To date, the data surrounding ACE2 activity in COVID-19 comorbidities as a risk factor for COVID-19 severity is conflicting. The list below summarizes research findings.

Humans:

• increased or no difference in ACE2 mRNA and proteins ~ patients with heart failure
• decreased ACE2 activity ~ patients with diabetes mellitus
• decreased or no difference in renal ACE2 expression ~ patients with diabetic nephropathy

Animal models:

• decreased vascular ACE2 activity ~ cardiac pathogenesis

As such, the evidence surrounding the (comorbidity ACE2 expression ~ COVID-19 severity) hypothesis is lacking.