Filled symbols indicate family members with either systemic mastocytosis (SM), according to WHO criteria, or mast cell activation syndrome (MCAS); open symbols denote clinically healthy family members. Squares, males; circles, females; symbols with a diagonal line through, deceased. Mild, moderate and severe indicate the clinical intensity of the mast cell activation disease. The arrow indicates the index patient. Bold type: genetic alterations detected in the tyrosine kinase, KIT. GNNK(–/+): ratio of the GNNK(–) over the GNNK(+) isoform (i.e., the amount of PCR amplification product without and with the tetrapeptide sequence glycine-asparagine-asparagine-lysine [GNNK]).