Serum N-Glycan Profiling of Patients with Narcolepsy Type 1 Using LC-MS/MS

The neurological condition known as narcolepsy type 1 (NT1) is an uncommon condition marked by extreme daytime sleepiness, cataplexy, sleep paralysis, hallucinations, disrupted nocturnal sleep, and low or undetectable levels of orexin in the CSF fluid. NT1 has been hypothesized to be an immunological disorder; its treatment is currently only symptomatic, and misdiagnosis is not uncommon. This study compares the N-glycome of NT1 patients with healthy controls in search of potential glycan biomarkers using LC-MS/MS. A total of 121 candidate N-glycans were identified, 55 of which were isomeric N-glycan structures and 65 were not. Seventeen N-glycan biomarker candidates showed significant differences between the NT1 and control cohorts. All of the candidate glycan biomarkers were isomeric except HexNAc₆Hex₇Fuc₀NeuAc₁ (6701) and HexNAc₆Hex₇Fuc₁NeuAc₂ (6712). Therefore, with isomeric and nonisomeric structures, a total of 20 candidate N-glycan biomarkers are reported in this study, and interestingly, all are either sialylated or sialylated-fucosylated and upregulated in NT1 relative to the control. The distribution levels of all the identified N-glycans show that the sialylated glycan type is the most abundant in NT1 and is majorly disialylated, although the trisialylated subtype is three-fold higher in NT1 compared to the healthy control. The first isomers of HexNAc₅Hex₆Fuc₀NeuAc₃ (5603), HexNAc₆Hex₇Fuc₀NeuAc₂ (6702), and HexNAc₆Hex₇Fuc₁NeuAc₄ (6714) expressed a high level of fold changes (FC) of 1.62, 2.19, and 2.98, respectively. These results suggest a different N-glycome profile of NT1 and a relationship between sialylated glycan isomers in NT1 disease development or progression. The revelation of N-glycan expression alterations in this study may improve NT1 diagnostic methods, understanding of NT1 pathology, and the development of new targeted therapeutics.