Unexpected Fat Distribution in Adolescents With Narcolepsy

Body Weight and Metabolic Rate Changes in Narcolepsy: Current Knowledge and Future Directions

Narcolepsy is a known auto-immune disease that presents mainly in the teenage years with irresistible sleep attacks. Patients with narcolepsy, especially NT1, have been found to have a high prevalence of obesity and other metabolic derangements. This narrative review aimed to address the relationship between narcolepsy and changes in weight and metabolic rate, and discuss potential mechanisms for weight gain and metabolic changes and future research agendas on this topic. This article will provide a balanced, up-to-date critical review of the current literature, and delineate areas for future research, in order to understand the pathophysiological metabolic changes in narcolepsy. Articles using predefined keywords were searched for in PubMed and Google Scholar databases, with predefined inclusion and exclusion criteria. Compared to controls, patients with narcolepsy are more likely to be obese and have higher BMIs and waist circumferences. According to recent research, weight gain in narcolepsy patients may be higher during the disease's outset. The precise mechanisms causing this weight gain remains unknown. The available information, albeit limited, does not support differences in basal or resting metabolic rates between patients with narcolepsy and controls, other than during the time of disease onset. The evidence supporting the role of orexin in weight gain in humans with narcolepsy is still controversial, in the literature. Furthermore, the available data did not show any appreciable alterations in the levels of CSF melanin-concentrating hormone, plasma and CSF leptin, or serum growth hormone, in relation to weight gain. Other mechanisms have been proposed, including a reduction in sympathetic tone, hormonal changes, changes in eating behavior and physical activity, and genetic predisposition. The association between increased body mass index and narcolepsy is well-recognized; however, the relationship between narcolepsy and other metabolic measures, such as body fat/muscle distribution and metabolic rate independent of BMI, is not well documented, and the available evidence is inconsistent. Future longitudinal studies with larger sample sizes are needed to assess BMR in patients with narcolepsy under a standard protocol at the outset of narcolepsy, with regular follow-up.

Narcolepsy: Comorbidities, complexities and future directions

Patients with narcolepsy live with a lifelong sleep-wake disorder, impairing their quality of life, productivity, educational and employment outcomes. Clinicians are becoming aware that a significant aspect of the burden of this disease relates to frequent comorbid conditions, including aspects of the patient's emotional, metabolic, sleep and immune health. This review explores the literature describing the comorbidities seen in patients with narcolepsy, to enhance understanding of these often complex presentations. It hopes to encourage a multidisciplinary approach, to collaborate with patients and a broad clinical team, and to maximise clinical and quality of life outcomes, for those living with narcolepsy.

Narcolepsy treatment in Sweden: An observational study

OBJECTIVES

To describe the pharmacological treatments (2005-2017) and the healthcare utilization (1997-2016) for patients with narcolepsy in Sweden in order to create a framework for future organizational and economic analyses.

MATERIAL & METHODS

Patients of all ages with a diagnosis of narcolepsy registered in the National Patient Registry in specialist care in Sweden were included and information on treatments for narcolepsy was retrieved from The Swedish Prescribed Drug Register.

RESULTS

We collected 2508 patients with narcolepsy, 43,3% men and 56,7% women and 47,9% were prescribed modafenil, 33,8% metylphenidate and 26,2% amphetamine. In total, 3817 treatments were initiated. Patients treated with amphetamine had a higher mean age. More women than men used modafinil, methylphenidate, amphetamine and antidepressants. The narcolepsy population had more outpatient than inpatient healthcare. Patients treated with sodium oxybate had more outpatient visits than other narcolepsy patients, before and during treatment (p = .00).

CONCLUSIONS

This study gives valuable information on pharmaceutical treatments and healthcare utilization for patients with narcolepsy and can be used to estimate the healthcare cost in the future. Patients with sodium oxybate treatment had more outpatient visits than other patients before and during treatment which may be due to the need to monitor potentially severe side-effects or may indicate that patients with sodium oxybate treatment have a severe disease. The number of included patients was less than expected; however, this may depend on patients escaping our collection of data, which does not contain information from primary care.

Human adipose tissue is a putative direct target of daytime orexin with favorable metabolic effects: A cross-sectional study

OBJECTIVE

Orexin/hypocretin (Ox) and its receptors (OxR), a neuroendocrine system centrally regulating sleep/wakefulness, were implicated in the regulation of peripheral metabolism. It was hypothesized that human adipose tissue constitutes a direct target of the OxA/OxR system that associates with distinct metabolic profile(s).

METHODS

Serum Ox levels and abdominal subcutaneous and visceral adipose tissue expression of Ox/HCRT, OxR1/HCRTR1, and OxR2/HCRTR2 were measured in n = 81 patients.

RESULTS

Higher morning circulating Ox levels were associated with improved lipid profile and insulin sensitivity, independently of BMI (β = -0.363, p = 0.018 for BMI-adjusted homeostatic model of insulin resistance). Adipose HCRT mRNA was detectable in <20% of patients. Visceral HCRT expressers were mostly (80%) males and, compared with nonexpressers, had lower total and LDL cholesterol. HCRTR1 was readily detectable, and HCRTR2 was undetectable. HCRTR1 mRNA and OxR1 protein expression were higher in subcutaneous than visceral adipose tissue, and among nonobese patients, patients with obesity, and patients with obesity and T2DM were 3.4 (1.0), 0.7 (0.1), 0.6 (0.1) (AU) (p < 0.001) and 1.0 (0.2), 0.5 (0.1), 0.4 (0.1) (AU) (p = NS), respectively. Higher visceral HCRTR1 expression was associated with lower fasting insulin and homeostatic model of insulin resistance, also after adjusting for BMI. In human adipocytes, HCRTR1 expression did not exhibit significant oscillation.

CONCLUSIONS

Human adipose tissue is a putative direct target of the OxA-OxR1 system, with higher morning input being associated with improved metabolic profile.

Endocrine and metabolic aspects of narcolepsy type 1 in children

STUDY OBJECTIVES

To study whether the onset of narcolepsy type 1 (NT1) in children and adolescents affects BMI, specific metabolic risk factors, the onset of puberty, longitudinal growth or other endocrine functions.

METHODS

A population-based study, comprising 34 patients, was performed with a clinical evaluation, an assessment of puberty and growth, actigraphy and blood samples at fasting, from patients and controls, to evaluate pituitary function, growth factors, thyroid gland, gonads, insulin sensitivity, appetite regulation and blood lipids.

RESULTS

In the post-H1N1 vaccination (PHV) narcolepsy group, the median BMI SDS was higher 6-12 months after the onset of narcolepsy (p < 0.01), but it was no different 10 years after the onset of narcolepsy (p = 0.91), compared with 12-24 months before the onset of narcolepsy. There was a correlation between an increase in BMI and a decrease in total energy expenditure (R = -0.74). In the nPHV group, weight and BMI changes were smaller and no significant changes were recorded. Early puberty was more common in patients with puberty onset after narcolepsy onset (n = 16/19) compared with patients with puberty onset before narcolepsy onset (n = 3/11, p = 0.02). There was no significant change in height SDS during the studied period. Although they were within normal ranges, both median HDL and median TSH levels were significantly lower in NT1 patients, compared with controls.

CONCLUSIONS

We found a high prevalence of large BMI gain in the period immediately after the onset of narcolepsy, which had almost normalized at the long-term follow-up. The onset of narcolepsy led to early puberty in both sexes. Linear growth was not affected. We did not find any strong indicators of metabolic disturbances.

Metabolic profile in patients with narcolepsy: a systematic review and meta-analysis

Narcolepsy, a sleep disorder characterized by loss of hypocretin neurons, has been associated with metabolic disturbances. Although the metabolic alterations in narcolepsy patients are widely investigated in the literature, the results are controversial. We performed a systematic search of literature to identify metabolic profiling studies in narcolepsy patients. A total of 48 studies were included in the meta-analysis. Narcolepsy patients exhibited higher prevalence of obesity (log OR = 0.93 [0.73-1.13], P < 0.001), diabetes mellitus (log OR = 0.64 [0.34, 0.94], P < 0.001), hypertension (log OR = 0.33 [0.11, 0.55], P < 0.001), and dyslipidemia (log OR = 1.19 [0.60, 1.77], P < 0.001) compared with non-narcoleptic controls. Narcolepsy was associated with higher BMI (SMD = 0.50 [0.32-0.68], P < 0.001), waist circumference (MD = 8.61 [2.03-15.19], P = 0.01), and plasma insulin (SMD = 0.61 [0.14-1.09], P = 0.01). Levels of fasting blood glucose (SMD = -0.25 [-0.61,0.10], P = 0.15), BMR-RMR (SMD = -0.17 [-0.52-0.18], P = 0.34), systolic blood pressure (SMD = 0.29 [-0.39-0.97], P = 0.40), diastolic blood pressure (SMD = 0.39 [-0.62, 1.40], P = 0.45), CSF melanin-concentrating hormone (MD = 5.56 [-30.79-41.91], P = 0.76), serum growth hormone (SMD = 7.84 [-7.90-23.57], P = 0.33), as well as plasma and CSF leptin (SMD = 0.10 [-1.32-1.51], P = 0.89 and MD = 0.01 [-0.02-0.04], P = 0.56, respectively) did not significantly differ between narcolepsy patients and controls. These findings necessitate early screening of metabolic alterations and cardiovascular risk factors in narcolepsy patients to reduce the morbidity and mortality rates.

Associations of plasma hypocretin-1 with metabolic and reproductive health: Two systematic reviews of clinical studies

The hypocretin system consists of two peptides hypocretin-1 and hypocretin-2 (HCRT1 and HCRT2). Hypocretin-containing neurons are located in the posterior and lateral hypothalamus, and have widespread projections throughout the brain and spinal cord. In addition to its presence in the cerebrospinal fluid (CSF), peripheral HCRT1 has been detected in plasma. Robust experimental evidence demonstrates functions of hypothalamic-originated HCRT1 in regulation of multiple biological systems related to sleep-wake states, energy homeostasis and endocrine function. In contrast, HCRT1 studies with human participants are limited by the necessarily invasive assessment of CSF HCRT1 to patients with underlying morbidity. Regulation by HCRT1 of energy homeostasis and reproduction in animals suggests similar regulation in humans and prompts these two systematic reviews. These reviews translate prior experimental findings from animal studies to humans and examine associations between HCRT1 and: 1) metabolic risk factors; 2) reproductive function in men, women and children. A total of 21 studies and six studies met the inclusion criteria for the two searches, respectively. Research question, study design, study population, assessments of HCRT1, reproductive, cardiometabolic data and main findings were extracted. Associations between HCRT1, metabolic and reproductive function are inconsistent. Limitations of studies and future research directions are outlined.

Measured resting metabolic rate, respiratory quotient, and body composition in patients with narcolepsy: a preliminary report of a case-control study

This case–control study compared the body composition, resting metabolic rate (RMR), and respiratory quotient (RQ) of narcolepsy patients with those of body mass index (BMI)- gender and age-matched controls. This study included 14 male patients with narcolepsy and 14 matched controls. The narcolepsy patients were subdivided into two subgroups (n = 7/each): those with cataplexy (NT1) and those without cataplexy (NT2). Anthropometric measurements, bioelectric impedance analysis, and indirect calorimetry were used in addition to the calculation of common body-composition indices (conicity index, abdominal volume index, and body adiposity index). Our results showed no significant difference in fat percentage, fat mass, fat-free mass, and TBW among NT1, NT2, and controls (p > 0.05). Compared to matched controls, there was a reduction of muscle mass in both NT1 and NT2 subgroups. The RMR was similar in all groups, while patients in the NT1/NT2 subgroups had a lower RQ, used more fat and fewer carbohydrates during the fasting period. These findings give an insight into the distinctive state of altered metabolism in patients with narcolepsy, especially the resting metabolic rate, which was not altered in NT1 vs. NT2 compared to the controls when matched for BMI, age, and gender.

Role of Brown Adipose Tissue in Adiposity Associated With Narcolepsy Type 1

Narcolepsy type 1 is a neurological sleep-wake disorder caused by the destruction of orexin (hypocretin)-producing neurons. These neurons are particularly located in the lateral hypothalamus and have widespread projections throughout the brain, where they are involved, e.g., in the regulation of the sleep-wake cycle and appetite. Interestingly, a higher prevalence of obesity has been reported in patients with narcolepsy type 1 compared to healthy controls, despite a normal to decreased food intake and comparable physical activity. This suggests the involvement of tissues implicated in total energy expenditure, including skeletal muscle, liver, white adipose tissue (WAT), and brown adipose tissue (BAT). Recent evidence from pre-clinical studies with orexin knock-out mice demonstrates a crucial role for the orexin system in the functionality of brown adipose tissue (BAT), probably through multiple pathways. Since BAT is a highly metabolically active organ that combusts fatty acids and glucose toward heat, thereby contributing to energy metabolism, this raises the question of whether BAT plays a role in the development of obesity and related metabolic diseases in narcolepsy type 1. BAT is densely innervated by the sympathetic nervous system that activates BAT, for instance, following cold exposure. The sympathetic outflow toward BAT is mainly mediated by the dorsomedial, ventromedial, arcuate, and paraventricular nuclei in the hypothalamus. This review focuses on the current knowledge on the role of the orexin system in the control of energy balance, with specific focus on BAT metabolism and adiposity in both preclinical and clinical studies.

Orexins/Hypocretins: Key Regulators of Energy Homeostasis

Originally described to be involved in feeding regulation, orexins/hypocretins are now also considered as major regulatory actors of numerous biological processes, such as pain, sleep, cardiovascular function, neuroendocrine regulation, and energy expenditure. Therefore, they constitute one of the most pleiotropic families of hypothalamic neuropeptides. Although their orexigenic effect is well documented, orexins/hypocretins also exert central effects on energy expenditure, notably on the brown adipose tissue (BAT) thermogenesis. A better comprehension of the underlying mechanisms and potential interactions with other hypothalamic molecular pathways involved in the modulation of food intake and thermogenesis, such as AMP-activated protein kinase (AMPK) and endoplasmic reticulum (ER) stress, is essential to determine the exact implication and pathophysiological relevance of orexins/hypocretins on the control of energy balance. Here, we will review the actions of orexins on energy balance, with special focus on feeding and brown fat function.