The U.S. FDA has granted Breakthrough Therapy Designation (BTD) for DX-2930 for the prevention of attacks of hereditary angioedema (HAE). DX-2930 is an investigational humanized monoclonal antibody against plasma kallikrein (pKal) currently under development by Dyax, a biopharmaceutical company based in Burlington, MA. HAE is a rare, autosomal dominant genetic disease characterized by episodic attacks of swelling affecting the extremities, gastrointestinal tract, genitalia and larynx. It is caused by mutations in the C1 inhibitor gene, which result in low levels of or dysfunctional C1 esterase inhibitor, a naturally occurring protein that inhibits pKal, a key mediator of inflammation in the blood. By antagonizing the function of pKal, DX-2930 is expected to prevent HAE attacks. The BTD is supported by the promising interim results of a Phase 1b clinical trial in HAE patients sponsored by Dyax. In addition, a proof-of-concept efficacy analysis also demonstrated that DX-2930 significantly reduced HAE attacks in comparison to placebo.