More particularly, in patients with COPD, a lung RNA-seq dataset showed a significant upregulation in the expression of ACE2 in comparison to subjects with normal spirometry (controls) (p = 0.00034) and ACE2 was significantly up-regulated in six out of seven lung transcriptome studies, suggesting that patients who have COPD or Pulmonary Arterial Hypertension (PAH) may have a higher risk of developing severe COVID-19 [59]. Here, ACE2 is linked to COVID-19.