Spark Therapeutics Inc. shares ONCE, +2.54% were halted Thursday as a U.S. Food and Drugs Administration advisory committee meets to review the company's gene therapy treatment for patients with vision loss caused by biallelic RPE65-mediated inherited retinal disease, or IRD. IRD is a group of rare blinding conditions caused by one of more than 220 different genes, the company said. The diseases cause night blindness that can develop to include peripheral vision loss or tunnel vision, and can result in blindness. There are currently no treatments approved for the condition. The FDA committee meeting is set to start at 8.30 a.m. Eastern and will review the gene therapy Luxturna, which has received orphan drug, breakthrough therapy and rare pediatric disease designations from the agency. The treatment showed positive results in a Phase 3 trial, data from which were published in The Lancet. The committee's ruling is non-binding, but is taken into consideration by the FDA when reviewing drug applications. Spark shares have gained 73% in 2017, while the S&P 500 SPX, -1.11% has gained 14%.