US regulators approved Spinraza in December for all types of SMA. But until now, Cambridge-based Biogen had only reported full data from a separate study of the drug in infants up to six months old who had Type 1, the most severe form.

The findings, to be presented at the American Academy of Neurology annual meeting in Boston, are likely to raise the pressure on health insurers that so far have refused to pay for the expensive drug — called Spinraza — for children with Type 2 and Type 3 spinal muscular atrophy.

Biogen Inc. released data Monday from a late-stage clinical trial showing its recently approved treatment for spinal muscular atrophy significantly improved motor function in older children with later-onset types of the neuromuscular disease.


The company, which won accelerated approval for Spinraza, had not completed its study of children age 2 to 12 at the time the Food and Drug Administration made its ruling, though it shared interim data with the agency.

“We’re hopeful that when [health plans] see this data, they will update their policies” to cover the drug in older children, said Biogen chief medical officer Alfred Sandrock.

The treatment’s list price of $750,000 for the first year, and $375,000 annually after that, makes it one of the costliest therapies on the market. Some of the nation’s largest health insurers, including Aetna Inc. and United HealthGroup, are covering Spinraza for all patients. Other insurance carriers are making decisions case by case, while some have said they would cover only Type 1 patients until they saw compelling data on later-onset patients.

Boston consultant Doug Hansen, whose 11-year-old son Tyler suffers from Type 3 SMA, has appealed to a state agency after Neighborhood Health Plan denied coverage of Spinraza for Tyler. The insurer last month said it will only cover treatment of Type 1 patients until it gets more data about how well the drug works in later-onset patients.


Hansen, however, noted that doctors at Boston Children’s Hospital and other medical centers already are prescribing Spinraza for all SMA patients following the FDA’s broad approval of the drug.

The new data from Biogen, he said, “makes Neighborhood Health Plan’s position, which was ridiculous on its face, even more ridiculous.”

In a statement, Neighborhood Health chief medical officer Anton B. Dodek said new data from drug trials are regularly reviewed by “an independent body of outside physicians and pharmacists that sets Neighborhood’s guidelines for prescription drug coverage.”

Sandrock said some children in the 15-month clinical trial could start crawling, sit upright, and stand without support after receiving spinal injections of Spinraza — movements they weren’t able to make before the study. The controlled trial enrolled 126 children with later-onset SMA. Two-thirds were given Spinraza, while one-third were given a placebo.

Biogen said Monday that the study demonstrated “highly statistically significant and clinically meaningful improvement in motor function” in the later-onset SMA patients.

The company’s stock price closed up $3.92 on the Nasdaq stock exchange Monday, to $276.86, an increase of 1.44 percent.

Biogen is the largest Massachusetts-based biotech. It is a global leader in multiple sclerosis medicines and also is working on several experimental drugs to treat Alzheimer’s disease.

Robert Weisman can be reached at robert.weisman@globe.com. Follow him on Twitter @GlobeRobW.