NRN1 and pulmonary emphysema: The candidate genes (CDKN2A, GSTM3, COL6A3, SERPINF1, NRN1, NEDD4 and ZNHIT6) had ontologies that were relevant to emphysema progression, including cell cycle regulation (CDKN2A) [23], collagen (COL6A3) [24], anti-angiogenesis (SERPINF1) [25] and oxidative stress (GSTM3) [26].