Lyons JJ, Chovanec J, O’Connell MP, et al. - Researchers investigated the prevalence as well as associated effect of tryptase genotypes on anaphylaxis in humans. This study involved cohorts with systemic mastocytosis (SM) and venom as well as idiopathic anaphylaxis from referral centers in Italy, Slovenia, and the US, and also healthy volunteers and controls with nonatopic disease. Experts found that healthy people and controls with nonatopic disease commonly had hereditary α-tryptasemia (HαT), a genetic trait caused by raised α-tryptase–encoding Tryptase-α/β1 ( TPSAB1) copy number causing raised basal serum tryptase level. HαT was found to be related to grade IV venom anaphylaxis and was shown to be more prevalent in both idiopathic anaphylaxis and SM vs controls. Overall, findings revealed that risk for severe anaphylaxis in humans was related to inherited variations in α-tryptase–encoding copies at TPSAB1.