Hymenoptera venom allergy in a single-center Israeli cohort: Clinical and laboratory characteristics

Clonal mast cell disorders and hereditary α-tryptasemia as risk factors for anaphylaxis

The association between Hymenoptera venom-triggered anaphylaxis (HVA) and clonal mast cell-related disorders (cMCD) has been known for decades. However, recent breakthroughs in peripheral blood screening for KIT p.D816V missense variant have revealed the true extent of this clinical association whilst adding to our understanding of the underlying aetiology. Thus, recent large studies highlighted the presence of KIT p.D816V among 18.2% and 23% of patients with severe Hymenoptera venom-triggered anaphylaxis. A significant proportion of those patients have normal serum basal tryptase (BST) levels, with no cutaneous findings such as urticaria pigmentosa or other systemic findings such as organomegaly that would have suggested the presence of cMCD. These findings of an increased prevalence suggest that the impact of cMCD on anaphylaxis could be clinically underestimated and that the leading question for clinicians could be changed from 'how many patients with cMCD have anaphylaxis?' to 'how many patients with anaphylaxis have cMCD?'. The discovery of hereditary α-tryptasemia (HαT)-a genetic trait caused by an increased copy number of the Tryptase Alpha/Beta 1 (TPSAB1) gene-, first described in 2016, is now known to underlie the majority of cases of elevated BST outside of cMCD and chronic kidney disease. HαT is the first common heritable genetic modifier of anaphylaxis described, and it is associated with increased risk for severe HVA (relative risk = 2.0), idiopathic anaphylaxis, and an increased prevalence of anaphylaxis in patients with cMCD, possibly due to the unique activity profile of α/β -tryptase heterotetramers that may potentiate immediate hypersensitivity reaction severity. Our narrative review aims to highlight recent research to have increased our understanding of cMCD and HαT, through recent lessons learned from studying their association with HVA. Additionally, we examined the studies of mast cell-related disorders in food and drug allergy in an effort to determine whether one should also consider cMCD and/or HαT in cases of severe anaphylaxis triggered by food or drugs.

Prevalence of mastocytosis and hymenoptera venom allergy in the United States

BACKGROUND

Mastocytosis is a risk factor for hymenoptera venom anaphylaxis (HVA). Current guidelines recommend measuring tryptase in patients with HVA and that those with mastocytosis pursue lifelong venom immunotherapy (VIT). Available data on HVA and mastocytosis largely derive from European single-center studies, and the prevalence of HVA with and without mastocytosis in the United States is unknown.

OBJECTIVE

We sought to determine the prevalence of HVA and mastocytosis in the United States using an insurance claims database and evaluate the impact of mastocytosis on VIT in patients with HVA in a US cohort.

METHODS

The IBM Watson Database, consisting of insurance claims from approximately 27 million US patients in 2018, was queried to identify patients with HVA and/or mastocytosis. Furthermore, a retrospective study of 161 patients undergoing VIT between 2015 and 2018 at the University of Michigan was conducted.

RESULTS

In the IBM Watson Database, the prevalence of HVA was 167 per 100,000 (0.167%) and the prevalence of mastocytosis 10 per 100,000 (0.010%) overall and 97 per 100,000 (0.097%) among those with HVA. Mastocytosis showed a 9.7-fold increase among patients with HVA versus the general population. In the U-M cohort, 2.6% of patients with VIT had mastocytosis. Tryptase level did not correlate with venom reaction severity but was higher in patients with systemic VIT reactions.

CONCLUSIONS

We observed a lower US HVA prevalence than previously reported. Mastocytosis was more common in US patients with HVA, though at lower rates than previously reported. In patients with VIT there was no correlation between tryptase level and reaction severity.