



Risk of Urea Cycle Disorder after Gastric Bypass (Bariatric) Surgery

There have been several cases of hyperammonemia (elevated ammonia levels) in individuals who have undergone gastric bypass (bariatric surgery). Some of these individuals died shortly after surgery, and some had a steady decline up to four years after surgery that led to coma or death due to elevated ammonia levels.  A number of the individuals were found to have a previously undiagnosed genetic mutation for a urea cycle disorder (ornithine transcarbamylase deficiency) and other cases were considered to have "secondary" or "acquired" urea cycle disorder due to malnourished states.1,2,3

Additionally, there is a risk that women who are unknowingly carriers for ornithine transcarbamylase deficiency (OTC) who may have previously been without symptoms prior to gastric bypass, may become symptomatic due to the nutritional deficiencies caused by gastric bypass and production of excessive ammonia in the body.

"Gastric bypass surgery (bariatric surgery) with secondary marked weight loss to the range of 80 to 100 pounds leads to the risk of developing high blood ammonia levels. The cause of this relationship, bariatric surgery-marked weight loss-poor nutrition-high blood ammonia, is not clearly understood.

In severely malnourished states, blood ammonia levels in some post gastric bypass patients increases to toxic levels, causing either direct brain toxicity from the ammonia, or toxicity through the high concentra-tion of glutamine (a neurotransmitter in the brain) in the brain as glutamic acid interacts with ammonia in the brain and is converted to glutamine. The brain toxicity leads to coma. If medical management does not decrease the ammonia production rapidly, the patient dies.

The relationship between the change in the function of the enzymes within the urea cycle and extreme malnutrition is yet to be understood. Caution should be taken by all patients who have bariatric surgery to maintain good nutrition during their weight loss and to stop losing weight once they achieve an average weight for their height."

James A. Bartley MD, PhD
Medical Geneticist
Associate Clinical Professor
Loma Linda University Children’s Hospital

“Because urea cycle disorders affect the body’s ability to metabolize proteins, any treatment that affects the body’s protein balance can either affect the current management of an already diagnosed patient or bring out symptoms in someone who was otherwise undiagnosed. Bariatric surgery is one such case. Treatment with gastric bypass is a significant stress to patients and can alter dietary protein intake and absorption. Therefore, the diagnosis of UCD should be considered in patients who respond poorly to bariatric surgery and in whom elevated blood ammonia levels are detected.”

Brendan Lee, MD, PhD

Howard Hughes Medical Inst.


Dept Medical Genetics

Baylor College of Medicine

A new study is being developed to understand the connections between gastric bypass and UCD. For more information or to report a case of UCD after gastric bypass, please contact us.


1. Ornithine Transcarbamylase Deficiency Presenting as Encephalopathy During Adulthood Following Bariatric Surgery. WT Hu, OH Kantarci, JL Merritt, P McGrann, JBDyck, CF Lucchinetti, M Tippmann-Peikert. Arch Neurol. 2007;64(1):126-128.

2. Fatal Hyperammonemic Encephalopathy After Gastric Bypass Surgery. A Fenves, CR Boland, R Lepe, P Rivera-Torres, SJ Spechler. The American Journal of Medicine, Volume 121, Issue 1 , Pages e1-e2, January 2008
3. Weight loss surgery triggered rare genetic disorder.



My wife went into a coma after gastric bypass surgery. The doctors had no idea what was wrong. One of the ICU doctors took an ammonia level. I called the National Urea Cycle Disorders Foundation and they got an expert in UCD to help my wife's doctors. She was transferred to his hospital and he was able to save her. She still has a lot of problems with her brain from the coma and now has to be treated for the OTC disorder.


"I want people to understand the risks involved in gastric bypass surgery. Last fall, she just started deteriorating. You just watched her get weaker and weaker. When her ammonia level would go up, things didn't make sense to her. She hurt all the time from last September until she passed. She was in constant pain."