The expanded promoter at duplicated TPSAB1 is conserved and has increased basal activity. (A) Normalized fluorescent reporter activity in unstimulated MonoMac-6 cells transfected with promoters cloned from endogenous (α^WT) or replicated (α^DUP) TPSAB1 loci. (B) BST from individuals grouped by TPSAB1 replication number. (C-D) Relative allelic frequency (C) and ratios (D) of α^WT-tryptase (y-axis) and α^DUP-tryptase (x-axis) associated 5′ variants determined by ddPCR. Dashed lines indicate predicted α^WT:α^DUP ratios by genotype. ∗P < .05.