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.

Mast Cell Activation Syndrome and Gut Dysfunction: Diagnosis and Management.

PURPOSE OF REVIEW: Mast cell activation syndrome (MCAS) is a clinical disorder that may explain irritable bowel syndrome (IBS) type symptoms as well as other allergic symptoms experienced by an individual. The diagnosis and treatment of MCAS with specific focus on gastrointestinal (GI) manifestations is reviewed. RECENT FINDINGS: Although biomarkers for MCAS remain elusive, testing for baseline serum tryptase will distinguish the type of mast cell disorder and urine tests for mast cell mediator metabolites may support the diagnosis. Endoscopy and Colonoscopy with biopsies is not used to diagnose MCAS but is important to rule out other conditions that may cause symptoms. There is increased awareness of the association between MCAS and autonomic dysfunction, small fiber neuropathy, and connective tissue disorders which all impact GI symptoms. MCAS is a disorder often of unknown etiology (idiopathic) and characterized by intermittent allergy type symptoms that affect multiple organ systems after exposure to a trigger. GI symptoms including abdominal cramping and loose stool are prominent and mimic those of IBS. Diagnostic testing is performed to assess for elevations in mast cell mediators during symptoms and to rule out other conditions. A comprehensive treatment plan includes medications that target mast cells, treatments for associated conditions including autonomic dysfunction, and management of comorbid psychiatric illness and nutritional deficits.

Mast Cell-Targeting Therapies in Mast Cell Activation Syndromes.

PURPOSE OF REVIEW: Provide an overview of the expanding landscape of mast cell (MC)-targeting treatments in mast cell activation syndromes (MCAS). RECENT FINDINGS: Tyrosine-kinase inhibitors (TKIs) targeting wild-type and mutated KIT can efficiently induce MC depletion. Avapritinib and midostaurin can also temper IgE-mediated degranulation. Avapritinib has been recently approved by the FDA for the treatment of indolent systemic mastocytosis (ISM). Targeting activation pathways and inhibitory receptors is a promising therapeutic frontier. Recently, the anti Siglec-8 antibody lirentelimab showed promising results in ISM. MCAS is a heterogeneous disorder demanding a personalized therapeutic approach and, especially when presenting as anaphylaxis, has not been formally captured as outcome in prospective clinical trials with TKI. Long-term safety of TKI needs to be addressed. New drugs under investigation in diseases in which non-neoplastic MCs play a pivotal role can provide important inputs to identify new efficient and safe treatments for MCAS.

Urine Mast Cell Mediators in the Evaluation and Diagnosis of Mast Cell Activation Syndrome.

PURPOSE OF REVIEW: Mast cell activation syndrome is defined by severe, episodic, and recurrent symptoms induced by mast cell mediators with objective measurement of increase in biomarkers of mast cell activation and treatment response with mast cell therapies. Increase in serum tryptase from baseline during a mast cell activation episode is currently the most accepted biomarker measurement of mast cell release. However, during symptomatic episodes, serum tryptase can be difficult to obtain as it is a venipuncture procedure. Other objective measures of mast cell activation are needed to complement serum tryptase. RECENT FINDINGS: Urine mast cell mediators can be collected at home and are non-invasive tests. There is emerging evidence for the utility of urine mast cell mediators including histamine, cysteinyl leukotrienes, and prostaglandins in the diagnosis of mast cell activation syndrome. In this review, clinically available urine mast cell mediators will be discussed including N-methylhistamine, leukotriene E4, and 2,3-dinor-11beta-prostaglandin F2 alpha. We discuss the rationale for the use of these urine mast cell mediators and examine the studies analyzing their performance for identifying mast cell activation.

Using the Right Criteria for MCAS.

PURPOSE OF REVIEW: The current article aims to provide a comprehensive update on diagnostic criteria for mast cell activation syndrome (MCAS), addressing challenges in diagnosing and classifying MCAS and its variants. RECENT FINDINGS: In recent years, there has been a significant increase in our knowledge regarding the underlying mechanisms responsible for the activation of mast cells (MCs) in various pathological conditions. Furthermore, a set of criteria and a classification for MCASs have been established. MCAS is characterized by the presence of typical clinical symptoms, a substantial elevation in serum tryptase levels during an attack compared to the patient's baseline tryptase levels, and a response to MC mediator-targeting therapy. In this report, a thorough examination was conducted on the contemporary literature relating to MCAS, with a focus on comparing the specificity, sensitivity, and robustness of MCAS-related parameters within proposals for diagnosing and classifying MCAS and its variants. Moreover, the significance of employing specific consensus criteria in the assessment and categorization of MCAS in individual patients was underscored, due to the escalating occurrence of patients receiving a misdiagnosis of MCAS based on nonspecific criteria.

Predictors of Clonality and Underlying Mastocytosis in Mast Cell Activation Syndromes.

PURPOSE OF REVIEW: Mast cell (MC) activation can present with a wide range of symptoms. The mechanisms that cause such activation are varied. One of them is the presence of clonal MCs which is defined, within other possible changes, by the presence of a somatic, activating mutation in the KIT gene. The clinical course and prognosis of patients with this underlying disease may be different from other causes of MC activation (MCA). For this reason, it is important to early diagnose, or at least suspect, which patients with MCA are due to clonal MCs. RECENT FINDINGS: The diagnosis of clonality must be made in a comprehensive manner. However, this paper reviews chronologically each of the stages from the patient's first visit to the doctor's office which can be indicative of clonality: clinical presentation of MCA, physical examination, analytical determinations of tryptase, and/or KIT mutational analysis and bone involvement, among others. The different clonality predictive scores proposed are also reviewed and compared. Although the gold standard for the diagnosis of certainty of MC clonality is the performance of a bone marrow (BM) biopsy, there are clinical symptoms, signs, and biological parameters suggestive of clonality, as well as predictive scores, which can guide (or rule out) an early diagnosis and avoid unnecessary BM biopsies.

Low Prevalence of Idiopathic Mast Cell Activation Syndrome Among 703 Patients With Suspected Mast Cell Disorders.

BACKGROUND: Idiopathic mast cell activation syndrome (iMCAS) is characterized by severe, episodic systemic mast cell (MC) activation and mediator-related symptoms, an event-related increase in serum tryptase levels, and response to MC-targeted therapies in the absence of underlying IgE-mediated allergy or clonal MC disorder. Studies indicating its prevalence using evidence-based diagnostic criteria are lacking. OBJECTIVE: To assess the prevalence and clinical and laboratory features of patients with iMCAS. METHODS: We conducted a retrospective evaluation of data from 703 consecutive patients (aged ≥18 years) referred to our center based on suspicion of having MC disorders. Patients underwent a thorough clinical workup including patient history, allergy tests, KIT D816V mutation analysis, and/or bone marrow investigation. Disease activity was prospectively assessed during follow-up visits. RESULTS: We identified 31 patients with confirmed iMCAS. Furthermore, hereditary α-tryptasemia was detected in three patients with baseline tryptase levels greater than 8 ng/mL. The most common clinical presentation during MCAS episodes was mucocutaneous symptoms in patients with iMCAS, especially urticaria or angioedema. However, these symptoms were less prevalent in patients with clonal MCAS (P = .015). The duration of diagnostic delay was significantly longer in patients with iMCAS compared to those with clonal MCAS (P = .02). CONCLUSIONS: The overall prevalence of iMCAS was 4.4% in the entire cohort, which indicates that iMCAS is an uncommon condition. To accurately diagnose iMCAS, it is crucial to evaluate suspected patients using the three diagnostic MCAS criteria. This involves performing a comprehensive allergy work-up including laboratory tests and ultrasensitive mutation analysis of KIT D816V. Subsequently, recommended diagnostic algorithms should be applied.

Comprehensive Assessment of Nutrition and Dietary Influences in Hypermobile Ehlers-Danlos Syndrome-A Cross-Sectional Study.

INTRODUCTION: Disorders of gut-brain interaction (DGBI) are common in patients with hypermobile Ehlers-Danlos syndrome/hypermobility spectrum disorder (hEDS/HSD). Food is a known trigger for DGBI symptoms, which often leads to dietary alterations and, increasingly, nutrition support. We aimed to explore dietary behaviors and influencing factors in patients with hEDS/HSD. METHODS: In a cross-sectional study, patients with hEDS/HSD were recruited from Ehlers-Danlos Support UK (nontertiary) and tertiary neurogastroenterology clinics to complete questionnaires characterizing the following: dietary behaviors, nutrition support, DGBI (Rome IV), gastrointestinal symptoms, anxiety, depression, avoidant restrictive food intake disorder (ARFID), mast cell activation syndrome, postural tachycardia syndrome (PoTS), and quality of life. We used stepwise logistic regression to ascertain which factors were associated with dietary behaviors and nutrition support. RESULTS: Of 680 participants (95% female, median age 39 years), 62.1% altered their diet in the last year and 62.3% regularly skipped meals. Altered diet was associated with the following: reflux symptoms ( P < 0.001), functional dyspepsia ( P = 0.008), reported mast cell activation syndrome ( P < 0.001), and a positive screen for ARFID, specifically fear of eating and low interest ( P < 0.001). Approximately 31.7% of those who altered their diet required nutrition support. The strongest predictor of requiring nutrition support was a positive screen for ARFID, specifically fear of eating (OR: 4.97, 95% CI: 2.09-11.8, P < 0.001). DISCUSSION: Altered diet is very common in the patients with hEDS/HSD we studied and influenced by functional dyspepsia, reflux symptoms, and ARFID. Those with ARFID have a 4-fold increased risk of requiring nutrition support, and therefore, it is paramount that psychological support is offered in parallel with dietary support in the management of DGBI in hEDS/HSD.

Clinical impact of the TPSAB1 genotype in mast cell diseases: A REMA study in a cohort of 959 individuals.

BACKGROUND: A close association between hereditary alpha-tryptasemia (HAT) and mast cell (MC) disorders has been previously reported. However, the relationship between HAT and the diagnostic subtypes and clinical features of MC disorders still remains to be established. OBJECTIVE: To determine the prevalence of HAT in healthy donors (HD) vs patients with different diagnostic subtypes of MC activation syndromes (MCAS) and mastocytosis, and its relationship with the clinical behavior of the disease. METHODS: A total of 959 subjects were studied including 346 healthy donors (HD), 464 mastocytosis, and 149 non-clonal MCAS patients. Molecular studies to assess the TPSAB1 genotype were performed, and data on serum baseline tryptase (sBT) and basal MC-mediator release episodes and triggers of anaphylaxis were collected. RESULTS: HAT was detected in 15/346 (4%) HD versus 43/149 (29%) non-clonal MCAS and 84/464 (18%) mastocytosis cases. Among mastocytosis, HAT was more frequently found in patients with MC-restricted KITD816V (21% vs. 10% among multilineage KITD816V patients; p = .008). Overall, median sBT was higher in cases presenting with HAT (28.9 vs. 24.5 ng/mL; p = .008), while no significant differences in sBT were observed among HAT+ mastocytosis patients depending on the presence of 1 vs. ≥2 extra copies of the α-tryptase gene (44.1 vs. 35.2 ng/mL, p > .05). In turn, anaphylaxis was more frequently observed in HAT+ versus HAT- mastocytosis patients (76% vs. 65%; p = .018), while HAT+ and HAT- patients who did not refer anaphylaxis as the presenting symptom (n = 308) showed a similar prevalence of subsequent anaphylaxis (35% vs. 36%, respectively). CONCLUSION: The frequency of HAT in MC disorders varies according to the diagnostic subtype of the disease. HAT does not imply a higher risk (and severity) of anaphylaxis in mastocytosis patients in whom anaphylaxis is not part of the presenting symptoms of the disease.

Dysautonomia, Hypermobility Spectrum Disorders and Mast Cell Activation Syndrome as Migraine Comorbidities.

PURPOSE OF REVIEW: Dysautonomia refers to the dysfunction of the autonomic nervous system and encompasses a wide variety of autonomic symptoms and disorders. The most common autonomic disorders are postural orthostatic tachycardia syndrome (POTS), neurocardiogenic syncope (NCS), and orthostatic hypotension (OH), which may be encountered in clinical practice as part of a triad of dysautonomia, hypermobility spectrum disorders (HSD), and mast cell activation syndrome (MCAS). Migraine is one of the most common comorbidities of POTS, HSD, and MCAS; conversely, these conditions are also prevalent in patients with migraine, especially in those with multiple systemic symptoms, such as chronic dizziness, lightheadedness, orthostatic intolerance, joint pain, and allergic symptoms. Diagnostic criteria, pathophysiologic mechanisms, and therapeutic considerations in patients with migraine and comorbid dysautonomia, HSD, and MCAS are reviewed. RECENT FINDINGS: Numerous studies indicate a significant overlap and shared pathophysiology in migraine, dysautonomia, HSD, and MCAS. In clinical setting, dysautonomia, HSD, and MCAS may present a diagnostic and therapeutic challenge in patients with migraine and require a high index of suspicion on the part of the neurologist. Diagnosis and treatment of these complex disorders in patients with migraine is essential to comprehensive patient-centric care, reduced symptom burden, and improved functional impairment secondary to both migraine and comorbidities.

Prognostic factors for the long term outcome after surgical celiac artery decompression in MALS.

BACKGROUND: The median arcuate ligament syndrome (MALS) is a rare disease caused by compression of the celiac artery (ORPHA: 293208). Surgical treatment of MALS aims to restore normal celiac blood flow by laparoscopic celiac artery decompression. However, surgical success rates vary widely between patients, therefore adequate selection of patients is essential to improve surgical outcome. Symptoms of MALS might also overlap with other chronic multi-system disorders such as mast cell activation syndrome (MCAS). So far, no clinical or radiological parameter was found to be predictive of the postoperative outcome. We, therefore, aim to study preclinical parameters in one of the largest MALS cohorts with the focus to identify patients that would benefit from surgical MAL release. RESULTS: By analyzing 20 MALS patients that underwent surgical celiac artery decompression, we found 60% of patients (12/20) had a postoperative relief of their symptoms and a simultaneous decrease of analgetic use. No demographic, radiologic or operative parameter was able to predict postoperative symptom relief. However, mast cell activation syndrome correlated significantly (p = 0.04) with persistent symptoms after the operation. CONCLUSIONS: Overall, laparoscopic MAL release can provide immediate symptomatic relief. Despite the missing predictive value of demographic and imaging data, our data show a correlation between persistent symptoms and a co-existing mast cell activation syndrome. This suggests that MCAS symptoms might be interpreted as MALS symptoms in the presence of celiac artery stenosis and therefore surgical treatment should be evaluated carefully. Overall, the selection of patients who are most likely to respond to surgical MAL release may best be accomplished by an interdisciplinary team of gastroenterologists, radiologists and surgeons.

Learned cautions regarding antibody testing in mast cell activation syndrome.

OBJECTIVES: To describe patterns observed in antibody titer trendlines in patients with mast cell activation syndrome (MCAS, a prevalent but underrecognized chronic multisystem inflammatory disorder of great clinical heterogeneity) and offer clinical lessons learned from such pattern recognition. METHODS: The available records of 104 MCAS patients drawn from the authors' practices were reviewed, including all antibody tests therein. RESULTS: All patients had positive/elevated antibodies of various sorts at various points, but for most of the antibodies which were found to be positive at least some points, the diseases classically associated with those antibodies were not present, marking such antibodies as clinically insignificant mimickers (likely consequent to inflammatory effects of MCAS on the immune system itself driving spurious/random antibody production) rather than "on-target" and pathogenic antibodies reflecting true disease warranting treatment. We also observed two distinct patterns in trendlines of the titers of the mimickers vs. the trendline pattern expected in a true case of an antibody-associated disease (AAD). CONCLUSIONS: Our observations suggest most positive antibody tests in MCAS patients represent detection of clinically insignificant mimicking antibodies. As such, to reduce incorrect diagnoses of AADs and inappropriate treatment in MCAS patients, caution is warranted in interpreting positive antibody tests in these patients. Except in clinically urgent/emergent situations, patience in determining the trendline of a positive antibody in an MCAS patient, and more carefully assessing whether the AAD is truly present, is to be preferred.

Cluster-Analytic Identification of Clinically Meaningful Subtypes in MCAS: The Relevance of Heat and Cold.

BACKGROUND: Mast cell activation syndrome (MCAS) is a clinically heterogeneous disease with allergy-like symptoms and abdominal complaints. Its etiology is only partially understood and it is often overlooked. AIMS: The aim of this study was to identify subgroups of MCAS patients to facilitate diagnosis and allow a personalized therapy. METHODS: Based on data from 250 MCAS patients, hierarchical and two-step cluster analyses as well as association analyses were performed. The data used included data from a MCAS checklist asking about symptoms and triggers and a set of diagnostically relevant laboratory parameters. RESULTS: Using a two-step cluster analysis, MCAS patients could be divided into three clusters. Physical trigger factors were particularly decisive for the classification as they showed remarkable differences between the three clusters. Cluster 1, labeled high responders, showed high values for the triggers heat and cold, whereas cluster 2, labeled intermediate responders, presented with high values for the trigger heat and low values for cold. The third cluster, labeled low responders, did not react to thermal triggers. The first two clusters showed more divers clinical symptoms especially with regard to dermatological and cardiological complaints. Subsequent association analyses revealed relationships between triggers and clinical complaints: Abdominal discomfort is mainly triggered by histamine consumption, dermatological discomfort by exercise, and neurological symptoms are related to physical exertion and periods of starvation. The reasons for the occurrence of cardiological complaints are manifold and triggers for respiratory complaints still need better identification. CONCLUSION: Our study identified three distinct clusters on the basis of physical triggers, which also differ significantly in their clinical symptoms. A trigger-related classification can be helpful in clinical practice for diagnosis and therapy. Longitudinal studies should be conducted to further understand the relationship between triggers and symptoms.