FIGURE 1.

KCNJ18 mutations in TPP and SPP patients. A, chromatograms of partial sequences of KCNJ18 showing one heterozygous point mutation with guanine 501 mutated to adenosine (GTG → ATG), leading to a single amino acid substitution from valine to methionine (V168M), was found in two TPP patient (26- and 32-year-old males), one heterozygous point mutation with cytosine 127 mutated to thymidine (CGC → TGC), leading to the substitution of arginine 43 by cysteine (R43C), was found in a SPP patient (24-year-old male), and one heterozygous point mutation with guanine 598 mutated to cytosine (GCC → CCC), leading to alanine 200 to proline (A200P) mutation, was found in another SPP patient (52-year-old male). Bold letters above the nucleotide sequence represent corresponding coding amino acids. Mutated nucleotides are pointed by arrows, and mutated codons are surrounded by a red box. WT and Mu designate wild type allele and mutant allele respectively. B, membrane topology of Kir2.6 shows the relative locations of mutations. C, amino acid sequence alignment of three mutation sites from each of the four members of the inward rectifying K⁺ channels is shown. Mutations are indicated by red rectangles.