• Paediatric interstitial lung disease
• Surfactant protein
• GM-CSF autoantibody
• Hypersensitivity pneumonitis
• NEHI
• Paediatric Lung Disease
• Pulmonary alveolar proteinosis
• TTF-1

The presentation of childhood interstitial lung disease (chILD) is non-specific,1 and chILD is usually low on the list of diagnoses in children with combinations of respiratory symptoms, feeding difficulties and failure to thrive. However, if a diagnosis is not considered, it will never be made. In this issue of the Journal, Fletcher et al describe nearly 800 French children, suggesting that chILD may not be as rare as once thought.2 The French RespiRare network has long been systematically collecting incidence and prevalence data of rare diseases, and in this excellent publication, they report a chILD prevalence of 44/million children (95% CI 40.76 to 47.46) and thus a computed incidence of 4.4/million children (95% CI 3.44 to 5.56). This is similar to a recent Spanish study,3 and far greater than previous studies,4 5 which were likely underestimated due to incomplete ascertainment. The major strength of the present study is the collection of data from a well-organised network spanning the whole of France, with multiple different ways of ensuring chILDs were captured. Despite this, cases may still have been missed. For example, it is a surprise that they reported not a single ILD related to e-cigarettes.6 Newborns with rapidly progressive disease due to …