Ten Years of Hereditary Alpha-Tryptasemia: The Common Gene Variant Reshaping Anaphylaxis Care

Ten years ago, a team led by Jonathan Lyons at the United States National Institute of Allergy and Infectious Diseases described a genetic trait that had been hiding in plain sight in the blood of millions of people. Writing in Nature Genetics in 2016, the researchers showed that individuals with unexplained elevations of basal serum tryptase, an enzyme released by mast cells, carried extra copies of a gene called TPSAB1. The condition, now known as hereditary alpha-tryptasemia, or HαT, has since become one of the most consequential discoveries in modern allergy and immunology, and a new editorial in Frontiers in Allergy marks a decade of progress while taking stock of the questions that remain open.

The genetics are deceptively simple. TPSAB1 encodes alpha-tryptase, one of the major serine proteases stored in the granules of mast cells, the immune cells that orchestrate allergic reactions. Most people carry a single copy of the alpha-encoding gene. In hereditary alpha-tryptasemia, germline copy numbers of TPSAB1 are increased, and the trait is passed down in an autosomal dominant fashion. Each additional alpha-tryptase allele drives tryptase production higher, and the result is a measurably elevated baseline level of the enzyme in the bloodstream. Roughly four to six percent of Western populations carry the trait, making it the most common identified cause of elevated basal serum tryptase in otherwise healthy individuals.

What makes the trait so challenging for clinicians is that its effects vary enormously from person to person. Approximately one third of carriers never develop any symptoms at all, while others experience a bewildering array of multisystem complaints, including flushing, itching, gastrointestinal disturbance, and recurrent systemic reactions that can resemble anaphylaxis. Early reports linked HαT to connective tissue abnormalities, dysautonomia, joint hypermobility, and postural orthostatic tachycardia syndrome, but those associations were later disproven. The current consensus, strongly reinforced by the new editorial, is that HαT should be understood as a genetic trait rather than a disease entity, one whose clinical relevance depends heavily on context.

That context matters most when the immune system is already primed for trouble. Although HαT does not intrinsically cause allergic sensitization, accumulating evidence indicates that it amplifies both the frequency and the severity of anaphylaxis in defined clinical settings. The clearest example is Hymenoptera venom allergy, where carriers of extra alpha-tryptase copies react more often and more violently to stings. Similar patterns have emerged in food allergy, idiopathic anaphylaxis, and reactions to high-risk medications such as antibiotics and monoclonal antibodies. Emerging data further suggest that HαT may influence mast cell homeostasis and immune responses within the gastrointestinal tract, extending its reach beyond classic anaphylactic shock.

The new Frontiers Research Topic brings together studies that illustrate how the field has matured. In one contribution, Puxkandl and colleagues found HαT in ninety-three percent of individuals with increased basal serum tryptase levels, confirming overwhelmingly that the trait is the explanation for elevated readings of this enzyme. Their cohort was strikingly female-predominant, showed an unexpected association with thyroid disease, and reported anaphylaxis, predominantly of low grade, in more than half of the patients. These observations frame two recurring themes across the collection: the need to interpret tryptase measurements against a patient’s genotype, and the unresolved extent to which the trait truly confers excess anaphylaxis risk.

Two complementary reviews tackled the diagnostic problem directly. Crupi and colleagues argued that basal serum tryptase must be read in a context-dependent manner, noting that HαT adds approximately nine to ten nanograms per milliliter of tryptase for every supernumerary alpha-allele. Conventional thresholds, such as values above twenty or above two hundred nanograms per milliliter, lose their meaning when genotype is unknown, because a carrier can have a high baseline that reflects inherited overexpression rather than pathology. McMurray and colleagues went further, presenting evidence that basal tryptase, interpreted against an individual’s tryptase genotype, is the single most accurate screening test for systemic mastocytosis, a clonal disorder in which abnormal mast cells accumulate in organs.

The management consequences of ignoring genotype can be serious. McMurray and colleagues highlighted an easily overlooked point: tyrosine kinase inhibitors, the mainstay drugs for systemic mastocytosis, do not eliminate production of wild-type tryptase by the body’s normal mast cells. Patients who have both systemic mastocytosis and HαT are therefore not expected to normalize their tryptase levels even with effective disease-modifying therapy. Without knowledge of their genotype, such patients risk inappropriate dose escalation or premature discontinuation of treatment, as clinicians mistake an inherited baseline for treatment failure.

The relationship between HαT and clonal mast cell disorders was dissected most explicitly by two research groups, Chantran and Arock and Polivka and colleagues, who confirmed a consistent overrepresentation of the trait across mast cell disorder cohorts, accompanied by higher rates of anaphylaxis and a shift toward low-burden, non-cutaneous subtypes. Chantran and Arock offered three possible explanations, positioning HαT as a tryptase modifier, a symptom modifier, or a candidate causal factor, and suggested that much of the apparent enrichment reflects ascertainment bias rather than a true pathophysiological link. Polivka and colleagues translated the uncertainty into practical guidance, recommending first-line peripheral blood genotyping for HαT alongside testing for the KIT D816V mutation, the hallmark of systemic mastocytosis. Because peripheral blood KIT assays have low sensitivity in patients without skin involvement, they cautioned that negative results cannot exclude disease, and they argued against routine family screening given the low estimated prevalence of clonal disease among carriers.

Beyond the allergy clinic, the Research Topic explored the trait’s effects on the gut and on food allergy. Lang reviewed HαT in food allergy and concluded that although the prevalence of food allergy among carriers appears comparable to that in the general population, alpha-tryptase behaves as a gene-dose-dependent risk factor for reaction severity, paralleling its effect in venom anaphylaxis, which makes TPSAB1 genotyping a candidate biomarker for predicting how severe a reaction may be. Vainer and Peterson argued that the gastrointestinal symptoms of HαT, which often mimic irritable bowel syndrome, likely represent a distinct entity driven by PAR-2, a protease-activated receptor that tryptase can cleave, and they proposed a mediator-directed treatment ladder. Galeas-Pena and colleagues gave this idea molecular substance, demonstrating that HαT-associated inflammatory bowel disease is marked by increased intestinal mast cell abundance and selective upregulation of the receptors MRGPRX2 and SIGLEC-8, suggesting a mast-cell-centric, IgE-independent endotype. Simeone and colleagues presented a unifying model in which alpha-beta tryptase heterotetramers act through the receptors EMR2 and PAR-2 to modify mucosal immunity.

The editors of the collection, Mark Kacar, Peter Kopac, and Jonathan Lyons, are candid about the field’s limitations: causality remains unresolved, penetrance is incomplete, and there is a near-total absence of data from individuals of non-European ancestry. Yet the preponderance of evidence now supports a coherent picture of HαT as a common modifier of mast cell-mediated immediate hypersensitivity, one that unifies the reported associations with clonal mast cell disease and non-clonal mast cell phenotypes alike. The trait is best viewed as a naturally occurring overexpression model of alpha-tryptase, existing on a spectrum of expression in humans, whose pathogenic potential may arise from the unique biochemistry of tryptase heterotetramers, from the increased numbers of mast cells found in the tissues of symptomatic carriers, or from mechanisms not yet characterized. Because human tryptases, and indeed human mast cells themselves, are recent evolutionary innovations unique to our species, animal models offer limited help, meaning the next decade of discovery will depend on continued study of the people who carry this remarkably common gene variant.

Subject of Research: Hereditary alpha-tryptasemia, a common TPSAB1 copy number trait modifying mast cell–mediated disease and anaphylaxis

Article Title: Editorial: Hereditary alpha-tryptasemia: 10 years on

Article References: Kacar, M., Kopac, P., & Lyons, J. J. (2026). Editorial: Hereditary alpha-tryptasemia: 10 years on. Frontiers in Allergy, 7, Article 1980092. https://doi.org/10.3389/falgy.2026.1980092

Image Credits: AI Generated

DOI: 10.3389/falgy.2026.1980092

Keywords: hereditary alpha-tryptasemia, TPSAB1, tryptase, mast cells, anaphylaxis, systemic mastocytosis, food allergy, Hymenoptera venom allergy, gastrointestinal symptoms, genetics, allergy, precision medicine