Missense, nonsense, and frameshift mutations in the human anion exchanger 1 (AE1) have been associated with inherited distal renal tubular acidosis and hereditary spherocytosis. These two disorders are almost always mutually exclusive. However, we have recently found an unusual exception, i.e, a patient with complete distal renal tubular acidosis and severe hereditary spherocytosis. DNA sequencing revealed a novel mutation AE1 E522K (Band 3 Kaohsiung) combined with AE1 G701D mutation in this patient. We hypothesize these AE1 mutations cause these two disorders because of trafficking defect. To elucidate this hypothesis, we analyzed protein trafficking and subcellular location of AE1 and these mutants transfected into MDCK cells. Our results showed that they formed homodimers or heterodimers with each other. Homodimers of the wild-type and E522K mutant were localized at the plasma membrane, whereas the G701D mutant largely remained in the cytoplasm. On the other hand, heterodimers of either E522K or G701D and the wild-type AE1 were located in the plasma membrane, whereas E522K/G701D heterodimers remained in the cytoplasm. As for erythroid isoform of anion exchanger 1, analysis of protein trafficking and subcellular localization of the wild-type erythroid isoform of human anion exchanger 1 and these mutants transfected into k562 cells also showed that they can form homodimers or heterodimers with each other. Erythroid AE1 E522K/G701D cell-surface expression was significantly lower compared with WT homodimer expression. This result coincided with that erythroid AE1 of the patient¡¦s red cell membrane can be detected 28% that of normal control in immunoblotting. Our study shows that the compound E522K/G701D mutation of human anion exchanger 1 causes trafficking defects in kidney and red blood cell lines, and these may explain the complete distal renal tubular acidosis and hereditary spherocytosis of the patient.