By Bill Berkrot
NEW YORK (Reuters) - An experimental therapy for a rare, often fatal genetic disorder appears to offer hope for infants and very young children with the condition, according to data from a small clinical trial reported in the New England Journal of Medicine on Wednesday.
The enzyme-replacement drug, asfotase alfa, acquired by Alexion Pharmaceuticals Inc with its $610 million purchase of Canada-based Enobia Pharma, could become the first approved treatment for the metabolic disease hypophosphatasia, or HPP.
The condition is a genetic enzyme deficiency that causes bone softening and muscle weakness and can lead to severe lung problems and damage to other vital organs. It affects about 1 in 100,000 newborns worldwide, according to the National Institutes of Health. About half of infants with a severe form of the disease do not survive beyond one year.
In the study of 11 babies and toddlers under three with life-threatening HPP, treatment with asfotase alfa resulted in "striking" improvements in skeletal problems and dramatic improvements in lung function and mobility, researchers reported.
"I'm thrilled to see babies who were really doomed responding to the treatment," Dr Michael Whyte, the study's lead investigator, said in a telephone interview.
"The therapy is proving not only life-saving but also health-restoring," added Whyte, of Shriners Hospitals for Children in St. Louis, who has been working on this ultra-rare disease for more than 30 years.
Videos accompanying the online version of the study in the New England Journal of Medicine show dramatic motor skill improvements of two of the trial subjects. In one, a three-year-old who was unable to stand prior to therapy is shown climbing the steps of a small plastic slide after 24 weeks of treatment.
Respiratory function improved in all patients, researchers said. Ten of the 11 needed breathing support before treatment. After 48 weeks of treatment, only three of the nine children who remained on therapy needed help breathing.
Breathing problems arise as the shape of the chest becomes deformed due to soft bones in the thorax, which compromises lung function, Whyte explained.
'SHE CAN STAND ON HER OWN'
Evie Jayne Elsaesser of Omaha, Nebraska, who got into the trial at just two and a half months old, has been on the therapy for more than two years.
Doctors had been so sure she would survive no more than a few hours that her parents planned a funeral prior to her birth. Even after Evie proved sturdier than expected, her doctor told her parents she would likely survive only five or six months.
"We've had two and a half years that we didn't think we would have," Evie's mother, Lindsey Elsaesser, told Reuters.
"She can stand on her own now. She can walk around furniture when she holds on," said Elsaesser, adding that Evie rarely needs oxygen to assist her breathing anymore.
HPP is caused by a genetic deficiency of an enzyme known as tissue non-specific alkaline phosphatase (TNSALP), which causes life-long abnormalities in metabolism of calcium and phosphate.
All subjects in the mid-stage study had HPP symptoms before they were six months old, including failure to thrive, fractures, substantial motor delay or regression, and kidney problems.
One patient was pulled from the study after the initial drug dosing, and another child died from sepsis after 7.5 months of therapy, according to the study.
The sepsis was thought to be unrelated to the treatment, Whyte said, adding that the child had shown pronounced bone improvement. "He was certainly going in the right direction."
The other nine children remain on the therapy, developed by Enobia, in an extension study.
Skeletal healing was "striking" at week 24 in all but one of the patients, researchers said, noting that the one exception was a child who had virtually no bone in a scan taken prior to the study. Improvement is still being observed in the patients receiving continued therapy, researchers added.
The drug is initially administered with a single intravenous infusion. That is followed by shots given three times per week, with dosages that can be increased if children show signs of worsening symptoms, such as failure to thrive, deteriorating lung function, or lack of evidence that bones are improving on bone scans .
The most common side effect associated with the treatment was a rash at the injection site. There were three cases of serious side effects possibly connected with the treatment -- one case each of respiratory distress, hearing loss and craniosynsotosis, in which a baby's skull bones fuse prematurely.
Alexion has said it hopes to apply for U.S. approval for the treatment in 2014. The company is also studying the drug to treat HPP in older children and adults.
"We're just so thankful that people put the time and effort into researching something that's so rare," Elsaesser said.
(Reporting By Bill Berkrot; editing by John Wallace)