Inward rectifier potassium channels are characterised by a greater tendency to allow potassium to flow into the cell rather than out of it. Their voltage dependence is regulated by the concentration of extracellular potassium; as external potassium is raised, the voltage range of the channel opening shifts to more positive voltages. The inward rectification is mainly due to the blockage of outward current by internal magnesium. Inward rectifier potassium channel 13 (KCNJ13) has a very low single channel conductance, low sensitivity to block by external barium and cesium, and no dependence of its inward rectification properties on the internal blocking particle magnesium. Defect in KCNJ13 causes snowflake vitreoretinal degeneration (SVD), which is developmental and progressive hereditary eye disorder that affects multiple tissues within the eye []. Defect in KCNJ13 can also cause Leber congenital amaurosis 16 (LCA16), which is a severe dystrophy of the retina, typically becoming evident in the first years of life [].
