Possible association between HLA-B7 and narcolepsy

Sleep medicine, sleep research, and sleep education: a whole life devoted to sleep

This article describes my participation in sleep medicine, sleep research, and sleep education, mainly in Europe, between the years 1970 and 2000.

Population genetics and external proficiency testing for HLA disease associations

Numerous associations of HLA variants with susceptibility to diseases, namely, those with an immunopathological component, have been described to date. The strongest HLA associations were incorporated into the standard algorithms for the diagnostics. Disease-associated HLA variants are routinely detected by various techniques including DNA-based assays. For the identification of HLA markers or their combinations with the highest diagnostic value and those with frequent clinical indications (e.g., HLA-B*27, -B*57:01, -DQ2/-DQ8, -DQB1*06:02), diagnostic tests that focus on a single or limited number of specific HLA antigens/alleles, have already been developed; the use of complete typing for particular HLA loci is a relevant alternative. Importantly, external proficiency testing (EPT) became an integral part of good laboratory practice for HLA disease associations in accredited laboratories and not only supports correct "technical" identification of the associated HLA variants, but also adequate interpretation of the results to the clinicians. In the present article selected aspects of EPT for HLA disease associations related to population genetics are reviewed and discussed with the emphasis on the optimal level of HLA typing resolution, population-based differences in disease associated HLA alleles within the allelic group, distribution and linkage disequilibrium of HLA alleles in particular populations and interpretation of the presence of less common HLA variants/haplotypes. In conclusion, the laboratories that perform and interpret the tests to the clinicians, producers of the certified diagnostics and EPT providers should consider, among others, the genetic characteristics of the populations in order to optimise the diagnostic value of the tests for disease-associated HLA variants.

Vaccine-associated inflammatory diseases of the central nervous system: from signals to causation

PURPOSE OF REVIEW

As the most cost-effective intervention in preventive medicine and as a crucial element of any public health program, vaccination is used extensively with over 90% coverage in many countries. As approximately 5-8% of the population in developed countries suffer from an autoimmune disorder, people with an autoimmune disease are most likely to be exposed to some vaccines before or after the disease onset. In fact, a number of inflammatory disorders of the central nervous system have been associated with the administration of various vaccines. These adverse events, be they spurious associations or genuine reactions to the vaccine, may lead to difficulties in obtaining public trust in mass vaccination programs. There is, thus, an urgent need to understand whether vaccination triggers or enhances autoimmune responses.

RECENT FINDINGS

By reviewing vaccine-associated inflammatory diseases of the central nervous system, this study describes the current knowledge on whether the safety signal was coincidental, as in the case of multiple sclerosis with several vaccines, or truly reflected a causal link, as in narcolepsy with cataplexy following pandemic H1N1 influenza virus vaccination.

SUMMARY

The lessons learnt emphasize a central role of thorough, ideally prospective, epidemiological studies followed, if the signal is deemed plausible or real, by immunological investigations.

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.

Understanding hereditary diseases using the dog and human as companion model systems

Animal models are requisite for genetic dissection of, and improved treatment regimens for, human hereditary diseases. While several animals have been used in academic and industrial research, the primary model for dissection of hereditary diseases has been the many strains of the laboratory mouse. However, given its greater (than the mouse) genetic similarity to the human, high number of naturally occurring hereditary diseases, unique population structure, and the availability of the complete genome sequence, the purebred dog has emerged as a powerful model for study of diseases. The major advantage the dog provides is that it is afflicted with approximately 450 hereditary diseases, about half of which have remarkable clinical similarities to corresponding diseases of the human. In addition, humankind has a strong desire to cure diseases of the dog so these two facts make the dog an ideal clinical and genetic model. This review highlights several of these shared hereditary diseases. Specifically, the canine models discussed herein have played important roles in identification of causative genes and/or have been utilized in novel therapeutic approaches of interest to the dog and human.

Genes for normal sleep and sleep disorders

Sleep and wakefulness are complex behaviors that are influenced by many genetic and environmental factors, which are beginning to be discovered. The contribution of genetic components to sleep disorders is also increasingly recognized as important. Point mutations in the prion protein, period 2, and the prepro-hypocretin/orexin gene have been found as the cause of a few sleep disorders but the possibility that other gene defects may contribute to the pathophysiology of major sleep disorders is worth in-depth investigations. However, single gene disorders are rare and most common disorders are complex in terms of their genetic susceptibility, environmental effects, gene-gene, and gene-environment interactions. We review here the current progress in the genetics of normal and pathological sleep.

THEGENETICS OFNARCOLEPSY

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

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 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.

L-tyrosine in the treatment of narcolepsy

Narcolepsy is a disorder characterized by the sudden urge to sleep. The biochemical etiology of this disorder is believed to be due to dopamine abnormalities. Since the precursor of dopamine is L-tyrosine, the administration of this amino acid may prove beneficial in the treatment of narcolepsy. Preliminary research apparently supports this hypothesis.

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.

Narcolepsy-cataplexy in Israeli Jews is associated exclusively with the HLA DR2 haplotype. A study at the serological and genomic level

Narcolepsy is a very rare disease among Israeli Jews with a frequency of 7/3 X 10(6). An investigation of the association of narcolepsy with the human leukocyte antigen system was conducted in Israeli Jews at the serologic and genomic levels. The human leukocyte antigen class I and class II antigen typing of 7 clinically diagnosed narcoleptics, 3 individuals suffering from sleep disorders other than narcolepsy, and 11 healthy matched controls revealed that all narcoleptic patients (100%) investigated in the present study carried the HLA-DR2 haplotype, whereas patients with other sleep disorders did not. The HLA-B7 and DR2 occurred jointly in 57% (4/7) of the narcoleptic patients, as compared to 2% in randomly selected Israeli healthy controls. Restriction fragment length polymorphism analysis was performed with several restriction enzymes and three cDNA probes for DQ alpha, DQ beta, and DR beta genes on genomic DNAs obtained from narcoleptics and patients with other sleep disorders, matched controls, and 3 homozygous typing cells representing the DR2 subtypes Dw2, Dw12, and DwAZH. The restriction fragment length polymorphism analysis showed that all narcoleptics (7 of 7) shared virtually identical restriction fragment length polymorphisms with one of the homozygous typing cells (GSO), which defines DR2,Dw2. The frequency of the DR2,Dw2 haplotype in the healthy Israeli population is 3.2%. Other non-narcoleptic patients did not share these restriction fragment length polymorphisms. These findings indicate that narcolepsy is associated worldwide with the HLA-DR2,Dw2 haplotype.

The distribution of HLA-A,B, DR antigens in Chinese myasthenia gravis

The association of HLA antigens with Myasthenia Gravis (MG) in many different races is well known. In this study, HLA-A, B and DR antigens were typed on 65 Chinese MG and 232 controls for HLA-A, B and 61 for DR antigens. A2 and DRw9 increased significantly in patients with MG (p less than 0.025 and p less than 0.05 respectively). DR2 and DR4 had the opposite influence (both p less than 0.005). Several alleles were shown to have relatively high values of P D/A and relative risk but low P A/D and E.F, which suggests the marker heterogeneity of MG. Comparisons of clinically different types of MG, variations of the age of onset and thymic pathology did not show any statistically significant difference in HLA distributions. The clinical implications were discussed.

HLA and narcolepsy in a German population

In this paper the first MHC data including HLA-A, B, C, DR, DQ and complement BF, C4A, C4B determinants in German narcoleptics are presented together with the first family studies in European Caucasoids. 57 out of 58 unrelated patients (98.3%) were positive for DR2 and DQw1, respectively. In contrast to all other reports, one patient with typical signs of narcolepsy was found to be DR2/DQw1 negative. Data showing significant increase in the frequency of B7, and normal frequencies of B35 were discordant with data from Japanese patients. Definition of the extended DR2 linked haplotypes, deduced from 6 families, revealed that 5 out of 12 were DQw1, DR2, BFS, C4B1, C4A3, B7 (Cw7), while 11/12 had DR2, DQw1, BFS, C4A3, C4B1 in common. In one multiple case family two genotypically different DR2 haplotypes were identified in affected siblings. Results from the family study were concordant with a dominant mode of inheritance with incomplete penetrance of a hypothetical disease susceptibility gene.

Human histocompatibility leukocyte antigen (HLA) haplotype frequencies estimated from the data on HLA class I, II, and III antigens in 111 Japanese narcoleptics

In order to deduce the predominant haplotypes in Japanese narcoleptics, we have studied a total of 111 Japanese patients with narcolepsy and six multiple-case families for HLA class I and class II antigens, and for class III HLA-linked complement markers. In Japanese narcoleptics, the most frequent haplotypes were B35-DR2, B15-DR2, and B51-DR2. These haplotypes were rare in normal Japanese population. In contrast, the most frequent haplotype of HLA-DR2 in normal Japanese, A24-C blank-Bw52-C4A*2 B*Q0-BF *S-C2*C-DR2-DQw1, had a decreased frequency to one-third of the normal controls. Haplotypes B35-DR2, B15-DR2, and B51-DR2, which were more frequent among Japanese narcoleptics, were different from the haplotype found more frequently among Caucasoid narcoleptics, A3-Cw7-B7-DR2-DQw1. Haplotype analysis on six families showed that B35-DR2 and other rare haplotypes in normal Japanese were associated with narcolepsy. There were four cases without any signs of narcolepsy among 19 subjects with the disease susceptibility haplotypes. This finding suggests an incomplete penetrance of hypersomnia. Haplotype analysis of family members was also useful for the early detection of the high risk children to narcolepsy.

HLA antigens in Japanese patients with narcolepsy. All the patients were DR2 positive

A surprisingly high association between an HLA-DR locus antigen and narcolepsy was revealed in the Japanese. All 40 Japanese patients with narcolepsy (22 males and 18 females) were confirmed to be DR2 positive. However, the DR2 of the patients was found to associate negatively with Bw52, whereas Bw52-DR2 is the commonest haplotype in normal Japanese population. These data suggested that a "disease" allele predisposing to narcolepsy was inherited with relatively rare haplotypes with DR2 in the Japanese.