Spark Therapeutics is charging $850,000 for its recently approved gene therapy drug, Luxturna, which treats a rare eye condition that leads to blindness. The actual price will be lower after Spark negotiates discounts with health insurers, but uninsured patients and people with high deductibles and coinsurance rates pay based on the list price.

Why it matters: Luxturna is now the most expensive drug on the market, although many other rare-disease drugs also cost more than $500,000.

More details: The drug company said it is working with insurers to offer rebates if Luxturna doesn't work, and it is talking with the federal government to allow insurers to pay for the therapy over several years instead of having to make one large upfront payment.

Go deeper: The $850,000 price tag for Luxturna is above what is considered to be a fair, value-based price, according to a draft analysis from a group that evaluates drug prices.