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Children's Health: Babies with rare muscle disorder given a chance at life

Researcher says costly enzyme replacement therapy for Pompe disease is 'almost a miracle'

Infants suffering from a rare but fatal genetic disorder of the muscles have been given a chance of survival thanks to a new, and expensive, intravenous treatment.

The condition, called Pompe disease, affects about one in 40,000 births and is marked by a deficiency in a protein, or enzyme, called acid alpha-glucosidase (GAA).

“It’s a rapidly progressive disease; it’s very sad to watch the children because they continue to lose motor milestones and become floppy,” says Dr. Priya Sunil Kishnani, associate professor of pediatrics at Duke University Medical Center in Durham, N.C. “The heart muscle initially thickens and then it starts to (enlarge), the babies become progressively weaker with no ability to move their limbs, and they ultimately die of cardiac failure or respiratory failure,” usually before 12 months of age.

Kishnani and her colleagues tested two different doses of genetically engineered GAA in 18 children under the age of six months with rapidly progressing Pompe disease. All survived to at least 18 months of age, and 15 did not need any breathing assistance.

“It’s a life-saving treatment,” Kishnani says. “I’ve seen so many of these babies die before therapy that this was almost a miracle. … These children were living free of ventilators and their heart size was not just stabilizing, it was decreasing close to the normal range with normal function.”

Along with normal growth, the children started to gain motor milestones like rolling, head holding, sitting up, standing, and walking and running. The oldest child from this trial is now 44 months of age. The oldest child from a previous trial of the drug is older than seven and is currently in Grade 2 at school.

Kishnani says these kids require ongoing treatment and close monitoring, and while some may have residual weakness or fatigue, “I would expect them to lead a regular life.”

The most common side-effects of the treatment include skin reactions, fever, chills, and changes in heart rate and blood pressure. There is also the potential for severe reactions to the infusion, but this has been seen in fewer than three per cent of children treated to date.

“Until this therapy came along there was really nothing we could do other than provide supportive care to the child and the family,” says Dr. Robin Casey, director of the inherited metabolic disorders program in the department of medical genetics at Alberta Children’s Hospital in Edmonton.

In Canada, fewer than 100 people are estimated to have Pompe disease. Casey estimates that treatment for an adult would cost about $400,000 per year and for an infant $30,000 to $40,000. For patients without private insurance or some other non-government source of funding, access to therapy could be an issue, unless provinces decide to cover the cost of the drug. The treatment is sold under the brand name Myozyme by Genzyme Canada Inc.