Milked enzyme thwarts muscle disorder

From Philadelphia, at the annual meeting of the American Society of Human Genetics

A controversy over rabbit’s milk and hamster ovaries provides background drama to a successful attempt to use a human enzyme to treat the rare genetic disorder Pompe’s disease.

This fatal condition weakens the body’s muscles, particularly the heart and the muscles that power breathing. While people with milder forms of the condition live into their teens and adulthood, babies born with the severest form of Pompe’s disease rarely survive their first year.

The illness stems from genetic mutations depriving the body of an enzyme, alpha-glucosidase, that degrades a complex sugar, glycogen, into a simpler one, glucose. A buildup of glycogen ultimately causes the muscles to fail.

For more than a decade, Ans van der Ploeg of Sophia Children’s Hospital and Arnold Reuser of Erasmus University, both in Rotterdam, have pursued the idea of replacing the missing enzyme. By using rabbits genetically altered to produce human alpha-glucosidase in their milk, the researchers were finally able to test this strategy.

In one recent trial, four infants with Pompe’s disease received weekly infusions of the enzyme collected from rabbit milk. The treatment dramatically reduced the amount of glycogen in the infant’s muscle cells. The babies’ skeletal muscles became stronger, and their hearts didn’t enlarge—as they usually do in Pompe’s disease to compensate for the weakening.

“We’ve seen babies sitting and standing, milestones not normally achieved in babies with Pompe’s disease,” says van der Ploeg, who calls the treatment “life saving.” She expresses concern, however, over a plan by the firms sponsoring her trial—Genzyme of Cambridge, Mass., and Pharming of Leiden, the Netherlands—to switch production of the enzyme into hamster ovary cells. The investigator contends the shift could threaten the supply of the enzyme for her patients.

Genzyme officials counter that it’s easier and cheaper to produce the enzyme in hamster cells and that a research team at Duke University has already used alpha-glucosidase made this way to treat several infants with Pompe’s disease.