Our IHC analysis, conducted on biopsy specimens from 15 patients with IgAN, 10 with MCD, 10 with MN, 10 with FSGS, and 9 healthy controls, revealed a predominant expression of CTSS within the microvilli located in renal tubular epithelial cells of the kidney, as depicted in Figure 7A. Here, CTSS is linked to focal segmental glomerulosclerosis.