In the initial polymorphism screening for KCNJ6, a total of nine SNPs were identified in the whole exon, 5′-flanking, and exon-intron boundary regions (Figure 1). Polymorphisms that might cause significant functional changes, such as nonsynonymous or insertion/deletion polymorphisms, were not found in the polymorphism screening of the human KCNJ6 gene in the present study, possibly attributable to the importance and high conservation of mammalian GIRK channels. A possible explanation derives from studies in weaver mice, in which only a single missense mutation in the pore region of the mouse Kcnj6 gene causes various aberrant changes in cerebellar granule cells [30], membrane permeability [31], loss of K+ selectivity [32], [33], significantly lower analgesia compared with wildtype mice [3], and lack of activating effects of ethanol [34]. The Kcnj6 gene orthologs might be under purifying selection over many generations of the species, including human and mouse, because of the profound functional constraints attributable to the importance of these orthologs in these organisms.
