CTSD expression was found to be altered in the renal tubular epithelium in patients with DN [111], and very recently, a urinary proteomic study conducted on a large cohort of type 1 diabetic subjects identified cathepsin D as a promising biomarker of rapid eGFR (estimated glomerular filtration rate) decline, which reflects kidney injury [112]. The gene discussed is CTSD; the disease is type 1 diabetes mellitus.