies in African-Americans suggest a primary effect of DQB1*06:02, but this observation has been difficult to confirm in other populations because of high linkage disequilibrium between DRB1*15:01/3 and DQB1*06:02 in most populations. In this study, we studied human leucocyte antigen (HLA) class II in 202 Chinese narcolepsy patients (11% from South China) and found all patients to be DQB1*06:02 positive. Comparing cases with 103 unselected controls, and 110 and 79 controls selected for the presence of DQB1*06:02 and DRB1*15:01, we found that the presence of DQB1*06:02 and not DRB1*15:01 was associated with narcolepsy. In particular, Southern Chinese haplotypes such as the DRB1*15:01-DQA1*01:02-DQB1*06:01 and DRB1*15:01-DQA1*01:02-DQB1*05 were not associated with narcolepsy. As reported in Japanese, Koreans, African-Americans and Caucasians, additional protective effects of DQA1*01 (non-DQA1*01:02) and susceptibility effects of DQB1*03:01 were observed. These results illustrate the extraordinary conservation of HLA class II effects in narcolepsy across populations and show that DRB1*15:01 has no effect on narcolepsy susceptibility in the absence of DQB1*06:02. The results are also in line with a previously proposed 'HLA-DQ allelic competition model' that involves competition between non-DQA1*01:02, non-DQB1*06:02 'competent' (able to dimerize together) DQ1 alleles and the major DQα*01:02/ DQβ*06:02 narcolepsy heterodimer to reduce susceptibility.

Use of PCR with sequence-specific primers for high-resolution human leukocyte antigen typing of patients with narcolepsy

Background

Narcolepsy is a neurologic disorder characterized by excessive daytime sleepiness, symptoms of abnormal rapid eye movement (REM) sleep, and a strong association with HLA-DRB1^*1501, -DQA1^*0102, and -DQB1^*0602. Here, we investigated the clinico-physical characteristics of Korean patients with narcolepsy, their HLA types, and the clinical utility of high-resolution PCR with sequence-specific primers (PCR-SSP) as a simple typing method for identifying DRB1^*15/16, DQA1, and DQB1 alleles.

Methods

The study population consisted of 67 consecutively enrolled patients having unexplained daytime sleepiness and diagnosed narcolepsy based on clinical and neurological findings. Clinical data and the results of the multiple sleep latency test and polysomnography were reviewed, and HLA typing was performed using both high-resolution PCR-SSP and sequence-based typing (SBT).

Results

The 44 narcolepsy patients with cataplexy displayed significantly higher frequencies of DRB1^*1501 (Pc= 0.003), DQA1^*0102 (Pc=0.001), and DQB1^*0602 (Pc=0.014) than the patients without cataplexy. Among patients carrying DRB1^*1501-DQB1^*0602 or DQA1^*0102, the frequencies of a mean REM sleep latency of less than 20 min in nocturnal polysomnography and clinical findings, including sleep paralysis and hypnagogic hallucination were significantly higher. SBT and PCR-SSP showed 100% concordance for high-resolution typing of DRB1^*15/16 alleles and DQA1 and DQB1 loci.

Conclusions

The clinical characteristics and somnographic findings of narcolepsy patients were associated with specific HLA alleles, including DRB1^*1501, DQA1^*0102, and DQB1^*0602. Application of high-resolution PCR-SSP, a reliable and simple method, for both allele- and locus-specific HLA typing of DRB1^*15/16, DQA1, and DQB1 would be useful for characterizing clinical status among subjects with narcolepsy.

Clinical and therapeutic aspects of childhood narcolepsy-cataplexy: a retrospective study of 51 children

STUDY OBJECTIVE

to report on symptoms and therapies used in childhood narcolepsy-cataplexy.

DESIGN, PATIENTS, AND SETTING

retrospective series of 51 children who completed the Stanford Sleep Inventory. HLA-DQB1*0602 typing (all tested, and 100% positive), polysomnography or Multiple Sleep Latency Test (76%), and cerebrospinal fluid hypocretin-1 measurements (26%, all with low levels) were also conducted. Prospective data on medication response was collected in 78% using a specially designed questionnaire.

MEASUREMENTS AND RESULTS

patients were separated into children with onset of narcolepsy prior to (53%), around (29%), and after (18%) puberty. None of the children had secondary narcolepsy. Clinical features were similar across puberty groups, except for sleep paralysis, which increased in frequency with age. Common features included excessive weight gain (84% ≥ 4 kg within 6 months of onset of narcolepsy) and earlier puberty (when compared with family members), notably in subjects who gained the most weight. Streptococcus-positive throat infections were reported in 20% of cases within 6 months of onset of narcolepsy. Polysomnographic features were similar across groups, but 3 prepubertal children did not meet Multiple Sleep Latency Test diagnostic criteria. Regarding treatment, the most used and continued medications were modafinil (84% continued), sodium oxybate (79%), and venlafaxine (68%). Drugs such as methylphenidate, tricyclic antidepressants, or selective serotonin reuptake inhibitors were often tried but rarely continued. Modafinil was reported to be effective for treating sleepiness, venlafaxine for cataplexy, and sodium oxybate for all symptoms, across all puberty groups. At the conclusion of the study, half of children with prepubertal onset of narcolepsy were treated "off label" with sodium oxybate alone or with the addition of one other compound. In older children, however, most patients needed more than 2 drugs.

CONCLUSION

this study reports on the clinical features of childhood narcolepsy and documents the safe use of treatments commonly used in adults in young children.

Genome-wide association study identifies new HLA class II haplotypes strongly protective against narcolepsy

Narcolepsy is a rare sleep disorder with the strongest human leukocyte antigen (HLA) association ever reported. Since the associated HLA-DRB1*1501-DQB1*0602 haplotype is common in the general population (15-25%), it has been suggested that it is almost necessary but not sufficient for developing narcolepsy. To further define the genetic basis of narcolepsy risk, we performed a genome-wide association study (GWAS) in 562 European individuals with narcolepsy (cases) and 702 ethnically matched controls, with independent replication in 370 cases and 495 controls, all heterozygous for DRB1*1501-DQB1*0602. We found association with a protective variant near HLA-DQA2 (rs2858884; P < 3 x 10(-8)). Further analysis revealed that rs2858884 is strongly linked to DRB1*03-DQB1*02 (P < 4 x 10(-43)) and DRB1*1301-DQB1*0603 (P < 3 x 10(-7)). Cases almost never carried a trans DRB1*1301-DQB1*0603 haplotype (odds ratio = 0.02; P < 6 x 10(-14)). This unexpected protective HLA haplotype suggests a virtually causal involvement of the HLA region in narcolepsy susceptibility.

[Brazilian guidelines for the diagnosis of narcolepsy]

This manuscript contains the conclusion of the consensus meeting on the diagnosis of narcolepsy based on the review of Medline publications between 1980-2010. Narcolepsy is a chronic disorder with age at onset between the first and second decade of life. Essential narcolepsy symptoms are cataplexy and excessive sleepiness. Cataplexy is defined as sudden, recurrent and reversible attacks of muscle weakness triggered by emotions. Accessory narcolepsy symptoms are hypnagogic hallucinations, sleep paralysis and nocturnal fragmented sleep. The clinical diagnosis according to the International Classification of Sleep Disorders is the presence of excessive sleepiness and cataplexy. A full in-lab polysomnography followed by a multiple sleep latency test is recommended for the confirmation of the diagnosis and co-morbidities. The presence of two sleep-onset REM period naps in the multiple sleep latency test is diagnostic for cataplexy-free narcolepsy. A positive HLA-DQB1*0602 with lower than 110pg/mL level of hypocretin-1 in the cerebrospinal fluid is required for the final diagnosis of cataplexy- and sleep-onset REM period -free narcolepsy.

Does narcolepsy symptom severity vary according to HLA-DQB1*0602 allele status?

STUDY OBJECTIVES

To investigate associations between HLA-DQB1*0602 allele status and measures of narcolepsy symptom severity.

DESIGN

Cross-sectional study of population-based narcolepsy patients.

SETTING

King County, Washington.

PARTICIPANTS

All prevalent cases (n = 279) of physician-diagnosed narcolepsy ascertained from 2001-2005.

INTERVENTIONS

N/A.

MEASUREMENTS

Narcolepsy diagnosis was based on cataplexy status, diagnostic sleep study results, and chart review. The number of HLA-DQB1 alleles was determined from buccal genomic DNA. Symptom severity instruments included the Epworth Sleepiness Scale (ESS), the Ullanlinna Narcolepsy Scale (UNS), age of symptom onset, subjective sleep latency and duration, and various clinical sleep parameters. We used linear regression adjusted for African American race and an extended chi-square test of trend to assess relationships across ordered groups defined by allele number (0, 1, or 2).

RESULTS

Narcolepsy patients were 63% female and 82% Caucasian, with a mean age of 47.6 years (SD = 17.1). One hundred forty-one (51%) patients had no DQB1*0602 alleles; 117 (42%) had one; and 21 (7%) had two. In the complete narcolepsy sample after adjustment for African American race, we observed a linear relationship between HLA-DQB1*0602 frequency and sleepiness as defined by the ESS (P < 0.01), narcolepsy severity as defined by UNS (P < 0.001), age of symptom onset (P < 0.05), and sleep latency (P < 0.001). In univariate analyses, HLA-DQB1*0602 frequency was also associated with napping (P < 0.05) and increased car and work accidents or near accidents (both P < 0.01). Habitual sleep duration was not associated with HLA status. These race-adjusted associations remained for the ESS (P < 0.05), UNS (P < 0.01), and sleep latency (P < 0.001) when restricting to narcolepsy with cataplexy.

CONCLUSIONS

Narcolepsy symptom severity varies in a linear manner according to HLA-DQB1*0602 allele status. These findings support the notion that HLA-DQ is a disease-modifying gene.

A case-control study of the environmental risk factors for narcolepsy

BACKGROUND

Despite the acknowledged importance of environmental risk factors in the etiology of narcolepsy, there is little research on this topic. This study sought to fill this gap in the literature and assess the risk of stressors and infectious diseases using a case-control study.

METHODS

Cases (n = 63) were recruited through the Stanford Center for Narcolepsy. All were HLA-DQB1*0602 positive, met conventional Multiple Sleep Latency Test criteria, and reported unambiguous cataplexy. Controls (n = 63) were nonrelated family members of cases and local community members. A self-administered questionnaire was used to assess the frequency and timing of possible risk factors.

RESULTS

Of the infectious diseases examined, only flu infections and unexplained fevers carried a significant risk. Several of the stressors carried a significant risk including a major change in sleeping habits. When the timing of all risk factors was considered, exposure prior to puberty increased the risk for developing narcolepsy.

CONCLUSIONS

These findings emphasize the importance of environmental risk factors in the etiology of narcolepsy. This highlights the need for further research on this aspect of narcolepsy so a complete understanding of a disorder that affects 1 in 2,000 individuals can emerge.

Diagnosis of narcolepsy and idiopathic hypersomnia. An update based on the International Classification of Sleep Disorders, 2nd edition

Defining the precise nosological limits of narcolepsy and idiopathic hypersomnia is an ongoing process dating back to the first description of the two conditions. The most recent step forward has been done within the preparation of the second edition of the "International classification of sleep disorders" published in June 2005. Appointed by Dr Emmanuel Mignot, the Task Force on "Hypersomnias of central origin, not due to a circadian rhythm sleep disorder, sleep related breathing disorder, or other causes of disturbed nocturnal sleep" thoroughly revisited the nosology of narcolepsy and of idiopathic hypersomnia. Narcolepsy is now distinguished into three different entities, narcolepsy with cataplexy, narcolepsy without cataplexy and narcolepsy due to medical condition, and idiopathic hypersomnia into two entities, idiopathic hypersomnia with long sleep time and idiopathic hypersomnia without long sleep time. Nevertheless there are still a number of pending issues. What are the limits of narcolepsy without cataplexy? Is there a continuum in the pathophysiology of narcolepsy with and without cataplexy? Should sporadic and familial forms of narcolepsy with cataplexy appear as subgroups in the classification? Are idiopathic hypersomnia with long sleep time and idiopathic hypersomnia without long sleep time, two forms of the same condition or two different conditions? Is there a pathophysiological relationship between narcolepsy without cataplexy and idiopathic hypersomnia without long sleep time?

Clinical and neurobiological aspects of narcolepsy

Narcolepsy is characterized by excessive daytime sleepiness (EDS), cataplexy and/or other dissociated manifestations of rapid eye movement (REM) sleep (hypnagogic hallucinations and sleep paralysis). Narcolepsy is currently treated with amphetamine-like central nervous system (CNS) stimulants (for EDS) and antidepressants (for cataplexy). Some other classes of compounds such as modafinil (a non-amphetamine wake-promoting compound for EDS) and gamma-hydroxybutyrate (GHB, a short-acting sedative for EDS/fragmented nighttime sleep and cataplexy) given at night are also employed. The major pathophysiology of human narcolepsy has been recently elucidated based on the discovery of narcolepsy genes in animals. Using forward (i.e., positional cloning in canine narcolepsy) and reverse (i.e., mouse gene knockout) genetics, the genes involved in the pathogenesis of narcolepsy (hypocretin/orexin ligand and its receptor) in animals have been identified. Hypocretins/orexins are novel hypothalamic neuropeptides also involved in various hypothalamic functions such as energy homeostasis and neuroendocrine functions. Mutations in hypocretin-related genes are rare in humans, but hypocretin-ligand deficiency is found in many narcolepsy-cataplexy cases. In this review, the clinical, pathophysiological and pharmacological aspects of narcolepsy are discussed.

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.

DQB1*0301 and DQB1*0601 Modulate Narcolepsy Susceptibility in Koreans

The association of narcolepsy with HLA-DQB1*0602 is established in Japanese, African-Americans, European, and North American Caucasians. We examined DRB1, DRB3, DRB4, DRB5, DQA1, and DQB1 in 163 patients with centrally mediated daytime sleepiness (100 with narcolepsy) and 211 Korean controls. In this population, the DQB1*0602 association was always evident in the context of the DRB1*1501-DQA1*0102-DQB1*0602 haplotype. The DQB1*0602 association was highest in cases with hypocretin deficiency (100% vs 13% in controls), most of which had narcolepsy-cataplexy (81%). A weaker DQB1*0602 (45%) association was present in cases without cataplexy. No human leukocyte antigen (HLA) association was present in idiopathic hypersomnia or in cases with normal cerebrospinal fluid (CSF) hypocretin-1. As in other populations, DQB1*0602 homozygosity increased risk in cases with cataplexy and/or hypocretin deficiency (odds ratio = 2.0 vs heterozygotes). Non-DQB1*0602 allelic effects were also observed but could not be interpreted in the context of DQB1*0602 overabundance and linkage disequilibrium. We therefore next analyzed compound heterozygote effects in 77 subjects with either hypocretin deficiency or cataplexy and one copy of DRB1*1501-DQA1*0102-DQB1*0602, a sample constructed to maximize etiologic homogeneity. In this analysis, we found additional predisposing effects of DQB1*0301 and protective effects for DQA1*0103-DQB1*0601. Unexpectedly, the predisposing effects of DQB1*0301 were present in the context of various DQA1-bearing haplotypes. A predisposing effect of DQA1*0303 was also suggested. These results indicate a remarkable consistency in the complex HLA association present in narcolepsy across multiple ethnic groups.

Association of HLA-DR and -DQ genes with narcolepsy in Koreans: comparison with two control groups, randomly selected subjects and DRB1*1501-DQB1*0602--positive subjects

The purpose of this study was to investigate the association of human leukocyte antigen (HLA) class II alleles with narcolepsy-cataplexy susceptibility in Koreans. The distribution of HLA-DRB1 and -DQB1 alleles and presence or absence of DRB3/4/5 alleles were examined in 60 narcoleptic patients with clear-cut cataplexy, and the results were compared with two groups of healthy controls: 200 randomly selected controls and 144 DRB1*1501-DQB1*0602 positive controls. All of the narcoleptic patients were DRB1*1501 and DQB1*0602 positive, and their frequencies were significantly higher in patients than in random controls (100% vs 17.0%, p(c) = 2.3 x 10(-30), OR = 583.96; 100% vs 16.5%, p(c) = 3.9 x 10(-31), OR = 605.00). The HLA association in Koreans was as tight as that reported in Japanese. Several DRB1 (*0101, *0405, *0901) and DQB1 alleles (*0303, *0401, *0501, *0601, *0604) were found to have weak protective effects against narcolepsy. DRB4 showed strong protective effect, and this was also significant when compared with DRB1*1501-DQB1*0602 positive controls (18.3% vs 44.4%, p(c) = 0.001, OR = 0.28). DRB3 (OR = 1.86) and DQB1*0301 (OR = 2.45) were found to have weak predisposing effect, when compared with DRB1*1501-DQB1*0602 positive controls. The protective effect of DRB4 has to be further studied in other populations.

Genetic analysis of the HLA region of Japanese patients with type 1 autoimmune hepatitis

BACKGROUND/AIMS

Genetic predisposition to type 1 autoimmune hepatitis (AIH) is linked mainly to HLA-class II genes. The aim of this study is to scan the HLA region for additional genes which may contribute to type 1 AIH susceptibility.

METHODS

We performed association analysis using HLA class I and II alleles and 18 polymorphic microsatellite markers distributed throughout the HLA region. We specifically assessed tumor necrosis factor (TNF)-alpha gene polymorphisms.

RESULTS

The frequencies of HLA-DRB1*0405, DRB4 and DQB1*0401 alleles were significantly higher in AIH patients. The association study revealed the presence of three segments in the HLA region showing significantly low P (Pc) values. The first segment was located around the HLA-DR/-DQ subregion, the second was around the HLA-B54 allele, and the third was around two microsatellites near the TNF gene cluster. However, stratification analysis for the effect of DRB1*0405 eliminated association of the latter two segments. Haplotype D of the TNF-alpha promoter gene polymorphisms was weakly associated with susceptibility, but was found to be not significant after stratification analysis.

CONCLUSIONS

The most influential gene on type 1 AIH pathogenesis in Japanese is the HLA-DRB1. Other genes in the HLA region, including TNF-alpha, have little or no association with type 1 AIH susceptibility.

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.

TNFA promoter polymorphisms and narcolepsy

Narcolepsy is a debilitating sleep disorder that affects up to 0.05% of individuals in Caucasian populations. It is highly associated with the HLA-DR2 group antigen or the HLA-DRB1*1501-DQB1*0602 haplotype, respectively. However, the HLA association by itself cannot sufficiently explain the increased risk to family members, as HLA-DR2 is quite common in the general population and most people harboring the respective genotype do not develop any symptoms of narcolepsy. Situated in the HLA class II region, the TNFA gene is translated into the pro-inflammatory cytokine TNF-alpha. TNFA promoter polymorphisms have been linked to several inflammatory and autoimmune diseases. We analyzed three SNP of the TNFA promoter and one adjacent microsatellite in 103 patients and 96 controls. The T-allele of the C-857T polymorphism was strongly associated with narcolepsy in the subgroup of DRB1*15/16 (HLA-DR2 type) negative patients, but not in DRB1*15/16 positive patients. These results point towards an etiological influence of TNFA alleles in narcolepsy and support previous findings suggesting genetic heterogeneity and differences in pathophysiological characteristics of HLA-DR2 positive and negative narcolepsy.

Sarcoidosis susceptibility and resistance HLA-DQB1 alleles in African Americans

Sarcoidosis, in the United States, more commonly and severely affects African Americans. HLA associations with sarcoidosis have been reported, but most studies used case-control designs, which may produce biased results because of population stratification. We examined transmission of HLA-DQB1 alleles in 225 African American families with at least one offspring with sarcoidosis. Of five low-resolution HLA-DQB1 alleles, *02 and *06 showed significant deviation in transmission patterns to affected offspring. High-resolution typing of these allelic subsets revealed that HLA-DQB1*0201 was transmitted to affected offspring half as often as expected (p = 0.001), whereas DQB1*0602 was transmitted to affected offspring about 20% more often than expected (p = 0.029). Examining interactions between *0201 and *0602 alleles and environmental exposures showed that *0602 varied little with respect to exposure, but sarcoidosis risk associated with *0201 often depended on exposure status. Alternatively, the *0602 allele in affected probands was associated with radiographic disease progression, but the *0201 allele showed no significant correlation with phenotype. Major differences in the amino acid sequences encoded by *0201 and *0602 alleles exist, which may explain the differential effects these alleles have on sarcoidosis susceptibility and progression in African Americans.

The major histocompatibility complex gene region and sarcoidosis susceptibility in African Americans

Investigators have intensively evaluated the major histocompatibility (MHC) complex for sarcoidosis susceptibility genes with the majority of reports implicating the human leukocyte antigen (HLA)-DRB1 gene. Because most studies have been performed in white and Asian populations, we sought to determine which MHC genes might be risk factors for sarcoidosis in African Americans. We genotyped six microsatellite markers spanning 11.6 megabases that overlapped the MHC region on chromosome 6p21-22 in 225 nuclear families ascertained by African American probands with a history of sarcoidosis. Using a family-based association methods approach, we performed multiallelic tests of association between each marker and sarcoidosis. A statistically significant association was detected between sarcoidosis and the DQCAR marker (p = 0.002) less than two kilobases telomeric from the HLA-DQB1 gene. Typing two additional markers in this region revealed that DQCAR-G51152 haplotypes, spanning a 38-kilobase region across the HLA-DQB1 gene, were associated with sarcoidosis on a global level (p = 0.022). Analysis of individual DQCAR and G51152 alleles showed that the DQCAR 178 (expected = 21.0; observed = 10; p = 0.0005) and G51152 217 (expected = 25.6; observed = 14; p = 0.0009) alleles were transmitted to affected offspring less often than expected; whereas the DQCAR 182 allele was transmitted more often than expected (expected = 52.6; observed = 66; p = 0.002). Our results indicate that HLA-DQB1 and not HLA-DRB1 plays an important role in sarcoidosis susceptibility in African Americans. Identification of the specific HLA-DQB1 alleles that influence sarcoidosis susceptibility in African Americans and the study of their antigenic-binding properties may reveal why African Americans suffer disproportionately from this disease.

Narcolepsy and the HLA region

Narcolepsy was first shown to be tightly associated with HLA-DR2 and DQ1 in 1983, suggesting a possible autoimmune mechanism. Early investigations failed to demonstrate this hypothesis, postulating that HLA-DR2 was only a linkage marker for another, unknown narcolepsy-causing gene. The autoimmune hypothesis is now being re-evaluated under the light of recent results. Like many other autoimmune disorders, narcolepsy usually starts during adolescence, is human leukocyte antigen (HLA)-associated, multigenic and environmentally influenced. Furthermore, HLA-association studies indicated a primary HLA-DQ effect with complex HLA class II allele interactions and a partial contribution of HLA to overall genetic susceptibility. Finally, recent result suggests that human narcolepsy is associated with the destruction of a small number of hypothalamic neurons containing the peptide hypocretins (orexins). This data is consistent with an immune destruction of hypocretin-containing cells as the most common etiology for human narcolepsy.

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

Narcolepsy is characterized by excessive daytime sleepiness and abnormal manifestations of rapid eye movement sleep such as cataplexy. The authors review the clinical features of narcolepsy, including epidemiology, symptoms, diagnosis, and treatment, in detail. Recent findings show that a loss of hypocretin-producing neurons lies at the root of the signs and symptoms of narcolepsy. The authors review the current state of knowledge on hypocretin anatomy, physiology, and function with special emphasis on the research regarding the hypocretin deficiency in narcolepsy, which may also explain associated features of the disorder, such as obesity. Lastly, they discuss some future perspectives for research into the pathophysiology of sleep/wake disorders, and the potential impact of the established hypocretin deficiency on the diagnosis and treatment of narcolepsy.

Complex HLA-DR and -DQ interactions confer risk of narcolepsy-cataplexy in three ethnic groups

Human narcolepsy-cataplexy, a sleep disorder associated with a centrally mediated hypocretin (orexin) deficiency, is tightly associated with HLA-DQB1*0602. Few studies have investigated the influence that additional HLA class II alleles have on susceptibility to this disease. In this work, 1,087 control subjects and 420 narcoleptic subjects with cataplexy, from three ethnic groups, were HLA typed, and the effects of HLA-DRB1, -DQA1, and -DQB1 were analyzed. As reported elsewhere, almost all narcoleptic subjects were positive for both HLA-DQA1*0102 and -DQB1*0602. A strong predisposing effect was observed in DQB1*0602 homozygotes, across all ethnic groups. Relative risks for narcolepsy were next calculated for heterozygous DQB1*0602/other HLA class II allelic combinations. Nine HLA class II alleles carried in trans with DQB1*0602 were found to influence disease predisposition. Significantly higher relative risks were observed for heterozygote combinations including DQB1*0301, DQA1*06, DRB1*04, DRB1*08, DRB1*11, and DRB1*12. Three alleles-DQB1*0601, DQB1*0501, and DQA1*01 (non-DQA1*0102)-were found to be protective. The genetic contribution of HLA-DQ to narcolepsy susceptibility was also estimated by use of lambda statistics. Results indicate that complex HLA-DR and -DQ interactions contribute to the genetic predisposition to human narcolepsy but that additional susceptibility loci are also most likely involved. Together with the recent hypocretin discoveries, these findings are consistent with an immunologically mediated destruction of hypocretin-containing cells in human narcolepsy-cataplexy.