25Mg2+ uptake was similar in wildtype (Slc41a3+/+) and Slc41a3−/− mice, although Slc41a3−/− animals exhibited increased intestinal mRNA expression of Mg2+ transporters Trpm6 and Slc41a1. Remarkably, some of the Slc41a3−/− mice developed severe unilateral hydronephrosis. Here, SLC41A1 is linked to hydronephrosis.