A new DRB1*1202 allele (DRB1*12022) found in association with DQA1*0102 and DQB1*0602 in two black narcoleptic subjects

[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.

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.

Neuronal degeneration in canine narcolepsy

Narcolepsy is a lifelong illness characterized by persistent sleepiness, hypnagogic hallucinations, and episodes of motor paralysis called cataplexy. We have tested the hypothesis that a transient neurodegenerative process is linked to symptom onset. Using the amino-cupric silver stain on brain sections from canine narcoleptics, we found elevated levels of axonal degeneration in the amygdala, basal forebrain (including the nucleus of the diagonal band, substantia innominata, and preoptic region), entopeduncular nucleus, and medial septal region. Reactive neuronal somata, an indicator of neuronal pathology, were found in the ventral amygdala. Axonal degeneration was maximal at 2-4 months of age. The number of reactive cells was maximal at 1 month of age. These degenerative changes precede or coincide with symptom onset. The forebrain degeneration that we have observed can explain the major symptoms of narcolepsy.

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.