Parents whose children are battling a genetic disease called spinal muscular atrophy are calling on the provinces to fund a drug that's considered a life-changer, but also one of the most expensive medications in the world.

The drug is called nusinersen, sold under the name Spinraza, and is the only approved treatment for spinal muscular atrophy, or SMA. SMA is a genetic disease that destroys motor neurons in the spinal cord, damaging children’s ability to move. The disease is progressive, leading to paralysis in many, and often death in the most severe forms of the condition.

Spinraza is the first medication shown to be effective at halting and sometimes reversing some of the effects of SMA. The drug is injected into the spine and works by delivering pieces of synthetic DNA to increase a key protein that’s missing in people with SMA.

But the cost of using the drug is high: approximately US$750,000 for the first year of treatment.

Health Canada recently approved the drug for sale in Canada. But CADTH (Canadian Agency for Drugs and Technologies in Health), which makes recommendations to the provinces about whether to cover the costs of new medications, recommended that Spinraza be used by only a subset of SMA patients.

It said in December that those children with the most severe form of SMA, Type 1, who are diagnosed in infancy, would benefit most.

So far, no province has agreed to fund the drug.

On Sunday, nine families in British Columbia whose children have SMA gathered together to call on the provinces to offer the drug to all kids with SMA.

Susi Vander Wyk, of the advocacy group Cure SMA Canada, says it’s only fair that all children who could benefit from the drug should be able to access it, rather than watch their condition worsen. http://curesma.ca/latest-news/

“It’s unacceptable that children will die in the process, that children will lose abilities,” she told CTV Vancouver.

Natalie Essex, now four years old, has been using Spinraza as part of a clinical trial. SMA left Essex unable to crawl or sit up on her own, but since she began using the drug, she has learned to stand with the assistance of a walker.

The clinical trial Natalie’s enrolled in is drawing to a close, however, and her family isn’t sure what will happen next.

The B.C. Ministry of Health says its Drug Benefit Council is currently reviewing Spinraza to decide whether to offer funding.

Biogen, the manufacturer of Spinraza in Canada, tell CTV News they hope to work with "health care systems and government to ensure that patients who may benefit will have access" to the drug.

Meanwhile, parents of children with SMA are calling on the provinces to cooperate to negotiate with Biogen for a better price.

With a report from CTV Vancouver’s Scott Roberts