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:

• SMAC-A
• Documented anaphylaxis due to Hymenoptera venom with cardiovascular symptoms or
• History of at least one event of anaphylaxis as determined by the Investigator's clinical assessment and judgment based on available medical history, clinical presentation, and supporting documentation without a clearly identifiable trigger(s) or allergen(s) (otherwise idiopathic anaphylaxis) OR
• SMAC-AGS: History of anaphylaxis after eating mammalian meat (e.g. pork, beef) AND history of elevated alpha-gal (galactose-alpha 1, 3 galactose) serum IgE as determined by the Investigator's clinical assessment and supporting medical history documentation 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:

• Either hypermobile Ehlers-Danlos syndrome or documented history of hypermobility spectrum disorder.
• Postural orthostatic tachycardia syndrome with one or more systemic symptoms.
• 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.
• Cohort 4 participants must have documented diagnosis of Mastocytosis in the Skin (MIS) with previously undetected KIT D816V mutation in peripheral blood (PB) or bone marrow (BM) OR Diagnosed cutaneous mastocytosis or physical examination findings indicative of "cutaneous mastocytosis".

Key Exclusion Criteria:

• Participants previously diagnosed with any of the following:

• Monoclonal mast cell activation syndrome with a known KIT mutation
• Any subtype of systemic mastocytosis
• 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.