SPP1 and focal segmental glomerulosclerosis: Fatima et al. [41] recently suggested the elevated expression of CD44 in human renal biopsy as a marker for activated parietal epithelial cells in patients with recurrent FSGS, and Nakamura et al. [42] also reported a positive correlation between upregulation of CD44, hyaluronic acid, and osteopontin in biopsy specimens with early stage of the crescent formation in human crescentic glomerulonephritis.