PTGDS and chronic obstructive pulmonary disease: The magnitude of fold difference in expression between COPD groups, based on FEV1, was greater than 1.8 for eight of these genes (NNMT, THBS1, HLA-DPB1, IGHD, ETS2, ELF1, PTGDS and CYRBD1) (Figure 1A and 1B (b&c)).