This is a multicenter screening study to characterize the prevalence of the KIT D816V mutation in participants with suspected clonal mast cell disease.

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.

Adult participants with suspected clonal mast cell disease