These are perhaps the toughest cases that doctors face: A patient comes in critically ill — dying, really — with few clues as to what is going on. The I.C.U. doctors examined the young woman as soon as she arrived but had no better understanding of what was causing her coma. They asked for help from neurology, cardiology and infectious diseases. Those doctors were baffled as well. An M.R.I. revealed that the girl’s brain had swollen and was now pushing up against the unyielding limits of the skull. If the cause of the swelling was not found and reversed, she would certainly die.
An EEG (electroencephalogram) suggested that the patient’s rigid posture might be a result of an ongoing seizure. The patient was started on anti-seizure medicines. Although the seizures stopped, the patient didn’t wake up. Indeed, it was clear that she was getting worse. Her eyes, initially reactive to light, became fixed and dilated. And when icy water was squirted into her ear — a stimulation that would normally cause a strong involuntary reaction — nothing happened, indicating that her brain was not working, even at the most basic level.
The team stopped all potentially sedating medications to see if they were contributing to the problem. There was no improvement. And so, after a thorough work-up and thoughtful care, eight days after this young woman was brought to the hospital, she was taken off the breathing machine. Without its assistance, she breathed no more, so the team pronounced her brain-dead.
A Diagnosis Too Late
Why did this happen? The family asked over and over, but the doctors who had cared for the young woman couldn’t tell them. Her brain had swollen, and that swelling killed her, but beyond these basic facts they simply didn’t have an explanation.
The family, though grieving, decided to donate the young woman’s organs. Her heart, liver and kidneys found grateful recipients. Then the family took their child’s ashes home and made plans to scatter them in a beloved place.
A few weeks after the young woman’s death, her father got a call from the Donor Network of Arizona. The recipient of his daughter’s liver had died, too, just days after the transplant surgery. Shocked, the transplant team immediately went to work to find out what happened. The answer was a surprise. The liver donor had been born with a genetic defect. She was missing the genes that made a chemical called ornithine transcarbamylase (OTC) — a vital enzyme whose job is to help the liver break down proteins. Proteins are the building blocks of muscles, and something as simple as eating meat, or stressing the body through, say, fasting or surgery, can release additional proteins into the system. When something goes wrong with the process that breaks down protein, toxic levels of ammonia can build up, which in turn attacks the nervous system and the brain.
The Liver as Main Clue
Hyperammonemia, the medical word for high levels of ammonia, is usually caused by a liver so damaged by alcohol or disease that it can’t perform even its most basic jobs — including the breakdown of proteins. Doctors routinely test ammonia levels in patients who have liver failure, often from cirrhosis or hepatitis. But patients with OTC deficiency usually don’t have a bad liver; theirs simply fails to do this one job. And because the organ is working fine in all other ways, doctors don’t suspect hyperammonemia as a cause of coma or brain swelling. If this young woman’s ammonia level had been checked, it would have been high — maybe 10 times the normal level.
OTC deficiency is not the only unusual cause of elevated ammonia. There are other diseases — some inherited, like OTC deficiency; others acquired, like herpes and certain cancers — that can do it as well. Medications, including iron and anti-seizure drugs, can also cause elevated ammonia levels. A simple blood test, performed when no other cause of coma is found, may save a life. And in the case of this young woman, possibly two.
An Unsuspected Killer
The gene for OTC is on the X chromosome, and so boys, who have only one X chromosome, are more likely to have symptoms from their OTC deficiency. Because girls have two X chromosomes, if one is defective, the other can sometimes make up for it. But for reasons that are not well understood, in the right setting, maybe after a protein-rich meal or with significant stress, like an illness, the condition can manifest in girls too, prompting their ammonia levels to spike upward. That’s probably what happened to this patient when she got sick and confused three months earlier. And that is what killed her and her liver’s recipient.
As the parents read up on OTC, they recognized several symptoms in their daughter. Like many with OTC deficiency, she had always had a bad stomach — feeling nauseated or vomiting for reasons they never understood. And she rarely ate meat — she’d never liked it.
The rest of the family was tested for OTC deficiency, and the girl’s father found that he, too, had the defective gene. This discovery explained so much to him — why, for example, there were times when he literally felt too tired to move or even speak. That lethargy, he now believes, is a response to a high ammonia level. These days he takes a supplement that provides the chemicals his enzyme can’t produce. And he avoids the foods that can raise his ammonia.
All this information came too late to help their daughter. But perhaps others will find it useful. That, at least, is her parents’ prayer.