Nasal epithelial brush
STERILE
Nasal epithelial cells will be collected at the baseline visit by brushing nylon flocked swabs (FLOQSwabs®, COPAN, CA, USA) against the lateral side of the inferior turbinate of both nostrils. Two swabs will be transferred into sterile National Lab Cryovials, and two swabs will be transferred into sterile National Lab Cryovials filled with RNAlater™ stabilisation solution. All cryovials will be stored at -80°C until DNA and RNA extraction and subsequent determination of DNA methylation and RNA-sequencing.