CACNA1B and cardiac arrhythmia: Recently, Groen et al. (6) identified the missense variant c.4166G>A; (p.R1389H) (rs184841813) in CACNA1B [MIM 601012] as the likely causative mutation in a Dutch pedigree with five subjects affected by autosomal dominant M-D lacking mutations in SGCE. Unique features in the pedigree were lower limb orthostatic high-frequency myoclonus, attacks of limb painful cramps and cardiac arrhythmias in three of the affected subjects (7).