Characterization of Loss-Of-Function KCNJ2 Mutations in Atypical Andersen Tawil Syndrome

FIGURE 1. Resting ECG and exercise ECG from the probands 1 and 2. Traces from proband 1 shows (A) resting ECG with U wave (arrow) and (B) PVCs during exercise test (120 W workload). Traces from proband 2 shows (C) resting ECG with U wave (arrow) and (D) polymorphic PVCs at exercise (50 W workload) during the first Cardiopulmonary exercise test (CPET) before medical treatment was started.

FIGURE 2. Dominant negative effect of mutations p. Arg82Trp (R82W) and p. Pro186Gln (P186Q) on Kir2.1 function. (A) Mutations reduce the activity of homotetrameric channels. The histogram displays the average whole-cell currents recorded in Xenopus oocytes injected with 2 ng of RNA coding for either wild-type Kir2.1 (WT), Kir2.1R82W (R82W), or Kir2.1P186Q (P186Q). Oocytes injected with 50 ng of Kir2.1P186Q were also tested (P186Q x25). Measurements were done successively in extracellular solutions containing 2 mM K+ (Low K + ), 96 mM K+ (High K + ), and 3 mM Ba2+ and 96 mM K+ (Ba 2+ ). (B,C) Effect of mutations varies gradually with the ratio of WT to mutant subunits. (B) The histogram displays the average whole-cell currents recorded in Xenopus oocytes injected with RNAs coding for wild-type Kir2.1 (WT) or Kir2.1P186Q (P186Q), or with a mixture of RNAs coding for WT and mutant with ratios of 4:1 or 1:1. The currents were calculated as the difference between the current measured in High K+ solution and the current measured in Low K+ solution. They are here normalized to the currents obtained with only WT subunits. (C) Same for mutation R82W. Numbers above bars indicate the number of…

FIGURE 3. Model fitting reveals that one mutant subunit is sufficient to impair the function of Kir2.1 tetrameric channels. (A) Assuming random assembly of WT and mutant subunits, the probability of occurrence of channels having exactly n WT subunits (Pn) follows a binomial distribution (equation shown at top). That probability Pn is shown as a function of the fraction of wild-type subunits (p) for each possible value of n (n indicated next to the curves). (B) Probability of a channel having n or more WT subunits calculated using the distributions of (A) (n indicated next to the curves). The straight dotted line represents the probability of a WT channel if WT subunits and mutant subunits could not co-assemble. The symbols represent normalized K+ current. The percent deviation of the experimental data from each model, calculated from the rmsd (root mean-square deviation) is for p. Pro186Gln: 3.6% (n = 4), 28% (n ≥ 3), 46% (n ≥ 2), 56% (n ≥ 1), and 33% (no WT/mutant mixing; dotted straight line); and for R82W: 9.4% (n = 4), 33% (n ≥ 3), 49% (n ≥ 2), 59% (n ≥ 1), and 37% (no WT/mutant mixing; dotted straight line). For both mutants, the experimental data match best the model n = 4, meaning…