RBL-2H3 basophilic leukemia cells depleted for Munc13-4 exhibit reduced Ca2+-dependent secretory granule exocytosis that is restored by wild-type but not by Ca2+ binding–deficient Munc13-4 (Boswell et al., 2012; Woo et al., 2017). Here, UNC13D is linked to acute basophilic leukemia.