Serum tryptase measurements in patients with myelodysplastic syndromes

Reversible Elevation of Tryptase Over the Individual's Baseline: Why is It the Best Biomarker for Severe Systemic Mast Cell Activation and MCAS?

PURPOSE OF REVIEW

Mast cell (MC) activation syndromes (MCAS) are conditions defined by recurrent episodes of severe systemic anaphylaxis or similar systemic events triggered by MC-derived mediators that can be measured in biological fluids. Since some symptoms of MC activation may occur due to other, non-MC etiologies and lead to confusion over diagnosis, it is of crucial importance to document the involvement of MC and their products in the patients´ symptomatology.

RECENT FINDINGS

The most specific and generally accepted marker of severe systemic MC activation is an event-related, transient increase in the serum tryptase level over the individual baseline of the affected individual. However, baseline concentrations of serum tryptase vary among donors, depending on the genetic background, age, kidney function, and underlying disease. As a result, it is of critical importance to provide a flexible equation that defines the diagnostic increase in tryptase qualifying as MCAS criterion in all patients, all situations, and all ranges of baseline serum tryptase. In 2012, the consensus group proposed the 120% + 2 ng/ml formula, which covers the great majority of groups, including cases with low, normal, or elevated basal serum tryptase level. This formula has been validated in subsequent studies and has proven to be a robust and consistent diagnostic criterion of MCAS. The present article is discussing the impact of this formula and possible limitations as well as alternative markers and mediators that may be indicative of MCAS.

The Normal Range of Baseline Tryptase Should Be 1 to 15 ng/mL and Covers Healthy Individuals With HαT

Physiological levels of basal serum tryptase vary among healthy individuals, depending on the numbers of mast cells, basal secretion rate, copy numbers of the TPSAB1 gene encoding alpha tryptase, and renal function. Recently, there has been a growing debate about the normal range of tryptase because individuals with the hereditary alpha tryptasemia (HαT) trait may or may not be symptomatic, and if symptomatic, uncertainty exists as to whether this trait directly causes clinical phenotypes or aggravates certain conditions. In fact, most HαT-positive cases are regarded as asymptomatic concerning mast cell activation. To address this point, experts of the European Competence Network on Mastocytosis (ECNM) and the American Initiative in Mast Cell Diseases met at the 2022 Annual ECNM meeting and discussed the physiological tryptase range. Based on this discussion, our faculty concluded that the normal serum tryptase range should be defined in asymptomatic controls, inclusive of individuals with HαT, and based on 2 SDs covering the 95% confidence interval. By applying this definition in a literature screen, the normal basal tryptase in asymptomatic controls (HαT-positive persons included) ranges between 1 and 15 ng/mL. This definition should avoid overinterpretation, unnecessary referrals, and unnecessary anxiety or anticipatory fear of illness in healthy individuals.

Secretory and Membrane-Associated Biomarkers of Mast Cell Activation and Proliferation

Mast cells (MCs) are immune cells distributed in many organs and tissues and involved in the pathogenesis of allergic and inflammatory diseases as a major source of pro-inflammatory and vasoactive mediators. MC-related disorders are heterogeneous conditions characterized by the proliferation of MC within tissues and/or MC hyper-reactivity that leads to the uncontrolled release of mediators. MC disorders include mastocytosis, a clonal disease characterized by tissue MC proliferation, and MC activation syndromes that can be primary (clonal), secondary (related to allergic disorders), or idiopathic. Diagnosis of MC disorders is difficult because symptoms are transient, unpredictable, and unspecific, and because these conditions mimic many other diseases. Validation of markers of MC activation in vivo will be useful to allow faster diagnosis and better management of MC disorders. Tryptase, being the most specific MC product, is a widely used biomarker of proliferation and activation. Other mediators, such as histamine, cysteinyl leukotrienes, and prostaglandin D2, are unstable molecules and have limitations in their assays. Surface MC markers, detected by flow cytometry, are useful for the identification of neoplastic MC in mastocytosis but, so far, none of them has been validated as a biomarker of MC activation. Further studies are needed to identify useful biomarkers of MC activation in vivo.

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

BACKGROUND

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.

OBJECTIVE

To determine the utility of tryptase genotyping among individuals with moderate elevations in BST at a regional health system.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

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

PURPOSE OF REVIEW

To discuss our evolving understanding of the genetic variation in human tryptases and recent advances in associated clinical phenotypes.

RECENT FINDINGS

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.

SUMMARY

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.

A Double Histochemical/Immunohistochemical Staining for the Identification of Canine Mast Cells in Light Microscopy

Immunohistochemistry (IHC) is a widely used technique in diagnostic pathology, but the simultaneous analysis of more than one antibody at a time with different chromogens is rather complex, time-consuming, and quite expensive. In order to facilitate the identification of mast cells (MCs) during immunohistochemical analysis of membrane and/or nuclear markers, we propose a new staining method that includes the association of IHC and toluidine blue as a counterstain. To achieve this goal, we tested c-kit, Ki67, and cannabinoid receptor 2 on several cases of cutaneous canine mast cell tumors (MCTs), cutaneous mastocytosis, and atopic dermatitis. The results obtained show how this double staining technique, although limited to non-cytoplasmic markers and of little use in poorly differentiated MCTs in which MC metachromasia is hard to see, can be used during the evaluation of nuclear and/or membranous immunohistochemical markers in all canine cutaneous disorders, especially if characterized by the presence of a low number of MCs. It can help to evaluate those MCTs in which neoplastic MCs must be clearly distinguished from inflammatory cells that can infiltrate the tumor itself, in facilitating the calculation of the Ki67 index. Moreover, it can be used to study the expression of new markers in both animal and human tissues containing MCs and in MC disorders.

State-of-the-Art on Biomarkers for Anaphylaxis in Obstetrics

Anaphylaxis is an unpredictable systemic hypersensitivity reaction and constitutes a high risk of maternal and fetal morbidity and mortality when occurring during pregnancy. Currently, the acute management of anaphylaxis is based on clinical parameters. A total serum tryptase is only used to support an accurate diagnosis. There is a need to detect other biomarkers to further assess high-risk patients in obstetrics. Our objective is to present biomarkers in this complex interdisciplinary approach beyond obstetrician and anaesthetic management. Candidate biomarkers derive either from mediators involved in immunopathogenesis or upcoming molecules from systems biology and proteomics. Serum tryptase is determined by singleplex immunoassay method and is important in the evaluation of anaphylactic mast cell degranulation but also in the assessment of other risk factors for anaphylaxis such as systemic mastocytosis. Another category of biomarkers investigates the IgE-mediated sensitization to triggers potentially involved in the etiology of anaphylaxis in pregnant women, using singleplex or multiplex immunoassays. These in vitro tests with natural extracts from foods, venoms, latex or drugs, as well as with molecular allergen components, are useful because in vivo allergy tests cannot be performed on pregnant women in such a major medical emergency due to their additional potential risk of anaphylaxis.

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.

[Tryptase: A practical guide for the physician]

Tryptase is the most abundant endopeptidase released by mast cells degranulation, involved in many pro and anti-inflammatory processes. Normal serum tryptase range is 0-11.4 μg/L. Tryptase is a useful diagnostic tool for anaphylaxis, systemic mastocytosis (SM) and mast cell activation syndrome (MCAS), where specific threshold values must be used. SM diagnosis criteria include evidence of dense mast cell infiltrate either in the bone marrow or the affected organ (such as skin), presence of KIT D816V mutation and elevated serum tryptase level (>20 μg/L). In SM, tryptase level is correlated with the burden of mast cells in bone marrow. MCAS should be considered in case of severe and recurrent typical clinical signs of systemic mast cell activation involving at least two organs, associated with an increase in serum tryptase level of 20% + 2 μg/L from the individual's baseline. Anaphylaxis is the most severe among hypersensitivity reactions. A clonal mast cell disorder is a central question in anaphylaxis and appropriate explorations should be conducted in these patients. Triggers for anaphylactic reactions vary significantly in the general population and in patients with MS or MCAS. Finally, physicians must be aware of the many pathological and physiological situations that affect tryptase levels.

Elevated Serum Tryptase in Non-Anaphylaxis Cases: A Concise Review

One of the most important blood tests in the field of allergy, mast cell tryptase has numerous diagnostic uses, particularly for anaphylactic reactions and for the diagnosis of mastocytosis. However, there are numerous other non-anaphylactic conditions where clinicians may see elevated serum tryptase (hypertryptasemia) and the practicing clinician ought to be aware of these important differential diagnoses. Such conditions include systemic mastocytosis, hematological malignancies, and chronic kidney disease. This article provides a comprehensive, updated summary on the variety of non-anaphylactic conditions where hypertryptasemia may be seen.

Why the 20% + 2 Tryptase Formula Is a Diagnostic Gold Standard for Severe Systemic Mast Cell Activation and Mast Cell Activation Syndrome

Mast cell activation syndrome (MCAS) is a condition characterized by recurrent episodes of clinically relevant, systemic, severe reactions to mast cell (MC)-derived mediators released in the context of anaphylaxis or another acute MC-related event. It is important to document MC involvement in these reactions in order to establish the diagnosis MCAS. The most specific and reliable marker of systemic MC activation is an acute and substantial event-related (transient) increase in the serum tryptase level over the individual's baseline value. However, the baseline level of tryptase varies depending on the underlying disease and the genetic background. For example, an estimated 3-5% of healthy individuals exhibit duplications or multiple copies of the TPSAB1 gene encoding for alpha-tryptase, and over 30% of all patients with myeloid neoplasms, including mastocytosis, have elevated basal tryptase levels. Therefore, it is of utmost importance to adjust the event-related diagnostic (MCAS-confirming) increase in tryptase over the individual baseline in a robust approach. To address this challenge, the 20% + 2 formula was proposed by the consensus group in 2012. Since then, this approach has been validated in clinical practice by independent groups and found to be sound. In the current article, we discuss the emerging importance and value of the 20% + 2 formula in clinical practice and its role as a criterion of severe systemic MC activation and MCAS.

Proposed Diagnostic Algorithm for Patients with Suspected Mast Cell Activation Syndrome

Mast cell activation (MCA) accompanies diverse physiologic and pathologic processes and is one of the more frequently encountered conditions in medicine. MCA-related symptoms are usually mild and often transient. In such cases, histamine receptor blockers and other mediator-targeting drugs can usually control MCA. In severe cases, an MCA syndrome (MCAS) may be diagnosed. However, overt MCAS is an unusual condition, and many patients referred because of suspected MCAS are diagnosed with other diseases (autoimmune, neoplastic, or infectious) unrelated to MCA or suffer from MCA-related (eg, allergic) disorders and/or comorbidities without fulfilling criteria of an overt MCAS. These considerations are important as more and more patients are informed that they may have MCA or even MCAS without completing a thorough medical evaluation. In fact, in several instances, symptoms are misinterpreted as MCA/MCAS, and other clinically relevant conditions are not thoroughly pursued. The number of such referrals is increasing. To avoid such unnecessary referrals and to prevent misdiagnoses, we here propose a diagnostic algorithm through which a clinically relevant (systemic) MCA can be suspected and MCAS can subsequently be documented or excluded. In addition, the algorithm proposed should help guide the investigating care providers to consider the 2 principal diagnoses that may underlie MCAS, namely, severe allergy and systemic mastocytosis accompanied by severe MCA. Although validation is required, we anticipate that this algorithm will facilitate the management of patients with suspected MCAS.

Mast cells and cancer

Mast cells (MCs) are a potent proangiogenic factor in tumors, they product several pro-angiogenic factors such as fibroblast growth factor 2 (FGF-2), vascular epithelial growth factor (VEGF), tryptase and chymase. Tryptase is a serine protease classified as α-tryptase and β-tryptase, both produced by MCs. Tryptase degrades the tissues, playing an important role in angiogenesis and in the development of metastases. Serum tryptase increases with age, with increased damage to cells and risk of developing a malignancy and it could be considered the expression of a fundamental role of MCs in tumor growth or, on the contrary, in the antitumor response. Many biomarkers have been developed in clinical practice for improving diagnosis and prognosis of some neoplasms. Elevated tryptase levels are found in subgroups of patients with haematologic and solid cancers. In the current review, we want to update the perspectives of tryptase as a potential biomarker in daily practice in different neoplasms.

Acute Myeloid Leukemia With Inv(16)(p13q22) Associated With Hidden Systemic Mastocytosis: Case Report and Review of Literature

Systemic mastocytosis (SM) is a condition associated with clonal neoplastic proliferation of mast cells. In up to 40% of systemic mastocytosis cases, an associated clonal hematological disease of non-mast cell lineage, such as acute myeloid leukemia (AML), is diagnosed before, simultaneously with, or after the diagnosis of SM. Herein, we report a case of a 30-year-old man diagnosed with AML with inv(16) (p13;q22) CBFB:MYH11. Associated mastocytosis was not noted at diagnosis and was only detected in the bone marrow at time of remission after successful chemotherapy. The diagnosis of mastocytosis was based on the demonstration of a multifocal dense mast cell infiltrate in the marrow biopsy with aberrant immunophenotype, with coexpression of tryptase, CD117, and CD25. The mast cells showed atypical morphology mostly with irregular nuclear contour, bilobed or multilobed nuclei with cytoplasmic hypogranulation or irregular metachromatic granule distribution, and some cells with eccentric nucleus or spindle shape. Reexamination of the pretherapeutic bone marrow with immunostain for tryptase and CD25 revealed that mastocytosis was present from the start but masked by extensive blast proliferation. This case indicates that mast cell infiltrates are sometimes underappreciated at the original diagnosis of AML with inv(16) and that the concurrent diagnosis of SM with AML requires a high index of suspicion supported with comprehensive morphologic and immunohistochemical evaluation for a neoplastic mast cell proliferation.

Serum Mast Cell Tryptase as a Marker of Posttraumatic Joint Contracture in a Rabbit Model

OBJECTIVES

Mast cells have been identified as key mediators of posttraumatic joint contracture, and stabilizing medications (ketotifen) have been shown to decrease contracture severity. Serum mast cell tryptase (SMCT) levels are used clinically to monitor mast cell-mediated conditions. The goals of this study were to determine if SMCT levels are elevated in the setting of joint contracture, if they can be decreased in association with ketotifen therapy, and if they correlate with contracture severity.

METHODS

This study used a previously developed rabbit model in which 39 animals were divided into 4 groups: operatively created joint contracture (ORC, n = 13), operatively created contracture treated with ketotifen at 2 doses (KF0.5, n = 9; KF1.0, n = 9), and healthy rabbits (NC, n = 8). Range of motion measures were performed at 8 weeks after the surgery. Serum samples were collected on postoperative days 1, 3, 5, 7, 21, 35, and 49. SMCT levels were measured using a rabbit-specific enzyme-linked immunosorbent assay.

RESULTS

Levels of SMCT were highest in the operatively created joint contracture group and were significantly greater compared with both ketotifen groups (P < 0.001). Levels were highest at postoperative day 1 with a trend to decrease over time. A positive correlation between SMCT levels and contracture severity was observed in all operative groups (P < 0.05).

CONCLUSIONS

Levels of SMCT are elevated in the setting of joint contracture, decreased in association with ketotifen therapy, and positively correlated with contracture severity. This is the first study to establish a relationship between SMCT and joint injury. Measurement of SMCT may be valuable in identifying those at risk of posttraumatic joint contracture.

The serum tryptase test: an emerging robust biomarker in clinical hematology

During the past few years, a number of molecular markers have been developed in clinical hematology, most of them related to specific gene defects. However, there is also an unmet need to develop novel serologic parameters to improve diagnostics and prognostication in daily practice. Among these, the serum tryptase appears to be a most reliable biomarker of myeloid neoplasms. Elevated tryptase levels are found in subgroups of patients with mastocytosis, myelodysplastic syndrome, myeloproliferative neoplasm, acute myeloid leukemia, chronic myeloid leukemia and chronic eosinophilic leukemia. In these patients, the tryptase level is of diagnostic and/or prognostic significance. In mastocytosis, an elevated tryptase level is a minor criterion of systemic disease and in BCR-ABL1(+) chronic myeloid leukemia, elevated tryptase at diagnosis correlates with treatment responses and overall survival. In patients with elevated tryptase, the enzyme also serves as follow-up parameter and can be employed to measure treatment-responses. In the current article, we review and update the perspectives of tryptase and provide recommendations for use of this conventional biomarker in daily practice.

Anaphylaxis as a clinical manifestation of clonal mast cell disorders

Clonal mast cell disorders comprise a heterogeneous group of disorders characterized by the presence of gain of function KIT mutations and a constitutively altered activation-associated mast cell immunophenotype frequently associated with clinical manifestations related to the release of mast cells mediators. These disorders do not always fulfil the World Health Organization (WHO)-proposed criteria for mastocytosis, particularly when low-sensitive diagnostic approaches are performed. Anaphylaxis is a frequent presentation of clonal mast cell disorders, particularly in mastocytosis patients without typical skin lesions. The presence of cardiovascular symptoms, e.g., hypotension, occurring after a hymenoptera sting or spontaneously in the absence of cutaneous manifestations such as urticaria is characteristic and differs from the presentation of anaphylaxis in the general population without mastocytosis.

Systemic mastocytosis

Systemic mastocytosis (SM) is a clonal disorder of hematopoietic system characterized by abnormal growth and accumulation of mast cells in various tissues. Its clinical spectrum ranges from mild disease to an aggressive course with life-threatening conditions. Some of the clinical signs or symptoms of SM (hyperhidrosis, syncope and hypotensive/tachycardiac attacks) require consideration of pheochromocytoma and carcinoid syndrome in the differential diagnosis. The diagnosis relies on the demonstration of mast cell aggregates in bone marrow or extracutaneous tissues. The World Health Organization categorizes SM into 6 variants: indolent SM, SM with associated clonal hematological nonmast cell lineage disease, aggressive SM, mast cell leukemia, mast cell sarcoma and extracutaneous mastocytosis. Patients with indolent SM have a favorable prognosis with a life expectancy comparable with the healthy population, and symptomatic treatment is usually sufficient. However, more aggressive forms may be life threatening, and cytoreductive treatment is indicated in most cases.

Evaluation of the WHO criteria for the classification of patients with mastocytosis

Diagnosis and classification of mastocytosis is currently based on the World Health Organization (WHO) criteria. Here, we evaluate the utility of the WHO criteria for the diagnosis and classification of a large series of mastocytosis patients (n=133), and propose a new algorithm that could be routinely applied for refined diagnosis and classification of the disease. Our results confirm the utility of the WHO criteria and provide evidence for the need of additional information for (1) a more precise diagnosis of mastocytosis, (2) specific identification of new forms of the disease, (3) the differential diagnosis between cutaneous mastocytosis vs systemic mastocytosis, and (4) improved distinction between indolent systemic mastocytosis and aggressive systemic mastocytosis. Based on our results, a new algorithm is proposed for a better diagnostic definition and prognostic classification of mastocytosis, as confirmed prospectively in an independent validation series of 117 mastocytosis patients.

Standards and impact of hematopathology in myelodysplastic syndromes (MDS)

The diagnosis, classification, and prognostication of patients with myelodysplastic syndromes (MDS) are usually based on clinical parameters, analysis of peripheral blood and bone marrow smears, and cytogenetic determinants. However, a thorough histologic and immunohistochemical examination of the bone marrow is often required for a final diagnosis and exact classification in these patients. Notably, histology and immunohistology may reveal dysplasia in megakaryocytes or other bone marrow lineages and/or the presence of clusters of CD34-positive precursor cells. In other cases, histology may reveal an unrelated or co-existing hematopoietic neoplasm, or may support the conclusion the patient is suffering from acute myeloid leukemia rather than MDS. Moreover, histologic investigations and immunohistology may reveal an increase in tryptase-positive cells, a coexisting systemic mastocytosis, or bone marrow fibrosis, which is of prognostic significance. To discuss diagnostic algorithms, terminologies, parameters, and specific issues in the hematopathologic evaluation of MDS, a Working Conference involving a consortium of US and EU experts, was organized in June 2010. The outcomes of the conference and resulting recommendations provided by the faculty, are reported in this article. These guidelines should assist in the diagnosis, classification, and prognostication in MDS in daily practice as well as in clinical trials.

Standards and impact of hematopathology in myelodysplastic syndromes (MDS)

The diagnosis, classification, and prognostication of patients with myelodysplastic syndromes (MDS) are usually based on clinical parameters, analysis of peripheral blood and bone marrow smears, and cytogenetic determinants. However, a thorough histologic and immunohistochemical examination of the bone marrow is often required for a final diagnosis and exact classification in these patients. Notably, histology and immunohistology may reveal dysplasia in megakaryocytes or other bone marrow lineages and/or the presence of clusters of CD34-positive precursor cells. In other cases, histology may reveal an unrelated or co-existing hematopoietic neoplasm, or may support the conclusion the patient is suffering from acute myeloid leukemia rather than MDS. Moreover, histologic investigations and immunohistology may reveal an increase in tryptase-positive cells, a coexisting systemic mastocytosis, or bone marrow fibrosis, which is of prognostic significance. To discuss diagnostic algorithms, terminologies, parameters, and specific issues in the hematopathologic evaluation of MDS, a Working Conference involving a consortium of US and EU experts, was organized in June 2010. The outcomes of the conference and resulting recommendations provided by the faculty, are reported in this article. These guidelines should assist in the diagnosis, classification, and prognostication in MDS in daily practice as well as in clinical trials.

Variable presence of KITD816V in clonal haematological non-mast cell lineage diseases associated with systemic mastocytosis (SM-AHNMD)

In a substantial number of patients with systemic mastocytosis (SM), an associated clonal haematological non-mast cell lineage disease (AHNMD) is detectable. Although most of these patients display KIT mutations, especially KIT(D816V), little is known about their exact frequency and their distribution in AHNMD subtypes. We examined 48 patients with SM-AHNMD for the presence of mutant KIT in the SM and AHNMD components of the disease. Mast cells and AHNMD cells were obtained from immunostained bone marrow sections by laser microdissection and examined by melting point analysis of nested-PCR products. KIT(D816V) was found in AHNMD cells in the vast majority of patients with SM-chronic myelomonocytic leukaemia (CMML, 89%). Unexpectedly, KIT(D816V) was far less frequently detectable in AHNMD cells in patients with SM-myeloproliferative neoplasm (MPN, 20%) and SM-acute myeloid leukaemia (AML, 30%). None of the patients with lymphoproliferative AHNMDs displayed KIT codon 816 mutations in AHNMD cells (0/8). In FIP1L1/PDGFRA-positive chronic eosinophilic leukaemia (CEL), neither the SM nor the CEL component of the disease exhibited the KIT mutation. Our findings demonstrate that KIT codon 816 mutations are variably present in AHNMD cells in patients with SM-AHNMD, depending on the subtype of AHNMD. The high frequency of KIT(D816V) in neoplastic mast cells and leukaemic myelomonocytic cells in SM-CMML may point to a common precursor in these patients, and may have implications for the biology of the disease and the development of KIT-targeting therapies.

Predictors of severe systemic anaphylactic reactions in patients with Hymenoptera venom allergy: importance of baseline serum tryptase-a study of the European Academy of Allergology and Clinical Immunology Interest Group on Insect Venom Hypersensitivity

BACKGROUND

Severe anaphylaxis to honeybee or vespid stings is associated with a variety of risk factors, which are poorly defined.

OBJECTIVE

Our aim was to evaluate the association of baseline serum tryptase concentrations and other variables routinely recorded during patient evaluation with the frequency of past severe anaphylaxis after a field sting.

METHODS

In this observational multicenter study, we enrolled 962 patients with established bee or vespid venom allergy who had a systemic reaction after a field sting. Data were collected on tryptase concentration, age, sex, culprit insect, cardiovascular medication, and the number of preceding minor systemic reactions before the index field sting. A severe reaction was defined as anaphylactic shock, loss of consciousness, or cardiopulmonary arrest. The index sting was defined as the hitherto first, most severe systemic field-sting reaction. Relative rates were calculated with generalized additive models.

RESULTS

Two hundred six (21.4%) patients had a severe anaphylactic reaction after a field sting. The frequency of this event increased significantly with higher tryptase concentrations (nonlinear association). Other factors significantly associated with severe reactions after a field sting were vespid venom allergy, older age, male sex, angiotensin-converting enzyme inhibitor medication, and 1 or more preceding field stings with a less severe systemic reaction.

CONCLUSION

In patients with honeybee or vespid venom allergy, baseline serum tryptase concentrations are associated with the risk for severe anaphylactic reactions. Preventive measures should include substitution of angiotensin-converting enzyme inhibitors.

Elevated tryptase levels selectively cluster in myeloid neoplasms: a novel diagnostic approach and screen marker in clinical haematology

BACKGROUND

Recent data suggest that tryptase, a mast cell enzyme, is expressed in neoplastic cells in myeloid leukaemias. In several of these patients, increased serum tryptase levels are detectable.

MATERIALS AND METHODS

We have determined serum tryptase levels in 914 patients with haematological malignancies, including myeloproliferative disorders (n = 156), myelodysplastic syndromes (MDS, n = 241), acute myeloid leukaemia (AML, n = 317), systemic mastocytosis (SM, n = 81), non-Hodgkin's lymphoma (n = 59) and acute lymphoblastic leukaemia (n = 26). Moreover, tryptase was measured in 136 patients with non-neoplastic haematological disorders, 102 with non-haematological disorders and 164 healthy subjects.

RESULTS

In healthy subjects, the median serum tryptase was 5.2 ng mL(-1). Elevated serum tryptase levels were found to cluster in myeloid neoplasm, whereas almost all patients with lymphoid neoplasms exhibited normal tryptase. Among myeloid neoplasms, elevated tryptase levels (> 15 ng mL(-1)) were recorded in > 90% of patients with SM, 38% with AML, 34% with CML and 25% with MDS. The highest tryptase levels, often > 1000 ng mL(-1), were found in advanced SM and core-binding-factor leukaemias. In most patients with non-neoplastic haematological disorders and non-haematological disorders analysed in our study, tryptase levels were normal, the exception being a few patients with end-stage kidney disease and helminth infections, in whom a slightly elevated tryptase was found.

CONCLUSIONS

In summary, tryptase is a new diagnostic marker of myeloid neoplasms and a useful test in clinical haematology.

Utility of the World Heath Organization classification criteria for the diagnosis of systemic mastocytosis in bone marrow

In the World Health Organization classification, one major and four minor criteria are specified for the diagnosis of systemic mastocytosis. We report our experience using these criteria to diagnose systemic mastocytosis involving bone marrow. A total of 59 patients with clinically suspected systemic mastocytosis underwent comprehensive bone marrow examination, including immunophenotyping by immunohistochemistry and/or flow cytometry and molecular studies for KIT exon 17 mutations. Serum tryptase levels were also assessed. Of these 59, 53 (90%) patients met the diagnostic criteria for systemic mastocytosis. In these patients, multifocal dense infiltrates of mast cells, the major criterion, was observed in 36 (68%) patients. Atypical mast cell morphology was observed in 53 (100%), an aberrant immunophenotype was identified in 50 of 52 (96%), KIT mutation was present in 33 of 44 (75%), and an elevated serum tryptase (>20 ng/ml) was detected in 44 of 52 (85%). In the six patients in which bone marrow examination could not confirm systemic mastocytosis, one had systemic mastocytosis involving spleen, one patient had chronic idiopathic myelofibrosis, and four had no specific diagnosis, but systemic mastocytosis was still considered most likely. Of these six patients, atypical mast cell morphology was identified in five, aberrant immunophenotype in five, KIT mutation in two, and elevated serum tryptase in two. None of these cases met the major criteria. We conclude that the World Health Organization criteria are useful for the diagnosis of systemic mastocytosis in bone marrow specimens. The results also show the relative values of traditional morphologic criteria (ie, major criterion) and the results of ancillary testing (ie, minor criteria). However, as illustrated by the case of splenic systemic mastocytosis as well as the patient with chronic idiopathic myelofibrosis, the current World Health Organization system is neither completely sensitive nor specific for systemic mastocytosis.

Gastrointestinal manifestations of dermatologic disorders

The skin and the gastrointestinal tract may be affected concurrently by the same diseases. Pathogenetically, these conditions may be primarily dermatologic diseases involving the gastrointestinal (GI) tract or systemic diseases involving the skin, GI tract, and liver simultaneously. The correct diagnosis of such conditions relies on the ability of the gastroenterologist to recognize the underlying dermatologic disorder. The goal of this clinical review article is to increase gastroenterologists' awareness and understanding of some of these conditions. Case vignettes are presented and the relevant literature reviewed for epidermolysis bullosa, mastocytosis, hereditary hemorrhagic telangiectasia, and melanoma. This review focuses on increasing gastroenterologists' ability to recognize, diagnose, comprehend, and manage patients with these dermatologic conditions who have GI manifestations. Advances in molecular genetics that provide insight into the underlying pathophysiology and histopathology of these lesions are highlighted.

Systemic mastocytosis: a concise clinical and laboratory review

CONTEXT

Systemic mastocytosis is characterized by abnormal growth and accumulation of neoplastic mast cells in various organs. The clinical presentation is varied and may include skin rash, symptoms related to release of mast cell mediators, and/or organopathy from involvement of bone, liver, spleen, bowel, or bone marrow.

OBJECTIVE

To concisely review pathogenesis, disease classification, clinical features, diagnosis, and treatment of mast cell disorders.

DATA SOURCES

Pertinent literature emerging during the last 20 years in the field of mast cell disorders.

CONCLUSIONS

The cornerstone of diagnosis is careful bone marrow histologic examination with appropriate immunohistochemical studies. Ancillary tests such as mast cell immunophenotyping, cytogenetic/molecular studies, and serum tryptase levels assist in confirming the diagnosis. Patients with cutaneous disease or with low systemic mast cell burden are generally managed symptomatically. In the patients requiring mast cell cytoreductive therapy, treatment decisions are increasingly being guided by results of molecular studies. Most patients carry the kit D816V mutation and are predicted to be resistant to imatinib mesylate (Gleevec) therapy. In contrast, patients carrying the FIP1L1-PDGFRA mutation achieve complete responses with low-dose imatinib therapy. Other therapeutic options include use of interferon-alpha, chemotherapy (2-chlorodeoxyadenosine), or novel small molecule tyrosine kinase inhibitors currently in clinical trials.

Definitions and standards in the diagnosis and treatment of the myelodysplastic syndromes: Consensus statements and report from a working conference

The classification, scoring systems, and response criteria for myelodysplastic syndromes (MDS) have recently been updated and have become widely accepted. In addition, several new effective targeted drugs for patients with MDS have been developed. The current article provides a summary of updated and newly proposed markers, criteria, and standards in MDS, with special reference to the diagnostic interface and refinements in evaluations and scoring. Concerning the diagnostic interface, minimal diagnostic criteria for MDS are proposed, and for patients with unexplained cytopenia who do not fulfill these criteria, the term 'idiopathic cytopenia of uncertain significance' (ICUS) is suggested. In addition, new diagnostic and prognostic parameters, histopathologic and immunologic determinants, proposed refinements in scoring systems, and new therapeutic approaches are discussed. Respective algorithms and recommendations should facilitate diagnostic and prognostic evaluations in MDS, selection of patients for therapies, and the conduct of clinical trials.

Diagnostic evaluation and classification of mastocytosis

During the past few years, mastocytosis research has reached important milestones, including the formulation of diagnostic criteria, definition of markers, and targeting of mutated KIT. Important aims for the future are to standardize diagnostic assays and techniques, and to achieve harmonization among centers as a basis for the design of multicenter clinical trials in SM, including the rare ASM and MCL subvariants.

Mastocytosis and Hymenoptera venom allergy

PURPOSE OF REVIEW

Mastocytosis is a rare disease characterized by increased mast cells in skin and/or internal organs. We evaluate the impact of mastocytosis on diagnosis and treatment of Hymenoptera venom allergy.

RECENT FINDINGS

Patients with Hymenoptera venom allergy who suffer from mastocytosis develop life-threatening sting reactions more often than those who do not. When patients with Hymenoptera venom allergy were systematically examined for mastocytosis, it was found to be represented to an abnormally high extent. Most patients with mastocytosis tolerate venom immunotherapy with no or only minor systemic symptoms. Venom immunotherapy was found to be marginally less effective in patients with mastocytosis than in those without evidence of mast cell disease (defined as absent cutaneous mastocytosis combined with a serum tryptase concentration of <11.4 microg/l). Several deaths from sting reactions were reported in patients with mastocytosis after venom immunotherapy was stopped. These patients should have venom immunotherapy for the rest of their lives.

SUMMARY

Patients suffering from mastocytosis and Hymenoptera venom allergy are at risk from a particularly severe sting anaphylaxis. They need optimal diagnosis and treatment. In patients presenting with Hymenoptera venom allergy, screening tests by measurement of serum tryptase concentration, and a careful skin examination, are highly recommended.

Diagnostic Value of Tryptase in Anaphylaxis and Mastocytosis

Serum (or plasma) levels of total and mature tryptase measurements are recommended in the diagnostic evaluation of systemic anaphylaxis and systemic mastocytosis, but their interpretation must be considered in the context of a complete workup of each patient. Total tryptase levels generally reflect the increased burden of mast cells in patients with all forms of systemic mastocytosis (indolent systemic mastocytosis, smoldering systemic mastocytosis, systemic mastocytosis associated with a hematologic clonal non-mast cell disorder, aggressive systemic mastocytosis, and mast cell leukemia) and the decreased burden of mast cells associated with cytoreductive therapies in these disorders. Causes of an elevated total tryptase level other than systemic mastocytosis must be considered, however, and include systemic anaphylaxis, acute myelocytic leukemia, various myelodysplastic syndromes, hypereosinophilic syndrome associated with the FLP1L1-PDGFRA mutation, end-stage renal failure, and treatment of onchocerciasis. Mature (beta) tryptase levels generally reflect the magnitude of mast cell activation and are elevated during most cases of systemic anaphylaxis, particularly with parenteral exposure to the inciting agent.

Systemic mastocytosis

Systemic mastocytosis is a fascinating disease with diverse clinical features. There have been numerous advances in understanding the basis of clinical manifestations of this disease and of its molecular pathogenesis in the last several decades. The development of methods to study mast cell biology using cell culture and murine models has proven invaluable in this regard. Clarification of the roles of mast cells in various biological processes has expanded our understanding of their importance in innate immunity, as well as allergy. New diagnostic methods have allowed the design of detailed criteria to assist in distinguishing reactive mast cell hyperplasia from systemic mastocytosis. Variants and subvariants of systemic mastocytosis have been defined to assist in determining prognosis and in management of the disease. Elucidation of the roles of the Kit receptor tyrosine kinase and signal transduction pathway activation has contributed to development of potential targeted therapeutic approaches that may prove useful in the future.

Activity of the tyrosine kinase inhibitor PKC412 in a patient with mast cell leukemia with the D816V KIT mutation

The majority of patients with systemic mast cell disease express the imatinib-resistant Asp816Val (D816V) mutation in the KIT receptor tyrosine kinase. Limited treatment options exist for aggressive systemic mastocytosis (ASM) and mast cell leukemia (MCL). We evaluated whether PKC412, a small-molecule inhibitor of KIT with a different chemical structure from imatinib, may have therapeutic use in advanced SM with the D816V KIT mutation. We treated a patient with MCL (with an associated myelodysplastic syndrome (MDS)/myeloproliferative disorder [MPD]) based on in vitro studies demonstrating that PKC412 could inhibit D816V KIT-transformed Ba/F3 cell growth with a 50% inhibitory concentration (IC50) of 30 nM to 40 nM. The patient exhibited a partial response with significant resolution of liver function abnormalities. In addition, PKC412 treatment resulted in a significant decline in the percentage of peripheral blood mast cells and serum histamine level and was associated with a decrease in KIT phosphorylation and D816V KIT mutation frequency. The patient died after 3 months of therapy due to progression of her MDS/MPD to acute myeloid leukemia (AML). This case indicates that KIT tyrosine kinase inhibition is a feasible approach in SM, but single-agent clinical efficacy may be limited by clonal evolution in the advanced leukemic phase of this disease.

Ph-Chromosome-positive chronic myeloid leukemia with associated bone marrow mastocytosis

The concurrent development of chronic myeloid (CML) or myelomonocytic (CMML) leukemia in patients with systemic mastocytosis (SM) is a well recognized phenomenon. Although the leukemia often resembles CML in morphological and in clinical terms, a Ph-Chromosome-positive variant has not been reported in SM so far. We here describe a 43-year-old female patient with typical Ph-Chromosome-positive CML in whom a co-existing bone marrow mastocytosis, a special subvariant of SM, was diagnosed. RT-PCR analysis revealed the typical p210 kDa form of BCR/ABL in leukemic cells. The diagnosis SM was based on the typical focal aggregates of spindle-shaped mast cells (MC) in the bone marrow, expression of CD25 in MC, and the c-kit mutation D816V, which was detectable in microdissected bone marrow MC, but not in microdissected leukemic cells, suggesting the presence of two different (sub)clones of neoplastic cells. Therapy with the BCR/ABL-targeting drug Imatinib (STI571) resulted in complete cytogenetic remission of CML. Together, our case provides further evidence for the biologic diversity of leukemias that may occur in patients with SM. The exact knowledge of the pathology and target-profile of the associated leukemias in SM have important therapeutic implications.

Mastocytosis: pathology, genetics, and current options for therapy

Mast cell disorders are defined by an abnormal accumulation of tissue mast cells (MCs) in one or more organ systems. Symptoms in mastocytosis result from MC-derived mediators and, less frequently, from destructive infiltration of MCs. Cutaneous mastocytosis (CM) is a benign disease of the skin and may regress spontaneously. Systemic mastocytosis (SM) is a persistent disease in which a somatic c-kit mutation at codon 816 is usually detectable in MCs and their progenitors. The clinical course in these patients is variable ranging from asymptomatic for years to highly aggressive and rapidly devastating. The WHO discriminates five categories of SM: indolent SM (ISM), aggressive SM (ASM), SM with associated clonal hematological non-MC-lineage disease (AHNMD), and mast cell leukemia (MCL). The c-kit mutation D816V is quite common and may be found in all SM-categories. In SM-AHNMD, additional genetic abnormalities have been reported, whereas no additional defects are yet known for ASM or MCL. Patients with ISM and CM are treated with "mediator-targeting" drugs, whereas patients with ASM or MCL are candidates for cytoreductive therapy. The use of "Kit-targeting" tyrosine kinase inhibitors such as STI571 (Imatinib, Gleevec), has also been suggested. However, the D816V mutation of c-kit is associated with relative resistance against STI571. Therefore, these patients require alternative targeted drugs or new drug-combinations. In patients with SM-AHNMD, separate treatment plans for the SM-component and the AHNMD should be established. Examples include the use of STI571 in patients with SM plus hypereosinophilic syndrome (SM-HES) and the FIPL1/PDGFRA fusion gene target, or chemotherapy for eradication of AML in patients with SM-AML.

Diagnosis and classification of mast cell proliferative disorders: delineation from immunologic diseases and non–mast cell hematopoietic neoplasms

In mast cell (MC) disorders (mastocytosis), clinical symptoms are caused by the release of chemical mediators from MCs, the pathologic infiltration of neoplastic MCs in tissues, or both. Cutaneous mastocytosis is a benign disease in which MC infiltration is confined to the skin. In pediatric cases cutaneous mastocytosis might regress spontaneously. Systemic mastocytosis (SM) is more frequently diagnosed in adults and is a persistent (clonal) disease of bone marrow-derived myelomastocytic progenitors. The somatic c-kit mutation D816V is found in the majority of such patients. The natural clinical course in SM is variable. Whereas most patients remain at the indolent stage for many years, some have aggressive SM (ASM) at diagnosis. Other patients have an associated clonal hematologic non-MC lineage disease (AHNMD). MC leukemia (MCL) is a rare disease variant characterized by circulating MCs and fatal disease progression. The diagnoses of ASM, SM-AHNMD, and MCL might be confused with a variety of endocrinologic, vascular, or immunologic disorders. It is therefore of particular importance to be aware of the possibility of an underlying (malignant) MC disease in patients with unexplained vascular instability, unexplained (anaphylactoid) shock, idiopathic flushing, diarrhea, headache, and other symptoms that might be mediator related. An important diagnostic clue in such cases is an increased serum tryptase level. The current review provides an overview of mastocytosis and its subvariants and a practical guide that might help to delineate mastocytosis from unrelated systemic disorders.

Systemic mastocytosis associated with acute myeloid leukemia: case report and implications for disease pathogenesis

Mastocytosis may be associated with clonal nonmast cell lineage hematologic diseases, including myelodysplastic syndromes, myeloproliferative disorders, and acute myeloid leukemia. Here we present a patient with the simultaneous diagnosis of mastocytosis and an acute myeloid leukemia, M2 subtype in the French-American-British classification, with t(8;21) carrying a population of immature mast cell precursors, and discuss this presentation in the context of a potential pathogenetic cellular link between this leukemia and mastocytosis.

Effect of sex and haplotype on plasma tryptase levels in healthy adults

BACKGROUND

The total level of alpha-tryptase and ss-tryptase in serum or plasma is used as a clinical indicator of the mast cell burden.

OBJECTIVE

The effect of the tryptase haplotype and of sex on the total tryptase level of healthy individuals was determined.

METHODS

A novel hot-stop PCR technique was used to determine the tryptase genotype, and a standard fluoroenzyme immunoassay was used to measure total plasma tryptase levels in 106 healthy subjects. Mx modeling and the QTL association routine of Mendel 5.0 were used to analyze the data.

RESULTS

Tryptase haplotypes exhibit a 1 (betaalpha/betaalpha):2 (betabeta/betaalpha):1 (betabeta/betabeta) distribution, monomorphic for ss at 1 position and allelic for ss and alpha at the other position. The betaalpha haplotype has a frequency of 0.49. The betaalpha haplotype increases total tryptase levels by 0.5 ng/mL from the overall mean, whereas female sex increases the level by 0.2 ng/mL from the mean.

CONCLUSION

The tryptase haplotype and sex each have a statistically significant effect on the total plasma tryptase level of healthy subjects.

Tryptase precursors are preferentially and spontaneously released, whereas mature tryptase is retained by HMC-1 cells, Mono-Mac-6 cells, and human skin-derived mast cells

Tryptase (alpha and beta) levels in serum are used to assess mast cell involvement in human disease. Using cultured cells, the current study examines the hypothesis that protryptase(s) are spontaneously secreted by mast cells at rest, whereas mature tryptase(s) are stored in secretory granules until their release by activated cells. HMC-1 cells have only beta-tryptase genes and the corresponding mRNA. Mono-Mac-6 cells have both alpha- and beta-tryptase genes but preferentially express alpha-tryptase. Mono-Mac-6 cells spontaneously secrete most of their tryptase, which consists of alpha-protryptase, whereas mature tryptase is retained inside these cells. HMC-1 cells also spontaneously secrete most of their tryptase, identified as beta-protryptase, and retain mature tryptase. Skin-derived mast cells retain most of their tryptase, which is mature, and spontaneously secrete protryptase(s). Total tryptase levels in plasma are detectable but no different in healthy subjects with and without the gene for alpha-tryptase, consistent with pro forms of both alpha- and beta-tryptase being spontaneously secreted. Thus, protryptase(s) are spontaneously secreted by resting mast cells, whereas mature tryptase is retained by mast cells until they are activated to degranulate.