Obstructive sleep apnea (OSA) is recurrent episodes of partial or complete obstruction of the upper airway during sleep that causes intermittent hypoxia and sleep fragmentation and leads to cardiometabolic and neurocognitive sequelae. Chronic intermittent hypoxia, sleep fragmentation of OSA, and insufficient sleep have been significantly associated with higher risks of neurocognitive impairment, including mild cognitive impairment (MCI) and Alzheimer's disease. Thus, sleep and circadian function might be modifiable neurocognitive impairment factors.

The significance of the study is to understand the relationships of MCI with sleep apnea and sleep-related symptoms, which helps pave the groundwork for further research.

Obstructive sleep apnea (OSA) is recurrent episodes of partial or complete obstruction of the upper airway during sleep that causes intermittent hypoxia and sleep fragmentation. Chronic intermittent hypoxia, sleep fragmentation of OSA, and insufficient sleep have been significantly associated with higher risks of neurocognitive impairment, including mild cognitive impairment (MCI) and Alzheimer's disease. Thus, sleep and circadian function might be modifiable neurocognitive impairment factors.

A recent review of 11 studies involving 5826 subjects [96% with OSA and 9% with MCI or Alzheimer's disease] suggests OSA is a modifiable risk factor for cognitive decline. Thus, improving sleep, sleep apnea and circadian function could be a high-value intervention target to alleviate cognitive impairment and decline in subjects with MCI.

The study aims to understand the relationships of prevalent sleep apnea and sleep-related symptoms with neurocognitive status in patients who presented with the main complaint of neurocognitive impairment ( to the Memory clinic). The information would help pave the groundwork for further research.

Inclusion Criteria:

• Aged 18 years and above
• Clinical diagnosis of mild cognitive impairment (MCI) based on Petersen's criteria. The criteria include the following: (1) memory problems, (2) objective memory disorder, (3) absence of other cognitive disorders or repercussions on daily life, (4) normal general cognitive function and (5) absence of dementia OR,
• Diagnosis of subjective cognitive impairment, based on the subject's own complaint of cognitive impairment but with an unremarkable assessment of the Hong Kong version of Montreal Cognitive Assessment scores
• Able to speak and read Chinese
• Adequate visual and auditory to perform a cognitive test

Exclusion Criteria:

• Diagnosed psychiatric illness with or without medication, e.g. major depressive disorder.
• Other clear organic causes of cognitive impairment, e.g. old stroke, brain tumour, dementia with Lewy body, Parkinson's disease, normal pressure hydrocephalus, neurosyphilis, autoimmune encephalitis, substance abuse, history of alcohol abuse.
• Diagnosis of major unstable illness or cancer on active treatment
• Unable to perform Home Sleep Apnea Test
• Those patients who require legal guardians

This cross-sectional study aims to recruit subjects with mild or subjective cognitive impairment in Queen Mary Hospital, Hong Kong.