Intermediate hypocretin-1 cerebrospinal fluid levels and typical cataplexy: their significance in the diagnosis of narcolepsy type 1

STUDY OBJECTIVES

The diagnosis of narcolepsy type 1 (NT1) is based upon the presence of cataplexy and/or a cerebrospinal fluid (CSF) hypocretin-1/orexin-A level ≤ 110 pg/mL. We determined the clinical and diagnostic characteristics of patients with intermediate hypocretin-1 levels (111-200 pg/mL) and the diagnostic value of cataplexy characteristics in individuals with central disorders of hypersomnolence.

METHODS

Retrospective cross-sectional study of 355 people with known CSF hypocretin-1 levels who visited specialized Sleep-Wake Centers in the Netherlands. For n = 271, we had full data on cataplexy type ("typical" or "atypical" cataplexy).

RESULTS

Compared to those with normal hypocretin-1 levels (>200 pg/mL), a higher percentage of individuals with intermediate hypocretin-1 levels had typical cataplexy (75% or 12/16 vs 9% or 8/88, p < .05), and/or met the diagnostic polysomnographic (PSG) and Multiple Sleep Latency Test (MSLT) criteria for narcolepsy (50 vs 6%, p < .001). Of those with typical cataplexy, 88% had low, 7% intermediate, and 5% normal hypocretin-1 levels (p < .001). Atypical cataplexy was also associated with hypocretin deficiency but to a lesser extent. A hypocretin-1 cutoff of 150 pg/mL best predicted the presence of typical cataplexy and/or positive PSG and MSLT findings.

CONCLUSION

Individuals with intermediate hypocretin-1 levels or typical cataplexy more often have outcomes fitting the PSG and MSLT criteria for narcolepsy than those with normal levels or atypical cataplexy. In addition, typical cataplexy has a much stronger association with hypocretin-1 deficiency than atypical cataplexy. We suggest increasing the NT1 diagnostic hypocretin-1 cutoff and adding the presence of clearly defined typical cataplexy to the diagnostic criteria of NT1. Clinical trial information: This study is not registered in a clinical trial register, as it has a retrospective database design.

H1N1 hemagglutinin-specific HLA-DQ6-restricted CD4+ T cells can be readily detected in narcolepsy type 1 patients and healthy controls

Following the 2009 H1N1 influenza pandemic, an increased risk of narcolepsy type 1 was observed. Homology between an H1N1 hemagglutinin and two hypocretin sequences has been reported. T cell reactivity to these peptides was assessed in 81 narcolepsy type 1 patients and 19 HLA-DQ6-matched healthy controls. HLA-DQ6-restricted H1N1 hemagglutinin-specific T cell responses were detected in 28.4% of patients and 15.8% of controls. Despite structural homology between HLA-DQ6-hypocretin and -H1N1 peptide complexes, T cell cross-reactivity was not detected. These results indicate that it is unlikely that cross-reactivity between H1N1 hemagglutinin and hypocretin peptides presented by HLA-DQ6 is involved in the development of narcolepsy.