Experimental Drug Offers Hope for Rare Bone Disease: Study

WEDNESDAY, March 7 (HealthDay News) — A new therapy may be the
first to offer hope for children born with a rare disease that affects
bone development, sometimes so severely that babies die because they’re
missing a rib cage to protect their lungs.

The inherited disorder is called hypophosphatasia, and the new
medication is asfotase alfa. It works by replacing an enzyme that’s
missing in those with hypophosphatasia. Enzymes are substances responsible
for speeding up certain chemical reactions. In hypophosphatasia, the
missing enzyme is necessary for proper bone growth and normal metabolism.

A small study of babies and children younger than 3 who had
debilitating or life-threatening hypophosphatasia found that treatment
with asfotase alfa strengthened bones and improved lung function. After 48
weeks of treatment, many could start bearing weight on their legs and some
infants were even taking their first steps.

“We saw striking improvements in these patients with severe
hypophosphatasia who received the enzyme replacement,” said the study’s
lead author, Dr. Michael Whyte, medical-scientific director of the Center
for Metabolic Bone Disease and Molecular Research at Shriners Hospitals
for Children in St. Louis. Whyte is also a professor at Washington
University School of Medicine in St. Louis, which conducted the study
jointly with Shriners and other institutions.

Results of the research are published in the March 8 issue of the
New England Journal of Medicine.

Severe hypophosphatasia affects about 1 in 100,000 babies born in the
United States, according to the National Library of Medicine. It’s
estimated that more people may have the disease, but in far milder forms.
The severity of the disease can range from life-threatening to simply
causing dental problems in adults, according to background information in
the article.

The enzyme in hypophosphatasia that isn’t available in sufficient
quantity is called alkaline phosphatase. It’s responsible for the
mineralization of bones and teeth. Mineralization is the process that
causes minerals like calcium and phosphorus to be deposited in developing
bones and teeth, according to the National Library of Medicine. Without
enough alkaline phosphatase, several other substances can build up and
cause damage.

There are no approved medical treatments for hypophosphatasia,
according to the study.

The current study involved 11 children. All were given an initial
intravenous infusion of asfotase alfa, followed by shots of the medication
three times a week.

Parents of one baby removed their child from the trial during the
initial intravenous treatment. A second baby died from an unrelated
infection after more than seven months of treatment.

The remaining nine children have received at least 18 months of
treatment with asfotase alfa.

X-rays taken at the start of the study and at weeks 24 and 48 showed
significant improvement in bone formation after treatment. In addition,
the babies showed improvement in lung function, physical skills, and in
the development of intelligence, according to the study.

The treatment was “very well tolerated,” Whyte said. And, he added,
there was no evidence that the children were developing resistance to the
drug.

Treatment with asfotase alfa needs to be ongoing, and it’s not yet
clear if there are long-term side effects. Whyte and his colleagues are
continuing to study the patients enrolled in this trial. He said that he
believes children born with the severe or life-threatening form of the
disease should be given this medication, even though it’s still considered
experimental. The reason, he said, is the severe form of this disease is
“invariably lethal, usually soon after birth.”

Dr. Spyros Mezitis, an endocrinologist at Lenox Hill Hospital in New
York City, said the research is promising and groundbreaking. “They’re
correcting an inborn error of metabolism and mimicking what the body
does,” he said. “It would be like making someone with type 1 diabetes
start making insulin on their own, rather than just replacing it from the
outside. I think this will serve as a model for other types of diseases.”

But, he added, the current patients will need to be closely monitored
as they grow, and that there is a need for further studies.

The study was funded by Shriners Hospitals and Enobia Pharma, which was
acquired last month by Alexion Pharmaceuticals. Whyte was a consultant for
Enobia Pharma, according to a Washington University news release.

More information

Read more about hypophosphatasia from the Magic Foundation.

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