The U.S. FDA granted Orphan Drug Designation to SPK-9001 for the treatment of hemophilia B. SPK-9001 is developed by Spark Therapeutics, a biotechnology company based in Philadelphia, PA, and it is currently under collaborative development agreement with global pharmaceutical company Pfizer. Hemophilia B is a rare X-linked genetic disorder caused by mutations of the factor IX gene, resulting in missing or defective factor IX and consequently leading to increased propensity for bleeding. SPK-9001 is a bio-engineered adeno-associated viral (AAV) vector composed of a bioengineered AAV capsid and a codon-optimized expression cassette encoding a high-specific activity variant of human coagulation factor IX. It can potentially deliver a high-activity factor IX gene to the liver. It is currently under a Phase I/II study for evaluation of safety and efficacy.