Elevated Basal Serum Tryptase Research Articles

Standardized indolent systemic mastocytosis evaluations across a health care system: implications for screening accuracy

AbstractTimely diagnosis of systemic mastocytosis (SM) remains challenging because of care heterogeneity. We implemented a standardized approach for SM screening and diagnosis using a novel health care system–wide international screening registry. A retrospective analysis assessed rates of SM, cutaneous mastocytosis (CM), and molecular diagnoses before and 2 years after care standardization. The accuracy of individual and combined SM screening tests, basal serum tryptase (BST) ≥11.5 and ≥20.0 ng/mL, REMA ≥2, monomorphic maculopapular CM (MPCM), and elevated BST based upon tryptase genotype, was analyzed. Tryptase genotyping and high-sensitivity KIT p.D816V testing increased substantially 2 years after care standardization. SM diagnoses doubled from 47 to 94, and KIT p.D816V molecular diagnoses increased from 24 to 79. Mean BST and KIT p.D816V variant allele frequency values were significantly lower in patients diagnosed after standardization. Hereditary-alpha tryptasemia prevalence was increased in SM before care standardization (4/30 [13.3%]) but reflected the general population prevalence 2 years later at (5/76 [6.6%]). Elevated BST based upon genotype and BST ≥11.5 ng/mL had the highest sensitivities at 84.2% and 88.3%, respectively. The presence of monomorphic MPCM, elevated BST based upon tryptase genotype, and the combination of REMA ≥2 with elevated BST based upon tryptase genotype had specificities >90%. BST >20.0 ng/mL had low sensitivity and specificity and was not required to establish any indolent SM (ISM) diagnosis. Care standardization increased SM diagnosis rates, particularly in patients with low BSTs. Stratifying BST based upon genotype had the best overall sensitivity and specificity of any ISM screening test and improved the REMA score specificity.

The Clinical Features of Hereditary Alpha-Tryptasemia—Implications for Interdisciplinary Practice.

Hereditary alpha-tryptasemia (HAT) is a genetic predisposition of autosomal dominant inheritance that leads to a high normal (≥ 8-11.4 μg/L) or pathologically elevated (>11.4 μg/L) basal serum tryptase (BST) concentration. Its prevalence in the United Kingdom and France is reportedly 5%-6%; its prevalence in Germany is unknown. Symptomatic persons with HAT suffer from a complex constellation of symptoms. As described in this review, HAT is an important differential diagnosis in interdisciplinary practice. This review is based on publications about HAT retrieved by a selective search in PubMed, on relevant presentations at scientific meetings, and on our clinical experience. We also collected our own data on the prevalence and clinical manifestations of HAT. According to the literature, HAT is very common among patients in medical centers with BST values of 8 μg/L or above (64-74%). HAT is most commonly associated with neuropsychiatric symptoms such as exhaustion (85%), depressive episodes (59%), sleep disturbances (69%), and memory impairment (59%-68%), followed by gastrointestinal symptoms such as irritable bowel (30%-60%), nausea (51%), and reflux (49%-77%). Typical mast cell-mediated symptoms, such as flushing (47%), itch (69%), urticaria (37%), and anaphylaxis (14%-28%), are reported as well. Less commonly reported are cardiovascular manifestations, such as hypotonia, dizziness, and tachycardia (34%), and joint hypermobility (28%). HAT is more common among patients with sytemic mastocytosis (SM; 12%-21%). It is often associated with severe anaphylaxis induced by insect toxins or unknown triggers. The therapeutic options include treatment with antihistamines, mast-cell stabilizers, or IgE antibodies. A diagnosis of hereditary alpha-tryptasemia can be strongly suspected on the basis of thorough history-taking and BST measurement and then confirmed by molecular genetic testing.

Liquid Biopsy Enhances Diagnostic Workup of Hereditary Alpha-Tryptasemia (HaT) and Systemic Mastocytosis (SM) in Patients with Mast Cell-Mediated Symptoms and Elevated Basal Tryptase Levels

Background and Objectives Hereditary alpha-Tryptasemia (HaT) and Systemic Mastocytosis (SM) both display elevated basal serum tryptase (BST) levels and share mast cell-mediated digestive, neuropsychiatric, cardiovascular, cutaneous and musculoskeletal symptoms. Lack of awareness and numerous differential diagnoses complicate and often delay diagnosis, while patients suffer from impaired quality of life and do not receive suitable treatment. HaT is defined by an autosomal dominant inherited amplification of an alpha-Tryptase encoding TPSAB1 gene and is found in 5-6% of the general population. SM is characterized by an activating cKIT D816V mutation that can be detected in 90% of patients. Currently, there is no test available to discriminate between HaT and SM. We aimed to establish a non-invasive blood test supporting the diagnostic workup of these still unrecognized entities. Methods We established a customized digital droplet (dd)PCR triplex assay to detect HaT and a highly sensitive ddPCR singleplex assay for cKIT D816V mutation. We designed a clinical assessment form to record the symptoms. We identified the frequency of HaT and cKIT D816V mutation in genomic DNA isolated from peripheral blood buffy coat samples in 112 patients presenting to our institution with suspected mast cell-mediated symptoms and highly normal (>8-11.4ng/ml) or elevated (>11.4 ng/ml) BST levels (prevalence cohort, Fig. 1). For symptom assessment, we performed blood testing and symptom assessment in these 112 patients and 34 additional patients presenting with suspected SM (n=146, symptom cohort, Fig. 2). As a control cohort we tested 62 age- and sex-matched patients presenting with BST levels < 6 ng/ml (thus not suspected to have HaT or SM). Results HaT accounted for 82 out of 112 cases (73.2%) of BST levels of 8 ng/ml or higher, while cKIT D816V indicating SM was identified in only 5 cases. In 28 patients (24,1%) no HaT genotype or cKIT D816V mutation was detected. One patient with negative cKIT D816V testing but clinical signs of SM was confirmed by bone marrow biopsy, increasing SM prevalence to 6/112 (5.4%). Interestingly the HaT and SM proportions increased to 91% (HaT) and 7.5% (SM) when higher BST cut-off level of 11.4 ng/ml and to 92,9% (HaT) and 28.6% (SM) when higher BST cut-off level of 20 ng/ml were used (Fig. 1). Of note, 21.4% of patients with BST > 20 ng/ml had both, HaT and SM, and no patient with BST >20 ng/ml was tested negative for HaT and SM. In the symptom cohort, we found significant differences in type and severity of symptoms between HaT, SM and the control group. The occurrence of digestive symptoms was up to twice as high in HaT or SM compared to the control group, for flatulence (HaT 83.5%; control group 53.2%) and diarrhea (SM 68.8%; control group 25.8%) or heartburn (SM 56.3%; control group 25.8%). Nausea was significantly more common in HaT (51.7%) than in SM patients (21.9%). HaT patients more frequently reported neuropsychiatric symptoms compared to control group and SM patients. This included memory impairment (HaT 45.9%; SM 23.3%; control group 16.1%) sleep disturbances (HaT 55.8%; SM 43.8%; control group 33.3%) and fatigue (HaT 67.4%; SM 50.0%; control group 37.7%). Conclusions Simultaneous, non-invasive testing for cKIT D816V and HaT in patients with suspected mast cell mediator symptoms allows discrimination of HaT from SM. Adding BST > 8 ng/ml and >11,4ng/ml to the diagnostic workup in symptomatic individuals increases the pretest probability to detect HaT to 73.8% and 91.0%. Diagnosed patients experience mental relieve through personal and medical acknowledgement of their symptoms and suitable treatment can be initiated. According to our results, HaT testing should be initiated in all individuals presenting with mast cell mediator symptoms and BST > 8 ng/ml, and cKIT testing should be initiated in patients with BST >11.4 ng/ml. In patients with BST >20 ng/ml, cKIT D816V positive blood testing or signs of advanced SM, bone marrow based diagnostic workup is still mandatory to cover diagnostic criteria for SM according to WHO.

Venom Anaphylaxis: Decision Points for a More Aggressive Workup.

Diagnostic testing of patients who present for evaluation of insect venom allergy can involve many levels of investigation. A detailed initial history is critical for diagnosis and prognosis. The severity of previous sting reactions and the presence or absence of urticaria or hypotension predict severe future sting reactions and underlying mast cell disorders. Venom skin tests and specific IgE measurement can confirm the diagnosis but have limited positive predictive value for the frequency and severity of future sting reactions. Testing for serum IgE to recombinant venom component allergens can distinguish true allergy from cross-reactivity to honey bee and yellowjacket venoms. Basophil activation tests can improve the detection of venom allergy and predict the severity of reactions and the efficacy of venom immunotherapy but are limited in availability. An elevated basal serum tryptase level is an important marker for severe sting anaphylaxis and underlying mast cell disorders (eg, hereditary α-tryptasemia and clonal mast cell disease). When there is high suspicion (eg, using the Red Espanola de Mastocytosis score), bone marrow biopsy is the definitive tool to characterize mast cell disorders that are associated with the most severe outcomes in patients with insect sting allergy.

Genetically defined individual reference ranges for tryptase limit unnecessary procedures and unmask myeloid neoplasms.

Serum tryptase is a biomarker used to aid in the identification of certain myeloid neoplasms, most notably systemic mastocytosis, where basal serum tryptase (BST) levels>20ng/mL are a minor criterion for diagnosis. Although clonal myeloid neoplasms are rare, the common cause for elevated BST levels is the genetic trait hereditary α-tryptasemia (HαT) caused by increased germline TPSAB1 copy number. To date, the precise structural variation and mechanism(s) underlying elevated BST in HαT and the general clinical utility of tryptase genotyping, remain undefined. Through cloning, long-read sequencing, and assembling of the human tryptase locus from an individual with HαT, and validating our findings invitro and in silico, we demonstrate that BST elevations arise from overexpression of replicated TPSAB1 loci encoding canonical α-tryptase protein owing to coinheritance of a linked overactive promoter element. Modeling BST levels based on TPSAB1 replication number, we generate new individualized clinical reference values for the upper limit of normal. Using this personalized laboratory medicine approach, we demonstrate the clinical utility of tryptase genotyping, finding that in the absence of HαT, BST levels >11.4 ng/mL frequently identify indolent clonal mast cell disease. Moreover, substantial BST elevations (eg, >100 ng/mL), which would ordinarily prompt bone marrow biopsy, can result from TPSAB1 replications alone and thus be within normal limits for certain individuals with HαT.

ELEVATED BASELINE SERUM TRYPTASE AND HEREDITARY ALPHA TRYPTASEMIA (HAT)

<h3>Introduction</h3> Hereditary alpha tryptasemia (HaT) is an autosomal dominant genetic trait characterized by elevated basal serum tryptase levels due to extra allelic copies of the tryptase alpha/beta 1 (TPSAB1) gene. HaT has been associated with multisystem complaints and as a modifier of mast cell-associated disorders and anaphylaxis. <h3>Case Description</h3> A 38-year-old male presented for evaluation of food and environmental allergies. He had severe oropharyngeal symptoms and a throat-closing sensation immediately after ingesting raw fruits and tree nuts. He also had symptoms of perennial allergic rhinoconjunctivitis with seasonal variation. Allergy skin testing showed IgE sensitivities to tree, grass and weed pollens, dust mites, mold spores, cat, dog, and cockroach. He had no IgE sensitivities to any of the fruits tested. He had IgE sensitivities to walnut, hazelnut, and almond. Given the severity of his oropharyngeal symptoms a baseline serum tryptase was checked, which was elevated at 20.3 mcg/L. Repeat determinations again showed baseline serum tryptase above 20 mcg/L. CBC with differential and CMP were within normal limits. 24-hour urinary histamine and N-methylhistamine were both within normal. Kit D16 mutation analysis was negative. TPSAB1 copy number analysis showed extra allelic alpha-tryptase copies, consistent with hereditary alpha tryptasemia (HaT). The patient received counseling and standard treatment for environmental/food allergies and tolerates allergen-specific immunotherapy. <h3>Discussion</h3> HaT is an inherited condition considered a biochemical trait and can be present in around 5% of the general population. Patients with elevated baseline serum tryptase may benefit from testing for extra allelic copies of TPSAB1.

Hereditary alpha-tryptasemia.

To discuss our evolving knowledge about the genetic variations in human tryptase and recent advances in associated clinical phenotypes. Hereditary alpha-tryptasemia (HAT) is an autosomal dominant genetic trait and a common cause of elevated basal serum tryptase (BST) in Western populations. It is a risk factor for severe anaphylaxis and an established modifier of mast cell mediator-associated symptoms among patients with systemic mastocytosis (SM). The unique properties of naturally occurring alpha/beta-tryptase heterotetramers may explain certain elements of phenotypes associated with HAT. Understanding the physiology of tryptases and how this may relate to the clinical features associated with HAT is the first step in identifying optimal medical management and targets for novel therapeutics.

Incorporating Tryptase Genotyping Into the Workup and Diagnosis of Mast Cell Diseases and Reactions

The measurement of mast cell tryptase levels in serum has found utility in the diagnosis and management of both clonal mast cell disorders and severe mast cell-dependent systemic reactions in the form of anaphylaxis. A more recent discovery is that a majority of individuals with elevated basal serum tryptase levels have increased germline TPSAB1 gene copy number encoding α-tryptase. This genetic trait is referred to as hereditary α-tryptasemia (HαT) and affects nearly 6% of the general population. In clinical practice, the presence or absence of HαT should thus now be determined when defining what constitutes an abnormal serum tryptase level in the diagnosis of mastocytosis. Further, as rises in serum tryptase levels are used to support the diagnosis of systemic anaphylaxis, variability in baseline serum tryptase levels should be factored into how significant a rise in serum tryptase is required to confirm the diagnosis of a systemic allergic reaction. In practicality, this dictates that symptomatic individuals undergoing evaluation for a mast cell-associated disorder or reaction with a baseline serum tryptase level exceeding 6.5 ng/mL should be considered for tryptase genotyping in order to screen for HαT. This review provides detailed information on how to use the results of such testing in the diagnosis and management of both mastocytosis and anaphylaxis.

Hereditary alpha-tryptasemia modifies clinical phenotypes among individuals with congenital hypermobility disorders.

Hereditary alpha-tryptasemia (HαT) is an autosomal dominant (AD) genetic trait characterized by elevated basal serum tryptase ≥8 ng/mL, caused by increased α-tryptase-encoding TPSAB1 copy number. HαT affects 5% to 7% of Western populations and has been associated with joint hypermobility. Hypermobility disorders are likewise frequently AD, but genetic etiologies are often elusive. Genotyping of individuals with hypermobility spectrum disorder (n = 132), hypermobile Ehlers-Danlos syndrome (n = 78), or axial skeletal abnormalities with hypermobility (n = 56) was performed. Clinical features of individuals with and without HαT were compared. When analyzing our combined cohorts, dysphagia (p = 0.007) and retained primary dentition (p = 0.0003) were significantly associated with HαT, while positive associations with anaphylaxis (p = 0.07) and pruritus (P = 0.5) did not reach significance likely due to limited sample size. Overall, HαT prevalence is not increased in individuals with hypermobility disorders, rather linked to a unique endotype, demonstrating how HαT may modify clinical presentations of complex patients.

Resolving the genetics of human tryptases: implications for health, disease, and clinical use as a biomarker.

To discuss our evolving understanding of the genetic variation in human tryptases and recent advances in associated clinical phenotypes. Serum tryptase levels have long been used as biomarkers in clinical practice to diagnose mast cell-associated disorders and mast cell-mediated reactions but the contribution of specific secreted isoforms of human tryptases and their role(s) in health and disease has only recently begun to be illuminated. It is now recognized that hereditary alpha-tryptasemia (HαT) is a common genetic trait and the commonest cause for elevated basal serum tryptase (BST), where it can both contribute to mast cell-associated phenotypes, and potentially confound their correct diagnosis. Expression of different tryptase isoforms is now recognized to be associated with specific clinical phenotypes including clonal and nonclonal mast cell-associated disorders as well as certain asthma endotypes. These disparate impacts on clinical disorders may result from differences in enzymatic activities of mature α-tryptases and β-tryptases, and the unique substrate profile and stability of heterotetrameric mature α/β-tryptases recently described to naturally occur. Variable copy number and isoform expression of tryptases differentially impact diseases and reactions associated with mast cells in humans. Recent advances in understanding of genetics governing BST levels have refined our understanding and the clinical use of this biomarker. In the future, incorporation of tryptase genotyping will likely be integral to the work-up and trial design of patients with phenotypes impacted by mast cells ranging from asthma to mastocytosis.

Elevated Basal Serum Tryptase: Disease Distribution and Variability in a Regional Health System

Hereditary-alpha tryptasemia (HαT) is the most common etiology for elevated basal serum tryptase (BST). However, the utility of tryptase genotyping of individuals with elevated BST in general clinical practice remains undefined. Moreover, studies showing associations between elevated BST and chronic kidney disease (CKD), myelodysplastic syndrome (MDS), rheumatoid arthritis, or eosinophilic esophagitis did not include tryptase genotyping. To determine the utility of tryptase genotyping among individuals with moderate elevations in BST at a regional health system. Clinical and laboratory data from 109 subjects with basal tryptase values of 7.5 ng/mL or greater who were tested for HαT or had a disorder previously linked to elevated BST were collected retrospectively by chart review. Fifty-eight subjects had elevated BST defined as 11.5 ng/mL or greater. HαT was found in 63.8% (n= 37), 12.1% (n= 7) had CKD, and 20.7% (n= 12) had clonal myeloid disorders. A total of 6.9% (n= 4) with elevated BST had negative testing for HαT, CKD, and myeloid neoplasms. Two subjects with CKD, 1 subject with MDS, and 1 with myeloid hypereosinophilic syndrome had negative testing for HαT. Among subjects with elevated BST and more than 1 tryptase measurement, 41.5% (n= 22) had BST variability that exceeded the 20% plus 2 formula. Increased BST variability was found in subjects with HαT, all forms of mastocytosis, CKD, MDS, and those with no associated diagnosis. HαT, CKD, and clonal myeloid disorders or a combination of the 3 constitute approximately 90% of individuals with elevated BST in clinical practice. Myeloid neoplasms were over-represented in this cohort relative to population prevalence data suggesting tryptase measurement selection bias by clinicians or higher prevalence. Elevated BST is associated with increased tryptase variability, regardless of etiology.

Defining baseline variability of serum tryptase levels improves accuracy in identifying anaphylaxis

Acute increases of ≥20%+ 2 ng/mL (20+ 2 rule) over basal serum tryptase (BST) is the recommended threshold supporting a clinical diagnosis of anaphylaxis. Prospective studies have demonstrated high sensitivity for this algorithm after parenteral exposure, but specificity has not been evaluated. We sought to define a serum tryptase change that distinguishes baseline variability from anaphylaxis on the basis of intraindividual variation in BST. Ninety-three total subjects with atopy (n= 62) or hereditary α-tryptasemia (HαT) (n= 31) and ≥2 BST measurements were identified. Sequential BST variability measurements were modeled and threshold ratios that optimized sensitivity and/or specificity determined. Models were tested in 22 individuals with physician-diagnosed anaphylaxis and validated in independent cohorts of individuals with HαT (n= 33), indolent systemic mastocytosis (ISM) (n= 52), and ISM+ HαT (n= 12). Mature tryptase levels were measured in HαT (n= 19) and ISM (n= 20). An online application was developed for clinical use. As a result of BST variability, 9.7% (9/93) of primary cohort patients, and 18% (6/33) of HαT, 30% (16/53) of ISM, and 25% (3/12) of ISM+ HαT patients from validation cohorts met the 20+ 2 rule despite absent immediate hypersensitivity symptoms; mature tryptase was noncontributory among individuals with HαT or ISM at baseline. Aratio of acute tryptase/BST exceeding 1.685 provided the optimized diagnostic rule for jointly maximizing sensitivity and specificity. Statistically significant improvement in specificity relative to the 20+ 2 rule was observed among individuals with elevated BST caused by HαT and ISM. Using an acute tryptase/BST ratio of 1.685 improves specificity of measured changes among individuals with HαT and ISM while maintaining high sensitivity for confirmation of anaphylaxis.

Biphasic anaphylaxis after first dose of messenger RNA coronavirus disease 2019 vaccine with positive polysorbate 80 skin testing result

Biphasic anaphylaxis after first dose of messenger RNA coronavirus disease 2019 vaccine with positive polysorbate 80 skin testing result

Hereditary alpha tryptasemia in identical twins

Elevated serum tryptase level supports the diagnoses of anaphylactic reactions and mast cell (MC) disorders, and is a marker of increased MC burden, activation, and degranulation.1 Recently, Lyons et al2 described hereditary alpha tryptasemia (HAT) as an autosomal dominant condition characterized by an increased copy number of the TPSAB1 gene, encoding for alpha tryptase, and mild-to-moderate elevated basal serum tryptase levels. Patients with HAT were described to present with urticaria, dysautonomia, and gastrointestinal symptoms.

Hereditary Alpha-Tryptasemia: a Commonly Inherited Modifier of Anaphylaxis

Hereditary alpha-tryptasemia (HαT) is an autosomal dominant genetic trait and a common cause of elevated basal serum tryptase in Western populations. It is a risk factor for severe anaphylaxis among individuals with venom allergy and an established modifier of anaphylaxis and mast cell mediator-associated symptoms among patients with systemic mastocytosis. Understanding the physiology of tryptases and how this may relate to the clinical features associated with HαT is the first step in identifying optimal medical management and targets for novel therapeutics. HαT prevalence is increased in both clonal and non-clonal mast cell-associated disorders where it augments symptoms of immediate hypersensitivity, including anaphylaxis. The unique properties of naturally occurring α/β-tryptase heterotetramers may explain certain elements of phenotypes associated with HαT, though additional mechanisms are being evaluated. This review provides an overview of the clinical and translational studies that have identified HαT as a modifier of mast cell-associated disorders and anaphylaxis and discusses mechanisms that may potentially explain some of these clinical findings.

Small intestinal immunopathology and GI-associated antibody formation in hereditary alpha-tryptasemia

Hereditary alpha-tryptasemia (HαT) is characterized by elevated basal serum tryptase due to increased copies of the TPSAB1 gene. Individuals with HαT frequently present with multisystem complaints, including anaphylaxis and seemingly functional gastrointestinal (GI) symptoms. We sought to determine the prevalence of HαT in an irritable bowel syndrome cohort and associated immunologic characteristics that may distinguish patients with HαT from patients without HαT. Tryptase genotyping by droplet digital PCR, flow cytometry, cytometry by time-of-flight, immunohistochemistry, and other molecular biology techniques was used. HαT prevalence in a large irritable bowel syndrome cohort was 5% (N= 8/158). Immunophenotyping of HαT PBMCs (N≥ 27) revealed increased total and class-switched memory B cells. In the small bowel, expansion of tissue mast cells with expression of CD203c, HLA-DR, and FcεRI, higher intestinal epithelial cell pyroptosis, and increased class-switched memory B cells were observed. IgG profiles in sera from individuals with HαT (N= 21) significantly differed from those in individuals with quiescent Crohn disease (N= 20) and non-HαT controls (N= 19), with increased antibodies directed against GI-associated proteins identified in individuals with HαT. Increased mast cell number and intestinal epithelial cell pyroptosis in the small intestine, and class-switched memory B cells in both the gut and peripheral blood associated with IgG reactive to GI-related proteins, distinguish HαT from functional GI disease. These innate and adaptive immunologic findings identified in association with HαT are suggestive of subclinical intestinal inflammation in symptomatic individuals.

Increased TPSAB1 Copy Number in a Family With Elevated Basal Serum Levels of Tryptase.

Background: Some recent familial studies have described a pattern of autosomal dominant inheritance for increased basal serum tryptase (BST), but no correlation with mRNA expression and gene dose have been reported.Objective: We analyzed TPSAB1 mRNA expression and gene dose in a four-member family with high BST and in two control subjects.Methods: Blood samples were collected from the family and control subjects. Complete morphologic, immunophenotypical, and molecular bone marrow mast cell (MC) studies were performed. mRNA gene expression and gene dose were performed in a LightCycler 480 instrument. Genotype and CNV were performed by quantitative real-time digital PCR (qdPCR).Results: CNV analysis revealed a hereditary copy number gain genotype (3β2α) present in all the family members studied. The elevated total BST in the family members correlated with a significant increase in tryptase gene expression and dose.Conclusions and Clinical Relevance: We present a family with hereditary α-tryptasemia and elevated BST which correlated with a high expression of tryptase genes and an increased gene dose. The family members presented with atypical MC-mediator release symptoms or were even asymptomatic. Clinicians should be aware that elevated BST does not always mean an MC disorder.

Routine KIT p.D816V screening identifies clonal mast cell disease in patients with Hymenoptera allergy regularly missed using baseline tryptase levels alone

Clonal mast cell disorders and elevated basalserum tryptase (BST) levels with unknown cause(s)are associated with severe Hymenoptera venom-triggered anaphylaxis (HVA). However, some individuals with clonal disease have a normal BST level (<11.4 ng/mL). Our aim was to evaluate whether screening for KIT p.D816V in the blood is a useful clinical tool to risk-stratify patients with venom allergy. We prospectively recruited 374 patients with Hymenoptera allergy and no overt signs of mastocytosis who were referred to our center during the years 2018 and 2019. KIT p.D816V was determined in their peripheral blood by quantitative PCR, and tryptase genotyping was performed by droplet digital PCR. In all, 351 patients (93.9%) had normal levels of BST, and KIT p.D816V was detected in 8% of patients (28 of 351), predominantly in patients with the most severe Mueller grade IV anaphylaxis (18.2% [24 of 132] vs 1.8% in patients with lower grades [4 of 88 with grade III and 0 of 131 with other grades]; P< .001). In grade IV patients with a normal BST level, KIT p.D816V was associated with more severe symptoms, including a significantly higher frequency of loss of consciousness (58.3% [14 of 24] vs 34.3% [37 of 108]; P= .03) and absence of skin symptoms (41.7% [10 of 24] vs 15.7% [17 of 108]; P= .004). Among patients with a normal BST level, KIT p.D816V (OR= 10.25 [95% CI= 3.75-36.14]; P< .0001) was the major risk factor associated with severe HVA. Hereditary α-tryptasemia (HαT) due to increased germline copies of TPSAB1 encoding α-tryptase was the most common cause (65.2% [15 of 23]) of elevated BST level in patients with HVA, and together with KIT p.D816V, it accounted for 90% of BST level elevations (20 of 23) in patients with HVA. These results indicate that routine KIT p.D816V screening identifies clonal disease in high-risk patients withHVA who are regularly missed when BST level is used alone.

The Genetic Basis and Clinical Impact of Hereditary Alpha-Tryptasemia

Hereditary alpha-tryptasemia (HαT) is an autosomal dominant genetic trait found in 4% to 6% of the general population and defined by excess copies of alpha-tryptase at TPSAB1. Elevated basal serum tryptase (sBT >8 ng/mL) is a defining feature of HαT and appears to result from increased pro-alpha-tryptase synthesis and secretion rather than mast cell activation. It is estimated that approximately one-third of individuals with HαT have associated symptoms, including cutaneous, gastrointestinal, atopic, musculoskeletal, autonomic, and neuropsychiatric manifestations. HαT is found at a disproportionately high rate in systemic mastocytosis and idiopathic anaphylaxis, and is a modifying factor that independently increases the incidence and severity of anaphylaxis. The varied phenotypes associated with HαT may, in part, result from coinheritance of other genetic variants, increased expression of α-/ß-tryptase heterotetramers, and/or overexpression of pro-alpha-tryptase, although further studies are needed. There is an accurate diagnostic test available to confirm HαT in patients that can be used in combination with sBT to help risk-stratify individuals in whom bone marrow biopsy is being considered. There is no specific treatment for symptoms associated with HαT, and management is focused on controlling clinical manifestations with mast cell mediator antagonists, aspirin, inhalers, epinephrine, omalizumab, and involvement of other specialists.

Genetic Regulation of Tryptase Production and Clinical Impact: Hereditary Alpha Tryptasemia, Mastocytosis and Beyond.

Tryptase is a serine protease that is predominantly produced by tissue mast cells (MCs) and stored in secretory granules together with other pre-formed mediators. MC activation, degranulation and mediator release contribute to various immunological processes, but also to several specific diseases, such as IgE-dependent allergies and clonal MC disorders. Biologically active tryptase tetramers primarily derive from the two genes TPSB2 (encoding β-tryptase) and TPSAB1 (encoding either α- or β-tryptase). Based on the most common gene copy numbers, three genotypes, 0α:4β, 1α:3β and 2α:2β, were defined as “canonical”. About 4–6% of the general population carry germline TPSAB1-α copy number gains (2α:3β, 3α:2β or more α-extra-copies), resulting in elevated basal serum tryptase levels. This condition has recently been termed hereditary alpha tryptasemia (HαT). Although many carriers of HαT appear to be asymptomatic, a number of more or less specific symptoms have been associated with HαT. Recent studies have revealed a significantly higher HαT prevalence in patients with systemic mastocytosis (SM) and an association with concomitant severe Hymenoptera venom-induced anaphylaxis. Moreover, HαT seems to be more common in idiopathic anaphylaxis and MC activation syndromes (MCAS). Therefore, TPSAB1 genotyping should be included in the diagnostic algorithm in patients with symptomatic SM, severe anaphylaxis or MCAS.