FLCN mutations are found in approximately 10% of primary spontaneous pneumothorax (PSP) patients and are associated with multiple pulmonary cysts in the mid and lower lobes of the lungs. Similar clinical features are also seen in PSP patients who do not carry any identifiable FLCN mutations. Ding et al., (2015) recently assessed FLCN expression levels in 71 such PSP patients: compared to control lung tissue FLCN expression was lower in 35% of these patient and higher in 13%. To determine if the altered expression resulted from promoter methylation the FLCN cis-regulatory regions were analysed. No significant changes were identified suggesting this is not the cause of altered FLCN expression in these pulmonary cysts.