Narcolepsy and H1N1 vaccination: a link?

Hits and misses with animal models of narcolepsy and the implications for drug discovery

INTRODUCTION

Narcolepsy is a chronic and rare neurological disorder characterized by disordered sleep. Based on animal models and further research in humans, the dysfunctional orexin system was identified as a contributing factor to the pathophysiology of narcolepsy. Animal models played a larger role in the discovery of some of the pharmacological agents with established benefit/risk profiles.

AREAS COVERED

In this review, the authors examine the phenotypes observed in animal models of narcolepsy and the characteristics of clinically used pharmacological agents in these animal models. Additionally, the authors compare the effects of clinically used pharmacological agents on the phenotypes in animal models with those observed in narcolepsy patients.

EXPERT OPINION

Research in canine and mouse models have linked narcolepsy to the O×R2mutation and orexin deficiency, leading to new diagnostic criteria and a drug development focus. Advancements in pharmacological therapies have significantly improved narcolepsy management, with insights from both clinical experience and from animal models having led to new treatments such as low sodium oxybate and solriamfetol. However, challenges persist in addressing symptoms beyond excessive daytime sleepiness and cataplexy, highlighting the need for further research, including the development of diurnal animal models to enhance understanding and treatment options for narcolepsy.

Characterization of the Increase in Narcolepsy following the 2009 H1N1 Pandemic in Sweden

(1) Background: In the context of the H1N1 pandemic and the Pandemrix vaccination campaign, an increased number of narcolepsy cases were noted in several countries. In Sweden, this phenomenon was attributed to the effect of the Pandemrix vaccination in the first place. Studies from China indicated that narcolepsy could occur as a consequence of the H1N1 infection itself. We performed an analysis of the increase, with a specific interest in age and sex distribution. We also aimed to validate the origin of the excess cases, post hoc. (2) Methods: Data for narcolepsy patients (ICD code G 47.4, both type 1 and type 2) distributed by sex and age at 5-year intervals, annually between 2005 and 2017, were retrieved from the National Patient Register. Information on the total population was collected from the Swedish Population Register. (3) Results: The number of narcolepsy cases increased markedly from 2009 to 2014 compared to the period before 2009. A particular increase in 2011 among children and teenagers was observed. The sex ratio did not change significantly during the study period. (4) Conclusions: Our results support an association between the increased prevalence of narcolepsy cases and Pandemrix vaccination, but the effect of the virus itself cannot be ruled out as a contributing factor.

Pediatric sleep: current knowledge, gaps, and opportunities for the future

This White Paper addresses the current gaps in knowledge, as well as opportunities for future studies in pediatric sleep. The Sleep Research Society's Pipeline Development Committee assembled a panel of experts tasked to provide information to those interested in learning more about the field of pediatric sleep, including trainees. We cover the scope of pediatric sleep, including epidemiological studies and the development of sleep and circadian rhythms in early childhood and adolescence. Additionally, we discuss current knowledge of insufficient sleep and circadian disruption, addressing the neuropsychological impact (affective functioning) and cardiometabolic consequences. A significant portion of this White Paper explores pediatric sleep disorders (including circadian rhythm disorders, insomnia, restless leg and periodic limb movement disorder, narcolepsy, and sleep apnea), as well as sleep and neurodevelopment disorders (e.g. autism and attention deficit hyperactivity disorder). Finally, we end with a discussion on sleep and public health policy. Although we have made strides in our knowledge of pediatric sleep, it is imperative that we address the gaps to the best of our knowledge and the pitfalls of our methodologies. For example, more work needs to be done to assess pediatric sleep using objective methodologies (i.e. actigraphy and polysomnography), to explore sleep disparities, to improve accessibility to evidence-based treatments, and to identify potential risks and protective markers of disorders in children. Expanding trainee exposure to pediatric sleep and elucidating future directions for study will significantly improve the future of the field.

Paediatric narcolepsy: a review of diagnosis and management

Narcolepsy is a chronic disabling neurological sleep disorder that requires lifelong treatment. We have outlined the clinical features of narcolepsy, the assessment and diagnosis process and have summarised the existing treatment options for children and adolescents with narcolepsy. In the future, the approach to management of paediatric narcolepsy should ideally be in a multidisciplinary setting, involving specialists in sleep medicine, sleep physiology, neurologists and psychologists/psychiatrists. A multidisciplinary approach will help to manage the potential impact of narcolepsy on children and adolescents who are in a stage of their life that is critical to their physical, emotional and social development and their academic attainment.

Should rare immunologic, neurologic, and other adverse events be indications to withhold vaccination?

Millions of illnesses, hospitalizations, and deaths are prevented by vaccination worldwide. This discussion examines vaccine safety concerns from the past several decades of immunization research. Both immunologic and non-immunologic side effects are reviewed, and clarification is provided regarding some highly-publicized myths regarding vaccine safety.

Clinical update on central hypersomnias

The central hypersomnias encompass a range of conditions causing persisting or intermittent excessive daytime sleepiness (EDS). These conditions therefore present not infrequently in general clinical sleep practice, and remain in the differential for patients presenting with sleepiness. Our understanding of the pathophysiology, diagnosis and management of these conditions has progressed significantly over recent years, and in this article we review this group of disorders, focussing in particular on recent changes in classification and diagnosis, pathophysiological advances, and novel treatment options.

Narcolepsy Following Yellow Fever Vaccination: A Case Report

Narcolepsy with cataplexy is a rare, but important differential diagnosis for daytime sleepiness and atonic paroxysms in an adolescent. A recent increase in incidence in the pediatric age group probably linked to the use of the Pandemrix influenza vaccine in 2009, has increased awareness that different environmental factors can “trigger” narcolepsy with cataplexy in a genetically susceptible population. Here, we describe the case of a 13-year-old boy with narcolepsy following yellow fever vaccination. He carries the HLA DQB1*0602 haplotype strongly associated with narcolepsy and cataplexy. Polysomnography showed rapid sleep onset with rapid eye movement (REM) latency of 47 min, significant sleep fragmentation and a mean sleep latency of 1.6 min with sleep onset REM in four out of four nap periods. Together with the clinical history, these findings are diagnostic of narcolepsy type 1. The envelope protein E of the yellow fever vaccine strain 17D has significant amino acid sequence overlap with both hypocretin and the hypocretin receptor 2 receptors in protein regions that are predicted to act as epitopes for antibody production. These findings raise the question whether the yellow fever vaccine strain may, through a potential molecular mimicry mechanism, be another infectious trigger for this neuro-immunological disorder.

Risk of Narcolepsy after AS03 Adjuvanted Pandemic A/H1N1 2009 Influenza Vaccine in Adults: A Case-Coverage Study in England

STUDY OBJECTIVES

An increased risk of narcolepsy has been observed in children following ASO3-adjuvanted pandemic A/H1N1 2009 (Pandemrix) vaccine. We investigated whether this risk extends to adults in England.

METHODS

Six adult sleep centers in England were visited between November 2012 and February 2014 and vaccination/clinical histories obtained from general practitioners. Suspected narcolepsy cases aged older than 17 y were selected. The risk of narcolepsy following Pandemrix was calculated using cases diagnosed by the time of the center visits and those with a diagnosis by November 30, 2011 after which there was increased awareness of the risk in children. The odds of vaccination in cases and in matched population data were compared using a case-coverage design.

RESULTS

Of 1,446 possible cases identified, most had onset before 2009 or were clearly not narcolepsy. Of the 60 remaining cases, 20 were excluded after expert review, leaving 40 cases with narcolepsy; 5 had received Pandemrix between 3 and 18 mo before onset. All the vaccinated cases had cataplexy, two received a diagnosis by November 2011 and two were aged 40 y or older. The odds ratio for vaccination in cases compared to the population was 4.24 (95% confidence interval 1.45-12.38) using all cases and 9.06 (1.90-43.17) using cases with a diagnosis by November 2011, giving an attributable risk of 0.59 cases per 100,000 doses.

CONCLUSIONS

We found a significantly increased risk of narcolepsy in adults following Pandemrix vaccination in England. The risk was lower than that seen in children using a similar study design.

No Evidence for Disease History as a Risk Factor for Narcolepsy after A(H1N1)pdm09 Vaccination

OBJECTIVES

To investigate disease history before A(H1N1)pdm09 vaccination as a risk factor for narcolepsy.

METHODS

Case-control study in Sweden. Cases included persons referred for a Multiple Sleep Latency Test between 2009 and 2010, identified through diagnostic sleep centres and confirmed through independent review of medical charts. Controls, selected from the total population register, were matched to cases on age, gender, MSLT-referral date and county of residence. Disease history (prescriptions and diagnoses) and vaccination history was collected through telephone interviews and population-based healthcare registers. Conditional logistic regression was used to investigate disease history before A(H1N1)pdm09 vaccination as a risk-factor for narcolepsy.

RESULTS

In total, 72 narcolepsy cases and 251 controls were included (range 3-69 years mean19-years). Risk of narcolepsy was increased in individuals with a disease history of nervous system disorders (OR range = 3.6-8.8) and mental and behavioural disorders (OR = 3.8, 95% CI 1.6-8.8) before referral. In a second analysis of vaccinated individuals only, nearly all initial associations were no longer statistically significant and effect sizes were smaller (OR range = 1.3-2.6). A significant effect for antibiotics (OR = 0.4, 95% CI 0.2-0.8) and a marginally significant effect for nervous system disorders was observed. In a third case-only analysis, comparing cases referred before vaccination to those referred after; prescriptions for nervous system disorders (OR = 26.0 95% CI 4.0-170.2) and ADHD (OR = 35.3 95% CI 3.4-369.9) were statistically significant during the vaccination period, suggesting initial associations were due to confounding by indication.

CONCLUSION

The findings of this study do not support disease history before A(H1N1)pdm09 vaccination as a risk factor for narcolepsy.

Narcolepsy patients have antibodies that stain distinct cell populations in rat brain and influence sleep patterns

Narcolepsy is a chronic sleep disorder, likely with an autoimmune component. During 2009 and 2010, a link between A(H1N1)pdm09 Pandemrix vaccination and onset of narcolepsy was suggested in Scandinavia. In this study, we searched for autoantibodies related to narcolepsy using a neuroanatomical array: rat brain sections were processed for immunohistochemistry/double labeling using patient sera/cerebrospinal fluid as primary antibodies. Sera from 89 narcoleptic patients, 52 patients with other sleep-related disorders (OSRDs), and 137 healthy controls were examined. Three distinct patterns of immunoreactivity were of particular interest: pattern A, hypothalamic melanin-concentrating hormone and proopiomelanocortin but not hypocretin/orexin neurons; pattern B, GABAergic cortical interneurons; and pattern C, mainly globus pallidus neurons. Altogether, 24 of 89 (27%) narcoleptics exhibited pattern A or B or C. None of the patterns were exclusive for narcolepsy but were also detected in the OSRD group at significantly lower numbers. Also, some healthy controls exhibited these patterns. The antigen of pattern A autoantibodies was identified as the common C-terminal epitope of neuropeptide glutamic acid-isoleucine/α-melanocyte-stimulating hormone (NEI/αMSH) peptides. Passive transfer experiments on rat showed significant effects of pattern A human IgGs on rapid eye movement and slow-wave sleep time parameters in the inactive phase and EEG θ-power in the active phase. We suggest that NEI/αMSH autoantibodies may interfere with the fine regulation of sleep, contributing to the complex pathogenesis of narcolepsy and OSRDs. Also, patterns B and C are potentially interesting, because recent data suggest a relevance of those brain regions/neuron populations in the regulation of sleep/arousal.

Narcolepsy: a clinical review

Despite the classic tetrad of clinical features that typify it, narcolepsy remains much under-diagnosed, in part, because of the wide spectrum of clinical phenotypes, but also because of its insidious onset, usually in a young person. The median time to diagnosis from first symptoms remains very long, around 10 years in the UK. Conversely, in the specialist setting, it is likely over-diagnosed, largely because of failure to exclude other causes of hypersomnia. There is an over-reliance on a biological marker of the condition, the multiple sleep latency test (MSLT), which, like many tests, has a significant false-positive and false-negative rate. This review aims to discuss some of the difficulties in achieving a diagnosis, interpretation of investigations, differential diagnosis, and appropriate management of patients with narcolepsy.

Developmental roles of brain histamine

Histamine appears early during brain development, has been shown to regulate fetal and adult brain-derived stem cells in a receptor type-dependent manner, and has widespread actions on systems involved in arousal and movement. Developmental studies in both rodents and zebrafish have elucidated the spatiotemporal patterning of the histaminergic system and, in zebrafish, have revealed the mechanisms whereby histamine regulates the number of hypocretin/orexin (hcrt) neurons, which in turn may regulate the number of histaminergic cells. Recent demonstrations of increased numbers of histaminergic neurons in patients with narcolepsy highlight the importance, for our understanding of both normal and pathological brain function, of understanding these interactions. Here, we review recent research into the developmental roles of histamine and suggest key areas for future research.

A/H1N1 antibodies and TRIB2 autoantibodies in narcolepsy patients diagnosed in conjunction with the Pandemrix vaccination campaign in Sweden 2009-2010

Narcolepsy is a lifelong sleep disorder related to hypocretin deficiency resulting from a specific loss of hypocretin-producing neurons in the lateral hypothalamic area. The disease is thought to be autoimmune due to a strong association with HLA-DQB1*06:02. In 2009 the World Health Organization (WHO) declared the H1N1 2009 flu pandemic (A/H1N1PDM09). In response to this, the Swedish vaccination campaign began in October of the same year, using the influenza vaccine Pandemrix(®). A few months later an excess of narcolepsy cases was observed. It is still unclear to what extent the vaccination campaign affected humoral autoimmunity associated with narcolepsy. We studied 47 patients with narcolepsy (6-69 years of age) and 80 healthy controls (3-61 years of age) selected after the Pandemrix vaccination campaign. The first aim was to determine antibodies against A/H1N1 and autoantibodies to Tribbles homolog 2 (TRIB2), a narcolepsy autoantigen candidate as well as to GAD65 and IA-2 as disease specificity controls. The second aim was to test if levels and frequencies of these antibodies and autoantibodies were associated with HLA-DQB1*06:02. In vitro transcribed and translated [(35)S]-methionine and -cysteine-labeled influenza A virus (A/California/04/2009/(H1N1)) segment 4 hemagglutinin was used to detect antibodies in a radiobinding assay. Autoantibodies to TRIB2, GAD65 and IA-2 were similarly detected in standard radiobinding assays. The narcolepsy patients had higher median levels of A/H1N1 antibodies than the controls (p = 0.006). A/H1N1 antibody levels were higher among the <13 years old (n = 12) compared to patients who were older than 30 years (n = 12, p = 0.014). Being HLA-DQB1*06:02 positive was associated with higher A/H1N1 antibody levels in both patients and controls (p = 0.026). Serum autoantibody levels to TRIB2 were low overall and high binders did not differ between patients and controls. We observed an association between levels of A/H1N1 antibodies and TRIB2 autoantibody levels particularly among the youngest narcolepsy patients (r = 0.819, p < 0.001). In conclusion, following the 2009 influenza pandemic vaccination, A/H1N1 antibody levels were associated with young age-at-onset narcolepsy patients positive for HLA-DQB1*06:02. The possibility that TRIB2 is an autoantigen in narcolepsy remains to be clarified. We could verify autoantibody responses against TRIB2 which needs to be determined in larger patient cohorts and control populations.