The Relationship Between Apolipoprotein ε4 Carrier Status and Sleep Characteristics in Cognitively Normal Older Adults

Reduced rapid eye movement sleep in late middle-aged and older apolipoprotein E ɛ4 allele carriers

STUDY OBJECTIVES

Apolipoprotein E ɛ4 (APOE4) is the strongest genetic risk factor for Alzheimer's disease (AD). In addition, APOE4 carriers may exhibit sleep disturbances, but conflicting results have been reported, such that there is no clear consensus regarding which aspects of sleep are impacted. Our objective was to compare objective sleep architecture between APOE4 carriers and non-carriers, and to investigate the modulating impact of age, sex, cognitive status, and obstructive sleep apnea (OSA).

METHODS

A total of 198 dementia-free participants aged >55 years old (mean age: 68.7 ± 8.08 years old, 40.91% women, 41 APOE4 carriers) were recruited in this cross-sectional study. They underwent polysomnography, APOE4 genotyping, and a neuropsychological evaluation. ANCOVAs assessed the effect of APOE4 status on sleep architecture, controlling for age, sex, cognitive status, and the apnea-hypopnea index. Interaction terms were added between APOE4 status and covariates.

RESULTS

Rapid eye movement (REM) sleep percentage (F = 9.95, p = .002, ηp2 = 0.049) and duration (F = 9.23, p = .003, ηp2 = 0.047) were lower in APOE4 carriers. The results were replicated in a subsample of 112 participants without moderate-to-severe OSA. There were no significant interactions between APOE4 status and age, sex, cognitive status, and OSA in the whole sample.

CONCLUSIONS

Our results show that APOE4 carriers exhibit lower REM sleep duration, including in cognitively unimpaired individuals, possibly resulting from early neurodegenerative processes in regions involved in REM sleep generation and maintenance.

Associations of sleep duration and daytime sleepiness with plasma amyloid beta and cognitive performance in cognitively unimpaired, middle-aged and older African Americans

STUDY OBJECTIVES

Given the established racial disparities in both sleep health and dementia risk for African American populations, we assess cross-sectional and longitudinal associations of self-report sleep duration (SRSD) and daytime sleepiness with plasma amyloid beta (Aβ) and cognition in an African American (AA) cohort.

METHODS

In a cognitively unimpaired sample drawn from the African Americans Fighting Alzheimer's in Midlife (AA-FAiM) study, data on SRSD, Epworth Sleepiness Scale, demographics, and cognitive performance were analyzed. Aβ40, Aβ42, and the Aβ42/40 ratio were quantified from plasma samples. Cross-sectional analyses explored associations between baseline predictors and outcome measures. Linear mixed-effect regression models estimated associations of SRSD and daytime sleepiness with plasma Aβ and cognitive performance levels and change over time.

RESULTS

One hundred and forty-seven participants comprised the cross-sectional sample. Baseline age was 63.2 ± 8.51 years. 69.6% self-identified as female. SRSD was 6.4 ± 1.1 hours and 22.4% reported excessive daytime sleepiness. The longitudinal dataset included 57 participants. In fully adjusted models, neither SRSD nor daytime sleepiness is associated with cross-sectional or longitudinal Aβ. Associations with level and trajectory of cognitive test performance varied by measure of sleep health.

CONCLUSIONS

SRSD was below National Sleep Foundation recommendations and daytime sleepiness was prevalent in this cohort. In the absence of observed associations with plasma Aβ, poorer self-reported sleep health broadly predicted poorer cognitive function but not accelerated decline. Future research is necessary to understand and address modifiable sleep mechanisms as they relate to cognitive aging in AA at disproportionate risk for dementia.

CLINICAL TRIAL INFORMATION

Not applicable.

Day-to-day sleep variability with Alzheimer's biomarkers in at-risk elderly

INTRODUCTION

Measuring day-to-day sleep variability might reveal unstable sleep-wake cycles reflecting neurodegenerative processes. We evaluated the association between Alzheimer's disease (AD) fluid biomarkers with day-to-day sleep variability.

METHODS

In the PREVENT-AD cohort, 203 dementia-free participants (age: 68.3 ± 5.4; 78 males) with a parental history of sporadic AD were tested with actigraphy and fluid biomarkers. Day-to-day variability (standard deviations over a week) was assessed for sleep midpoint, duration, efficiency, and nighttime activity count.

RESULTS

Lower cerebrospinal fluid (CSF) ApoE, higher CSF p-tau181/amyloid-β (Aβ)42, and higher plasma p-tau231/Aβ42 were associated with higher variability of sleep midpoint, sleep duration, and/or activity count. The associations between fluid biomarkers with greater sleep duration variability were especially observed in those that carried the APOE4 allele, mild cognitive impairment converters, or those with gray matter atrophy.

DISCUSSION

Day-to-day sleep variability were associated with biomarkers of AD in at-risk individuals, suggesting that unstable sleep promotes neurodegeneration or, conversely, that AD neuropathology disrupts sleep-wake cycles.

Insomnia and risk of dementia in a large population-based study with 11-year follow-up: The HUNT study

Despite evidence suggesting that insomnia is associated with the risk of dementia and cognitive dysfunction, studies have shown mixed results. Dementia has a long prodromal phase, and studies with long follow-up are required to avoid reverse causality. In our 11-year follow-up study, we assessed whether probable insomnia disorder (PID) based on diagnostic criteria, and insomnia symptoms were associated with risk of all-cause dementia, Alzheimer's disease (AD) and cognition, measured with the Montreal Cognitive Assessment scale. We also examined if Apolipoprotein E genotype modified any associations with dementia through interaction. We analysed data from 7492 participants in the Norwegian Trøndelag Health Study. PID was not associated with all-cause dementia (odds ratio = 1.03, 95% confidence interval = 0.74-1.43), AD (odds ratio = 1.07, 95% confidence interval = 0.71-1.60) or Montreal Cognitive Assessment score (regression coefficient = 0.37, 95% confidence interval = -0.06 to 0.80). The insomnia symptom "difficulties maintaining sleep" was associated with a lower risk of all-cause dementia (odds ratio = 0.81, 95% confidence interval = 0.67-0.98), AD (odds ratio = 0.73, 95% confidence interval = 0.57-0.93), and better Montreal Cognitive Assessment score, mean 0.40 units (95% confidence interval = 0.15-0.64). No interaction with Apolipoprotein E genotype was found. PID and insomnia symptoms did not increase the risk of dementia in our study. More research with longer follow-up is needed, and future studies should explore if the associations to dementia risk vary across insomnia subtypes.

The impact of sleep components, quality and patterns on glymphatic system functioning in healthy adults: A systematic review

OBJECTIVE

The glymphatic system is thought to be responsible for waste clearance in the brain. As it is primarily active during sleep, different components of sleep, subjective sleep quality, and sleep patterns may contribute to glymphatic functioning. This systematic review aimed at exploring the effect of sleep components, sleep quality, and sleep patterns on outcomes associated with the glymphatic system in healthy adults.

METHODS

PubMed®, Scopus, and Web of Science were searched for studies published in English until December 2021. Articles subjectively or objectively investigating sleep components (total sleep time, time in bed, sleep efficiency, sleep onset latency, wake-up after sleep onset, sleep stage, awakenings), sleep quality, or sleep pattern in healthy individuals, on outcomes associated with glymphatic system (levels of amyloid-β, tau, α-synuclein; cerebrospinal fluid, perivascular spaces; apolipoprotein E) were selected.

RESULTS

Out of 8359 records screened, 51 studies were included. Overall, contradictory findings were observed according to different sleep assessment method. The most frequently assessed sleep parameters were total sleep time, sleep quality, and sleep efficiency. No association was found between sleep efficiency and amyloid-β, and between slow-wave activity and tau. Most of the studies did not find any correlation between total sleep time and amyloid-β nor tau level. Opposing results correlated sleep quality with amyloid-β and tau.

CONCLUSIONS

This review highlighted inconsistent results across the studies; as such, the specific association between the glymphatic system and sleep parameters in healthy adults remains poorly understood. Due to the heterogeneity of sleep assessment methods and the self-reported data representing the majority of the observations, future studies with universal study design and sleep methodology in healthy individuals are advocated.

Correlations between sleep disturbance and brain structures associated with neurodegeneration in the National Alzheimer's Coordinating Center Uniform Data Set

This study aimed to 1) determine the association between sleep disturbance and brain structure volumes, 2) the moderation effect of apolipoprotein ε4 genotype on sleep disturbance and brain structures, and 3) the moderation effect of sleep disturbance on cognitive status and regional brain volumes. Using the National Alzheimer's Coordinating Center Uniform Data Set (n = 1,533), multiple linear regressions were used to evaluate the association between sleep disturbance and brain volumes. Sleep disturbance was measured using one question from the NPI-Q. After controlling for intracranial volume, age, sex, years of education, race, ethnicity, and applying the FDR correction, total cerebrospinal fluid volume, left lateral ventricle volume, total lateral ventricle volume, and total third ventricle volume demonstrated significantly higher means for those with sleep disturbance. Total brain volume, total white and gray matter volume, total cerebrum brain volume (including gray but not white matter), left hippocampus volume, total hippocampal volume, the left, right, and total frontal lobe cortical gray matter volume, and the left, right, and total temporal lobe cortical gray matter volume demonstrated significantly lower mean volumes for those with sleep disturbance. Sleep disturbance moderated the association between cognitive status and lateral ventricular volumes. These findings suggest that disrupted sleep is associated with atrophy across multiple brain regions and ventricular hydrocephalus ex vacuo.

Insomnia symptom severity and cognitive performance: Moderating role of APOE genotype

INTRODUCTION

We evaluated whether insomnia symptom severity was associated with cognitive function, and whether this relationship was modified by biomarkers associated with Alzheimer's disease risk.

METHODS

We examined insomnia symptoms and neuropsychological performance 3.4 years later in 511 dementia-free Framingham Heart Study participants (62.65 ± 8.7 years, 50.9% male). Additionally, we explored insomnia symptoms combined with self-reported short habitual sleep duration and effect modification by apolipoprotein E (APOE) ε4 allele status.

RESULTS

More severe insomnia symptoms were associated with lower performance on global cognition, and immediate and delayed Logical Memory recall, especially when insomnia symptoms were combined with short sleep duration. The association between insomnia symptoms and poorer memory recall was more pronounced in APOE ε4 allele carriers.

DISCUSSION

Insomnia symptom severity was associated with worse subsequent global cognitive and memory performance, which was especially apparent in APOE ε4 allele carriers, suggesting that poor sleep might be particularly detrimental when the brain is already vulnerable to neurodegeneration.

Sleep Time Estimated by an Actigraphy Watch Correlates With CSF Tau in Cognitively Unimpaired Elders: The Modulatory Role of APOE

There is increasing evidence of the relationship between sleep and neurodegeneration, but this knowledge is not incorporated into clinical practice yet. We aimed to test whether a basic sleep parameter, as total sleep estimated by actigraphy for 1 week, was a valid predictor of CSF Alzheimer’s Disease core biomarkers (amyloid-β-42 and –40, phosphorylated-tau-181, and total-tau) in elderly individuals, considering possible confounders and effect modifiers, particularly the APOE ε4 allele. One hundred and twenty-seven cognitively unimpaired volunteers enrolled in the Valdecilla Study for Memory and Brain Aging participated in this study. Seventy percent of the participants were women with a mean age of 65.5 years. After adjustment for covariates, reduced sleep time significantly predicted higher t-tau and p-tau. This association was mainly due to the APOE ε4 carriers. Our findings suggest that total sleep time, estimated by an actigraphy watch, is an early biomarker of tau pathology and that APOE modulates this relationship. The main limitation of this study is the limited validation of the actigraphy technology used. Sleep monitoring with wearables may be a useful and inexpensive screening test to detect early neurodegenerative changes.

Alzheimer's Disease in Patients with Obstructive Sleep Apnea Syndrome

BACKGROUND

Obstructive sleep apnea syndrome (OSAS) is a disorder with high prevalence among adults and is an independent risk factor for various diseases, especially those affecting the central nervous system (CNS). Continuous positive airway pressure (CPAP) is usually the optimal choice of treatment for OSAS. Alzheimer's disease (AD) is a neurodegenerative disease affecting a large proportion of the elderly population. The purpose of this study was to collect information concerning the two pathological entities and investigate the effectiveness of CPAP in the treatment of AD.

MATERIALS AND METHODS

In this review, Twenty articles were found concerning OSAS and AD, of which one article was about treatment with donepezil and seven articles considered treatment with CPAP.

RESULTS

Serious OSAS and short sleep duration are associated with a high risk of developing dementia. Respiratory distress during sleep is associated with developing mild cognitive impairment at younger ages. The cerebrovascular damage of AD patients is correlated with the severity of OSAS. Lower cerebrospinal fluid levels are associated with memory disturbances and oxygen saturation parameters in patients with OSAS-AD. Continuous use of CPAP is related to the delayed onset of cognitive impairment and is suggested as an effective method of protecting cognitive function, depression, sleep quality and architecture, and daytime sleepiness in AD patients with good compliance. Treatment of CPAP patients with OSAS-AD is suggested as an effective method of protecting cognitive function.

CONCLUSION

Clinicians dealing with AD patients should consider CPAP treatment when OSAS coexists.

Effects of Six-Month Aerobic Exercise Intervention on Sleep in Healthy Older Adults in the Brain in Motion Study: A Pilot Study

Background

Sleep disturbances have been shown to be associated with the presence of the apolipoprotein (APOE) ɛ4 allele, the well-known genetic risk factor for late-onset sporadic Alzheimer's disease (AD).

Objective

This study quantifies the effects of a six-month aerobic exercise intervention on objective and subjective sleep quality in middle-aged to older individuals including those at increased genetic risk for late-onset sporadic Alzheimer's disease (AD), who carry the apolipoprotein (APOE) ɛ4 risk allele.

Methods

199 sedentary men and women without significant cognitive impairments were enrolled in the Brain in Motion study, a quasi-experimental single group pre-test/post-test study with no control group. Participants completed a six-month aerobic exercise intervention and consented to genetic testing. Genotyping of APOE confirmed that 54 individuals were carriers of the ɛ4 allele. Participants' subjective quality of sleep was assessed with the Pittsburgh Sleep Quality Index (PSQI) pre- and post-intervention. A convenience sample of participants (n = 29, APOE ɛ4+ = 7) consented to undergo two nights of in-home polysomnography (PSG) pre- and post intervention. Sleep architecture and respiratory variables were assessed.

Results

The six-month aerobic exercise intervention significantly improved participants' total PSQI score, sleep efficiency, and sleep latency in the full sample (n = 199). PSG results showed that total sleep time and sleep onset latency significantly improved over the course of the exercise intervention only in individuals who carried the APOE ɛ4 allele. These results are, however, exploratory and need to be carefully interpreted due to the rather small number of APOE ɛ4+ in the PSG subgroup.

Conclusions

The six-month aerobic exercise intervention significantly improved participants' sleep quality with beneficial effects on PSG shown in individuals at increased genetic risk for late-onset sporadic AD.