DDAH1 and idiopathic pulmonary fibrosis: Among 870 genes, seven genes previously reported to be involved in IPF are claudin-5 (CLDN5), haptoglobin (HP), tumor protein P53-inducible nuclear protein 1 (TP53INP1), dimethylarginine dimethylaminohydrolase 1 (DDAH1), collagen type III alpha 1 (COL3α1), matrix metalloproteinase 7 (MMP7) and cathepsin K (CTSK) and their DNA methylation patterns are consistent with gene expression in published data (Sanders et al., 2012).