Although the ε-(γ-glutamyl)-lysine data suggest that this marker is less attractive as a prognostic biomarker, it does show notably elevated levels in CKD and may offer potential as a pharmacodynamic/target engagement marker for future trials of TG2 inhibitors in fibrotic diseases; equally, the ε-(γ-glutamyl)-lysine assay used here requires further validation. This evidence concerns the gene TGM2 and chronic kidney disease.