The data suggests that the pathophysiology and, by extension, etiology of this disorder are distinctly different from the other conditions studied. Conclusion: This data confirms the previous finding that undetectable hypocretin-1 levels are highly specific for HLA positive narcolepsy with cataplexy. Hypocretin-1 levels were not associated with age at diagnosis, age at lumbar puncture, body mass index at time of diagnosis, or body mass index at time of lumbar puncture. Although the sample size was small, subjects with the DQB1*0602 allele without cataplexy had lower hypocretin-1 levels than did other groups (other than the HLA and cataplexy positive group). Interventions: N/A Measurement & Results: Using analysis of variance techniques, statistically significant differences were found between the CSF hypocretin-1 levels in HLA positive patients and all other groups (P<0.01). Patients/Participants: Twenty-six patients with narcolepsy, with and without HLA DQB1*0602 and with and without cataplexy, as well as 15 neurologic controls. Setting: Data were collected at a sleep disorders center. Methods/Design: This study compared cerebrospinal (CSF) hypocretin 1 in 13 patients with HLA DQB1*0602 allele and cataplexy to 4 HLA negative patients with cataplexy, 3 HLA positive patients without cataplexy, and 6 HLA negative patients without cataplexy, plus 15 neurologic controls. The relationship between hypocretin-1 levels and narcolepsy without cataplexy or the DQB1*0602 allele is less clear. HLA-typing should precede CSF hcrt-1 measurements because hypocretin deficiency is rare in HLA-DQB1*0602-negative patients.Study Objectives: Hypocretin (orexin) deficiency (< 40 pg/ml) is highly associated with narcolepsy with cataplexy (89.5%) and more specifically with patients with cataplexy who are HLA DQB1*0602 positive (95.7%). The ICSD-2 criterion for low CSF hcrt-1 (< 30% of normal mean) is valid for diagnosing NC, but not NwC. The study provides evidence that hypocretin deficiency causes a more severe NC phenotype. Hypocretin-deficient NC patients had higher frequency of cataplexy, shorter mean sleep latency, more sleep onset REM periods (P < 0.05) and more awakenings (NS) than did NC patients with normal CSF hcrt-1. Thirty-nine of 41 NC and 4/13 NwC patients were HLA-DQB1*0602-positive (P < 0.01). In Danes, low CSF hcrt-1 was present in 40/46 NC, 3/14 NwC and 0/106 controls (P < 0.0001). Comparisons of hypocretin deficiency and frequency of HLA-DQB1*0602-positivity in the Danish and eligible NC and NwC populations (included via MEDLINE search), by (re)calculation of study results using the ICSD-2 criterion for low CSF hcrt-1 (< 30% of normal mean). Interviews, polysomnography, multiple sleep latency test, HLA-typing, and CSF hcrt-1 measurements in Danish patients with narcolepsy with cataplexy (NC) and narcolepsy without cataplexy (NwC), CSF hcrt-1 measurements in other hypersomnias, neurological and normal controls. The International Classification of Sleep Disorders (ICSD-2) criteria for low CSF hypocretin-1 levels (CSF hcrt-1) still need validation as a diagnostic tool for narcolepsy in different populations because inter-assay variability and different definitions of hypocretin deficiency complicate direct comparisons of study results.
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