Background <p>Dystonia is a common neurological hyperkinetic movement disorder that can be caused by mutations in anoctamin 3 (ANO3, TMEM16C), a phospholipid scramblase and ion channel. We previously reported patients that were heterozygous for the ANO3 variants S651N, V561L, A599D and S651N, which cause dystonia by unknown mechanisms.</p> Methods <p>We applied electrophysiology, Ca²⁺ measurements and cell biological methods to analyze the molecular mechanisms that lead to aberrant intracellular Ca²⁺ signals and defective activation of K⁺ channels in patients heterozygous for the ANO3 variants.</p> Results <p>Upon expression, emptying of the endoplasmic reticulum Ca²⁺ store (store release) and particularly store-operated Ca²⁺ entry (SOCE) were strongly inhibited, leading to impaired activation of K_Ca3.1 (KCNN) K⁺ channels, but not of Na⁺-activated K⁺ channels (K_Na; SLO2). The data provide evidence for a strongly impaired expression of store-operated ORAI1 Ca²⁺ influx channels in the plasma membrane of cells expressing ANO3 variants.</p> Conclusions <p>Dysregulated Ca²⁺ signaling by ANO3 variants may impair the activation of K⁺ channels in striatal neurons of the brain, thereby causing dystonia. Furthermore, the data provide a first indication of a possible regulation of protein expression in the plasma membrane by ANO3, as has been described for other anoctamins.</p>