Batshaw said urea cycle disorder specialists don't know why people like Pearson are able to survive so long without clinical symptoms. When doctors have gone back into the medical histories of patients, they often have found that protein made them feel sick, or that they had recurrent episodes of vomiting "thought to be of gastric origin when, in fact, they were due to accumulations of ammonia."
Proper treatment depends upon frequent blood monitoring. Some patients simply can follow a low-protein diet. Others must take essential amino acid supplements.
During an acute crisis, doctors use dialysis to remove ammonia from the blood. Many patients take medication that scrubs ammonia from the bloodstream. Typically, it's oral sodium phenylbutyrate called Buphenyl.
Doctors may give Ammonul, an FDA-approved injection of sodium benzoate and sodium phenylacetate. They may administer an intravenous combination of sodium benzoate and sodium phenylbutyrate, Batshaw said. Some require a liver transplant.
The hope long has been that gene therapy might one day give patients' bodies the ability to make the missing enzyme. However, gene therapy trials suffered an enormous blow with the death of 18-year-old Jesse Gelsinger, a young man from Arizona with partial OTC. Although he was able to control his condition with a low-protein diet and handfuls of daily pills, he was hopeful about taking less medication one day.
He volunteered for a gene therapy safety study at the University of Pennsylvania in 1999, but suffered multiple organ failure that researchers associated with the virus used to deliver copies of the gene for the missing enzyme into his liver.
Batshaw, who was part of the Penn study, is currently chief academic officer at Children's National Medical Center in Washington, D.C. He heads the Longitudinal Study of Urea Cycle Disorders, which is monitoring the health of about 450 patients -- about half of whom have OTC deficiency -- at a dozen sites in the United States, Canada and Switzerland.
He said he was unaware of anyone else with a urea cycle disorder becoming fatally ill after eating a high-protein diet like Pearson's.
Keith Ayoob, director of the nutrition clinic at the Rose R. Kennedy Center at the Albert Einstein College of Medicine in the Bronx, N.Y., said that what happened to Pearson "will not happen to the average person. If you don't have an enzyme disorder, you're not going to get this."
In light of Pearson's death, some people might wonder about the wisdom of a high-protein diet, especially the Atkins plan that initially relies solely on protein and fat but no carbohydrates.
"There have been reported cases of young women who have decided to go on an Atkins diet and it has unmasked a urea cycle disorder. Some survive and some don't," Batshaw said.
However, when healthy people follow high-protein diets, their bodies can handle byproducts of protein metabolism. Much of the ammonia leaves the body in perspiration. Their stomachs will slow down the rate at which they break down food.
Athletes like Pearson need more protein than their sedentary counterparts, said nutritionist Heidi Skolnik, who consults for the New York Giants and the New York Knicks, as well as the Juilliard School and School of American Ballet.