(The New York Times News Service) -- Ten-month-old Hannah Ostrea's life hinges on an expensive drug made by just one company, Genzyme Corp., based in Cambridge.

The drug, Cerezyme, combats Hannah's severe form of Gaucher disease, a rare genetic disorder that caused her liver and spleen to swell. After just a few months of intravenous treatments, she was able to roll on her belly and play for the first time, but without the drug she is unlikely to live into adulthood.

So when Hannah's mother, Carrie, heard Tuesday that the Allston plant where Genzyme makes Cerezyme had been shut down through July because of viral contamination, she was stunned.

"I think there should have been a stronger contingency plan," said Ostrea, who lives outside Houston. "I'm scared to death that we're going to lose the progress we made and ((the disease is)) going to kill her."

Officials at Genzyme, the state's largest biotechnology company, said some patients will have to skip doses of Cerezyme as a result of the shutdown, but they hope Hannah won't be one of them.

On Tuesday, the company reported that a virus was discovered in one of six bioreactors used to make Cerezyme and a second drug, Fabrazyme, cutting-edge treatments that cost about $200,000 a year per patient.

Fabrazyme treats another rare disorder called Fabry disease. Both drugs are made using ovary cells from Chinese hamsters through a complicated and precise process.

While the contaminating virus is not considered harmful to humans, and Genzyme's inventory of both drugs was cleared for release Wednesday by the US Food and Drug Administration, the plant will be decontaminated as a precaution. That will result in a temporary shortage of Cerezyme and Fabrazyme starting in late summer.

For the approximately 8,000 people worldwide who take one of the drugs, the incident -- and the rationing of doses -- is a stark reminder of how much their health depends on Genzyme.

Linda Rubenstein of Carlisle, a member of the nonprofit National Gaucher Foundation, said that since she started enzyme replacement therapy in 1992, the disease has been stopped "in its tracks."

But upon hearing of the contamination and shutdown, Rubenstein said, she and other patients worried they might be forced to go without the medicine that has changed their lives. For now, she has decided to place her faith in the company as she awaits more information.

"They have the miracle drug, so -- " Rubenstein said, her voice trailing off.

Wednesday, Genzyme sought to reassure patients that, for most of them, skipping a few doses will not seriously affect the health. Geoff McDonough, who heads Genzyme's genetic disease business unit, said the company plans to meet with physicians and patient group leaders early next week to set rationing guidelines.

In the case of Hannah Ostrea, he said, "We never want her to miss an infusion."

Genzyme has some experience with drug rationing. Late last year, the company knew its supply of Myozyme -- which treats another rare disorder, Pompe disease -- would be tight because it had not received FDA approval to produce the drug in a second plant. It asked some patients to volunteer to forgo treatments so that those with a more urgent need wouldn't miss a dose.

The patient community "came up with guidelines that said if you are an adult and if you fall into a certain clinical status, we'd like to ask you to miss a period of two doses," McDonough said. "And we managed to get through without having a single infant, toddler, or child having to miss an infusion."

McDonough said he expects a similar approach to be used this time.

Cerezyme was approved for use in the United States in 1994.

Fabrazyme went on the market in 2003.

Gaucher disease causes fatty substances to accumulate in the spleen, liver, lungs, bone marrow, and -- in the worse cases -- the brain. It can cause bruising, enlarged organs, and kidney and lung ailments.

Fabry disease prevents the body from breaking down oils, waxes, and fatty acids, leading to problems with eating, an enlarged heart, and kidney problems.

Dr. Gregory Pastores of New York University's School of Medicine said he treats hundreds of Gaucher and Fabry patients who take regular doses of the Genzyme drugs. The medications help prevent harmful levels of waste from accumulating in their bodies. The impact of missing doses depends on the individual, Pastores said, because they react differently to treatments.

"If what we are speaking of is a brief interruption ((in treatment)), it won't necessarily be a catastrophic scenario," Pastores said.

"It's obviously a peculiar situation, because if we are forced to ration, how are you doing to decide what patients need the drug -- and at what dose?"

In the United States, about 1,500 people take Cerezyme and about 800 use Fabrazyme. Rhonda Buyers, executive director of the National Gaucher Foundation, said that the foundation's medical board has been in regular contact with Genzyme and that it remains unclear how the existing inventory will be administered to patients or whether the shortage will be severe.

"Certainly the patient population is nervous about what's going to happen," she said. "When you don't know, it's a fear of the unknown."

Four other companies are currently conducting clinical trials on drugs to treat Gaucher disease, Buyers said.

Cerezyme patient Kevin R. Kline said he is prepared go without his treatment for a while to help others who need the drug more. Every two weeks for years, the New Jersey man has gone to a clinic to receive an infusion, an hourslong treatment paid for by his insurance company.

Because he has been using the drug for so long, Kline said, most of the potentially harmful waste has been purged from his system.

"If I need to take a little hiatus, I will be less affected by it than someone who just started" treatment, Kline said.

Jack Johnson, who has Fabry disease, says he hasn't heard much concern about the shutdown from other patients. Johnson, who lives in Missouri and founded the nonprofit Fabry Support and Information Group, said he has been monitoring an online forum where patients post questions.

"Thus far, nobody seems too alarmed," Johnson said Wednesday.

Ostrea said her daughter received her last infusion of Cerezyme on Monday, just a day before the plant's closure was announced. Each treatment costs $15,000 and is paid for by insurance.

Ostrea said she has been in daily contact with Genzyme officials, who she said have "gone out of their way" to make sure Hannah is getting the help she need.

And she is grateful that the company created a drug that treats so few people, even if it generates huge profits.

"I'm disappointed but I can't get mad" at Genzyme, Ostrea said. "It happened. Our hands are tied."

Copyright 2009 The New York Times News Service. All rights reserved.