Abstract
Narcolepsy type 1 is a chronic sleep disorder with significantly higher BMI reported in more than 50% of adolescent patients, putting them at a higher risk for metabolic syndrome in adulthood. Although well-documented, the body fat distribution and mechanisms behind weight gain in narcolepsy are still not fully understood but may be related to the loss of orexin associated with the disease. Orexin has been linked to the regulation of brown adipose tissue (BAT), a metabolically active fat involved in energy homeostasis. Previous studies have used BMI and waist circumference to characterize adipose tissue increases in narcolepsy but none have investigated its specific distribution. Here, we examine adipose tissue distribution in 19 adolescent patients with narcolepsy type 1 and compare them to 17 of their healthy peers using full body magnetic resonance imaging (MRI). In line with previous findings we saw that the narcolepsy patients had more overall fat than the healthy controls, but contrary to our expectations there were no group differences in supraclavicular BAT, suggesting that orexin may have no effect at all on BAT, at least under thermoneutral conditions. Also, in line with previous reports, we observed that patients had more total abdominal adipose tissue (TAAT), however, we found that they had a lower ratio between visceral adipose tissue (VAT) and TAAT indicating a relative increase of subcutaneous abdominal adipose tissue (ASAT). This relationship between VAT and ASAT has been associated with a lower risk for metabolic disease. We conclude that while weight gain in adolescents with narcolepsy matches that of central obesity, the lower VAT ratio may suggest a lower risk of developing metabolic disease.
Highlights
Narcolepsy type 1 is a chronic sleep disorder, characterized by excessive daytime sleepiness (EDS) with frequent uncontrollable sleep attacks, cataplexy; a sudden loss of muscle tone often related to the experience of strong emotions, and other sleep related symptoms [1, 2]
We found that total abdominal adipose tissue (TAAT) was higher in the narcolepsy patients compared to controls, p = 0.003 (Table 3), as well as BMI, p = 0.039, and age and sex corrected BMI z-scores BMIz, p = 0.004 (Table 2)
We found that abdominal subcutaneous adipose tissue (ASAT), a measure of subcutaneous tissue in the abdomen from the top of the femoral head to the top of the thoracic vertebrae T9 was higher in narcolepsy patients p = 0.003 (Table 3; Figure 3B)
Summary
Narcolepsy type 1 is a chronic sleep disorder, characterized by excessive daytime sleepiness (EDS) with frequent uncontrollable sleep attacks, cataplexy; a sudden loss of muscle tone often related to the experience of strong emotions, and other sleep related symptoms [1, 2]. Narcolepsy has been associated with a higher BMI [3]. Fat Distribution in Narcolepsy rapid weight gain, and significantly higher BMI was reported in a study on pediatric narcolepsy patients following the H1N1 vaccination in Sweden [5, 6]. High BMI in childhood is a known risk factor for metabolic syndrome and diabetes type 2 in adulthood [7, 8] and studies have demonstrated an increased risk in narcolepsy patients [9, 10]. BMI increase at narcolepsy onset is well-documented, the associated body fat distribution and the mechanisms behind weight gain in narcolepsy have still not been systematically investigated in humans. It has been suggested that loss of orexin producing neurons in the lateral hypothalamus may be involved [11]
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