Mild cognitive impairment in obstructive sleep apnea

Systematic Review: microRNAs as Potential Biomarkers in Mild Cognitive Impairment Diagnosis

The rate of progression from Mild Cognitive Impairment (MCI) to Alzheimer's disease (AD) is estimated at >10% per year, reaching up to 80-90% after 6 years. MCI is considered an indicator of early-stage AD. In this context, the diagnostic screening of MCI is crucial for detecting individuals at high risk of AD before they progress and manifest further severe symptoms. Typically, MCI has been determined using neuropsychological assessment tools such as the Montreal Cognitive Assessment (MoCA) or Mini-Mental Status Examination (MMSE). Unfortunately, other diagnostic methods are not available or are unable to identify MCI in its early stages. Therefore, identifying new biomarkers for MCI diagnosis and prognosis is a significant challenge. In this framework, miRNAs in serum, plasma, and other body fluids have emerged as a promising source of biomarkers for MCI and AD-related cognitive impairments. Interestingly, miRNAs can regulate several signaling pathways via multiple and diverse targets in response to pathophysiological stimuli. This systematic review aims to describe the current state of the art regarding AD-related target genes modulated by differentially expressed miRNAs in peripheral fluids samples in MCI subjects to identify potential miRNA biomarkers in the early stages of AD. We found 30 articles that described five miRNA expression profiles from peripheral fluid in MCI subjects, showing possible candidates for miRNA biomarkers that may be followed up as fluid biomarkers or therapeutic targets of early-stage AD. However, additional research is needed to validate these miRNAs and characterize the precise neuropathological mechanisms.

Cognitive profiles in obstructive sleep apnea: a cluster analysis in sleep clinic and community samples

STUDY OBJECTIVES

Although cognitive dysfunction is a recognized consequence of untreated obstructive sleep apnea (OSA), the deficit pattern is heterogeneous. Understanding this heterogeneity may identify those at risk of cognitive deficits and guide intervention strategies. To facilitate understanding, we examined whether distinct profiles of neuropsychological performance were present in OSA and, if so, how they are related to other OSA features.

METHODS

We studied sleep clinic (n = 121) and community (n = 398) samples with moderate-severe OSA (apnea-hypopnea index ≥ 15 events/h). Attention and memory were assessed using the Cognitive Drug Research system. Sleep was assessed using polysomnography in the clinic sample and dual channel (flow, oximetry) portable monitoring in the community sample. Latent profile analysis was used to determine structure of cognitive clusters. Discriminant function analysis was used to examine associations between nocturnal and diurnal features of OSA and profile membership.

RESULTS

Both samples were best characterized by a 3-profile solution: (1) strong thinkers (performed well across most domains and showed greater cognitive reserve); (2) inattentive fast thinkers (strong processing speed but poor ability to maintain attention); and (3) accurate slow thinkers (strengths in maintaining attention but poor processing speed). Profile membership was associated with mean overnight oxygen saturation and cognitive reserve in the clinic sample and the presence of cardiovascular disease and/or diabetes in the community sample.

CONCLUSIONS

These findings help explain the diversity of outcomes in previous studies of cognitive dysfunction in OSA by demonstrating that individual differences in cognitive reserve, nocturnal oxygen saturation, and comorbidities affect how cognition is impacted by OSA.

The Effect of Sleep Disordered Breathing on Olfactory Functions: Analysis by Apnea-Hypopnea Index

Objectives

One hypothesis of obstructive sleep apnea syndrome (OSAS) is that long-standing snoring vibrations and hypoxia of the nerves cause a local neuropathy in the upper airway during sleep. The aim of this study was to investigate olfactory function in subjects comprising snorers and untreated subjects with OSAS, and to correlate data with polysomnographic parameters.

Methods

Sixty-nine patients were evaluated for snoring from January 2010 to December 2013. The mild group (apneahypopnea index [AHI]<15) consisted of 19 subjects, and the moderate-severe group (AHI≥15) consisted of 50 subjects. Exclusion criteria were conductive olfactory dysfunction, previous tonsil or soft palatal surgery, central sleep apnea, and medications that are known to affect peripheral nerves. Nocturnal polysomnography and olfactory function test such as Korean version of Sniffin’s stick test I, II (KVSS I, II) were performed.

Results

There was a significant difference in body mass index, average oxygen saturation (SaO2), lowest SaO2, average snoring duration, and KVSS I, II between the two groups. AHI was related to odor threshold score, and average SaO2 was related to odor discrimination score. But, odor identification score showed no relation with AHI and average SaO2 except for age. Average SaO2 and AHI were closely related to the function of smell.

Conclusion

Hypoxia and low nasal airflow caused by OSAS may have an effect on the olfactory function. On comparison between the two groups, patients with a high AHI, especially those with OSAS, had an olfactory dysfunction. Also, low average oxygen is the main risk factor in determining the olfactory function. In people with OSAS, the possibility of olfactory dysfunction should be considered and an olfactory function test should be performed.