IL13 and asthma: Concerning IL-13 genetic predisposition, an endobronchial biopsy sample indicated an association between genetic variations in IL-13 and the thickness of the subepithelial layer (53) and genetic variations in CHI3L1 were correlated with severe asthma and increased YKL-40 expression in the airways, implying a potential link to airway remodeling (54).