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

ABSTRACT: Timely 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.

Mast cell activation syndrome: Current understanding and research needs.

Mast cell activation syndrome (MCAS) is a term applied to several clinical entities that have gained increased attention from patients and medical providers. Although several descriptive publications about MCAS exist, there are many gaps in knowledge, resulting in confusion about this clinical syndrome. Whether MCAS is a primary syndrome or exists as a constellation of symptoms in the context of known inflammatory, allergic, or clonal disorders associated with systemic mast cell activation is not well understood. More importantly, the underlying mechanisms and pathways that lead to mast cell activation in MCAS patients remain to be elucidated. Here we summarize the known literature, identify gaps in knowledge, and highlight research needs. Covered topics include contextualization of MCAS and MCAS-like endotypes and related diagnostic evaluations; mechanistic research; management of typical and refractory symptoms; and MCAS-specific education for patients and health care providers.

A randomized double-blinded trial to assess recurrence of systemic allergic reactions following COVID-19 mRNA vaccination.

BACKGROUND: Systemic allergic reactions (sARs) following coronavirus disease 2019 (COVID-19) mRNA vaccines were initially reported at a higher rate than after traditional vaccines. OBJECTIVE: We aimed to evaluate the safety of revaccination in these individuals and to interrogate mechanisms underlying these reactions. METHODS: In this randomized, double-blinded, phase 2 trial, participants aged 16 to 69 years who previously reported a convincing sAR to their first dose of COVID-19 mRNA vaccine were randomly assigned to receive a second dose of BNT162b2 (Comirnaty) vaccine and placebo on consecutive days in a blinded, 1:1 crossover fashion at the National Institutes of Health. An open-label BNT162b2 booster was offered 5 months later if the second dose did not result in severe sAR. None of the participants received the mRNA-1273 (Spikevax) vaccine during the study. The primary end point was recurrence of sAR following second dose and booster vaccination; exploratory end points included biomarker measurements. RESULTS: Of 111 screened participants, 18 were randomly assigned to receive study interventions. Eight received BNT162b2 second dose followed by placebo; 8 received placebo followed by BNT162b2 second dose; 2 withdrew before receiving any study intervention. All 16 participants received the booster dose. Following second dose and booster vaccination, sARs recurred in 2 participants (12.5%; 95% CI, 1.6 to 38.3). No sAR occurred after placebo. An anaphylaxis mimic, immunization stress-related response (ISRR), occurred more commonly than sARs following both vaccine and placebo and was associated with higher predose anxiety scores, paresthesias, and distinct vital sign and biomarker changes. CONCLUSIONS: Our findings support revaccination of individuals who report sARs to COVID-19 mRNA vaccines. Distinct clinical and laboratory features may distinguish sARs from ISRRs.

High burden of clonal mast cell disorders and hereditary α-tryptasemia in patients who need Hymenoptera venom immunotherapy.

BACKGROUND: In patients who require venom immunotherapy (VIT), there is a need to identify underlying mast cell (MC) disorders since these may affect the risk and severity of future sting reactions and the long-term effectiveness of VIT. METHODS: 1319 individuals with Hymenoptera venom allergy (HVA) who needed VIT from referral centers in Slovenia, Austria, Croatia, and Poland underwent examination for KIT p.D816V in peripheral blood leukocytes (PBL) using a highly sensitive PCR test and tryptase genotyping by digital droplet PCR. We also included 183 control individuals with large local reactions (LLRs) to Hymenoptera stings and with asymptomatic sensitization to Hymenoptera venoms. RESULTS: 285 of 1319 individuals recommended for VIT (21.6%) were positive for KIT p.D816V in PBL, preferably those who present with severe reaction (33.9% [n = 207 of 610] with Ring-Messmer grade 3-4 vs. 11% [n = 78 of 709] with Grade 1-2; p < .0001), whereas only 1.3% (n = 2 of 152) of controls with LLR and none with asymptomatic sensitization (n = 31) had KIT p.D816V. KIT p.D816V allelic burden was higher in those with severe reaction (median 0.018% [n = 207] in Grade 3-4 vs. 0.001% [n = 78] in Grade 1-2; p < .0001), and the majority had normal baseline serum tryptase levels (69% [n = 196 of 285]). All KIT p.D816V-positive individuals (n = 41) who underwent bone marrow (BM) biopsy were found to have underlying clonal diseases, principally BM mastocytosis. HαT was also associated with severe HVA and symptoms (p < .01), and remarkably, 31.0% (n = 31 of 100) were found to have concomitant KIT p.D816V. Concomitant HαT and KIT p.D816V showed an additive effect, and having both was associated with the highest risk for severe HVA, even higher than having either HαT or KIT p.D816V alone (OR = 3.8; p < .01). CONCLUSIONS: By employing prospective universal tryptase genotyping and examination for KIT p.D816V in PBL in large HVA populations, we have demonstrated a high burden of clonal MC disorders and HαT in patients who require VIT.

Alpha-Tryptase as a Risk-Modifying Factor for Mast Cell-Mediated Reactions.

PURPOSE OF REVIEW: To provide an overview on the current understanding of genetic variability in human tryptases and summarize the literature demonstrating the differential impact of mature tryptases on mast cell-mediated reactions and associated clinical phenotypes. RECENT FINDINGS: It is becoming increasingly recognized that tryptase gene composition, and in particular the common genetic trait hereditary alpha-tryptasemia (HαT), impacts clinical allergy. HαT has consistently been associated with clonal mast cell disorders (MCD) and has also been associated with more frequent anaphylaxis among these patients, and patients in whom no allergic trigger can be found, specifically idiopathic anaphylaxis. Additionally, more severe anaphylaxis among Hymenoptera venom allergy patients has been linked to HαT in both retrospective and prospective studies. An increased relative number of α-tryptase-encoding gene copies, even in the absence of HαT, has also been associated with systemic mastocytosis and has been shown to positively correlate with the severity of mast cell-mediated reactions to vibration and food. These findings may be due to increased generation of α/ß-tryptase heterotetramers and differences in their enzymatic activity relative to ß-tryptase homotetramers. HαT is a naturally occurring overexpression model of α-tryptase in humans. Increased relative α-tryptase expression modifies immediate hypersensitivity symptoms and is associated with more frequent and severe mast cell-mediated reactions, ostensibly due to increased α/ß-tryptase heterotetramer production.

Clinically accessible amplitude-based multiplex ddPCR assay for tryptase genotyping.

Hereditary α tryptasemia (HαT) is an autosomal dominant trait characterized by increased TPSAB1 copy number (CN) encoding α-tryptase. The determination of HαT is being discussed as an important biomarker to be included in risk assessment models and future diagnostic algorithms for patients with mastocytosis and anaphylaxis. Due to the complex genetic structure at the human tryptase locus, genetic testing for tryptase gene composition is presently notably limited and infrequently pursued. This study aimed to develop, optimise and validate a multiplex droplet digital PCR (ddPCR) assay that can reliably quantify α- and ß-tryptase encoding sequences in a single reaction. To optimise the ddPCR conditions and establish an amplitude-based multiplex ddPCR assay, additional primers and probes, a thermal gradient with varying annealing temperatures, different primers/probe concentrations, and various initial DNA quantities were tested. Results obtained from all 114 samples analysed using multiplex ddPCR were identical to those obtained through the use of original duplex assays. Utilizing this multiplex ddPCR assay, in contrast to conducting distinct duplex ddPCRs, presents noteworthy benefits for tryptase genotyping. These advantages encompass a substantial threefold decrease in material costs and considerable time savings. Consequently, this approach exhibits high suitability and particularly captures interest for routine clinical implementation.

Underlying systemic mastocytosis in patients with unexplained osteoporosis: score proposal.

BACKGROUND: A score to predict the association between unexplained osteoporosis and an underlying systemic Mastocytosis (SM) is lacking. OBJECTIVE: This study aimed at identifying criteria able to predict the diagnosis of SM without skin involvement and provide an indication for bone marrow (BM) assessment. METHODS: We included 139 adult patients with unexplained osteoporosis and suspected SM. After BM evaluation, 63 patients (45.3 %) were diagnosed with SM, while the remaining 76 patients (54.7 %) negative for clonal mast cell (MC) disorders, constituted our control group. Univariate and multivariate analysis identified three independent predictive factors: age (<54 years: +1 point, >64 years: -1 point), serum basal tryptase (sBT) levels >19 ng/mL (+2 points) and vertebral fractures (+2 points). RESULTS: These variables were used to build the OSTEO-score, able to predict the diagnosis of SM before BM assessment with a sensitivity of 73.5 % and a specificity of 67.1 %. Patients with a score < 3 had a lower probability of having SM compared to patients with a score ≥ 3 (28.5 % and 71.4 %, respectively, p < 0.0001). When sBT levels were corrected for the presence of hereditary alpha-tryptasemia (HαT) using the BST calculater (https://bst-calculater.niaid.nih.gov/) recently published [1,2], the sensitivity of ΗαT-adjusted OSTEO-score increased to 87.8 %, and the specificity reached 76.1 %. Also, the positive predictive value of a score ≥ 3 increased to 85.2 %. CONCLUSIONS: Further studies are needed to validate these results and characterize the role of tryptase genotyping in patients with unexplained osteoporosis in reducing the risk of misdiagnosing patients with SM. Our proposed scoring model allows the identification of patients with the highest probability of having SM, avoiding unnecessary BM studies.

Deep phenotyping of post-infectious myalgic encephalomyelitis/chronic fatigue syndrome.

Post-infectious myalgic encephalomyelitis/chronic fatigue syndrome (PI-ME/CFS) is a disabling disorder, yet the clinical phenotype is poorly defined, the pathophysiology is unknown, and no disease-modifying treatments are available. We used rigorous criteria to recruit PI-ME/CFS participants with matched controls to conduct deep phenotyping. Among the many physical and cognitive complaints, one defining feature of PI-ME/CFS was an alteration of effort preference, rather than physical or central fatigue, due to dysfunction of integrative brain regions potentially associated with central catechol pathway dysregulation, with consequences on autonomic functioning and physical conditioning. Immune profiling suggested chronic antigenic stimulation with increase in naïve and decrease in switched memory B-cells. Alterations in gene expression profiles of peripheral blood mononuclear cells and metabolic pathways were consistent with cellular phenotypic studies and demonstrated differences according to sex. Together these clinical abnormalities and biomarker differences provide unique insight into the underlying pathophysiology of PI-ME/CFS, which may guide future intervention.