In a study assessing TPSAB1 germline copy number variants in 180 mastocytosis patients, 180 sex-matched control subjects, 720 patients with other myeloid neoplasms, and 61 additional mastocytosis patients of an independent validation cohort, α-tryptase encoding TPSAB1 copy number gains corresponding to HαT were identified in 17.2% of mastocytosis patients as compared to only 4.4% of the control population (p < 0.001) [65]. The gene discussed is TPSAB1; the disease is mastocytosis.