"A onetime treatment with Luxturna the first US Food and Drug Administrationapproved gene therapy for an inherited disorder will cost  per eye.  Spark Therapeutics Inc. the Philadelphiabased maker of voretigene neparvovec announced Wednesday in a statement httpir.sparktx.comnewsreleasesnewsreleasedetailssparktherapeuticsannouncesfirsttheirkindprogramsimprove that it reached an agreement in principle with Harvard Pilgrim and affiliates of Express Scripts to make the onetime treatment available to patients with a rare genetic defect that often leads to blindness.  The mutation affects both eyes usually at the same pace so most patients would need treatment for both eyes a Spark Therapeutics spokeswoman said. In some cases the gene therapy will be available under an outcomesbased rebate arrangement. The company also stated that its proposal to the Centers for Medicare and Medicaid Services the government program that covers about  million Americans would allow installment payments for the drug.  For a onetime therapy like Luxturna a nontraditional payment and distribution model is necessary to ensure needs of all parties  patients payers and providers  are addressed said Jennifer Luddy a spokeswoman for Express Scripts. At least one patient advocate disagrees. The new payment models announced today are merely a way to disguise a price that is simply too high David Mitchell president and founder of Patients For Affordable Drugs said in a statement https Spark Therapeutics is charging as much for Luxturna as they think they can get away with. Spark Therapeutics CEO Jeff Marrazzo coauthored a recent blog post in the journal Health Affairs https that said the current payment system  accustomed to ongoing treatment of chronic diseases  creates significant challenges for gene therapies and other treatments.  Onetimeonly treatments for rare genetic disorders are still unique he noted. The drug is intended for patients with retinal dystrophy due to a mutation of the RPE gene. This rare genetic defect causes severe visual impairment beginning in infancy and can eventually lead to blindness. The company believes the total population in the US Europe and select additional markets in the Americas and AsiaPacific is up to approximately  individuals who have the mutation targeted by Luxturna explained Monique da Silva a spokeswoman for Spark Therapeutics. The drug will be available in the United States in early spring with an estimated  to  people in the US standing to benefit from this treatment according to Spark. Luxturna is only the third gene therapy approved for use in the United States two others were also approved in . This is the first to correct an inherited genetic mutation. Luxturna is a liquid that is injected directly into the eye with a microscopic needle during a surgical procedure. The drug supplies a third gene  a normal RPE gene  to cells in the retina a layer of tissue lining the back of the eye. This third version of the gene does not remove or replace the two mutated genes causing the disease which remain inside the cells. However the normal gene delivered by the treatment is able to function within the retinal cells and correct vision problems. In the phase  clinical trial  out of  participants    who received the gene therapy demonstrated a gain in functional vision as assessed by a mobility test performed in a maze according to the company. Risks of the treatment include cataracts elevated eye pressure retinal tears and holes and inflammation. The companys offer of unusual payer models including rebates and installment payments will help ensure patients individual financial situation does not hinder access to treatment da Silva said.  New technologies such as gene and cell therapies hold out the potential to transform medicine FDA Commissioner Dr. Scott Gottlieb said in a statement https announcing the August approval of Kymriah considered to be the first gene therapy to be approved for the US market.  Follow CNN Health on Facebook and Twitter See the latest news and share your comments with CNN Health on Facebook https and Twitter httpstwitter.comcnnhealth. Kymriah is a leukemia treatment made by pharmaceutical giant Novartis. Similar to Luxturna Kymriah is a onetime treatment and its price tag is . However Novartis said this price will not be charged to patients who do not respond within a month of treatment."