Soluble urokinase receptor in a toddler with focal segmental glomerulosclerosis
Authors: Tetsuya Kitao, Takahisa Kimata, Eriko Kanda, Jiro Kino, Shogo Kato, Sohsaku Yamanouchi, Shoji Tsuji, Kazunari Kaneko
Journal: Kidney International (2014)

To the Editor: We read with great interest the article entitled ‘A multicenter cross-sectional study of circulating soluble urokinase receptor in Japanese patients with glomerular disease’ by Wada et al.1.Wada T. Nangaku M. Maruyama S. et al.A multicenter cross-sectional study of circulating soluble urokinase receptor in Japanese patients with glomerular disease.Kidney Int. 2014; 85: 641-648Abstract Full Text Full Text PDF PubMed Scopus (63) Google Scholar in the latest issue. In conflict with the results by Wei et al.,2.Wei C. El Hindi S. Li J. et al.Circulating urokinase receptor as a cause of focal segmental glomerulosclerosis.Nat Med. 2011; 31: 952-960Crossref Scopus (649) Google Scholar they concluded that soluble urokinase receptor (suPAR) is not a useful parameter for differentiating focal segmental glomerulosclerosis (FSGS) from the other glomerular diseases and is inversely correlated with estimated glomerular filtration rate (eGFR) in each patient. Although it is known that renal maturation assessed by GFR occurs rapidly during the first 3 years of age, when it reaches a level equivalent to that in adults,3.Kaneko K. Serum cystatin C as a possible marker to detect renal maturation.Pediatr Nephrol. 2010; 25: 561-562Crossref Scopus (4) Google Scholar both studies1.Wada T. Nangaku M. Maruyama S. et al.A multicenter cross-sectional study of circulating soluble urokinase receptor in Japanese patients with glomerular disease.Kidney Int. 2014; 85: 641-648Abstract Full Text Full Text PDF PubMed Scopus (63) Google Scholar,2.Wei C. El Hindi S. Li J. et al.Circulating urokinase receptor as a cause of focal segmental glomerulosclerosis.Nat Med. 2011; 31: 952-960Crossref Scopus (649) Google Scholar do not include such toddlers with renal development. Therefore, we would like to introduce our case of a 2-year-old Japanese boy with typical FSGS whose serum suPAR levels were repeatedly measured during renal maturation. The sera were collected at either nephrotic stage (n=15) or remission stage (n=8). The suPAR levels were measured with the same kit as that used in the previous studies.1.Wada T. Nangaku M. Maruyama S. et al.A multicenter cross-sectional study of circulating soluble urokinase receptor in Japanese patients with glomerular disease.Kidney Int. 2014; 85: 641-648Abstract Full Text Full Text PDF PubMed Scopus (63) Google Scholar,2.Wei C. El Hindi S. Li J. et al.Circulating urokinase receptor as a cause of focal segmental glomerulosclerosis.Nat Med. 2011; 31: 952-960Crossref Scopus (649) Google Scholar An eGFR was also calculated by a formula for Japanese children at each sampling.4.Nagami T. Uemura O. Ishikura K. et al.Creatinine-based equations to estimate glomerular filtration rate in Japanese children aged between 2 and 11 years old with chronic kidney disease.Clin Exp Nephrol. 2013; 17: 877-881Crossref Scopus (22) Google Scholar As shown in Table 1, all samples demonstrated the reference value (<3000pg/ml (ref. 2.Wei C. El Hindi S. Li J. et al.Circulating urokinase receptor as a cause of focal segmental glomerulosclerosis.Nat Med. 2011; 31: 952-960Crossref Scopus (649) Google Scholar)), and there was no significant difference in suPAR levels between nephrotic stage and remission stage.Table 1Serum levels of suPAR in conjunction with proteinuria and eGFR in a 2-year-old boy with typical FSGSParametersNephrotic stage (n=15) median (IQR)Remission stage (n=8) median (IQR)P-valueSerum suPAR (pg/ml)2192.4 (2000.6–2339.7)2445.8 (2006.8–2620.9)0.44eGFR (ml/min per 1.73m2)164.0 (141.7–201.3)145.9 (140.7–157.8)0.33Proteinuria (g/gCr)19.05 (10.81–38.22)0.09 (0.07–0.35)0.0001Abbreviations: eGFR, estimated glomerular filtration rate; FSGS, focal segmental glomerulosclerosis; IQR, interquartile range; suPAR, soluble urokinase receptor. Open table in a new tab Abbreviations: eGFR, estimated glomerular filtration rate; FSGS, focal segmental glomerulosclerosis; IQR, interquartile range; suPAR, soluble urokinase receptor. Thus, the suPAR is unlikely to be relevant to proteinuria even in toddlers showing renal development.