In bars = number of experiments. Error bar: standard error of the mean. doi:10.1371/journal.pone.0054131.gThe genetics of BrS is complex with incomplete penetrance and phenocopies [7]. In addition, the causality link of the SCN5A variants has been debated [7].It is possible that some BrS cases of the present cohort carry mutations in one or several of the 10 other BrS susceptibility genes. The prevalence of mutations in these 10 genes is low compared to the prevalence of SCN5A mutation which accounts for a maximum of 30 [5]. The sum of the prevalences of all the so far published gene mutations does exceed 50 which suggests that about half of BrS cases have mutation in up to now undiscovered genes. In conclusion, a TRPM4 mutation was found in 9 of 331 BrS patient (2.7 ), 23977191 and amutation or a predisposing factor was found in 11 patients of the same cohort (3.3 ). This suggests that TRPM4 accounts for a small percentage of BrS, and may thus explain that no mutations were found in a much smaller series [17]. Among the 4 mutants that were further studied, the most remarkable mutant is p.Lys914X since, as expected, it did not produce any current. On Western blots, this mutant gave bands of the same intensity as mock transfected HEK 293 cells consistent with endogenous expression of TRPM4 in this cell line [20] (Amarouch et al., in preparation). Nevertheless, using an anti-HA antibody (the HA tag is located at the N terminus of transfectedFigure 4. 4 IBP single channel currents. Inside-out single channel currents for WT and mutants TRPM4. Representative recordings at Vm = +40 and 240 mV and mean current/voltage relationship of WT (A) and mutants (B). No significant currents were detected for K914X mutant. (C): Single channel conductance g of WT and 
mutants. Mean values for 5 to 9 experiments. ND: not determined. doi:10.1371/journal.pone.0054131.gTRPM4 Mutations in Brugada SyndromeFigure 5. Na+/Cl2 permeability ratio and channels regulation. (A): PNa/PCl permeability ratio was estimated by changing the 145 mM NaCl solution to a 42 mM NaCl solution to measure the shift of the current-voltage relationship. Voltage ramp protocol from Vm = 2100 to +100 mV was applied as RE640 biological activity showed for L1075P. (B): Reversal potential (Vrev) was estimated for WT and mutants as showed in A. PNa/PCl was calculated according to the GHK equation. Similar results were obtained for mutants and WT. (C): Effect of [Ca2+]i on unitary channel activity was evaluated at Vm = +40 mV by reducing [Ca2+]i from 1023 M to 1026 M. A representative trace is provided for WT. Magnification allows observing single-channel currents. Label “c” indicates the current level corresponding to the closed state of all channels. (D): Mean of inhibition of channel activity with [Ca2+]i = 1026 M compare to 1023 M for WT and mutants. No significant differences were detected. (E): Channel sensitivity to voltage was evaluated in the whole-cell configuration by estimating NPo in function of voltage for each mutant during ramp protocols (see proceedings description in the text) as showed for WT and P779R. (F): Mean voltage for half maximal activity (V1/2) estimated from traces as showed in E. P779R exhibited a significant increase in V1/ 2. ** = significantly different from WT (p,0.01). Numbers in bars = number of experiments. doi:10.1371/journal.pone.0054131.gTRPM4), we could detect a clear band corresponding to the truncated protein in whole cell extract and in the plasma membrane. Since the nonsense mutation.In bars = number of experiments. Error bar: standard error of the mean. doi:10.1371/journal.pone.0054131.gThe genetics of BrS is complex with incomplete penetrance and phenocopies [7]. In addition, the causality link of the SCN5A variants has been debated [7].It is possible that some BrS cases of the present cohort carry mutations in one or several of the 10 other BrS susceptibility genes. The prevalence of mutations in these 10 genes is low compared to the prevalence of SCN5A mutation which accounts for a maximum of 30 [5]. The sum of the prevalences of all the so far published gene mutations does exceed 50 which suggests that about half of BrS cases have mutation in up to now undiscovered genes. In conclusion, a TRPM4 mutation was found in 9 of 331 BrS patient (2.7 ), 23977191 and amutation or a predisposing factor was found in 11 patients of the same cohort (3.3 ). This suggests that TRPM4 accounts for a small percentage of BrS, and may thus explain that no mutations were found in a much smaller series [17]. Among the 4 mutants that were further studied, the most remarkable mutant is p.Lys914X since, as expected, it did not produce any current. On Western blots, this mutant gave bands of the same intensity as mock transfected HEK 293 cells consistent with endogenous expression of TRPM4 in this cell line [20] (Amarouch et al., in preparation). Nevertheless, using an anti-HA antibody (the HA tag is located at the N terminus of transfectedFigure 4. Single channel currents. Inside-out single channel currents for WT and mutants TRPM4. Representative recordings at Vm = +40 and 240 mV and mean current/voltage relationship of WT (A) and mutants (B). No significant currents were detected for K914X mutant. (C): Single channel conductance g of WT and mutants. Mean values for 5 to 9 experiments. ND: not determined. doi:10.1371/journal.pone.0054131.gTRPM4 Mutations in Brugada SyndromeFigure 5. Na+/Cl2 permeability ratio and channels regulation. (A): PNa/PCl permeability ratio was estimated by changing the 145 mM NaCl solution to a 42 mM NaCl solution to measure the shift of the current-voltage relationship. Voltage ramp protocol from Vm = 2100 to +100 mV was applied as showed for L1075P. (B): Reversal potential (Vrev) was estimated for WT and 
mutants as showed in A. PNa/PCl was calculated according to the GHK equation. Similar results were obtained for mutants and WT. (C): Effect of [Ca2+]i on unitary channel activity was evaluated at Vm = +40 mV by reducing [Ca2+]i from 1023 M to 1026 M. A representative trace is provided for WT. Magnification allows observing single-channel currents. Label “c” indicates the current level corresponding to the closed state of all channels. (D): Mean of inhibition of channel activity with [Ca2+]i = 1026 M compare to 1023 M for WT and mutants. No significant differences were detected. (E): Channel sensitivity to voltage was evaluated in the whole-cell configuration by estimating NPo in function of voltage for each mutant during ramp protocols (see proceedings description in the text) as showed for WT and P779R. (F): Mean voltage for half maximal activity (V1/2) estimated from traces as showed in E. P779R exhibited a significant increase in V1/ 2. ** = significantly different from WT (p,0.01). Numbers in bars = number of experiments. doi:10.1371/journal.pone.0054131.gTRPM4), we could detect a clear band corresponding to the truncated protein in whole cell extract and in the plasma membrane. Since the nonsense mutation.
