A diminished expression of Qprt was found in several models of kidney injuries associated with ER stress — using DNA damage inducible transcript 3 (DDIT3), also known as C/EBP homologous protein, as a surrogate marker (23) — for instance, injection of Tun, a transgenic mouse model expressing mutant uromodulin (UmodC147W/+) that accumulates in the ER lumen, and streptozotocin-induced diabetic nephropathy (Figure 4, A–C). Here, QPRT is linked to diabetic kidney disease.