ROBO2 and chronic obstructive pulmonary disease: Finally, we examined the expression of several known genes found to be associated with COPD based on GWAS studies [23], including HHIP (Hedgehog Interacting Protein), FAM13A (Family With Sequence Similarity 13 Member A), ROBO2 (Roundabout Guidance Receptor 2), and ANKRD18A (Ankyrin Repeat Domain 18A).