Mutations of the K⁺ channel KCNJ10 (Kir4.1) are causative for a novel autosomal recessive disease, which is characterized by epilepsy, ataxia, sensorineural deafness, and a salt-wasting renal tubulopathy (EAST or SeSAME syndrome). Here, we investigated the functional and structural consequences of four KCNJ10 mutations found in EAST patients. When expressed in CHO and HEK293 cells, the KCNJ10 mutations R65P, G77R, and R175Q showed a considerable reduced channel function in whole cell patch clamp experiments and R199X resulted in a complete loss of function. Co-expression of KCNJ10 with KCNJ16 (a partner of KCNJ10 in native tissues) generally reduced the whole cell K⁺ conductance and did not improve the function of mutated channels. In single channel analysis KCNJ10 mutations revealed a strongly reduced mean open time compared to KCNJ10 wildtype. R65P and R175Q showed a remarkable shift of pH sensitivity to the alkaline range which is probably causative for the decreased current of these mutations. Furthermore, EAST mutations lead to structural changes: Electron microscopy of distal tubular cells of an EAST patient showed reduced basolateral infoldings in this nephron segment, which is probably a consequence of the impaired salt reabsorption capacity. In conclusion, the four EAST-causing mutations of KCNJ10 led to a complete or partial loss of function and co-expression of mutated channels with KCNJ16 did not improve the residual function. The impaired salt reabsorption capacity is reflected by morphological changes. In the future, pharmacological activation of residual channel function could help to improve clinical symptoms of EAST patients.