The role of cerebrospinal fluid hypocretin measurement in the diagnosis of narcolepsy and other hypersomnias

Elevated Tribbles homolog 2-specific antibody levels in narcolepsy patients

Narcolepsy is a sleep disorder characterized by excessive daytime sleepiness and attacks of muscle atonia triggered by strong emotions (cataplexy). Narcolepsy is caused by hypocretin (orexin) deficiency, paralleled by a dramatic loss in hypothalamic hypocretin-producing neurons. It is believed that narcolepsy is an autoimmune disorder, although definitive proof of this, such as the presence of autoantibodies, is still lacking. We engineered a transgenic mouse model to identify peptides enriched within hypocretin-producing neurons that could serve as potential autoimmune targets. Initial analysis indicated that the transcript encoding Tribbles homolog 2 (Trib2), previously identified as an autoantigen in autoimmune uveitis, was enriched in hypocretin neurons in these mice. ELISA analysis showed that sera from narcolepsy patients with cataplexy had higher Trib2-specific antibody titers compared with either normal controls or patients with idiopathic hypersomnia, multiple sclerosis, or other inflammatory neurological disorders. Trib2-specific antibody titers were highest early after narcolepsy onset, sharply decreased within 2-3 years, and then stabilized at levels substantially higher than that of controls for up to 30 years. High Trib2-specific antibody titers correlated with the severity of cataplexy. Serum of a patient showed specific immunoreactivity with over 86% of hypocretin neurons in the mouse hypothalamus. Thus, we have identified reactive autoantibodies in human narcolepsy, providing evidence that narcolepsy is an autoimmune disorder.

Cerebrospinal hypocretin, daytime sleepiness and sleep architecture in Parkinson's disease dementia

Excessive daytime sleepiness is common in Parkinson's disease and has been associated with Parkinson's disease-related dementia. Narcoleptic features have been observed in Parkinson's disease patients with excessive daytime sleepiness and hypocretin cell loss has been found in the hypothalamus of Parkinson's disease patients, in association with advanced disease. However, studies on cerebrospinal fluid levels of hypocretin-1 (orexin A) in Parkinson's disease have been inconclusive. Reports of sleep studies in Parkinson's disease patients with and without excessive daytime sleepiness have also been disparate, pointing towards a variety of causes underlying excessive daytime sleepiness. In this study, we aimed to measure cerebrospinal fluid hypocretin-1 levels in Parkinson's disease patients with and without dementia and to study their relationship to dementia and clinical excessive daytime sleepiness, as well as to describe potentially related sleep architecture changes. Twenty-one Parkinson's disease patients without dementia and 20 Parkinson's disease patients with dementia, along with 22 control subjects without sleep complaints, were included. Both Epworth sleepiness scale, obtained with the help of the caregivers, and mini-mental state examination were recorded. Lumbar cerebrospinal fluid hypocretin-1 levels were measured in all individuals using a radio-immunoassay technique. Additionally, eight Parkinson's disease patients without dementia and seven Parkinson's disease patients with dementia underwent video-polysomnogram and multiple sleep latencies test. Epworth sleepiness scale scores were higher in Parkinson's disease patients without dementia and Parkinson's disease patients with dementia than controls (P < 0.01) and scores >10 were more frequent in Parkinson's disease patients with dementia than in Parkinson's disease patients without dementia (P = 0.04). Cerebrospinal fluid hypocretin-1 levels were similar among groups (controls = 321.15 +/- 47.15 pg/ml; without dementia = 300.99 +/- 58.68 pg/ml; with dementia = 309.94 +/- 65.95 pg/ml; P = 0.67), and unrelated to either epworth sleepiness scale or mini-mental state examination. Dominant occipital frequency awake was slower in Parkinson's disease patients with dementia than Parkinson's disease patients without dementia (P = 0.05). Presence of slow dominant occipital frequency and/or loss of normal non-rapid eye movement sleep architecture was more frequent among Parkinson's disease patients with dementia (P = 0.029). Thus, excessive daytime sleepiness is more frequent in Parkinson's disease patients with dementia than Parkinson's disease patients without dementia, but lumbar cerebrospinal fluid hypocretin-1 levels are normal and unrelated to severity of sleepiness or the cognitive status. Lumbar cerebrospinal fluid does not accurately reflect the hypocretin cell loss known to occur in the hypothalamus of advanced Parkinson's disease. Alternatively, mechanisms other than hypocretin cells dysfunction may be responsible for excessive daytime sleepiness and the sleep architecture alterations seen in these patients.

Polymorphism located in TCRA locus confers susceptibility to essential hypersomnia with HLA-DRB1*1501-DQB1*0602 haplotype

Essential hypersomnia (EHS) exhibits excessive daytime sleepiness without cataplexy and is associated with the HLA-DRB1*1501-DQB1*0602 haplotype, similar to narcolepsy with cataplexy. Single-nucleotide polymorphism (SNP) rs1154155 located in the T-cell receptor alpha (TCRA) locus has been recently identified as a novel genetic marker of susceptibility for narcolepsy with cataplexy. We investigated whether the SNP was associated with EHS in the Japanese population. We found a significant association with EHS patients possessing the HLA-DRB1*1501-DQB1*0602 haplotype, compared with HLA-matched healthy individuals (P(allele)=0.008; P(positivity)=5 x 10(-4)), whereas no significant association was observed for EHS patients without this haplotype. Thus, TCRA is a plausible candidate for susceptibility to EHS patients positive for the HLA-DRB1*1501-DQB1*0602 haplotype.

Prevalence of the HLA-DQB1*0602 allele in narcolepsy and idiopathic hypersomnia patients seen at a sleep disorders outpatient unit in São Paulo

OBJECTIVE

Narcolepsy (with and without cataplexy) and idiopathic hypersomnia, are disorders with common features but with different HLA-DQB1*0602 allele prevalence. The present study describes the prevalence of HLA-DQB1*0602 allele in narcoleptics with and without cataplexy and in patients with idiopathic hypersomnia.

METHOD

Subjects comprised 68 patients who were diagnosed for narcolepsy or idiopathic hypersomnia and 23 healthy controls according to the International Classification of Sleep Disorders-2. Subjects comprised 43 patients with narcolepsy and cataplexy, 11 patients with narcolepsy but without cataplexy, 14 patients with idiopathic hypersomnia and 23 healthy controls. Genotyping of HLA-DQB1*0602 allele was performed for all subjects.

RESULTS

The prevalence of the HLA-DQB1*0602 allele was increased in idiopathic hypersomnia and in narcoleptic patients with and without cataplexy when compared to healthy subjects (p = 0.04; p = 0.03 and p < 0.0001, respectively).

CONCLUSIONS

This finding is in accordance with those of previous studies. The gold standard exam of narcolepsy with cataplexy is Hypocretin-1 dosage, but in patients without cataplexy and idiopathic hypersomnia, there are no specific diagnostic lab findings. The presence of the HLA-DQB1* 0602 allele may be important for the differential diagnosis of situations that resemble those sleep disorders such as secondary changes in sleep structure due to drugs' consumption.

Plasma adiponectin level and sleep structures in children with Prader-Willi syndrome

Adiponectin, an adipose tissue-derived hormone, has been negatively related to obstructive sleep apnea syndrome. Besides sleep apnea, children with Prader-Willi syndrome (PWS) may have excessive daytime sleepiness and rapid eye movement (REM) sleep abnormality. The aim of this study is to determine whether changes in sleep structures are related to plasma adiponectin levels in PWS. Correlations between adiponectin level and sleep variables were analyzed in 28 children with PWS and 18 controls. Overnight polysomnography was performed. The fasting plasma adiponectin levels were higher in the children with PWS than in the controls (P = 0.0006). In the PWS, Epworth sleepiness scale was significantly higher (P = 0.002); sleep latency (P = 0.003) and REM latency (P = 0.001) were significantly shortened; the apnea-hypopnea index (AHI) was significantly increased (P = 0.0001); and the duration of non-rapid eye movement (NREM) sleep stages 3 and 4 was decreased (P = 0.005). Multiple regression analysis revealed correlations between the adiponectin level and the total sleep time (beta = 0.688, P = 0.009), AHI (beta = 1.274, P = 0.010), REM latency (beta = -0.637, P = 0.021) and the percentage of NREM sleep (beta = -7.648, P = 0.002) in PWS. In children with PWS, higher plasma adiponectin levels were independently associated with several sleep variables, which was not observed in the control group. These results suggest a potential influence of elevated adiponectin level on the sleep structures in PWS.

[Narcolepsy with and without cataplexy: an uncommon disabling and unrecognized disease]

Although narcolepsy is a relatively uncommon condition, its impact on a child's life can be dramatic and disabling. Narcolepsy is characterized by excessive daytime sleepiness (EDS), with brief "sleep attacks" at very unusual times and usually associated with cataplexy (sudden loss of muscle control while awake, resulting in a fall, triggered by laughter). Other symptoms frequently reported are sleep paralysis (feeling of being unable to move or speak, even totally aware), hypnagogic hallucinations (vivid dreamlike experiences difficult to distinguish from reality) or disturbed night time sleep. Some children also experience depression or overweight-obesity. Although narcolepsy has been thoroughly studied, the exact cause is unknown. It appears to be a disorder of cerebral pathways that control sleep and wakefulness, involving dorsolateral hypothalamus and hypocretin. A genetic factor has been suggested, but narcolepsy in relatives is rare. Researchers have suggested that a set of genes combines with additional factors in a person's life to cause narcolepsy. The effective treatment of narcolepsy requires not only medication (usually stimulants, antidepressants and sodium oxybate), but also adjustments in life-style (scheduled naps). Management of this condition in children demands a comprehensive approach to the patient, that includes a correct diagnosis, pharmacological and non-pharmacological treatment and adjustments in the environment. These strategies can improve the child's self-esteem and ability to obtain a good education.

Neurochemical biomarkers in the differential diagnosis of movement disorders

In recent years, the neurochemical analysis of neuronal proteins in cerebrospinal fluid (CSF) has become increasingly accepted for the diagnosis of neurodegenerative dementia diseases such as Alzheimer's disease and Creutzfeldt-Jakob disease. CSF surrounds the central nervous system, and in the composition of CSF proteins one finds brain-specific proteins that are prioritized from blood-derived proteins. Levels of specific CSF proteins could be very promising biomarkers for central nervous system diseases. We need the development of more easily accessible biomarkers, in the blood. In neurodegenerative diseases with and without dementia, studies on CSF and blood proteins have investigated the usefulness of biomarkers in differential diagnosis. The clinical diagnoses of Parkinson's disease, dementia with Lewy bodies, multiple system atrophy, progressive supranuclear palsy, and corticobasal degeneration still rely mainly on clinical symptoms as defined by international classification criteria. In this article, we review CSF biomarkers in these movement disorders and discuss recent published reports on the neurochemical intra vitam diagnosis of neurodegenerative disorders (including recent CSF alpha-synuclein findings).

Modafinil and γ-hydroxybutyrate have sleep state-specific pharmacological actions on hypocretin-1 physiology in a primate model of human sleep

Hypocretin-1 is a hypothalamic neuropeptide that is important in the regulation of wake and the lack of which results in the sleep disorder narcolepsy. Using a monkey that has consolidated wake akin to humans, we examined pharmacological manipulation of sleep and wake and its effects on hypocretin physiology. Monkeys were given the sleep-inducing γ-hydroxybutyrate (GHB) and the wake-inducing modafinil both in the morning and in the evening. Cerebrospinal fluid hypocretin-1 concentrations changed significantly in response to the drugs only when accompanied by a behavioral change (GHB-induced sleep in the morning or modafinil-induced wake in the evening). We also found that there was a large (180-fold) interindividual variation in GHB pharmacokinetics that explains variability in sleep induction in response to the drug. Our data indicate that the neurochemical concomitants of sleep and wake are capable of changing the physiological output of hypocretin neurons. Sleep independent of circadian timing is capable of decreasing cerebrospinal fluid hypocretin-1 concentrations. Furthermore, hypocretin neurons do not seem to respond to an 'effort' to remain awake, but rather keep track of time spent awake as a wake-promoting counterbalance to extended wakefulness.

Narcolepsy and depression and the neurobiology of gammahydroxybutyrate

A voluminous literature describes the relationship between disturbed sleep and depression. The breakdown of sleep is one of the cardinal features of depression and often also heralds its onset. Frequent arousals, periods of wakefulness and a short sleep onset REM latency are typical polysomnographic features of depression. The short latency to REM sleep has been attributed to the combination of a monoaminergic deficiency and cholinergic supersensitivity and these irregularities have been proposed to form the biological basis of the disorder. A similar imbalance between monoaminergic and cholinergic neurotransmission has been found in narcolepsy, a condition in which frequent awakenings, periods of wakefulness and short sleep onset REM latencies are also characteristic findings during sleep. In many cases of narcolepsy, this imbalance appears to result from a deficiency of hypocretin but once established, whether in depression or narcolepsy, this disequilibrium sets the stage for the dissociation or premature appearance of REM sleep and for the dissociation of the motor inhibitory component of REM sleep or cataplexy. In the presence of this monoaminergic/cholinergic imbalance, gammahydroxybutyrate (GHB) may acutely further reduce the latency of REM sleep and induce cataplexy, in both patients with narcolepsy or depression. On the other hand, the repeated nocturnal application of GHB in patients with narcolepsy improves the continuity of sleep, prolongs the latency to REM sleep and prevents cataplexy. Evidence to date suggests that GHB may restore the normal balance between monoaminergic and cholinergic neurotransmission. As such, the repeated use of GHB at night and the stabilization of sleep over time makes GHB an effective treatment for narcolepsy and a potentially effective treatment for depression.

Feeding-elicited cataplexy in orexin knockout mice

Mice lacking orexin/hypocretin signaling have sudden episodes of atonia and paralysis during active wakefulness. These events strongly resemble cataplexy, episodes of sudden muscle weakness triggered by strong positive emotions in people with narcolepsy, but it remains unknown whether murine cataplexy is triggered by positive emotions. To determine whether positive emotions elicit murine cataplexy, we placed orexin knockout (KO) mice on a scheduled feeding protocol with regular or highly palatable food. Baseline sleep/wake behavior was recorded with ad libitum regular chow. Mice were then placed on a scheduled feeding protocol in which they received 60% of their normal amount of chow 3 h after dark onset for the next 10 days. Wild-type and KO mice rapidly entrained to scheduled feeding with regular chow, with more wake and locomotor activity prior to the feeding time. On day 10 of scheduled feeding, orexin KO mice had slightly more cataplexy during the food-anticipation period and more cataplexy in the second half of the dark period, when they may have been foraging for residual food. To test whether more palatable food increases cataplexy, mice were then switched to scheduled feeding with an isocaloric amount of Froot Loops, a food often used as a reward in behavioral studies. With this highly palatable food, orexin KO mice had much more cataplexy during the food-anticipation period and throughout the dark period. The increase in cataplexy with scheduled feeding, especially with highly palatable food, suggests that positive emotions may trigger cataplexy in mice, just as in people with narcolepsy. Establishing this connection helps validate orexin KO mice as an excellent model of human narcolepsy and provides an opportunity to better understand the mechanisms that trigger cataplexy.

Weak with sex: sexual intercourse as a trigger for cataplexy

INTRODUCTION

Sudden, often positive emotions are typical triggers for cataplexy in patients with narcolepsy-cataplexy (NC). Cataplexy during sexual intercourse and orgasm (orgasmolepsy) has been previously reported, but its frequency and characteristics are poorly known.

AIM

To assess frequency and features of loss of muscle tone during sexual intercourse in a series of patients with NC, other sleep-wake disorders, and healthy controls.

METHODS

Review of sleep questionnaires (including the Stanford Cataplexy Questionnaire) of 75 subjects (29 with NC, 26 with other sleep-wake disorders, and 20 healthy controls), followed by an interview with specific focus on muscle loss during sexual activity in suspicious cases.

MAIN OUTCOME MEASURES

Cataplexy during sexual intercourse and orgasm (orgasmolepsy).

RESULTS

Orgasmolepsy was reported by three NC patients (two female, one male), one male patient with behaviorally induced insufficient sleep syndrome (BIISS) and cataplexy-like symptoms, and none of the healthy controls. In the two female NC patients, orgasmolepsy occurred by each sexual intercourse, and the male patient reported orgasmolepsy only when in a relationship involving emotional commitment and trust. In the patient with BIISS and orgasmolepsy, cataplexy-like symptoms involved unilaterally upper or lower limbs in association with negative emotions or sports activities.

CONCLUSIONS

Cataplexy during sexual intercourse is a distinct feature of NC, which can, however, be reported rarely also by patients with other sleep-wake disorders. Insufficient arousal may favor the occurrence of cataplexy and cataplexy-like symptoms, including orgasmolepsy. Hypocretin deficiency and reward dysregulation in narcolepsy may further facilitate this phenomenon and contribute to its repetitive occurrence.

Specificity of direct transition from wake to REM sleep in orexin/ataxin-3 transgenic narcoleptic mice

To create operational criteria for polygraphic assessments of direct transitions from wake to REM sleep (DREM), as a murine analog of human cataplexy, we have analyzed DREM episodes in congenic lines of orexin/ataxin-3 transgenic [TG] mice and wild-type littermates. The sleep stage of each 10-second epoch was visually scored using our standard criteria. Specificity of DREM for narcoleptic TG mice and sensitivity to detect DREM was evaluated using different DREM criteria. We found that DREM transitions by 10-second epoch scoring are not specific for narcoleptic TG mice and also occur in WT mice during light period. These wake-to-REM transitions in WT mice (also seen in TG mice during light period) were characteristically different from DREM transitions in TG mice during dark period; they tended to occur as brief bouts of wakefulness interrupting extended episodes of REM sleep, suggesting that these transitions do not represent abnormal manifestations of REM sleep. We therefore defined the DREM transitions by requiring a minimum number of preceding wake epochs. Requiring no fewer than four consecutive epochs of wakefulness produced the best combination of specificity (95.9%) and sensitivity (66.0%). By definition, DREM in dark-period is 100% specific to narcolepsy and was 95.9% specific overall. In addition, we found that desipramine, a trycyclic anticataplectic, potently reduces DREM, while two wake-promoting compounds have moderate (D-amphetamine) and no (modafinil) effect on DREM; the effects mirror the anticataplectic effects of these compounds reported in canine and human narcolepsy. Our definition of DREM in murine narcolepsy may provide good electrophysiological measures for cataplexy-equivalent episodes.

Polymorphism located between CPT1B and CHKB, and HLA-DRB1*1501-DQB1*0602 haplotype confer susceptibility to CNS hypersomnias (essential hypersomnia)

Background

SNP rs5770917 located between CPT1B and CHKB, and HLA-DRB1*1501-DQB1*0602 haplotype were previously identified as susceptibility loci for narcolepsy with cataplexy. This study was conducted in order to investigate whether these genetic markers are associated with Japanese CNS hypersomnias (essential hypersomnia: EHS) other than narcolepsy with cataplexy.

Principal Findings

EHS was significantly associated with SNP rs5770917 (P_allele = 3.6×10⁻³; OR = 1.56; 95% c.i.: 1.12–2.15) and HLA-DRB1*1501-DQB1*0602 haplotype (P_positivity = 9.2×10⁻¹¹; OR = 3.97; 95% c.i.: 2.55–6.19). No interaction between the two markers (SNP rs5770917 and HLA-DRB1*1501-DQB1*0602 haplotype) was observed in EHS.

Conclusion

CPT1B, CHKB and HLA are candidates for susceptibility to CNS hypersomnias (EHS), as well as narcolepsy with cataplexy.

The involvement of hypothalamic sleep pathways in general anesthesia: testing the hypothesis using the GABAA receptor beta3N265M knock-in mouse

The GABA(A) receptor has been identified as the single most important target for the intravenous anesthetic propofol. How effects at this receptor are then translated into a loss of consciousness, however, remains a mystery. One possibility is that anesthetics act on natural sleep pathways. Here, we test this hypothesis by exploring the anesthetic sensitivities of GABAergic synaptic currents in three specific brain nuclei that are known to be involved in sleep. Using whole-cell electrophysiology, we have recorded GABAergic IPSCs from the tuberomammillary nucleus (TMN), the perifornical area (Pef), and the locus ceruleus (LC) in brain slices from both wild-type mice and mice that carry a specific mutation in the GABA(A) receptor beta(3) subunit (N265M), which greatly reduces their sensitivity to propofol, but not to the neurosteroid alphaxalone. We find that this in vivo pattern of anesthetic sensitivity is mirrored in the hypothalamic TMN and Pef nuclei, consistent with their role as direct anesthetic targets. In contrast, anesthetic sensitivity in the LC was unaffected by the beta(3)N265M mutation, ruling out this nucleus as a major target for propofol. In support of the hypothesis that orexinergic neurons in the Pef are involved in propofol anesthesia, we further show that these neurons are selectively inhibited by GABAergic drugs in vivo during anesthesia, and that a modulation in the activity of Pef neurons alone can affect loss of righting reflex. Overall, our results support the idea that GABAergic anesthetics such as propofol exert their effects, at least in part, by modulating hypothalamic sleep pathways.

Decreased CSF histamine in narcolepsy with and without low CSF hypocretin-1 in comparison to healthy controls

STUDY OBJECTIVE

To examine whether cerebrospinal fluid (CSF) histamine contents are altered in human narcolepsy and whether these alterations are specific to hypocretin deficiency, as defined by low CSF hypocretin-1.

METHODS

Patients meeting the ICSD-2 criteria for narcolepsy with and without cataplexy and who had CSF hypocretin-1 results available were selected from the Stanford Narcolepsy Database on the basis of CSF availability and adequate age and sex matching across 3 groups: narcolepsy with low CSF hypocretin-1 (n=34, 100% with cataplexy), narcolepsy without low CSF hypocretin-1 (n=24, 75% with cataplexy), and normal controls (n=23). Low CSF hypocretin-1 was defined as CSF < or =110 pg/mL (1/3 of mean control values). Six of 34 patients with low CSF hypocretin-1, six of 24 subjects with normal CSF hypocretin-1, and all controls were unmedicated at the time of CSF collection. CSF histamine was measured in all samples using a fluorometric HPLC system.

RESULTS

Mean CSF histamine levels were: 133.2 +/- 20.1 pg/mL in narcoleptic subjects with low CSF hypocretin-1, 233.3 +/- 46.5 pg/mL in patients with normal CSF hypocretin-1 (204.9 +/- 89.7 pg/mL if only patients without cataplexy are included), and 300.5 +/- 49.7 pg/mL in controls, reaching statistically significant differences between the 3 groups.

CONCLUSION

CSF histamine levels are reduced in human narcolepsy. The reduction of CSF histamine levels was more evident in the cases with low CSF hypocretin-1, and levels were intermediate in other narcolepsy cases. As histamine is a wake-promoting amine known to decrease during sleep, decreased histamine could either passively reflect or partially mediate daytime sleepiness in these pathologies.

CSF histamine contents in narcolepsy, idiopathic hypersomnia and obstructive sleep apnea syndrome

STUDY OBJECTIVE

To (1) replicate our prior result of low cerebrospinal fluid (CSF) histamine levels in human narcolepsy in a different sample population and to (2) evaluate if histamine contents are altered in other types of hypersomnia with and without hypocretin deficiency.

DESIGN

Cross sectional studies.

SETTING AND PATIENTS

Sixty-seven narcolepsy subjects, 26 idiopathic hypersomnia (IHS) subjects, 16 obstructive sleep apnea syndrome (OSAS) subjects, and 73 neurological controls were included. All patients were Japanese. Diagnoses were made according to ICSD-2.

RESULTS

We found significant reductions in CSF histamine levels in hypocretin deficient narcolepsy with cataplexy (mean +/- SEM; 176.0 +/- 25.8 pg/mL), hypocretin non-deficient narcolepsy with cataplexy (97.8 +/- 38.4 pg/mL), hypocretin non-deficient narcolepsy without cataplexy (113.6 +/- 16.4 pg/mL), and idiopathic hypersomnia (161.0 +/- 29.3 pg/ mL); the levels in OSAS (259.3 +/- 46.6 pg/mL) did not statistically differ from those in the controls (333.8 +/- 22.0 pg/mL). Low CSF histamine levels were mostly observed in non-medicated patients; significant reductions in histamine levels were evident in non-medicated patients with hypocretin deficient narcolepsy with cataplexy (112.1 +/- 16.3 pg/ mL) and idiopathic hypersomnia (143.3 +/- 28.8 pg/mL), while the levels in the medicated patients were in the normal range.

CONCLUSION

The study confirmed reduced CSF histamine levels in hypocretin-deficient narcolepsy with cataplexy. Similar degrees of reduction were also observed in hypocretin non-deficient narcolepsy and in idiopathic hypersomnia, while those in OSAS (non central nervous system hypersomnia) were not altered. The decrease in histamine in these subjects were more specifically observed in non-medicated subjects, suggesting CSF histamine is a biomarker reflecting the degree of hypersomnia of central origin.

Neurochemical approaches in the laboratory diagnosis of Parkinson and Parkinson dementia syndromes: a review

The diagnosis of Parkinson disease (PD) is rendered on the basis of clinical parameters, whereby laboratory chemical tests or morphological imaging is only called upon to exclude other neurodegenerative diseases. The differentiation between PD and other diseases of the basal ganglia, especially the postsynaptic Parkinson syndromes multisystem atrophy (MSA) and progressive supranuclear palsy (PSP), is of decisive importance, on the one hand, for the response to an appropriate therapy, and on the other hand, for the respective prognosis of the disease. However, particularly at the onset of symptoms, it is difficult to precisely distinguish these diseases from each other, presenting with an akinetic‐rigid syndrome. It is not yet possible to conduct a neurochemical differentiation of Parkinson syndromes. Therefore, a reliable biomarker is still to be found that might predict the development of Parkinson dementia. Since this situation is currently the subject of various different studies, the following synopsis is intended to provide a brief summary of the investigations addressing the field of the early neurochemical differential diagnosis of Parkinson syndromes and the early diagnosis of Parkinson dementia, from direct α‐synuclein detection to proteomic approaches. In addition, an overview of the tested biomarkers will be given with regard to their possible introduction as a screening method.

IGFBP3 colocalizes with and regulates hypocretin (orexin)

Background

The sleep disorder narcolepsy is caused by a vast reduction in neurons producing the hypocretin (orexin) neuropeptides. Based on the tight association with HLA, narcolepsy is believed to result from an autoimmune attack, but the cause of hypocretin cell loss is still unknown. We performed gene expression profiling in the hypothalamus to identify novel genes dysregulated in narcolepsy, as these may be the target of autoimmune attack or modulate hypocretin gene expression.

Methodology/Principal Findings

We used microarrays to compare the transcriptome in the posterior hypothalamus of (1) narcoleptic versus control postmortem human brains and (2) transgenic mice lacking hypocretin neurons versus wild type mice. Hypocretin was the most downregulated gene in human narcolepsy brains. Among many additional candidates, only one, insulin-like growth factor binding protein 3 (IGFBP3), was downregulated in both human and mouse models and co-expressed in hypocretin neurons. Functional analysis indicated decreased hypocretin messenger RNA and peptide content, and increased sleep in transgenic mice overexpressing human IGFBP3, an effect possibly mediated through decreased hypocretin promotor activity in the presence of excessive IGFBP3. Although we found no IGFBP3 autoantibodies nor a genetic association with IGFBP3 polymorphisms in human narcolepsy, we found that an IGFBP3 polymorphism known to increase serum IGFBP3 levels was associated with lower CSF hypocretin-1 in normal individuals.

Conclusions/Significance

Comparison of the transcriptome in narcolepsy and narcolepsy model mouse brains revealed a novel dysregulated gene which colocalized in hypocretin cells. Functional analysis indicated that the identified IGFBP3 is a new regulator of hypocretin cell physiology that may be involved not only in the pathophysiology of narcolepsy, but also in the regulation of sleep in normal individuals, most notably during adolescence. Further studies are required to address the hypothesis that excessive IGFBP3 expression may initiate hypocretin cell death and cause narcolepsy.

Pediatric narcolepsy

Narcolepsy is a disabling disease with a prevalence of 0.05%. It is characterized by excessive daytime sleepiness, cataplexy, sleep paralysis, hypnogogic hallucinations, automatic behavior, and disrupted nocturnal sleep. The presentation can be very variable, making diagnosis difficult. Loss of hypocretin containing neurons in the lateral hypothalamus has been noted in autopsy studies, and the cerebrospinal fluid level of hypocretin is reduced in patients with narcolepsy with cataplexy. New treatment options are available for the many symptoms of this disease. Early recognition and treatment can greatly improve the quality of life of patients with narcolepsy. A detail review of the epidemiology, pathophysiology, and management of narcolepsy in children is presented.

Olfactory dysfunction in patients with narcolepsy with cataplexy is restored by intranasal Orexin A (Hypocretin-1)

Until recently, olfactory dysfunction was an unknown feature of narcolepsy. Orexin A, also called hypocretin-1, is abnormally decreased or undetectable in the cerebrospinal fluid of narcoleptic patients with cataplexies. As hypothalamic orexin-containing neurons project throughout the entire olfactory pathway, from the olfactory mucosa to the olfactory cortex, disturbed orexinergic transmission may crucially be involved in impaired olfactory performance of narcolepsy patients. In our study we analysed the olfactory performance (threshold, discrimination, identification and sum score of these measurements, the TDI score) of narcoleptic patients with cataplexies (n = 10) and of age-, gender-, BMI- and smoker/non-smoker-matched healthy controls (n = 10). We then in a double-blind, randomized, placebo-controlled cross-over design applied orexin A intranasally to seven of the patients and measured 2-phenyl-ethyl alcohol (PEA) single-staircase odour detection thresholds. Compared to the controls, patients showed significantly lower scores for olfactory threshold (patients: median 8.0, range 4.0-10.5; controls: median 9.4, range 7.5-13.3; P < 0.05), discrimination (patients: median 12.5, range 10-15; controls: median 15.0, range 12-16; P < 0.005), identification (patients: median 13.0, range 10-16; controls: median 14.0, range 13-16; P < 0.05) and TDI score (patients: median 33.4, range 30-36; controls: median 38.4, range 35-43; P < 0.0001). In all patients, the PEA olfactory threshold score increased after administration of orexin A (median 11.5, range 6.5-13.25) compared to placebo (median 7.75, range 6.25-11.25; P < 0.05). Our results support the hypothesis that mild olfactory dysfunction is an intrinsic symptom of narcolepsy with cataplexies. The observation that intranasal orexin A restores olfactory function is in favour of this hypothesis. Furthermore, our data support that the pathophysiological mechanism underlying olfactory dysfunction in narcolepsy is the lack of CNS orexin.

Elevated peripheral visfatin levels in narcoleptic patients

OBJECTIVE

Narcolepsy is a severe sleep disorder that is characterized by excessive daytime sleepiness, cataplexies and a tendency towards obesity. Recent discoveries indicate that the major pathophysiology is a loss of hypocretin (orexin) producing neurons due to immunologically mediated degeneration. Visfatin is a recently described proinflammatory adipokine. It is identical to the immune modulating pre-B-cell colony enhancing factor (PBEF). Our study examines the hypothesis that visfatin levels are altered in narcoleptic patients.

METHODS

For the analysis, a total of n = 54 patients (n = 18 males and n = 36 females) with the diagnosis of narcolepsy according to DSM-IV and the International Classification of Sleep Disorders were examined (BMI mean 30.3+/-5.5, age mean 52.5+/-16.1 years). As a control group 39 unrelated (n = 12 males and n = 27 females) healthy volunteers with no sleep disorder according to DSM-IV were included (BMI mean 28.5+/-4.6, age mean 51.1+/-13.6 years). Peripheral visfatin levels were measured using a commercial enzyme immunoassay kit with a measurement range from 0.1-1000 ng/ml. Narcolepsy symptoms, severity and frequency of symptoms as well as the total duration of various aspects of the symptomatology were assessed by unstructured and structured clinical interviews in including the Stanford Center for Narcolepsy Sleep Inventory.

RESULTS

Circulating visfatin was found to be significantly increased in HLA DR2 positive narcoleptic patients compared to controls.

CONCLUSION

Taken together, our results add to the evidence of disturbed immunological regulation in patients with narcolepsy.

Association of narcolepsy-cataplexy with HLA-DRB1 and DQB1 in Mexican patients: a relationship between HLA and gender is suggested

Background

Narcolepsy-cataplexy is characterized by excessive daytime sleepiness with recurrent episodes of irresistible sleep, cataplexy, hallucinations and sleep paralysis. Its aetiology is unknown, but it is positively associated with the human leukocyte antigens (HLA) in all studied populations. The purpose of the present study was to investigate the association of HLA class II DRB1/DQB1 alleles with narcolepsy-cataplexy in Mexican Mestizo patients.

Methods

This is a case-control study of consecutive patients and ethnically matched controls. We included 32 patients diagnosed with typical narcolepsy-cataplexy, of the National Institute of Neurology, of the Institute of Psychiatry and at the Center of Narcolepsy at Stanford University. As healthy controls, 203 Mexican Mestizos were included. DRB1 alleles were identified using sequence based typing. A PCR-SSOP reverse dot blot was used for DQB1 typing. Allele frequency was calculated by direct counting and the significance of the differences was assessed using the Yates Chi square. Odds ratio and confidence intervals were evaluated.

Results

HLA-DRB1*1501 (OR = 8.2; pc < 0.0001) and DQB1*0602 (OR = 8.4; pc < 0.0001) were found positively associated with narcolepsy. When deleting DQB1*0602+ patients from the analysis, DQB1*0301 was also found increased (OR = 2.7; p = 0.035; pc = NS). DQB1*0602/DQB1*0301 genotype was present in 15.6% of the cases (OR = 11.5; p = 0.00035), conferring a high risk. DRB1*0407 (OR = 0.2; p = 0.016 pc = NS) and DQB1*0302(OR = 0.4; p = 0.017, pc = NS) were found decreased in the patients. The gender stratification analysis showed a higher risk in females carrying DRB1*1501 (OR = 15.8, pc < 0.0001) and DQB1*0602 (OR = 19.8, pc < 0.0001) than in males (OR = 5.0 for both alleles; p = 0.012, pc = NS for DRB1 & p = 0.0012, pc = 0.017 for DQB1). The susceptibility alleles found in Mexicans with narcolepsy are also present in Japanese and Caucasians; DRB1*04 linked protection has also been shown in Koreans. A stronger HLA association is suggested in females, in accordance with the sexual dimorphism claimed previously.

Conclusion

This knowledge may contribute to a better understanding of the disease pathogenesis in different populations. The evaluation of the risk to develop narcolepsy-cataplexy in carriers of the described alleles/genotypes may also be possible. A larger sample should be analysed in Mexican and in other Hispanic patients to confirm these results.

Management of narcolepsy

BACKGROUND

Narcolepsy is a rare chronic sleep disorder classically characterized by excessive daytime sleepiness. Other symptoms of the disease, including cataplexy, sleep paralysis, hypnagogic hallucinations and disturbed nocturnal sleep, may follow later. The disease can be incapacitating and frequently results in impaired psychosocial interaction. In the absence of a cure for narcolepsy, medical therapy is directed at symptom control.

OBJECTIVES

The aim of this study was to review the current approach to the treatment of narcolepsy.

METHODS

A search of three bibliographic databases (MEDLINE/PubMed, EMBASE and the Cochrane Library Database) was conducted from 1966 to January 2008 using the National Library of Medicine MeSH search terms narcolepsy and cataplexy. Relevant studies, case reports, review articles, editorials, short communications and chapters from selected textbooks were then extracted and manually cross-referenced.

RESULTS/CONCLUSIONS

Traditionally, stimulants have been used to improve the symptoms of excessive daytime sleepiness. However, the treatment of narcolepsy has evolved recently with the widespread use of newer drugs, including modafinil for daytime sleepiness, newer antidepressants for cataplexy and gamma-hydroxybutyrate (sodium oxybate) for both excessive daytime sleepiness and cataplexy.

Hypothalamic regulation of sleep and arousal

Normal waking is associated with neuronal activity in several chemically defined ascending arousal systems. These include monoaminergic neurons in the brainstem and posterior hypothalamus, cholinergic neurons in the brainstem and basal forebrain, and hypocretin (orexin) neurons in the lateral hypothalamus. Collectively, these systems impart tonic activation to their neuronal targets in the diencephalon and neocortex that is reflected in the low-voltage fast-frequency electroencephalogram patterns of wakefulness. Neuronal discharge in these arousal systems declines rapidly at sleep onset. Transitions from waking to sleep, therefore, involve coordinated inhibition of multiple arousal systems. An important source of sleep-related inhibition of arousal arises from neurons located in the preoptic hypothalamus. These preoptic neurons are strongly activated during sleep, exhibiting sleep/waking state-dependent discharge patterns that are the reciprocal of that observed in the arousal systems. The majority of preoptic sleep regulatory neurons synthesize the inhibitory neurotransmitter GABA. Anatomical and functional evidence supports the hypothesis that GABAergic neurons in the median preoptic nucleus (MnPN) and ventrolateral preoptic area (VLPO) exert inhibitory control over the monoaminergic systems and the hypocretin system during sleep. Recent findings indicate that MnPN and VLPO neurons integrate homeostatic aspects of sleep regulation and are important targets for endogenous sleep factors, such as adenosine and growth hormone releasing hormone.

Normal levels of cerebrospinal fluid hypocretin-1 and daytime sleepiness during attacks of relapsing-remitting multiple sclerosis and monosymptomatic optic neuritis

There is emerging evidence that multiple sclerosis (MS), the hypothalamic sleep-wake regulating neuropeptide hypocretin-1 (hcrt-1) and the sleep disorder narcolepsy may be connected. Thus, the major pathophysiological component of narcolepsy is lack of hcrt-1. Dysfunction of the hypocretin system has been reported in MS case reports with attacks of hypothalamic lesions, undetectable cerebrospinal fluid (CSF) hcrt-1 and hypersomnia, but not found during remission in small samples. Finally, daytime sleepiness, the major symptom of narcolepsy, is reported in several MS populations, and there are case reports of co-existent narcolepsy and MS. However, it is unknown whether hcrt-1 and daytime sleepiness generally change during MS attacks. We therefore analyzed whether daytime sleepiness (using the Epworth Sleepiness Scale (ESS)) and CSF hcrt-1 levels differed between MS attack and remission, in 48 consecutively referred patients with relapsing–remitting MS (RRMS) or monosymptomatic optic neuritis (MON). Twenty-seven patients were in attack and 21 in remission. ESS was normal both during attacks (5.4 ± 3.0) and remission (5.8 ± 2.6), and mean CSF hcrt-1 was normal (456 ± 41 pg/ml). No statistically significant differences were found between attack and remission. MRI scans revealed no hypothalamic lesions. The results show that the hypocretin system is intact and sleepiness is not typical in RRMS and MON without hypothalamic lesions on MRI.

Pediatric sleep pharmacology

This article reviews the most common pharmacologic options in the treatment of sleep disorders in children. Despite the high prevalence of sleep disorders in children, there is a paucity of education and information available on the pharmacologic management of sleep disorders in children. The principles of sleep physiology and pathophysiology that help provide more rational pharmacologic management are discussed. Medications are typically not Food and Drug Administration (FDA) approved for the pediatric age range or for the specific sleep disorder. Medications have a role for insomnia, narcolepsy, parasomnias, and sleep-related movement disorders. The available choices of hypnotics are reviewed. Medications to increase alertness of narcoleptics and decrease cataplexy are discussed. The use of dopaminergic agents for Restless Legs Syndrome is reviewed. The potential use of medication in sleep apnea is also reviewed. Pharmacologic guidelines need to be developed specifically for sleep disorders in children. Ideally, these guidelines should be FDA approved for the specific sleep disorder and for the pediatric age range. The development of easy to swallow, chewable or liquid forms of these medications are needed. Training programs should play the lead role in enhancing pediatricians' knowledge of the pharmacologic treatment of sleep disorders in children.

Neuroimaging insights into the pathophysiology of sleep disorders

Neuroimaging methods can be used to investigate whether sleep disorders are associated with specific changes in brain structure or regional activity. However, it is still unclear how these new data might improve our understanding of the pathophysiology underlying adult sleep disorders. Here we review functional brain imaging findings in major intrinsic sleep disorders (i.e., idiopathic insomnia, narcolepsy, and obstructive sleep apnea) and in abnormal motor behavior during sleep (i.e., periodic limb movement disorder and REM sleep behavior disorder). The studies reviewed include neuroanatomical assessments (voxel-based morphometry, magnetic resonance spectroscopy), metabolic/functional investigations (positron emission tomography, single photon emission computed tomography, functional magnetic resonance imaging), and ligand marker measurements. Based on the current state of the research, we suggest that brain imaging is a useful approach to assess the structural and functional correlates of sleep impairments as well as better understand the cerebral consequences of various therapeutic approaches. Modem neuroimaging techniques therefore provide a valuable tool to gain insight into possible pathophysiological mechanisms of sleep disorders in adult humans.

Anomalous hypothalamic responses to humor in cataplexy

BACKGROUND

Cataplexy is observed in a subset of patients with narcolepsy and affects approximately 1 in 2,000 persons. Cataplexy is most often triggered by strong emotions such as laughter, which can result in transient, yet debilitating, muscle atonia. The objective of this study was to examine the neural systems underlying humor processing in individuals with cataplexy.

METHODOLOGY/PRINCIPAL FINDINGS

While undergoing functional Magnetic Resonance Imaging (fMRI), we showed ten narcolepsy-cataplexy patients and ten healthy controls humorous cartoons. In addition, we examined the brain activity of one subject while in a full-blown cataplectic attack. Behavioral results showed that participants with cataplexy rated significantly fewer humorous cartoons as funny compared to controls. Concurrent fMRI showed that patients, when compared to controls and in the absence of overt cataplexy symptoms, showed pronounced activity in the emotional network including the ventral striatum and hypothalamus while viewing humorous versus non-humorous cartoons. Increased activity was also observed in the right inferior frontal gyri--a core component of the inhibitory circuitry. In comparison, the one subject who experienced a cataplectic attack showed dramatic reductions in hypothalamic activity.

CONCLUSIONS

These findings suggest an overdrive of the emotional circuitry and possible compensatory suppression by cortical inhibitory regions in cataplexy. Moreover, during cataplectic attacks, the hypothalamus is characterized by a marked decrease in activity similar to that observed during sleep. One possible explanation for these findings is an initial overdrive and compensatory shutdown of the hypothalamus resulting in full cataplectic symptoms.

Prader Willi Syndrome and excessive daytime sleepiness

Prader Willi Syndrome (PWS) is a rare genetic disorder characterized by a range of physical, psychological and physiological abnormalities. PWS patients may also demonstrate a range of abnormalities of sleep architecture and of breathing during sleep, and excessive daytime sleepiness (EDS). In the general population EDS is associated with Obstructive Sleep Apnea Syndrome (OSAS). In PWS, by contrast, OSAS is unlikely to fully explain EDS and other factors, including hypothalamic dysfunction are likely to contribute. The present review examines OSAS and hypothalamic dysfunction and other contributing factors to EDS in PWS.