Myoclonus-dystonia (M-D) is a very rare movement disorder, caused in ∼30–50% of cases by mutations in SGCE. The CACNA1B variant c.4166G>A; (p.R1389H) was recently reported as the likely causative mutation in a single 3-generation Dutch pedigree with five subjects affected by a unique dominant M-D syndrome and cardiac arrhythmias. The gene discussed is SGCE; the disease is cardiac rhythm disease.