The world’s most expensive medicine is about to hit the market.

A one-time treatment for a devastating infant muscle-wasting disease won approval from the U.S. Food and Drug Administration Friday. Its maker Novartis AG says the gene therapy will cost $2.125 million.

The therapy, called Zolgensma, treats an inherited disease called spinal muscular atrophy, or SMA, whose victims typically die before the age of two if untreated. It is the latest gene therapy—a technique that introduces new DNA into the body to correct a faulty gene—to win approval.

Gene therapies promise the chance to cure diseases whose diagnoses were death sentences, but the prices for the first few to be greenlighted raise concerns about whether they can be afforded by governments and health insurers that have been struggling to control health spending.

Zolgensma’s price tag makes it the world’s most expensive medicine by a large margin, with the next most expensive drug a gene therapy called Luxturna that is priced at $850,000. However, some drugs that are taken repeatedly would cost more over the lifetime of a patient.