The median (IQR) C-terminal (total) FGF23 concentration was 118 (82, 204) RU/ml, which is similar to what was observed in the large adult Chronic Renal Insufficiency Cohort (CRIC) study in subjects with eGFR 40–49 ml/min/1.73 m2 (135 [94,188] RU/ml), measured with the same C-terminal (total) FGF23 assay [2]. This evidence concerns the gene FGF23 and chronic kidney disease.