The Food and Drug Administration has approved the first drug to treat patients with spinal muscular atrophy, a savage disease that, in its most severe form, kills infants before they turn 2.
“This is a miracle — seriously,” Dr. Mary K. Schroth, a lung specialist in Madison, Wis., who treats children who have the disease, said of the approval, which was made last week. “This is a life-changing event, and this will change the course of this disease.” Dr. Schroth has previously worked as a paid consultant to Biogen, which is selling the drug.
The drug, called Spinraza, will not come cheap — and, by some estimates, will be among the most expensive drugs in the world.
Biogen, which is licensing Spinraza from Ionis Pharmaceuticals, said this week that one dose will have a list price of $125,000. That means the drug will cost $625,000 to $750,000 to cover the five or six doses needed in the first year, and about $375,000 annually after that, to cover the necessary three doses a year. Patients will presumably take Spinraza for the rest of their lives.
The pricing could put the drug in the cross hairs of lawmakers and other critics of high drug prices, and perhaps discourage insurers from covering it. High drug prices have attracted intense scrutiny in the last year, and President-elect Donald J. Trump has singled them out as an important issue.
“We believe the Spinraza pricing decision is likely to invite a storm of criticism, up to and including presidential tweets,” Geoffrey C. Porges, an analyst for Leerink Partners, said in a note to investors on Thursday.
Mr. Porges said the price could lead some insurers to balk or to limit the drug to patients who are the most severely affected, such as infants, even though the F.D.A. has approved Spinraza for all patients with the condition.
“What you will have is a standoff with payers,” he said in an interview on Thursday. “How is this all going to play out?”
The price of the drug would be comparable to some other drugs that treat rare diseases. A spokeswoman for Biogen said the company set the price after considering several factors, including the cost to the health care system and the clinical value it brought to patients. She said the company has also consulted insurers about covering the drug, and that while the talks are in their early stages, insurers have responded positively to the drug’s effectiveness.
“We are working to help ensure no patient will forgo treatment because of financial limitations or insurance status,” said the spokeswoman, Ligia Del Bianco.
She said Biogen, like many companies that sell expensive drugs, had set up a program to help families navigate insurance approvals and other logistics, and will provide financial assistance.
Kenneth Hobby, the president of Cure SMA, a patient advocacy group that invested $500,000 in early academic research that led to the development of Spinraza, said more important than the list price of the drug is whether patients who need it will get it.
“Are our families going to get access to the drug in the end?” he said.
About 1 in 10,000 babies are born with spinal muscular atrophy — or about 400 a year in the United States — and it is among the leading genetic causes of death in infants. People with the disease have a genetic flaw that makes them produce too little of a protein that supports motor neurons, leading muscles to atrophy. Spinraza addresses the underlying genetic cause of the disease and enables a backup gene to produce more of the necessary protein.
Blake Farrell, 6, has the disease. As an infant, Blake reached developmental milestones, learning to roll over, sit up and crawl at all the right times. “She was doing everything on target,” Kacey Farrell, Blake’s mother, said recently from the family’s home in Cincinnati.
But as she approached her first birthday, Blake started regressing. She struggled to sit on her own and stopped crawling. At 14 months, tests revealed that Blake had a moderate form of spinal muscular atrophy. As she got older, the muscle loss caused her bones to weaken, and she suffered fractures. She could no longer sit up in the bathtub, and had trouble swallowing food.
In May of 2015, when she was 4, Blake was accepted into a clinical trial for Spinraza, also known as nusinersen. A third of the patients in the study were given a placebo, so the Farrells were not sure if she was getting the real thing. But after receiving her first few doses, which were injected into her spinal fluid, Blake started to improve. She joined her two sisters in the bathtub, sitting up on her own. One day, she even scooted across the floor.
“I was just in shock,” Ms. Farrell said. “These were all things we hadn’t seen her do since she was 8 months old.”
In an analysis of 82 infants in the clinical trial that led to the approval, 40 percent of babies on the drug reached milestones such as sitting, crawling and walking. None of the babies that received a placebo did. The F.D.A. approved the drug months ahead of time and, because the drug treats a rare pediatric disease, granted Biogen a special voucher that it can use to gain priority review of a future drug that would not otherwise qualify for the program.
The F.D.A. said the most common side effects were respiratory infections and constipation, and there is a warning about possible low blood platelet counts and toxicity to the kidneys.
Even though trial investigators did not know which patient was receiving Spinraza, “anecdotally, it just seemed quickly obvious to us that some patients were following a very different trajectory than what we were used to seeing,” said Dr. John Brandsema of the Children’s Hospital of Philadelphia, one of the investigators.
He said that while the patients who improved were the most remarkable, the drug also appears to stop the progression of the disease in other patients.
“It’s hard not to use very exaggerated terms when you are talking about this, because it really is a pretty major step forward,” Dr. Brandsema said.
For now, Blake receives Spinraza free because she is enrolled in an extension study of the drug. But her father, Nick Farrell, a lawyer, said cost is a concern.
“That is a whole lot of money,” he said, adding that among parents of children with the disease, access is already a major topic. “The conversation has already started about, O.K., what’s the next step here?”