CLN5 and idiopathic pulmonary fibrosis: Impaired signaling of essential lung development pathways, such as fibroblast growth factor (FGF) [9, 10], Wingless/integrase-1 (WNT) signaling [11], or bone morphogenetic proteins (BMPs) [12], have been reported to contribute to the pathogenesis of adult chronic lung diseases, such as chronic obstructive pulmonary disease (COPD) or idiopathic pulmonary fibrosis (IPF) [13].