Are noradrenergic and orexinergic systems contributing to sleep‐wake patterns in early and late‐onset Alzheimer’s Disease?

Abstract

AbstractBackgroundNeuropsychiatric symptoms, including sleep‐wake disturbances, are more common in Early‐onset Alzheimer’s disease (EOAD) than in Late‐onset AD (LOAD)(Falgàs, EurJNeurol2022). The pattern of tau‐related degeneration of wake and sleep‐promoting neurons determine sleep‐wake profiles in neurodegenerative disorders (Oh, JAMANeurol2022). We hypothesize that distinct patterns of noradrenergic (locus coeruleus‐LC) and orexigenic (hypothalamus‐HT) degeneration contribute for the differential sleep‐wake patterns between EOAD and LOAD.MethodA group of 21 participants (7 EOAD, 18 LOAD) with a diagnosis of AD confirmed by cerebrospinal fluid biomarkers (CSF) were recruited from Hospital Clínic de Barcelona. Participants underwent sleep questionnaires (Pittsburg Sleep Quality Inventory‐PSQI and Epworth Sleepiness Scale‐ESS), 2‐week actigraphy (MotionWatch8, CamnTech) and 3T‐neuromelanin‐sensitive MRI to measure locus coeruleus (LC) and hypothalamus (HT) volumes. Sleep, napping, and circadian parameters were obtained (MotionWare).ResultThe preliminary results showed no differences in sex (71vs.61% women) or disease stage (CDR 0.5: 85% vs.72%). The amnestic phenotype was prevalent (100 vs.78%). EOAD had longer daytime napping (93.2±74 vs. 58.2±28min, p<0.05), later fell asleep times (0:42am vs. 11:30pm, p<0.05) and higher central phase measure (4.4±0.5 vs. 3.5±1 h, p<0.05, midpoint between fell asleep and wake‐up) than LOAD. Daytime napping correlated with ESS (r = 0.53, p<0.01). Other parameters such as actual sleep time, sleep efficiency, sleep latency, or fragmentation index showed no differences. PSQI did not correlate to any measures. LC‐volumes were lower in EOAD than in LOAD (24.4±7mm3 vs. 33.3±6 p<0.01). In contrast, HT‐ trended towards higher volumes in EOAD (416.8±38 vs. 392.9±36, p = 0.09), being inversely correlated to the age at onset (r = ‐0.47, p<0.05). The central phase measure was inversely correlated to LC‐volumes (r = ‐0.47, p<0.05) but not to HT. Further analyses with increased sample size, CSF noradrenaline and orexin will be performed.ConclusionGreater daytime sleepiness and circadian dysfunction could be main differing traits regarding sleep‐wake patterns between EOAD and LOAD. An opposite pattern of degeneration within wake‐promoting systems consisting of higher degeneration of the LC‐noradrenergic system and relative preservation of the HT‐orexigenic in EOAD in contrast to LOAD might underlie differing sleep‐wake phenotypes. Age‐related hypothalamic volume loss can be adding to AD driven loss resulting in higher volumes in EOAD.