A new gene therapy to treat a debilitating eye disorder is one step closer to regulatory approval in Europe. Gene therapy company MeiraGTx said the European Medicines Agency granted Priority Medicines (PRIME) designation to its candidate A002 for treatment of achromatopsia.

London-based MeiraGTx said its gene therapy candidate AOO2 received the PRIME designation following the company’s ongoing Phase I/II dose escalation study. A002 is an adeno-associated virus (AAV) gene therapy that is designed to deliver a codon-optimized CNGB3 cDNA under the control of the cone arrestin (CAR) promoter to photoreceptors in the back of the eye, according to company data. The treatment is delivered via a sub-retinal injection to cover the central region of the retina, including the fovea where the majority of cones are located.

Patients with achromatopsia face a myriad of vision problems. The syndrome is primarily known for total color blindness but also causes other vision issues, including light sensitivity, involuntary eye movement, legal blindness and poor visual acuity.

MeiraGTx said the EMA granted the PRIME designation based on non-clinical in vivo data and early clinical safety data from MeiraGTx’s ongoing Phase I/II dose escalation study. MeiraGTx has completed dosing of eight CNGB3 patients in the Phase I/II study and is currently treating patients in the third dose escalation cohort.

Zandy Forbes, president and chief executive officer of MeiraGTx, said the PRIME designation was good news for the company. Forbes said the company will work closely with the EMA to “accelerate A002 as a potential treatment option for patients living with this challenging and painful condition.”

“Having just received Rare Pediatric Disease Designation from the U.S. Food and Drug Administration (FDA) earlier this month, we are very pleased with the momentum of our ACHM program and the recognition by regulatory agencies of its potential to help those in need of effective treatment options,” Forbes said in a statement.

The FDA granted AOO2 the rare pediatric disease designation in February. In 2016 AOO2 received orphan drug designation from both the FDA and the EMA. In December the FDA awarded the rare pediatric disease designation to MeiraGTx’s A001gene therapy candidate for the treatment of patients with Leber's Congenital Amaurosis due to mutations in the RPE65 gene (LCA2). Like AOO2, AOO1 is an AAV therapy designed to deliver a codon-optimized RPE65 cDNA under the control of a synthetic RPE-specific promoter to the back of the eye.

AOO1 received the designation just days before the FDA approved Spark Therapeutics’ Luxturna (voretigene neparvovec), a gene therapy for a rare, genetic form of blindness. The approval marks the first time the FDA has approved a directly administered gene therapy that targets a disease caused by mutations in a specific gene. Luxturna is approved for the treatment of pediatric and adult patients with confirmed biallelic RPE65 mutation-associated retinal dystrophy. The disease can lead to vision loss and may cause complete blindness in certain patients.