Objectives: Obstructive sleep apnoea (OSA) exhibits variable susceptibility to end-organ morbidities. Previous studies suggest that physiological sequelae in individuals with OSA promote changes in microbiome, which also interact with metabolic and inflammatory mediators. Therefore, microbiome and metabolomic profiling could potentially reveal the pathological processes underlying OSA. The primary objectives of our study are 1)To investigate the differences in the composition of nasal and stool microbiome between children with OSA and non-OSA controls; 2)To investigate the differences in the urine metabolomic profiles between children with OSA and non-OSA controls.

Hypothesis to be tested: The microbiome composition and urine metabolomic profiles are different between children with OSA and non-OSA controls. Changes in microbiome composition are associated with specific urine metabolomic and inflammatory profiles in children with OSA.

Design and subjects: A prospective case-control study. Chinese children aged 6-11 years old with habitual snoring and polysomnography (PSG) confirmed OSA will be recruited as cases. Non-OSA healthy children will be recruited as controls. All subjects will undergo evaluation including questionnaires, anthropometric measurements, PSG, blood, urine, nasal and stool sampling.

Primary outcome measures: Microbiome and metabolomic profiles in children with OSA compared to non-OSA controls.

Analysis: Comparisons of the microbiome and metabolomic profiles between OSA children and controls. Correlations of microbiome and metabolomic profiles with inflammatory biomarkers and PSG measurements will be evaluated by regression analysis.

Expected results: This study will provide novel data regarding microbiome and metabolomic profiles, and their relationship with inflammatory biomarkers in children with OSA.

Inclusion Criteria:

• Children aged 6-11 years old

Exclusion Criteria:

• Previous upper airway surgery, genetic or syndromal disease, congenital or acquired neuromuscular disease, suspected or confirmed congenital or acquired immunodeficiency, known metabolic syndrome, craniofacial abnormalities, structural or congenital heart disease, use of medications or therapy that could affect immunity such as systemic corticosteroids, chemotherapy, radiation therapy, intravenous immunoglobulins.

Children who attend the Paediatric Respiratory and Sleep Clinic at the Prince of Wales Hospital (PWH) for suspected OSA