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Background: The search for risk factors for chronic kidney disease in children with focal segmental glomerulosclerosis (FSGS) is important in defining prognosis and individualized treatment. This study preliminarily investigated whether CD44 immunostaining in glomerular parietal epithelial cells (PECs) is a prognostic marker in pediatric FSGS. Methods: In this retrospective study, 26 patients with FSGS, biopsied from 1985 to 2010, were evaluated. Immunohistochemistry for CD44 was performed in all cases. For analysis purposes, patients were grouped according to whether or not they were positive for CD44 in PECs. The primary outcome was a decline in baseline estimated glomerular filtration rate (eGFR) of 50% or more. Results: Median follow-up was 6.9 years. Median renal survival was 14.5 years and probability of a 50% decline of eGRF was 30% in 10 years. Nine children exhibited the primary outcome and 7 developed end-stage renal disease (ESRD). In comparison with PEC CD44-negative patients ( n = 18), PEC CD44-positive patients ( n = 8) presented lower baseline eGFR (99 ± 41 versus 141 ± 44 ml/min/1.73 m, p = 0.035) and a significant decline in eGFR (−38.6 ± 39.5 versus −5.6 ± 25.3 ml/min/1.73 m/year, p = 0.018). No difference was observed in FSGS subtypes or other glomerular features. Presence of CD44 staining in PECs was significantly associated with the decline in baseline eGFR of 50% or more. Renal survival was significantly reduced in PEC CD44-positive patients (3.8 vs 14.6 years in C4d-negative, p < 0.05). Conclusion: Our preliminary findings indicate, for the first time, that positivity for CD44 in PECs seems to be a pathological marker of renal function deterioration in pediatric patients with FSGS. [ABSTRACT FROM AUTHOR]