HLA and narcolepsy in a German population

The impact of the HLA DQB1 gene and amino acids on the development of narcolepsy

INTRODUCTION

Narcolepsy is a chronic neurological and a genetic disorder of autoimmune origin, which is characterized by five main symptoms, including excessive day time sleepiness, sudden loss of muscle tone or cataplexy, sleep paralysis, hypnagogic hallucinations, and disturbed nocturnal sleep. While there are several diagnostic tests for Narcolepsy such as MSLT (mean sleep latency test), polysomnography and low range of hypocretin in cerebrospinal fluid (CSF), sensitivity and specificity in these methodologies are not sufficient enough. Therefore, methods with higher sensitivity for the accurate diagnosis and confirmation of the disease are necessary.

METHODS

According to the infrequent prevalence of narcolepsy disease, we scheduled a case-control association study with 20 narcoleptic patients and 150 healthy individuals in a high-resolution HLA typing procedure employing SSP-PCR.

RESULTS

Our study demonstrates that the DQB1*06:02 allele provides the highest susceptibility with absolute risk of 0.13%, for Narcolepsy (P = 1x10^-14, RR = 60.5, PcPPV = 0.13%), while, HLA-DQB1* 03:05 allele presents protection to Narcolepsy (P = 1x10^-4, PcPPV = 3.19x10^-4%). Furthermore, for the first time, the AA analysis displayed that AA serine¹⁸² and threonine¹⁸⁵ located on epitope of DQβ1 chain receptor (DQB1^{Ser182,Thr185}) present significant susceptibility for Narcolepsy (Pc= 87.03 × 10^-13, PcPPV = 0.024%) while, asparagine¹⁸² located on epitope of DQβ1 protein receptor (DQB1^Asn182) confers the highest protection against development of Narcolepsy (Pc= 2.16 × 10^-5, PcPPV = 0.0012%).

CONCLUSION

Thus, this can be proposed that the polymorphic differences in the epitope of the HLA receptor could contribute to their differential association with the Narcolepsy in Iranian population.

[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.

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.

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.

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.

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.

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.

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.

Benefits and risks of pharmacotherapy for narcolepsy

Narcolepsy is a life-long central nervous system (CNS) syndrome characterised by excessive sleepiness, cataplexy, sleep paralysis, hypnagogic hallucinations and disturbed night-time sleep. Unsuccessfully treated narcolepsy confers increased risks on patients and on society due to the patient's increased chance of becoming involved in vehicle crashes and workplace mishaps. The syndrome may be diagnosed by a clinical history positive for cataplexy and excessive daytime sleepiness and negative for other more common sleep disorders such as sleep apnoea and sleep deprivation. Night-time polysomnography and multiple sleep latency testing are helpful in differentiating narcolepsy from other sleep problems. Recent data from canine, murine, and human forms of narcolepsy indicate that genetically or developmentally mediated deficits in the hypocretin neurotransmitter system may cause some, but not all, forms of narcolepsy. Pharmacotherapy for narcolepsy is required to control symptoms and involves the use of CNS stimulants or modafinil to control sleepiness and antidepressant medications or sodium oxybate to control cataplexy. Modafinil and sodium oxybate have been developed and approved specifically for the indication of narcolepsy based on large, double-blind, placebo-controlled, parallel group efficacy and safety studies. The efficacy of drugs in the treatment of narcolepsy is variable from patient to patient and usually associated with adverse effects that can limit patient compliance and, therefore, symptom control. Nevertheless, the benefits of pharmacotherapy are judged to outweigh the risks to the patient. The favourable benefit-risk ratio of pharmacotherapy is greater if one considers the reduced risk to society of vehicle crashes and workplace mishaps that might be precipitated by attentional lapses or sleep attacks in the untreated or under-treated patient with narcolepsy.

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: genetic predisposition and neuropharmacological mechanisms. REVIEW ARTICLE

Narcolepsy is a disabling sleep disorder characterized by excessive daytime somnolence (EDS), cataplexy and REM sleep-related abnormalities. It is a frequently-occurring but under-diagnosed condition that affects 0.02 to 0.18% of the general population in various countries. Although most cases occur sporadically, familial clustering may be observed; the risk of a first-degree relative of a narcoleptic developing narcolepsy is 10-40 times higher than in the general population. The disorder is tightly associated with the specific human leukocyte antigen (HLA) allele, DQB1*0602 [most often in combination with HLA-DR2 (DRB1*15)]. Genetic transmission is, however, likely to be polygenic in most cases, and genetic factors other than HLA-DQ are also likely to be implicated. In addition, environmental factors are involved in disease predisposition; most monozygotic twins pairs reported in the literature are discordant for narcolepsy. Narcolepsy was reported to exist in canines in the early 1970s. Both sporadic and familial cases are also observed in this animal species. A highly-penetrant single autosomal recessive gene, canarc-1, is involved in the transmission of narcolepsy in Doberman pinschers and Labrador retrievers. Positional cloning of this gene is in progress, and a human homologue of this gene, or a gene with a functional relationship to canarc-1, might be involved in some human cases. Human narcolepsy is currently treated with central nervous system (CNS) stimulants for EDS and antidepressants for cataplexy and abnormal REM sleep. These treatments are purely symptomatic and induce numerous side effects. These compounds disturb nocturnal sleep in many patients, and tolerance may develop as a result of continuous treatment. The canine model is an invaluable resource for studying the pharmacological and physiological control of EDS and cataplexy. Experiments using canine narcolepsy have demonstrated that increased cholinergic and decreased monoaminergic transmission are likely to be at the basis of the pathophysiology of the disorder. Pharmacological studies have shown that blockade of norepinephrine uptake mediates the anticataplectic effect of currently prescribed antidepressants, while blockade of dopamine uptake and/or stimulation of dopamine release mediates the awake-promoting effect of CNS stimulants. Studies in canine narcolepsy also suggest that mechanisms and brain sites for triggering cataplexy are not identical to those regulating REM sleep. It may thus be possible to develop new pharmacological compounds that specifically target abnormal symptoms in narcolepsy, but do not disturb physiological sleep/wake cycles. (See also postscript remarks).

Significant association of a single nucleotide polymorphism in the tumor necrosis factor-alpha (TNF-alpha) gene promoter with human narcolepsy

Narcolepsy is a sleep disorder in which multiple factors, including environmental and genetic factors, are involved. A genetic factor strongly associated with the disorder has been found in the human leukocyte antigen (HLA) class II region: the haplotype, DRB1*1501-DQB1*0602, predisposes to narcolepsy. No susceptibility genes other than the HLA-haplotype have been found. In this paper, we performed an association study of the tumor necrosis factor-alpha (TNF-alpha) gene located in the HLA class III region with human narcolepsy, in which we examined the known single-nucleotide polymorphisms (SNPs) in the promoter region in 49 narcoleptic patients, who were all positive for DRBI*1501, and 111 healthy control individuals. The results indicated that the frequency of the genotype at position -857 (-857SNP) was significantly different between the patients and controls, and the allele frequencies of 857SNP revealed that the frequency of -857T was significantly increased in the patients as compared with that in the controls (P=0.0068). In addition, haplotypes presumed from HLA-DRB1, -857SNP and HLA-B loci suggested that -857T was mainly associated with DRB1 alleles other than DRB1*1501: the significant increase in frequency of -857T in the patients was not caused by allelic association with DRB1*1501. Therefore, it is conceivable that the TNF-alpha with 857T was associated with narcolepsy independently of the strong association of DRB1*1501 with the disorder. Altogether, the data presented here lead us to propose that TNF-alpha could be a new susceptibility gene in human narcolepsy.

Narcolepsy and idiopathic hypersomnolence

Narcolepsy is among the leading causes of excessive daytime sleepiness. Its classic form associates daytime sleepiness with cataplexy, sleep paralysis, hypnopompic hallucinations, and nocturnal disrupted sleep. This form is associated with HLA DQ betal-0602 in about 85% to 90% of affected subjects, independently of their ethnicity. But the definition of the variants of narcolepsy remains controversial, despite the fact that, in some cases, narcolepsy may be limited to daytime sleepiness. In its classic form, it is associated with two or more sleep onset rapid eye movement periods at the Multiple Sleep Latency Test. This test, performed after nocturnal polysomnography, can be helpful in diagnosing narcolepsy, in the absence of a convincing history of partial or complete attacks of cataplexy--a pathognomonic symptom. Investigation of narcoleptic Dobermans has indicated that a muscarinic cholinergic hypersensitivity exists in the brain of affected animals and abnormalities involve also the dopaminergic system. Despite its prevalence of 0.03% to 0.05%, it is still a neurologic entity often missed. Investigations of families of narcoleptics, including monozygotic twins, indicate that this syndrome is polygenic in nature with association of environmental factors. As the peak of onset of disabling symptoms occurs between 15 and 25 years of age, it is important to improve the treatment of this lifelong, disabling illness. Stimulants medications, independently of their mode of action, are prescribed to help daytime sleepiness, and tricyclic antidepressant drugs or serotonergic reuptake blockers are used on the other symptoms. But these medications have a limited efficacy. Short naps at regular intervals during the day are a strong therapeutic adjuvent.

HLA haplotypes, polysomnography, and pedigrees in a case series of patients with narcolepsy

An ongoing study of the genetics of narcolepsy ascertains families through a case series of narcoleptic probands using diagnostic criteria consisting of 1) clinical history of excessive somnolence, 2) a mean sleep latency on the multiple sleep latency test (MSLT) of less than 7.9 minutes, 3) the rapid eye movement (REM) sleep-related symptom of cataplexy, 4) nocturnal polysomnography ruling out sleep apnea syndrome, and 5) two or more transitions to REM sleep on the MSLT. All probands and first-degree relatives received clinical and laboratory evaluations as well as human leukocyte antigen (HLA) typing. Demographic characteristics of the 32 probands are as follows: 17 males and 15 females; mean age was 42.1 years (range 13-70 years). The polysomnographic data confirmed daytime sleepiness and increased tendency for REM sleep for the 32 probands. Nocturnal polysomnographic results are as follows: sleep latency, 3.2 minutes; total sleep time, 442 minutes. MSLT results are as follows: sleep latency, 3.1 minutes; REM latency, 6.9 minutes; number of REM periods, 3.2. HLA typing revealed the presence of the HLA haplotypes, DRB1*15 and DQB1*0602, in 21 narcoleptic probands, with two African-Americans having the DQB1*0602 but not the DRB1*15 allele. Among the 57 relatives of the 32 probands, 1/31 females and 7/26 males were found to be affected with narcolepsy (p < 0.02), which suggests a higher diagnostic rate in male relatives. The 21 probands who were positive for the DRB1*15 and DQB1*0602 haplotypes did not differ from the 10 probands who were negative for these alleles in terms of their nocturnal sleep parameters, MSLT findings, or clinical presentation. Three families with multiple individuals affected with narcolepsy are presented. Two families have more than one affected individual who does not have the high-risk HLA haplotype. In one of these families, the disease is segregating independently of any HLA haplotype. In the third family, there is cosegregation with HLA DRB1*15 and DQB1*0602. One family contains a pair of DNA-confirmed, monozygotic twins with narcolepsy who are discordant for cataplexy and have the HLA DR14(Dw9)/DQB1*0503 and DR4(Dw4)/DQB1*0302 haplotypes.

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

Narcolepsy is a sleep disorder that has been shown to be tightly associated with HLA DR15 (DR2). In this study, 58 non-DR15 patients with narcolepsy-cataplexy were typed at the HLA DRB1, DQA1 and DQB1 loci. Subjects included both sporadic cases and narcoleptic probands from multiplex families. Additional markers studied in the class II region were the promoters of the DQA1 and DQB1 genes, two CA repeat polymorphisms (DQCAR and DQCARII) located between the DQA1 and DQB1 genes, three CA repeat markers (G51152, T16CAR and G411624R) located between DQB1 and DQB3 and polymorphisms at the DQB2 locus. Twenty-one (36%) of these 58 non-DR15 narcoleptic patients were DQA1*0102 and DQB1*0602, a DQ1 subtype normally associated with DRB1*15 in DR2-positive narcoleptic subjects. Additional microsatellite and DQA1 promoter diversity was found in some of these non-DR15 but DQB1*0602-positive haplotypes but the known allele specific codons of DQA1*0102 and DQB1*0602 were maintained in all 21 cases. The 37 non-DQA1*0102/DQB1*0602 subjects did not share any particular HLA DR or DQ alleles. We conclude that HLA DQA1*0102 and DQB1*0602 are the most likely primary candidate susceptibility genes for narcolepsy in the HLA class II region.

Narcolepsy and immunity

Narcolepsy is a neurological disorder known to be associated with human leukocyte antigen (HLA)-DQB1*0602 in humans. In a canine model, the disorder is also genetically linked to a gene of high homology with the human mu-switch-like immunoglobulin (Ig) gene (current LOD score 13.6 at 0% recombination). Since association with HLA or other immune function polymorphic genes (T cell receptor of Ig, mainly) is a hallmark of most autoimmune diseases, it is proposed that autoimmunity may also play a role in the development of narcolepsy. Arguments for and against this hypothesis are reviewed. It is shown that both on the basis of the most recent molecular studies, and because of some of its clinical features, narcolepsy may be an autoimmune disorder. However, neither systemic nor central nervous system (CNS) evidence of any autoimmune abnormality have ever been found. To reconcile this discrepancy, it is suggested that the pathological immune process involved in narcolepsy could be difficult to detect because it is restricted to a very small region of the brain or targets a low abundance neuroeffector. Alternatively, it is possible that a more fundamental relationship is involved between sleep generation and immune regulation. The pathophysiology of narcolepsy may then involve new CNS-immune mechanisms that may shed new light on the sleep process itself.

A deletion in the second exon of an HLA-DRB1 allele found in a DR2-negative narcolepsy patient

In this report, we describe a new allele of the HLA-DRB 1 gene carrying a form of mutation that has not been observed before. It appeared in an HLA-DR2-negative narcolepsy patient who, besides HLA-DR4, revealed a serologic HLA-DR blank segregating with HLA-DQ1. Oligotyping showed that the new allele belongs to the HLA-DR8 group. Restriction analysis and DNA sequencing revealed the deletion of 12 bp as well as the substitution of 9 flanking base pairs between codons 36 and 43. The expression of the mutated gene was demonstrated by the presence of its messenger RNA and a few positive reactions with DR8 sera. Without interrupting the reading frame, the mutation leads to a gene product composed of a modified amino acid sequence. We anticipate that the mutation influences the conformation of the molecule with possible consequences concerning immune response.

HLA-DR2 negative narcolepsy in Australian Caucasians: clinical features, serology and sequence specific oligonucleotide typing

An almost invariable association with HLA-DR2 and DQw1 has previously been reported in Japanese and caucasian narcoleptics. We performed HLA typing in 18 Australian narcoleptics using serological techniques and sequence specific oligonucleotide probes. HLA-DQw1 was present in 15 patients and DR2 in 12; 3 patients with cataplectic narcolepsy were DR2-negative. The serological haplotype most strongly associated with narcolepsy was DRw15 (a subtype of DR2), DQw1. DRw15-positive patients were positive for the alleles DRB1*1501 and DQB1*0602 defined with oligonucleotide probes. We conclude that the association of narcolepsy with DR2 and DQw1 is not as strong as previously reported and the absence of DR2 or DQw1 does not preclude the diagnosis of classical narcolepsy, at least in caucasians. Secondly, DR2-positive narcoleptics possess characteristic serological subtypes and alleles defined with oligonucleotide probes that are also found in normals. Thirdly, the occurrence of DR2-negative cataplectic narcoleptics points to the existence of more than one narcolepsy susceptibility gene.

The neurobiology of narcolepsy

Narcolepsy is characterized by excessive sleepiness and abnormal manifestations of rapid eye movement (REM) sleep. Neurochemical studies of human and canine narcolepsy have demonstrated disturbed monoaminergic and cholinergic function and suggest that deficits of noradrenaline availability in specific brain regions may account for much of its disordered pathophysiology. Genetic susceptibility to narcolepsy is closely linked to a specific region of the major histocompatibility complex on chromosome 6 and an important direction for future research will be to unravel the relationship between this gene region and the neurochemical abnormalities of narcolepsy.

HLA class II-restricted binding of muramyl peptides to B lymphocytes of normal and narcoleptic subjects

The propensity for narcolepsy, a clinical sleep disorder of unknown etiology, is virtually totally included within the HLA-DR2,DQw1 (DRw15,DQw6) phenotype. The disorder is characterized by decreased sleep latency, early onset of rapid eye movement sleep, and a paucity of nocturnal slow-wave sleep. Muramyl peptides, naturally occurring bacterial cell wall peptidoglycans, potently enhance the duration and amplitude of slow-wave sleep in animals, bind to murine mononuclear cells, and exhibit a major histocompatibility complex-restricted immunoadjuvant effect in mice. We examined the binding of muramyl peptides to peripheral blood mononuclear leukocytes of HLA-typed normal (n = 13) and narcoleptic (n = 10) subjects. Muramyl peptides bound specifically and with high affinity to normal B- but not T-lymphocyte-enriched preparations. There was no significant specific binding to B-cell-enriched preparations from narcoleptic patients. Furthermore, B-lymphocyte-enriched preparations of normal individuals who had the HLA-DR2,DQw1 phenotype (n = 8) exhibited a lower level of specific binding than those of normals who did not have this phenotype (n = 5, p less than 0.001). These observations are an additional indication of the relevance of muramyl peptides to slow-wave sleep and provide a basis for a better understanding of the relation between narcolepsy and the MHC at the biochemical level.

The narcolepsy-associated DRw15,DQw6,Dw2 haplotype has no unique HLA-DQA or -DQB restriction fragments and does not extend to the HLA-DP subregion

Almost all patients with cataplectic narcolepsy are DR2-positive. It has been suggested that the non-DR2 allele/haplotype might not be neutral with respect to disease susceptibility. It has also been reported that Taq I DQA and Bam HI, Eco RI, Eco RV, and Pst I DQB restriction fragments might differentiate between narcoleptic and healthy DR2-positive individuals. In the present study, HLA class II gene polymorphisms were investigated by restriction fragment length polymorphism (RFLP) analysis in 47 Swedish patients with cataplectic narcolepsy, 100 random controls, and DR2-associated homozygous cell lines. All patients had Taq I DRB-DQA-DQB patterns corresponding to the DRw15,DQw6,Dw2 haplotype. The non-DR2 haplotype was found to be neutral. This genotyped group of patients allows firm rejection of a recessive mode of inheritance and supports a dominant or additive model. No DQA or DQB RFLPs were found that could differentiate between DR2-positive narcoleptics, DRw15,DQw6,Dw2-positive controls, or Dw2-homozygous cell lines. No significant Msp I HLA-DP association was found. No linkage disequilibrium was observed between the DRw15,DQw6,Dw2 haplotype and alleles of the DP subregion in patients or controls. Thus, the HLA-D region-associated narcolepsy susceptibility gene may be located telomeric to the HLA-DP subregion. No RFLPs have been observed that can locate the narcolepsy susceptibility gene closer to the DQ than to the DR subregion.

Familial patterns of narcolepsy

Familial patterns of narcolepsy were investigated in a clinic population of 334 unrelated narcoleptic patients. 40% of probands had at least 1 family member with an isolated daytime sleepiness complaint and 6% had a positive family history of narcolepsy. Multicase families were rare; only two families were found with 3 or more affected relatives. Family members often shared the same HLA-DR2 haplotype as the proband but did not have narcolepsy. However, the risk of disease for first-degree relatives was six to eighteen times greater than that for unrelated individuals. Although most patients were HLA-DR2+, 2 new HLA-DR2- individuals were found. The data predict that as many as 9% of unrelated North-American white patients with narcolepsy will be DR2-. Analysis of these and other data indicates that although strongly associated with disease, the HLA-DR2 haplotype is neither sufficient nor necessary for the development of narcolepsy.

Genetic factors in sleep disorders

Several sleep disorders have a genetic basis. These conditions include the narcoleptic syndrome, sleep walking, periodic movements in sleep, circadian delay syndromes and familial insomnia. These disorders illustrate different control mechanisms involved in sleep and wakefulness, including those determining the prevalence and timing of NREM and REM activity, somatomotor inhibition and excitation, autonomic discharge, and the circadian framework of sleep. The genetic defect in narcolepsy has been localised to the short arm of chromosome 6, but the chromosomal localisations of the genetic basis for the other disorders are not known. Also, with the possible exception of acetylcholine, no definite neurotransmitter involved in any aspect of sleep regulation has been positively identified and the biochemical defect in narcolepsy is not known.

Narcolepsy without unique MHC class II antigen association: studies in the canine model

Human narcolepsy is almost exclusively associated with the major histocompatibility complex (MHC) class II antigen HLA-DR2 and is the strongest HLA-disease association described to date. Canine narcolepsy resembles the human disease in its behavioral manifestations and responses to therapeutic drugs. Therefore, mixed leukocyte culture (MLC) was used to study differences in the canine MHC class II (DLA-D) antigens present in narcoleptic dogs to determine whether an analogous, unique DLA-D antigen could be identified in canine narcolepsy. Results show at least five different DLA-D antigens appear in potential narcoleptic haplotypes among the 29 dogs studied. The data demonstrate that, unlike man, in dogs there is no unique D locus antigen associated with narcolepsy and further suggest that linkage disequilibrium with a specific MHC antigen is unlikely to be essential for the manifestation of canine narcolepsy. Because human narcolepsy is thought to be multigenic, the canine narcolepsy-MHC dissociation suggests that the dog model may help elucidate the non-MHC narcolepsy gene(s).

Narcolepsy and HLA in the Japanese

Narcolepsy is characterized by excessive daytime sleepiness and cataplexy. It had been reported that 100% of Japanese and Caucasian narcoleptic patients are HLA-DR2 and HLA-DQw1 positive; last year, however, exceptionally rare cases of DR2-negative narcolepsy were reported. Conversely, we tested 190 Japanese narcoleptic patients, and all were still DR2 and DQw1 positive. Among several symptoms in narcoleptic patients, HLA-DR2 showed the strongest association with cataplexy. Exclusive association has been demonstrated between narcolepsy and a specific band of EcoRI-digested DQ beta fragments. In this paper Taq I-digested genomic DNAs were hybridized with a DQ alpha probe, and five specific bands were observed to associate strongly with particular HLA-DR or D specificities. Interestingly, the 6.0-kb band was found in 100% of 28 narcoleptic patients and in 54% of DR2-positive normal control subjects. For the time being, HLA-Dw2 is the better marker of the HLA-associating narcoleptic gene than is DR2, DQw1, 2.4-kb band of EcoRI-digested DQ beta, and 6.0-kb band of Taq I digested DQ alpha, because the frequency of DW2 is the lowest in normal control subjects.

No male segregation distortion of DR2 haplotypes in Japanese narcoleptic patients

Segregation of narcolepsy-associated DR2/DQw1 haplotypes was studied in 19 informative Japanese families. Each family consisted of a DR2-heterozygous patient, his or her spouse, and their children. In contrast to the previous study on Caucasian narcolepsy, no segregation distortion of the DR2/DQw1 haplotype was observed. The DR2/DQw1 haplotypes were inherited by 9 of 22 offspring from fathers (41%, p = 0.54) and by 10 of 14 offspring from mothers (71%, p = 0.16). These data show that there is no significant segregation distortion of the DR2/DQw1 haplotype in Japanese patients with narcolepsy.

Cellular approach for detecting narcolepsy-specific alterations in DR2 haplotypes

In an attempt to detect disease-associated genetic variations and/or exogenously induced alterations in DR2 haplotypes of narcolepsy patients, primed lymphocytes (PLs) were generated in nine families against DR2 haplotypes of narcolepsy patients and healthy family members. Twenty-four PL reagents were obtained and restimulated by cells of unrelated narcolepsy patients and DR2/Dw2-positive healthy individuals. The mean restimulation rates triggered by cells of patients or healthy controls, respectively, never differed significantly. In primary MLC as well as PLT combinations of patients and their HLA-identical siblings no significant stimulation was observed in both directions. We conclude that narcolepsy-specific alterations of class II molecules cannot be cellularly detected or do not exist on peripheral lymphocytes.

Taq I-generated HLA-DQ alpha polymorphism in Japanese patients with narcolepsy

Taq I-generated HLA-DQ alpha restriction fragment length polymorphism was examined in Japanese patients with narcolepsy. All patients were DR2 positive and shared a 6.0 kb fragment, although this fragment was found only in 54% of the healthy DR2-positive Japanese. This finding added the DQ alpha gene to the list of candidates for the possible narcolepsy-susceptibility gene. In contrast, there was no complete association between narcolepsy and DX alpha restriction fragment length polymorphism. These findings suggest that a narcolepsy-susceptibility gene is located closer to the DQ locus than to the DX locus.

Possible male segregation distortion of DR2 haplotypes in narcolepsy patients

Segregation of disease-associated DR2-linked haplotypes from patients with narcolepsy was studied in 18 German families. Of these, 13 were informative, as transmission could be traced from DR2 heterozygous patients to their healthy offspring. Although the composition of extended haplotypes was equal in males and females, DR2 was transmitted to 78.6% of the offspring by diseased fathers but only to 57.1% by diseased mothers. Compared to an expected 1:1 ratio according to Mendelian segregation this means a statistically significant deviation (p less than or equal to 0.03) for male but not for female patients. In contrast, transmission distortion was not observed with 30 DR2 haplotypes in 27 healthy families. These data represent a new example of male segregation distortion in an HLA-associated disorder.

Diagnostic criteria for narcolepsy and HLA-DR2 frequencies

HLA-DR2 frequencies were investigated in Japanese patients with narcolepsy as defined by various diagnostic criteria. The DR2 frequency was 100% when our criteria for narcolepsy were employed. The use of other criteria that lacked cataplexy as an obligatory symptom, however, reduced the DR2 frequency and led to an apparent "discovery" of DR2-negative cases with "narcolepsy". This observation indicates the necessity of precise diagnostic criteria in research on the HLA-narcolepsy association.