Physical Activity and Sleep/Wake Behavior, Anthropometric, and Metabolic Profile in Pediatric Narcolepsy Type 1

Objectives: Regular physical activity is routinely recommended in children and adolescents suffering from narcolepsy type 1 (NT1), but controlled studies analyzing its influence on sleep/wake behavior, metabolic, and anthropometric profile in pediatric NT1 are lacking. Methods: Fifty consecutive drug-naïve NT1 children and adolescents were assessed through actigraphic, clinical, and metabolic evaluations. Patients were compared with respect to their engagement in leisure-time physical activities (LTPA): patients engaged in LTPA (n = 30) and patients not engaged (No-LTPA, n = 20), respectively. Results: LTPA patients presented lower BMI, with different BMI categories distribution and higher HDL cholesterol, when compared with No-LTPA subjects. Increased night-sleep duration, higher sleep quality, and reduction of nap frequency were documented through actigraphy in LTPA subjects. Subjective sleepiness, as measured by ESS-CHAD, was also lower in LTPA subjects while cataplexy frequency proved similar between the two groups. Discussion: In pediatric NT1 patients, regular engagement in LTPA is associated with significant differences on sleepiness, anthropometric and metabolic profile and objectively assessed sleep/wake behavior. Engagement in LTPA is beneficial and should be strongly encouraged in pediatric NT1 patients.

Disease onset often occurs in childhood and early adolescence and is most frequently accompanied by a rapid weight gain, resulting in overweight or obesity (3)(4)(5)(6).
Although the mechanisms leading to weight gain in NT1 have yet to be elucidated (7), its management is of utmost importance as it represents an additional disease burden, negatively impacting on children's psychosocial functioning and increasing the cardiovascular and metabolic risk (5,8).
The promotion of regular physical activity is among the most effective approaches to control weight in overweight children and adolescents (9). Although never investigated in narcolepsy patients, engagement in physical activity is associated with increased sleep duration and higher sleep quality in healthy subjects and in primary insomnia patients (10,11).
In this study we analyzed the influence of regular physical activity on sleep/wake profile, sleepiness, metabolic and anthropometric features in a large cohort of drug-naïve NT1 children and adolescents.

Sleep and Napping Behavior Assessment
Nocturnal sleep and diurnal naps were assessed through seven days of at-home actigraphic monitoring (Micro Motionlogger Watch, Ambulatory Monitoring Inc.). Devices were placed on the non-dominant wrist and initialized to collect and store motor activity in 1-min epochs.
Actigraphy was performed before diagnostic hospitalization, during the regular school-week. The description of the actigraphic variables considered for this work is reported in the Supplementary Material (12).
Participants also filled in a daily sleep diary and indicated nocturnal rest period and diurnal naps through the event-marker button.

Physical Activity and Cataplexy Assessment
Participants and their parents underwent a brief interview aimed to collect information on physical activity and cataplexy.
Regular engagement in leisure-time physical activity (LTPA), and whether patients performed their habitual physical activity schedule during the recording week, has been assessed by questions validated in other studies (namely "Do you usually undertake physical/sporting activities after school?" and "During the last seven days, how many times did you perform physical/sporting activities after school that increase your heart rate and make you get out of breath some of the time?" (13,14). Information on type of activity, frequency (range 1-7 days), and duration were also collected. Cataplexy frequency and cataplexy occurrence, during or immediately after (within 15 min) performing physical/sporting activities, was also assessed through semi-structured clinical interview (12). Chronotype was assessed by means of the Italian version of the reduced Morningness-Eveningness questionnaire for Children and Adolescents (rMEQ-CA) (15); subjective sleepiness was assessed with the Epworth Sleepiness scale for children and adolescents (ESS-CHAD) (16).

Anthropometric and Metabolic Assessment
Height, weight, and body mass index (BMI) were measured for each participant by using a portable stadiometer (Harpenden Portable Stadiometer); BMI percentile was determined in comparison with the Italian growth percentile scales (17), with underweight defined as BMI <5th percentile, normal weight as BMI >5th and <85th percentile, overweight between 85th and 95th percentile, and obesity as BMI>95th (18). Blood samples were collected after fasting from midnight and analyzed for blood glucose, total cholesterol, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and triglycerides.

Statistical Analyses
For statistical purposes, NT1 children and adolescents were classified either as "LTPAs" (n = 30) if they were engaged in any type of LTPA for at least 60 min twice a week or "No-LTPAs" (n = 20). Individual information on physical activity schedule is reported as Supplementary Material (Table S1).
Group differences in demographic, clinical, anthropometric/metabolic data and actigraphic parameters were analyzed by means of chi-squared and independent sample t-test, followed by effect size computation (Cohen's d). Analyses were conducted with IBM SPSS Statistics 19 software (SPSS, Inc. Chicago, Ill); p-value < 0.05 was considered statistically significant.

RESULTS
Demographics, clinical, anthropometric, and metabolic data are reported in Table 1. Significant differences were observed in subjective sleepiness, with LTPAs presenting lower ESS-CHAD score than No-LTPAs, but not in objective sleep propensity or SOREMPs number at the MSLT. No differences were observed in cataplexy frequency. Significant differences were also observed in anthropometric/metabolic features, with LTPAs presenting lower BMI, a different BMI category distribution, and higher HDL cholesterol level than No-LTPAs. Actigraphic variables are reported in Table 2. Significant differences were observed in nocturnal sleep duration and quality, with LTPAs displaying increased eTST and sleep efficiency, reduced eWASO and SMA, despite increased frequency of nocturnal awakenings when compared to No-LTPAs. Concerning the daytime period, a significant increase of DMA, reduced eDTST and naps frequency were observed in LTPAs.

DISCUSSION
This is the first study that investigated anthropometric/metabolic features and sleep/wake profile with respect to engagement in physical/sporting activity among pediatric NT1 patients.
Overall, our results highlight a beneficial association between regular LTPA and several disease-related aspects. Although we confirmed the over-representation of overweight and obesity among pediatric NT1 patients (42% of subjects being overweight and 22% being obese) (4, 5), our results showed that NT1 subjects regularly engaged in LTPA (60% of this cohort) presented with overall lower BMI and lower prevalence of overweight and obesity (30% overweight, 17% obese) compared to No-LTPAs (60% overweight, 30% obese).
Moreover, regular involvement in LTPA turned out to be associated with favorable differences in lipid-lipoprotein profile as LTPAs present with higher levels of HDL-C and lower levels of triglycerides when compared to No-LTPAs, although the latter difference did not reach statistical significance. Although these results are in line with previous studies on healthy children and adolescents reporting higher HDL-C and lower triglycerides levels in physically active subjects, further confirmation is required by means of interventional studies in NT1 patients (19). Actigraphy objectively documented higher sleep quality (higher estimated sleep efficiency and lower eWASO and SMA) and increased sleep duration (higher eTST) in LTPAs compared to No-LTPAs, without significant differences in TIB and in the timing of nocturnal rest period, highlighting the positive association between regular physical activity and nocturnal sleep quality.
The abovementioned results are in line with results of previous studies in good sleepers and primary insomnia patients and, for the first time, these findings extend to patients suffering from NT1 (11,20).
Moreover, regular engagement in LTPA was also associated with a different diurnal behavior, as LTPAs took fewer naps, spending less time asleep during daytime. Differences in subjective sleepiness levels properly confirmed the actigraphic diurnal profile, with LTPAs displaying lower ESS-CHAD score than No-LTPAs. Engagement in LTPA was not associated with differences in cataplexy frequency. However, it is of high interest to highlight that none of the children and adolescents reported to experience cataplectic attacks during or immediately after having performed physical activity. This finding could have important clinical implications, since concerns have been raised about the potential adverse effect of physical activity on cataplexy frequency (21). Indeed, in a murine model of NT1, physical exercise (wheel running) increased the total amount of wakefulness to the detriment of a negative effect on cataplexy and authors pointed out the need to optimize cataplexy control to derive benefit from physical activity (21,22).
Our study suffers from the inherent limitations of a crosssectional design, in particular it precludes the possibility of ruling out reverse causation (i.e., children are able to perform physical/sports activities because they are not overweight or obese) and calls for further interventional studies, in pharmacologically untreated and treated patients. Moreover, food intake was not monitored in the present study.
Nonetheless, our study showed that regular engagement in leisure-time physical/sports activity is associated with significant differences in children's anthropometric features, sleepiness and sleep/wake profile and does not seem to trigger cataplexy, thus providing a first rationale to implement regular physical activity as a complementary non-pharmacological approach to assist the management of pediatric NT1 cases.

AUTHOR CONTRIBUTIONS
MF: conception of the study, acquisition of data, interpretation of data, statistical analyses, drafted the initial manuscript, and reviewed and revised the final version of manuscript. FP: conception of the study, interpretation of data, statistical analyses, and reviewed and revised the final version of manuscript. EA and VN: acquisition of data, interpretation of data, and reviewed and revised the final version of manuscript.
PP: conception of the study, interpretation of data, and reviewed and revised the final version of manuscript. GP: conception of the study, interpretation of data, drafted the initial manuscript, and reviewed and revised the final version of manuscript.