We report two novel mutations in Kir2.1 leading to Andersen´s Syndrome. The mutant channels were heterologously expressed in Xenopus oocytes and HEK293 cells and the amplitude of whole-cell currents was measured. In addition, surface expression was assayed with a chemiluminescence assay in oocytes and fluorescence microscopy in mammalian cells. No currents were detected when the mutants were expressed in Xenopus oocytes. Co-expression of mutant channels with Kir2.1 in oocytes led to a dominant-negative suppression of Kir2.1 currents. In addition co-expression with Kir2.2, Kir2.3 and Kir2.4 led to a similar reduction in current amplitudes, suggesting that heteromerisation could contribute to the phenotype of the disease and that Kir2.1 also heteromerises with Kir2.4 channels. Fluorescence microscopy of HEK cells transiently transfected with Kir2.1 channels fused to EGFP showed normal trafficking of both novel mutants. Both mutants reached the membrane, while no currents were detected with patch-clamp recordings. Fluorescence microscopy of wild-type Kir2.1-DsRed2 co-expressed with mutant channels fused to EGFP showed co-localisation of wild-type and mutant channels in the membrane. In fact, all previously reported Kir2.1 mutants from this region reach the membrane. This finding indicates the importance of this region for gating of Kir channels.