Defining hereditary alpha-tryptasemia as a risk/modifying factor for anaphylaxis: are we there yet?

Hereditary a-tryptasemia (HaT) is a common autosomal dominant genet-ic trait with variable penetrance associated with increased serum baseline tryptase (SBT) levels. Clinical manifestations may range from an absence of symptoms to overtly severe and recurrent anaphylaxis. Symptoms have been claimed to result from excessive activation of EGF-like module -con-taining mucin-like hormone receptor-like 2 (EMR2) and protease activat-ed receptor 2 (PAR-2) receptors by a/13-tryptase heterotetramers. Herein, we aimed to review the evidence on whether HaT can be considered a hereditary risk factor or a modifying factor for anaphylaxis. Increased SBT levels have been linked to an increased risk of anaphylaxis. Likewise, recent studies have shown that HaT might be associated with a higher risk of developing anaphylaxis and more severe anaphylaxis. The same has also been shown for patients with clonal mast cell disorders, in whom the co-existence of HaT might lead to a greater propensity for se-vere, potentially life-threatening anaphylaxis. However, studies leading to such conclusions are generally limited in sample size, while other studies have shown opposing results. As such, further studies investigating the po-tential association of HaT with anaphylaxis caused by different triggers, and different severity grades, in both patients with clonal mast cell activa-tion syndromes and the general population are still needed.