Differential mast cell mediators in systemic mastocytosis and hereditary α-tryptasemia

Background: Patients with systemic mastocytosis often have symptoms of mast cell activation, which is associated with elevated levels of urinary mast cell mediator metabolites. Patients with hereditary α-tryptasemia (HαT) may present with symptoms of mast cell activation. Whether levels of mast cell mediators are elevated in this patient population is not known.

Objective: The purpose of this study was to determine whether patients with HαT and symptoms of mast cell activation have elevated levels of urinary mediators and compare the levels with those in patients with systemic mastocytosis.

Methods: We retrospectively analyzed mast cell mediators in 63 patients with a confirmed diagnosis of HαT, 20 patients with a confirmed diagnosis of indolent systemic mastocytosis (ISM), and 23 healthy controls. All patients were referred to the Brigham and Women's Hospital Mastocytosis Center or the Mayo Clinic for evaluation of mast cell activation disorders.

Results: Our population was predominantly female (85.7%) with an average age of 53.8 years. The average baseline serum tryptase level was significantly higher in patients with ISM than in those with HαT (65.9 vs 19.3 ng/mL [P < .01]). When compared with patients with HαT, those with ISM had statistically significant increases in their levels of urinary N-methylhistamine (P < .01) and 2,3-dinor-11β-prostaglandin F2α (P < .05).

Conclusion: Patients with symptomatic HαT do not have elevations of mast cell urinary metabolites, suggesting that granule- and membrane-derived mediators may not drive symptoms in HαT.