Interleukin-1β Promoter Polymorphism Enhances the Risk of Sleep Disturbance in Alzheimer's Disease

Sleep alleviates Alzheimer's disease (AD)-related neuropathological processes, whereas sleep disturbance in AD patients is associated with elevated peripheral inflammatory cytokine levels. In the present study, we assessed interleukin (IL)-1 beta and APOE epsilon 4 polymorphisms for association with susceptibility of sleep disturbances in AD patients. A total of 123 pretreated AD patients and 120 age-, gender-and education level-matched healthy controls were recruited for two consecutive full-night polysomnography and measurement of Epworth Sleepiness Scale (ESS) scores for sleep-wake disturbance. Their genomic DNA was analyzed for IL-1 beta and APOE epsilon 4 SNPs using ligase detection reaction (LDR) technology. Blood levels of IL-1 beta, IL-6, and tumor necrosis factor alpha (TNF-alpha) were measured using ELISA after lipopolysaccharide (LPS) stimulation. The odds ratio and 95% confidence interval for genotype-specific risk were calculated using an unconditional logistic regression model and adjusted by age, gender, educational levels, body mass index (BMI), and activities of daily living (ADL). Compared to the non-APOE epsilon 4/epsilon 4 genotype, APOE epsilon 4/epsilon 4 significantly increased the risk of AD (APOE epsilon 4/epsilon 4 vs. non-APOE epsilon 4/epsilon 4, adjusted OR = 4.33, 95% CI = 1.33-14.10, p = 0.015). Compared to the IL-1 beta CC genotype (-31), the TT genotype significantly increased the risk of AD (TT vs. CC, adjusted OR = 1.72, 95% CI = 1.13-2.61, p = 0.010). AD patients carrying the APOE epsilon 4 allele and the IL-1 beta TT genotype showed less time in bed, longer sleep latency and REM latency, more awakenings, and a lower SWS percentage than those carrying CC/CT combined genotypes. In addition, blood IL-1 beta levels were significantly greater in AD patients carrying both the APOE epsilon 4 allele and the IL-1 beta-31TT genotype than in those carrying the APOE epsilon 4 allele and the -31 TC or CC genotype. In conclusion, this study provides the first evidence indicating that the IL-1 beta-31TT genotype and homozygous APOE epsilon 4 combined are associated with increased risk of developing AD with sleep disturbance.