HTRA1 and chronic obstructive pulmonary disease: Interestingly, pathways involved in rheumatic disease (p=0.015) appeared to be associated only with genes differentially upregulated in the control versus COPD dataset (CYP7B1, DPYS, HTRA1, IGFBP7, IGHD, SNAI2 and TMEM266), indicating genes in this pathway may be unique to COPD lung tissue and/or that rheumatic disease and COPD are strongly linked comorbidities.