KLK4 and hereditary angioedema: Ecallantide (DX-88), a Kunitz domain-derived inhibitor of kallikrein (a subgroup of serine proteases), was approved by the FDA in 2012 for treatment of hereditary angioedema (HAE), a rare, autosomal dominantly inherited blood disorder that manifests as an episodic swelling of the body (Schneider et al., 2007; Cicardi et al., 2010; Levy et al., 2010).