Approach to Idiopathic Anaphylaxis in Adolescents

Anaphylaxis is a potentially-life threatening condition. Adolescents are particularly vulnerable due to increased risk-taking behaviors, poor disease management, and minimized perception of risk. Although most anaphylaxis can be attributed to food, drug, or venom allergy via a detailed history and confirmatory studies, in nearly 1 in 5 cases, the cause may not be obvious. Clinical differentials including rare allergens, cofactors, mast-cell disorders, and mimic disorders can increase the likelihood of discovering of the cause of anaphylaxis.

The Normal Range of Baseline Tryptase Should Be 1 to 15 ng/mL and Covers Healthy Individuals With HαT

Physiological levels of basal serum tryptase vary among healthy individuals, depending on the numbers of mast cells, basal secretion rate, copy numbers of the TPSAB1 gene encoding alpha tryptase, and renal function. Recently, there has been a growing debate about the normal range of tryptase because individuals with the hereditary alpha tryptasemia (HαT) trait may or may not be symptomatic, and if symptomatic, uncertainty exists as to whether this trait directly causes clinical phenotypes or aggravates certain conditions. In fact, most HαT-positive cases are regarded as asymptomatic concerning mast cell activation. To address this point, experts of the European Competence Network on Mastocytosis (ECNM) and the American Initiative in Mast Cell Diseases met at the 2022 Annual ECNM meeting and discussed the physiological tryptase range. Based on this discussion, our faculty concluded that the normal serum tryptase range should be defined in asymptomatic controls, inclusive of individuals with HαT, and based on 2 SDs covering the 95% confidence interval. By applying this definition in a literature screen, the normal basal tryptase in asymptomatic controls (HαT-positive persons included) ranges between 1 and 15 ng/mL. This definition should avoid overinterpretation, unnecessary referrals, and unnecessary anxiety or anticipatory fear of illness in healthy individuals.

Mimics of Allergy and Angioedema: Scombroid, Mast Cell Activation Disorders, and Hereditary Alpha Tryptasemia

Scombroid poisoning, systemic mastocytosis, and hereditary alpha tryptasemia all present with episodes that resemble allergic reactions. Knowledge regarding systemic mastocytosis and hereditary alpha tryptasemia is quickly evolving. Epidemiology, pathophysiology, and strategies to identify and diagnose are discussed. Evidence-based management in the emergency setting and beyond is also explored and summarized. Key differences are described between these events and allergic reactions.

Mimics of Allergy and Angioedema: Scombroid, Mast Cell Activation Disorders, and Hereditary Alpha Tryptasemia

Scombroid poisoning, systemic mastocytosis, and hereditary alpha tryptasemia all present with episodes that resemble allergic reactions. Knowledge regarding systemic mastocytosis and hereditary alpha tryptasemia is quickly evolving. Epidemiology, pathophysiology, and strategies to identify and diagnose are discussed. Evidence-based management in the emergency setting and beyond is also explored and summarized. Key differences are described between these events and allergic reactions.

Diagnosis, Classification and Management of Mast Cell Activation Syndromes (MCAS) in the Era of Personalized Medicine

Mast cell activation (MCA) is seen in a variety of clinical contexts and pathologies, including IgE-dependent allergic inflammation, other immunologic and inflammatory reactions, primary mast cell (MC) disorders, and hereditary alpha tryptasemia (HAT). MCA-related symptoms range from mild to severe to life-threatening. The severity of MCA-related symptoms depends on a number of factors, including genetic predisposition, the number and releasability of MCs, organs affected, and the type and consequences of comorbid conditions. In severe systemic reactions, MCA is demonstrable by a substantial increase of basal serum tryptase levels above the individual’s baseline. When, in addition, the symptoms are recurrent, involve more than one organ system, and are responsive to therapy with MC-stabilizing or mediator-targeting drugs, the consensus criteria for the diagnosis of MCA syndrome (MCAS) are met. Based on the etiology of MCA, patients can further be classified as having i) primary MCAS where KIT-mutated, clonal, MCs are detected; ii) secondary MCAS where an underlying IgE-dependent allergy or other reactive MCA-triggering pathology is found; or iii) idiopathic MCAS, where neither a triggering reactive state nor KIT-mutated MCs are identified. Most severe MCA events occur in combined forms of MCAS, where KIT-mutated MCs, IgE-dependent allergies and sometimes HAT are detected. These patients may suffer from life-threatening anaphylaxis and are candidates for combined treatment with various types of drugs, including IgE-blocking antibodies, anti-mediator-type drugs and MC-targeting therapy. In conclusion, detailed knowledge about the etiology, underlying pathologies and co-morbidities is important to establish the diagnosis and develop an optimal management plan for MCAS, following the principles of personalized medicine.

Mast cell activation in the context of elevated basal serum tryptase: genetics and presentations

PURPOSE OF REVIEW

To describe inherited and acquired genetic variants and clinical entities associated with increased basal serum tryptase (BST), distinguish these levels from those which acutely rise due to mast cell activation, and finally to characterize the association between chronically elevated basal serum tryptase and episodic mast cell activation.

RECENT FINDINGS

Hereditary alpha-tryptasemia is a commonly inherited genetic cause for basally elevated serum tryptase and explains elevated BST in many individuals who do not have evidence of clonal myeloid or mast cell disease. When clonal myeloid disease is present, BST may be elevated and can be a biomarker of a number of disparate disorders of the myeloid compartment. Elevated BST is most commonly caused by hereditary alpha tryptasemia but may also be indicative of clonal myeloid disease. Clinical reports suggest that elevated BST is associated with increased risk for more severe systemic allergic reactions to a number of eliciting agents and exposures. Additional studies are needed to determine the role that inherited or acquired genetic variants associated with elevated BST and clonal or non-clonal myeloid diseases may play in these reactions.