Screening Study for KIT D816V Mutated Mast Cell Disease in Select Populations

Key Inclusion Criteria: * Cohort 1 participants must meet inclusion criteria for either SMAC-A or SMAC-B: 1\. SMAC-A * Documented anaphylaxis due to Hymenoptera venom with cardiovascular symptoms or * Documented anaphylaxis without known trigger(s) or allergen(s) warranting hospitalization, emergency room visit, and/or epinephrine with cardiovascular symptoms 2. SMAC-B * Episodic or recurrent signs and symptoms consistent with mast cell activation without known triggers or allergens in at least 2 of the following organ systems: skin, respiratory/naso-ocular, gastrointestinal tract, or cardiovascular. * Any clinical response on one or more optimally dosed therapies intended to mitigate mast cell mediators, as determined by the Investigator. * Cohort 2 participants must have confirmed, known diagnosis of 1 of the following criteria: 1. Either hypermobile Ehlers-Danlos syndrome or documented history of hypermobility spectrum disorder. 2. Postural orthostatic tachycardia syndrome with one or more systemic symptoms. 3. Early onset (≤50 years old) osteoporosis or osteopenia. * Cohort 3 participants must have documented diagnosis of 1 of the following, according to World Health Organization 5th edition criteria: chronic myelomonocytic leukemia or myelodysplastic syndrome/myeloproliferative neoplasm not otherwise specified. Key Exclusion Criteria: * Participants previously diagnosed with any of the following: 1. Monoclonal mast cell activation syndrome with a known KIT mutation 2. Cutaneous mastocytosis only (that is, no documentation of systemic mast cell disease via bone marrow biopsy) 3. Any subtype of systemic mastocytosis 4. Mast cell sarcoma * Cohort 2 only: Osteopenia or osteoporosis attributed to known genetic, endocrine, nutritional, or other medical conditions. Note: Additional protocol-defined criteria apply.