Provincial and territorial health plans will begin to cover treatment for infants affected by a rare and devastating genetic disorder, a medicine considered among the most expensive in the world.

Nusinersen, sold under the name Spinraza, is the first and only approved treatment for spinal muscular atrophy, which causes progressive muscle weakness and wasting, leading to severe handicaps and death before the age of two in the most severely affected patients.

Health Canada has approved the drug for sale in Canada. But the Canadian Agency for Drugs and Technologies in Health, which makes recommendations to the provinces about whether to cover the costs of new medications, recommended in December that Spinraza be covered only for those with Type 1 SMA, a form with onset in infancy. That recommendation was based on the conditions that there be a “substantial reduction in price” and on the collection of “real-world evidence” of the drug’s effectiveness.

The drug is injected into the spine and delivers pieces of synthetic DNA to boost production of the gene responsible for protein development that is missing in people with SMA.

But the drug costs approximately $708,000 for six doses in the first year of treatment and about half that for three doses each year after. The drug is intended to be delivered for life.

Under a deal announced Wednesday between drug-maker Biogen Canada and the pan-Canadian Pharmaceutical Alliance (pCPA), public health plans will cover patients diagnosed in infancy and Biogen will provide the drug to the most urgently affected patients in other groups who don’t have private insurance coverage.

"We at Cure SMA Canada are very happy to hear that an agreement was finally reached, offering treatment to our most critical patients. We will continue to advocate for our remaining patients who are left without treatment,” executive director Susi Vander Wyk said.

“We are hopeful and confident that the decision makers will not allow our remaining patients to continue on a path of progression while they watch others around the world, who are accessing Spinraza, gain in strength and abilities.”

SMA, which destroys motor neurons in the spinal cord, affects about one in 10,000 people, leaving those affected dependent on respiratory and feeding equipment and wheelchairs. It is the leading genetic cause of infant death worldwide.

“Through an extensive clinical development program, nusinersen has shown significant improvements in survival rates and motor function across a broad range of types and ages of SMA patients,” reads a statement announcing the deal.

"We are very pleased that we were able to reach an agreement that will make such a difference in the lives of people living with SMA in Canada and their families,” said Marina Vasiliou, vice-president and general manager of Biogen Canada.

“This is the first step towards access to nusinersen for a broad population of Canadian patients and we believe it also marks the beginning of a partnership between Biogen and pCPA that will provide treatment and hope to patients with rare diseases and neurological conditions in Canada."

The pCPA brings provinces, territories, and federal drug plans together to negotiate prices for publicly covered drugs. It has been negotiating a price for Spinraza since February.

Under the terms of the new agreement, participating drug plans from the pCPA will fund treatment in SMA Type 1 patients who meet clinical criteria.

Type 1 patients show symptoms at or before seven months and cannot sit unsupported. These patients typically have a life expectancy of two and make up about 60 per cent of diagnosed cases.

Patients with Type 2 SMA show signs and symptoms between seven months and 18 months of age. Most can sit unsupported but usually cannot walk independently. Life expectancy is over 25 years of age and is greatly improved by aggressive supportive care.

Type 3 SMA patients may show signs and symptoms between 18 months and 18 years. Declining mobility may result in the use of a wheelchair but these patients typically have a normal life expectancy and represent between 10 to 20 per cent of cases.

Biogen has submitted updated clinical trial data to regulators and is requesting reconsideration for broader public coverage of Spinraza to treat patients with other SMA types. It’s expected that review will be completed in early 2019.

Until then, Biogen will cover the drug for patients with the highest risk of losing motor function and who don’t have private insurance coverage under a compassionate access program. Urgency will be assessed by an independent steering committee of Canadian experts in SMA and rare diseases.

Nusinersen is approved for treatment of SMA by more than 40 countries.