Regenxbio, a Rockville, Md.-based biotechnology company focused on the development, commercialization and licensing of recombinant adeno-associated virus (AAV) gene therapy, today announced that the FDA has granted Rare Pediatric Disease designation to RGX-111, the company’s investigational gene therapy product candidate for the treatment of mucopolysaccharidosis type I (MPS I).

“The Rare Pediatric Disease designation builds upon the Orphan Drug designation granted earlier this year by the FDA to RGX-111 for MPS I, 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. “We plan to file an Investigational New Drug application for RGX-111 for the treatment of MPS I in the first half of 2016, and look forward to working with the FDA to advance this important gene therapy 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 (NDA) or biologics license application (BLA) for a rare pediatric disease may be eligible for a voucher which can be redeemed to obtain priority review for any subsequent marketing application.

MPS I is a rare neurodegenerative disease caused by deficiency of the a-l-iduronidase (IDUA) gene. More than 1,000 individuals with MPS I are estimated to be born each year worldwide. Symptoms include excessive accumulation of fluid in the brain, spinal cord compression and cognitive impairment. RGX-111 uses an AAV9 vector to deliver the IDUA gene to the central nervous system.