New treatment helps children with Pompe disease live longer

It can kill kids before their first birthday. The infantile form of Pompe disease is a death sentence if not treated. But now there is something keeping kids alive longer.

If Haley Hayes' parents could have one wish, it would be a cure for their six-year-old daughter. Haley was diagnosed with Pompe disease, a fatal, genetic illness when she was six months old.

"It was awful,” said Haley's mother, Krystal Hayes,. “That was probably just the worst news you could ever hear."

Haley lacks an enzyme that helps break down sugar. So it builds up in her heart and skeletal muscles, damaging them. At the time Haley was diagnosed, most babies with Pompe disease were expected to die.

But now, a once-a-week infusion, given to Haley while she paints pictures, has changed everything.

"We know it's basically keeping her alive at this moment, said Krystal."

Myozyme replaces the enzyme Haley lacks. Without it, most babies didn't make it to their first birthday.

"It's similar to providing insulin to someone who has diabetes,” said Dr. Priya s. Kishnani, Priya s. Kishnani of Duke University Medical Center. “So she needs to have this enzyme given to her throughout her life course to be able to live."

But some patients create antibodies that prevent them from responding to Myozyme. Duke University doctors found three chemotherapy drugs that wiped out the harmful antibodies in infants, allowing them to respond to Myozyme. These babies would have died, but the oldest is now five.

"It allows children to live. It allows them to have dreams,” said Dr. Kishnani.

Haley doesn't let it slow her down. Her parents cling tight to hopes for a cure and enjoy each precious day.

"Just treasure every milestone," said David Hayes, Hayley's father.

Their little girl reminds them of that with every smile.

While Haley takes Myozyme once a week, most patients take it once every two weeks.

Myozyme is not a cure. Since it's so new, doctors do not yet know how long kids treated with it will live.The oldest living child taking it is 13 years old.

Doctors say it is vital to start children with Myozyme as soon as possible.

BACKGROUND: Pompe disease is an inherited, neuromuscular disorder that causes progressive muscle weakness. It is a rare disease, affecting about 1 in every 40,000 births. Pompe disease is caused by a defective gene that results in a deficiency of an enzyme known as acid alpha-glucosidase (GAA). The lack of this enzyme results in excessive build-up of glycogen -- a form of sugar -- in a specialized compartment of muscle cells throughout the body. Researchers have identified up to 300 different mutations in the GAA gene that cause the symptoms of Pompe disease. The severity of the disease and the age of onset are related to the degree of enzyme deficiency. There are two types of Pompe disease. These include:
* Early onset (the infantile form): This is the result of complete or near-complete deficiency of GAA. Symptoms such as feeding problems, poor weight gain, muscle weakness, floppiness, and head lag usually start during the first months of life. Respiratory difficulties are often complicated by lung infections. The heart is also very enlarged. Many infants with Pompe disease also have enlarged tongues. Most babies die from cardiac or respiratory complications before their first birthday.
* Late onset (juvenile/adult form): This is the result of a partial deficiency of GAA. The onset can be as early as the first decade of childhood or as late as the sixth decade of adulthood. The primary symptom is muscle weakness that progresses to respiratory weakness. The heart is usually not involved. (SOURCE: NIH)

MYOZYME: Myozyme is a lysosomal glycogen-specific enzyme that essentially replaces the enzyme Pompe disease patients are lacking. The treatment has to be given throughout the course of a patient's life. "This is the first lifesaving treatment that is FDA approved for Pompe disease," Priya S. Kishnani, M.D., C.L. and Sue Chen Professor of Pediatrics/Division Chief, Medical Genetics, Duke University Medical Center, told Ivanhoe. "Prior to 2006, there was no treatment for Pompe disease other than symptomatic care."

HELPING MORE KIDS SURVIVE LONGER: Some children develop an immune reaction that blocks the effects of Myozyme treatment. However, researchers at Duke, along with collaborators at other centers, have found that a very low-dose combination of medicines typically used to treat cancer is successful in eliminating or preventing the immune response in these patients. The drugs -- rituximab, methotrexate, and gammaglobulins -- are a mix of chemotherapeutic agents. The chemo drugs allow the patients to tolerate and respond to the Myozyme treatment, which is the only therapy for these kids. "It was really rewarding because the babies did not make antibodies and continued to do well clinically," Dr. Kishnani said. "The oldest child is now over 5 years of age, remains antibody-negative and has come off all chemotherapy." Dr. Kishnani says prior to the chemo discovery, children who developed antibodies and could not benefit from Myozyme would have died. (SOURCE: Duke University press release)

Priya Kishnani, MD
Duke University Medical Center
(919) 681-9854

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