REGENXBIO, a biotechnology company focused on the development, commercialization and licensing of recombinant adeno-associated virus (AAV) gene therapy based on its proprietary NAV Technology Platform, has announced that the FDA has granted Rare Pediatric Disease Designation to RGX-121, REGENXBIO’s investigational gene therapy product candidate for the treatment of Mucopolysaccharidosis Type II (MPS II).

"Along with RGX-111 for the treatment of MPS I, this is our second MPS program to achieve a Rare Pediatric Disease Designation and builds upon the Orphan Drug Designation granted to RGX-121 at the end of 2015 by the FDA, underscoring the therapy’s potential to provide meaningful benefit to children struggling with this severely debilitating disease,” said Kenneth T. Mills, president and chief executive officer of REGENXBIO. “Both of these programs use our NAV AAV9 vector and we plan to file Investigational New Drug applications for RGX-111 and RGX-121 in the first half of 2017. We look forward to working with the FDA to advance this platform of gene therapies for MPS to patients in need.”

The FDA defines a rare pediatric disease as a disease that affects fewer than 200,000 individuals in the U.S., primarily aged from birth to 18 years. Under the FDA's Rare Pediatric Disease Priority Review Voucher program, a sponsor who receives an approval of a new drug application or biologics license application for a rare pediatric disease may be eligible for a voucher, which can be redeemed to obtain priority review for any subsequent marketing application and may be sold or transferred.

MPS II, also known as Hunter syndrome, is a rare, X-linked recessive disease caused by a deficiency in the lysosomal enzyme iduronate-2-sulfatase (IDS). Approximately 500 to 1,000 individuals with MPS II are estimated to be born each year worldwide. In severe forms of the disease, early developmental milestones may be met, but developmental delay is readily apparent by 18 to 24 months. Developmental progression begins to plateau between three and five years of age, with regression reported to begin around six and a half years. RGX-121 uses an AAV9 vector to deliver the IDS gene to the central nervous system.