The risk variant rs13143308T increases spontaneous electrical activity. (A) Spontaneous I_TI currents in patients with a normal or a risk variant at rs13143308. (B) I_TI frequency measured in myocytes without (normal) or with a risk variant. (C) I_TI amplitude measured in the myocytes from B. (D) Membrane potential recordings at −80 mV in myocytes from a patient with normal and one with a risk variant. (E) Frequency of spontaneous membrane depolarizations at −80 mV in patients with normal and risk variants. (F) Amplitude of the depolarizations in the myocytes from (E). P-values for the unpaired t-tests (C and F) or Mann–Whitney tests (B and E) are given above data points and the number of patients in parentheses.