Inclusion Criteria:  Case: Chinese children aged 6-11 years old with habitual snoring (≥3 nights per week) and polysomnography (PSG) confirmed OSA (obstructive apnoea hypopnoea index (OAHI) of ≥1/hour), with adenotonsillar hypertrophy and clinical indications for adenotonsillectomy will be recruited as cases.  Control: Non-OSA subjects (with PSG OAHI <1/hour) who undergo adenotonsillectomy for other reasons such as recurrent tonsillitis.  Exclusion Criteria:  Previous upper airway surgery, genetic or syndromal disease, congenital or acquired neuromuscular disease, congenital or acquired immunodeficiency, known metabolic syndrome, craniofacial abnormalities.