In some patients, this can be quite dramatic, as in the boy reported previously, who presented marked electrolyte abnormalities with the typical pattern of Gitelman syndrome (K: 3.2, Cl: 97, and bicarbonate: 33 mmol/l) and consequently received this as his clinical diagnosis, yet on genetic testing was found to have an HNF1B mutation.13 Here, HNF1B is linked to Gitelman syndrome.