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

Abstract Introduction: The utility of patient reported symptoms and serum tryptase levels in distinguishing those with systemic mastocytosis (SM) versus mast cell activation syndrome (MCAS) versus those not meeting formal diagnostic criteria for SM or MCAS has not been systematically examined. Methods: This study was approved by our institutional review board. Patients were referred for suspected SM based on symptoms of mast cell activation, osteopenia, skin rash, etc., or had an established diagnosis of SM. All patients were given a Mastocytosis Symptom Assessment Form (MastSAF) to complete at their initial evaluation. The MastSAF is comprised of 36 symptom questions to be graded on a scale of 0 (absent) to 10 (worst imaginable), and is organized around 9 symptom clusters: gastrointestinal (8 questions), constitutional (3 questions), musculoskeletal (5 questions), cutaneous (4 questions), neuropsychological (6 questions), genitourinary (3 questions), respiratory (4 questions), angioedema (1 question), and cardiovascular (2 questions). All patients underwent bone marrow biopsy and serum tryptase level assessment. SM was diagnosed by 2008 WHO criteria. In the presence of characteristic symptoms, if clonal or abnormal mast cells were not identified, and if serum/urine mast cell mediator levels were increased, then non-SM associated, non-monoclonal MCAS was diagnosed. Results: A total 53 patients were studied. 1) SM: Of 28 patients, 13 had indolent SM (ISM), 9 aggressive SM (ASM) and 6 SM with associated hematological disease (SM-AHD) The median total symptom score was 47 (range 8-159). The median (range) for SM subgroups was: ISM 51 (9-159), ASM 55 (19-157) and SM-AHD 27 (8-131) (p=0.2). The normalized median score for individual symptom categories (total median score/no. of symptoms per category) in order of severity was cutaneous 1.9, gastrointestinal 1.8, constitutional 1.7, neuropsychological 1.3, respiratory 1.3, musculoskeletal 0.9, cardiovascular 0.3, genitourinary 0.3, and angioedema 0. Symptom severity was not significantly different among the 3 SM subgroups, except for constitutional symptoms (median score ASM 9, ISM 4, SM-AHD 2.5, p=0.02). The median (range) tryptase level was 48.4 ng/mL (8.8-282); four patients (14%) had a baseline level <20 ng/mL. The median (range) tryptase level among SM subgroups was: ISM 46.9 (8.8-225), ASM 103 (29.4-282), and SM-AHD 43.5 (28.5-233) (p=0.1). When considering patients with tryptase level ≥50 versus <50 ng/mL, symptom scores were not significantly higher in the former group with the exception of constitutional (p=0.02) and genitourinary symptoms (p=0.04). 2) MCAS: 15 patients The median total symptom score was 127 (range 2-248). The normalized median score for individual symptom categories in order of severity was neuropsychological 4.5, musculoskeletal 4.2, cutaneous 4.0, constitutional 3.3, gastrointestinal 2.1, respiratory and cardiovascular 2.0 each, genitourinary 1.7, and angioedema 1.0. The median (range) serum tryptase level at referral was 12.7 ng/mL (1.7-25.8); five patients (33%) had a baseline level >20 ng/mL. 3) Neither SM/MCAS: 10 patients The median total symptom score was 119 (range 45-177). The normalized median score for individual symptom categories in order of severity was musculoskeletal 4.2, gastrointestinal 3.6, constitutional 3.3, neuropsychological 3.3, cutaneous 3.0, cardiovascular and genitourinary 2.0 each, respiratory 1.3, and angioedema 0. The median (range) serum tryptase level at referral (n=9) was 4.8 ng/mL (2.9-6.6). 4) Comparison: MCAS vs. SM: Symptom scores were significantly higher in MCAS as compared to SM (p<0.05), except for genitourinary and respiratory symptoms, which were not significantly different. ‘Neither SM/MCAS’ vs. SM: Symptom scores (total, gastrointestinal, constitutional, musculoskeletal, cutaneous, and neuropsychological) were significantly higher in the former group (p<0.05). Other symptom scores were not significantly different. Conclusions: The spectrum and severity of patient reported symptoms was broadly similar among WHO subcategories of SM, and serum tryptase level had limited if any correlation with symptom scores. Despite the significantly higher overall symptom burden in MCAS versus SM, tryptase levels in the former group were significantly lower with values >30 ng/mL unusual. Despite overlap, the top ranked symptoms in the 3 groups were different. Disclosures No relevant conflicts of interest to declare.

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Mast Cell Activation Syndrome: Improved Identification by Combined Determinations of Serum Tryptase and 24-Hour Urine 11β-Prostaglandin2α

The Journal of Allergy and Clinical Immunology In Practice ◽

10.1016/j.jaip.2014.06.011 ◽

2014 ◽

Vol 2 (6) ◽

pp. 775-778 ◽

Cited By ~ 34

Author(s):

Anupama Ravi ◽

Joseph Butterfield ◽

Catherine R. Weiler

Keyword(s):

Mast Cell ◽

Cell Activation ◽

Mast Cell Activation ◽

Serum Tryptase ◽

Mast Cell Activation Syndrome ◽

Activation Syndrome

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THE ANAPHYLAXIS HYPOTHESIS OF SUDDEN INFANT DEATH SYNDROME (SIDS): MAST CELL DEGRANULATION IN COT DEATH REVEALED BY ELEVATED CONCENTRATIONS OF TRYPTASE IN SERUM

PEDIATRICS ◽

10.1542/peds.98.2.320 ◽

1996 ◽

Vol 98 (2) ◽

pp. 320-320

Author(s):

Mary E. Bollinger ◽

Robert A. Wood

Keyword(s):

Mast Cell ◽

Infant Death ◽

Cell Activation ◽

Sudden Infant Death ◽

Mast Cell Activation ◽

Sudden Infant ◽

Specific Marker ◽

Serum Tryptase ◽

Cell Degeneration ◽

Cot Death

This study found that elevated concentrations of serum tryptase are associated with sudden unexplained infant death, and this may be consistent with anaphylaxis as a mechanism in some cases of SIDS. Further studies are needed to determine if mast cell degeneration in these cases is secondary to terminal respiratory failure or some other event common to most cases of SIDS. The measurement of 9α, 11β-PGF2, as a specific marker of mast cell activation was not helpful under the conditions of this study.

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Screening for Hereditary Alpha-Tryptasemia in Subjects with Systemic Mastocytosis (SM) and Non-SM Mast Cell Activation Symptoms

Blood ◽

10.1182/blood-2021-148154 ◽

2021 ◽

Vol 138 (Supplement 1) ◽

pp. 1500-1500

Author(s):

Fiorenza Irushani Vanderwert ◽

Benedetta Sordi ◽

Francesco Mannelli ◽

Boaz Palterer ◽

Francesca Gesullo ◽

...

Keyword(s):

Mast Cell ◽

Board Of Directors ◽

Copy Number ◽

Cell Activation ◽

Systemic Mastocytosis ◽

Mast Cell Activation ◽

Serum Tryptase ◽

Advisory Committees ◽

Coding Sequence ◽

History Of

Abstract Introduction Hereditary alpha-Tryptasemia (HαT) is a group of genetically defined traits that share increased copy number of TPSAB1 gene encoding for both the α- and β-alleles (Lyons et al 2018). Increased copy number (CN) of the α-tryptase coding sequence in TPSAB1 on one or both alleles represents the genetic base of HαT (Lyons et al 2016). HαT is characterized by mild elevation in serum tryptase levels and a variety of mast cell (MC) activation symptoms, including recurrent anaphylaxis. Prevalence in the general population is up to 5%, that increases up to 20% in systemic mastocytosis (SM); it has been suggested that HαT might be a germline variant predisposing to SM development. In SM, HαT correlated with higher incidence of mediator-related symptoms (Greiner G et al, Blood 2021). Due to its complexity, the assay for TPSAB1 CN is performed in few centers and the actual prevalence of HαT in selected subsets is still to be elucidated. To this end, we screened for HαT 2 groups of subjects, the first with MC activation symptoms and no evidence of SM, the second with diagnosis of SM according to WHO-2016. Methods Droplet digital PCR (ddPCR) was used to measure CN variation (CNV) in TPSAB1 by adapting standard CNV ddPCR protocol to genotype for both TPSAB1 and TPSB2 (Fig.1A). The high homology between α and β encoding isoforms and the presence of paralogous genes in a single locus makes TPSAB1 CNV detection very challenging. ddPCR was performed on genomic DNA with/without BamHI, using the PrimePCR ddPCR Copy Number reference AP3B1 (BioRad). Accuracy and precision of the ddPCR protocol was assessed by analyzing 10 samples in triplicate in 3 separate experiments. Data robustness and repeatability can be appreciated in Fig 1B. Results We studied 41 subjects with mediator-related symptoms and augmented basal serum tryptase (BST) (cohort 1) and 150 patients with ascertained diagnosis of mastocytosis (cohort 2). The BST threshold established for cohort 1 was equal or higher than 11 mcg/L. Median age was 64.7 yr, males 54%; median BST levels was 15.3 (range 12.3-21 mcg/L); 29% of the pts had history of anaphylaxis. In cohort 2, 134/150 (89.3%) pts had a diagnosis of SM, whereas 13/150 (8,6%) were Cutaneous Mastocytosis (CM). Among SM patients, 113(84.3%) presented with non-advanced SM variants. Advanced forms including aggressive SM (ASM) and SM with an associated hematological neoplasm (SM-AHN) were diagnosed in 6 (4.5%) and 8 (6%) respectively. In 3 pts, SM subtype was not available. Median age was 49 yr, males 55%; 41.7% of the pts had history of anaphylaxis. HαT was documented in 27 (65.9%) subjects in cohort 1, and 14 (9.3%) in cohort 2. In cohort 1, 3 α-tryptase (3α) copy number was observed more frequently (59.2% of HαT+ pts); conversely 3α and 2α-tryptase copy number were observed at a similar rate (42,8%) in cohort 2. HαT+ pts in cohort 1 presented significantly higher BST (17.1 vs 12.05 mgc/L, P<0.001), as previously reported (Greiner G et al, Blood 2021); however, occurrence of mediator related symptoms was comparable to HαT wt, 72% vs 71.4% , respectively; likewise for anaphylaxis (28% in HαT+ vs 33%). In cohort 2, BST levels were similar in HαT+ and HαT wt pts (24.6 and 24.3 mcg/L), as were anaphylaxis episodes (50% and 41%, respectively). A trend for lower MC burden in HαT+ as assessed by flow cytometry was demonstrated (% of bone marrow MC: 0.01% in HαT+ vs 0.07%) whereas no meaningful differences emerged regarding the symptom burden. In addition, a lower prevalence of KIT 816V mutation was observed in HαT+ (71.4% vs 89.5%; p=0.073). Conclusions In our study HαT+ was observed in around 10% of patients with SM, a prevalence lower than previously reported (Greiner et al, Blood 2021) and remarkably lower than in a selected cohort of subjects with raised BTL and history of mediator-released symptoms (66%). ddPCR represents a suitable method to investigate the presence of CNV in the α-tryptase coding sequence. Genetic testing for HαT+ should be considered in the diagnostic workout of patients presenting with anaphylaxis or MC mediator-related symptoms and no suspicion/evidence of SM. The clinical correlates of HαT in SM remain to be fully ascertained. Supported by IMH no.GR-2016-02362631 and AIRC, Mynerva project no21267 Figure 1 Figure 1. Disclosures Elena: CELGENE: Other: funding for meeting participation; PFIZER: Membership on an entity's Board of Directors or advisory committees; NOVARTIS: Membership on an entity's Board of Directors or advisory committees; GILEAD: Membership on an entity's Board of Directors or advisory committees. Vannucchi: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees.

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