FLCN and pneumothorax: Overall, although ‘apparent POPVs’ could represent true ‘pneumothorax-only variants’, it seems more likely that they are artefacts for the following reasons: (i) on average each apparent POPV is carried by fewer individuals than non-POPV variants, (ii) no unequivocal clustering of such variants was apparent in the FLCN gene or folliculin protein domains and (iii) POPVs were more likely to be found in younger patients who have a lower probability of manifesting age-related renal tumours.