GZMB and triple-A syndrome: 19, 20, 21 The human ACT is encoded by only one gene; however, extensive diversification and duplication in mice have resulted in 13 related serpina genes clustered at chromosome 12F1.19 Out of these, SA3N was identified to be the only extracellular inhibitor of GzmB.21 A previous study by our group had demonstrated efficacy for SA3N as an in vivo GzmB inhibitor in a murine model of AAA.20