Spinal muscular atrophy is a condition often fatal by age 2. Babies with the disorder have a rare genetic mutation that prevents the nervous system from controlling certain muscles. As they grow to be toddlers, these children struggle to move their limbs, to swallow food, to talk.

The Food and Drug Administration recently approved a single-dose gene therapy, Zolgensma, that has the potential to cure spinal muscular atrophy. That was cause for hope for the hundreds of patients suffering from it, along with their families and physicians — until its manufacturer, Novartis, announced the treatment’s price tag: about $2.1 million per patient.

That’s believed to be more than any one medication has ever cost. Pharmaceutical companies like Novartis receive a number of government incentives to develop treatments for rare and neglected diseases such as spinal muscular atrophy, including speedier drug approvals, generous tax breaks and extended patent protections. But because lawmakers have not tied such incentives to any price controls, and insurance may not cover all or any of the cost, families who desperately need Zolgensma are struggling to afford it.

Insult was added to this injury last week when agency officials said that Novartis had given regulators manipulated or mishandled data as part of its Zolgensma application and that the company waited until after the drug was approved to report the problem . Both the agency and the company say that they still consider Zolgensma safe and effective. But how can patients and their families know for sure? Zolgensma benefited from several F.D.A. programs intended to get urgently needed medications onto the market as quickly as possible, including a program that reduces the amount of data needed for agency approval.