Using exome sequencing and linkage analysis in a three-generation family with a unique dominant myoclonusdystonia-like syndrome with cardiac arrhythmias, we identified a mutation in the CACNA1B gene, coding for neuronal voltage-gated calcium channels Ca(V)2.2. This mutation (c.4166G>A; p.Arg1389His) is a disruptive-missense mutation in the outer region of the ion pore. The functional consequences of the identified mutation were studied using whole-cell and single-channel patch recordings. High-resolution analyses at the single-channel level showed that, when open, R1389H Ca(V)2.2 channels carried less current compared with WT channels. Other biophysical channel properties were unaltered in R1389H channels including ion selectivity, voltage-dependent activation or voltage-dependent inactivation. Ca(V)2.2 channels regulate transmitter release at inhibitory and excitatory synapses. Functional changes could be consistent with a gain-of-function causing the observed hyperexcitability characteristic of this unique myoclonus-dystonia-like syndrome associated with cardiac arrhythmias.