On May 23, 2018, Spark Therapeutics, Inc. (the “Company”) closed its previously announced transaction with Jazz Pharmaceuticals Ireland Limited (“Jazz”) to which the Company sold its Rare Pediatric Disease Priority Review Voucher (“PRV”) to Jazz in accordance with the terms of the Asset Purchase Agreement (the “Agreement”) entered into by the parties on April 30, 2018. The PRV was awarded to the Company by the U.S. Food and Drug Administration in connection with the approval of LUXTURNA™ (voretigene neparvovec-rzyl), a one-time gene therapy product indicated for the treatment of patients with confirmed biallelic RPE65 mutation-associated retinal dystrophy. In consideration for the PRV, Jazz paid the Company $110,000,000 upon closing of the PRV purchase.

The foregoing description of the Agreement does not purport to be complete and is subject to, and qualified in its entirety by reference to, the full text of the Agreement. The Company intends to file a copy of the Agreement with the Company's Quarterly Report on Form 10-Q for the quarter ended June 30, 2018.

About Spark Therapeutics, Inc. (NASDAQ:ONCE)

Spark Therapeutics, Inc. (Spark) is engaged in developing products in the field of gene therapy. The Company focuses on treating orphan diseases. It has a pipeline of product candidates targeting multiple rare blinding conditions, hematologic disorders and neurodegenerative diseases. Its SPK-RPE65 (voretigene neparvovec) targets genetic blinding conditions known as inherited retinal dystrophies (IRDs). Its product candidates include SPK-CHM and SPK-FIX. Its product development portfolio includes product candidates targeting expression of genes in the liver, with an initial focus on hematologic disorders. It is engaged in the development and commercialization of SPK-FIX product candidates for the treatment of hemophilia B. The Company is developing a lead product candidate for the treatment of a form of Batten disease in SPK-TPP1 program. The Company is also conducting preclinical studies on a product candidate for the treatment of Huntington’s disease, a hereditary genetic disorder.