Neighborhood Health Plan will cover a costly new drug for any member with spinal muscular atrophy, reversing a policy that limited coverage to patients with the most severe form of the disease.

The insurer said Tuesday that its turnabout was based on clinical data presented during last week’s annual meeting in Boston of the American Academy of Neurology. The data showed the drug, called Spinraza, was effective for later-onset patients with less severe forms of SMA.

Spinraza helps to improve motor function in children with the neurodegenerative disorder. In a 15-month clinical study, some later-onset children were able to 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 trial enrolled 126 children with types 2 and 3 spinal muscular atrophy. Two-thirds were given Spinraza, while one-third were given a placebo.

Biogen Inc., the Cambridge biotech selling the drug, priced it at $750,000 for the first year and $375,000 annually after that, making it one of the most expensive medicines on the US market. It was approved by the Food and Drug Administration in December for all patients, though Biogen last year had completed a clinical study only for Type 1 patients, the most severely affected.

Somerville-based Neighborhood Health “is in the process of changing its prescription drug policy to cover Spinraza for all spinal muscular atrophy patients,’’ the insurer’s chief medical officer, Anton B. Dodek, said in a statement. “While that process proceeds, [Neighborhood Health] as a matter of practice will cover Spinraza for all SMA patients.’’

The new practice by Neighborhood Health — which is owned by Partners HealthCare, the state’s largest hospital and physicians network — puts it in line with many other health insurers, including most in Massachusetts, that had already been covering the drug for all patients. But some insurers have yet to approve coverage for later-onset patients with types 2 and 3 spinal muscular atrophy.

“We’re very happy that no one will have to go through what we and other families had to go through with NHP,’’ said Doug Hansen, a Boston consultant who successfully appealed to a state agency the insurer’s denial of coverage for his 11-year-old son, Tyler.

Noting that at least one other Massachusetts family also recently won a state appeal against the health insurer, Hansen likened the change in Neighborhood Health’s Spinraza policy to “the guy who loses the fight saying ‘I don’t want to fight any more.’ ’’

Health insurers across the country increasingly are pushing back against a new generation of high-priced specialty medicines, though Neighborhood Health officials said their initial policy was based not on financial considerations, but on the medical evidence available at the time.

Biogen spokesman Matt Fearer said it was too soon to assess whether last week’s new data would spur changes at other insurers that, like Neighborhood Health, had limited Spinraza coverage.

“We’re hopeful this moves payers toward the decision Neighborhood made to support a broader patient population,’’ Fearer said. “And we’re working to educate them around the data.’’

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