Soluble urokinase receptor in a toddler with focal segmental glomerulosclerosis

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 in the latest issue. In conflict with the results by Wei et al.,2 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 both studies1, 2 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, 2 An eGFR was also calculated by a formula for Japanese children at each sampling.4 As shown in Table 1, all samples demonstrated the reference value (<3000 pg/ml (ref. 2)), and there was no significant difference in suPAR levels between nephrotic stage and remission stage.