Furthermore, a regression analysis of relationships between stages of chronic kidney disease and serum levels of 10 proteases found that only angiotensin-converting enzyme 2 and DPP-4 activities significantly correlated with estimated glomerular filtration rate (eGFR); in both cases, the relationship was inverse such that patients with the highest DPP-4 and angiotensin-converting enzyme 2 activities exhibited the lowest eGFR [57]. Here, ACE2 is linked to chronic kidney disease.