Urea cycle disorder is a group of genetic conditions that affect the function of proteins and enzymes that move ammonia out of your blood. Ammonia is toxic and can cause life-threatening side effects if your body can’t get rid of it. Limiting the amount of protein you eat in your diet and taking medicine or supplements helps treat this condition.
The urea cycle is a filtering process to remove toxic substances from your body and keep other substances that are good for you moving throughout your body.
Urea (carbamide) is a substance made by your liver. The urea cycle begins when you eat. Your body breaks down (metabolizes) protein that comes from food in your diet and turns it into amino acids, which are the building blocks of proteins. Amino acids help your body build muscle, transport nutrients and keep your organs functioning. Digestion of proteins leads to waste products that turn into ammonia. Ammonia is toxic to your body. To remove ammonia, enzymes, which are proteins that produce chemical reactions, convert ammonia into urea. The following amino acids are in urea, along with ammonia:
Enzymes move urea through your blood and kidneys. The final step of the urea process is to pass (excrete) urea from your body in your pee (urine).
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Urea cycle disorder is a group of conditions where the process that moves urea through your body isn’t working as it should. It’s usually the result of a missing protein or enzyme. Urea cycle disorder is a genetic condition, also known as an inborn error of metabolism that causes ammonia to build up in your blood (hyperammonemia), which is toxic to your body. Symptoms of this condition target your brain and organ function.
There are eight types of urea cycle disorders identified by the lack or malfunction (deficiency) of certain enzymes and proteins in your metabolism that process urea:
Urea cycle disorder can affect anyone since it’s a genetic condition. Newborns can receive a diagnosis a couple of days after they’re born through universal newborn screening blood tests. Sometimes symptoms aren’t noticeable until later in life and an adult can receive a diagnosis when symptoms become apparent.
Yes, urea cycle disorder is an inherited condition. Both of your parents need to pass a genetic mutation during fetal development for you to receive a diagnosis (autosomal recessive). Some types of urea cycle disorder pass onto children by attaching to a sex chromosome (X-linked) after conception.
Urea cycle disorder affects 1 in 35,000 people in the United States.
Early signs of urea cycle disorder are usually present soon after your baby is born but could happen at any age. Signs of urea cycle disorder include:
Symptoms of urea cycle disorder are the result of having too much ammonia in your blood (hyperammonemia). Symptoms range from mild to severe and could include:
Symptoms that affect your brain can be life-threatening.
A genetic mutation causes urea cycle disorder. There’s a different genetic mutation that causes each type including:
These genes are responsible for producing proteins and enzymes that move urea through your body. A genetic mutation causes your body to not produce enough of the proteins or enzymes that your body needs to function. If you have a type of urea cycle disorder, your body isn’t able to remove toxic ammonia from your body, where it collects in your blood and causes symptoms.
Your provider will diagnose urea cycle disorder after a physical exam to review your symptoms and take a complete medical history. They might order a blood or urine test to confirm a diagnosis.
Tests to diagnose urea cycle disorder include:
Treatment for urea cycle disorder focuses on lowering the amount of ammonia in your blood, which could include:
Severe cases of hyperammonemia could lead to a liver transplant.
Before starting treatment, talk to your provider about the possible side effects of new medication and procedures. Also, talk to your provider about any medicines or supplements you currently take to avoid drug interactions.
Eating a diet low in protein is best to help you manage urea cycle disorder. When your body breaks down (metabolizes) protein in foods you eat, it converts the protein into amino acids, which continue to convert into ammonia. If you have urea cycle disorder, your body isn’t able to naturally remove ammonia from your blood. If you eat a diet low in protein, you reduce your risk of building up ammonia in your blood.
Some of the most common foods that contain protein that you should limit in your diet include:
Since protein is an essential part of your diet, removing all protein from your diet could cause side effects like limiting your growth. Your provider might suggest you work closely with a dietitian or nutritionist to help you manage your diet to limit the amount of protein you eat. Sometimes your provider will recommend taking vitamins, minerals or amino acid supplements to make up for a limited protein intake.
Your newborn receives protein from your chest milk (breastmilk). While it’s possible to chest feed your child, your provider will closely monitor how it affects your newborn. If your baby needs to reduce their protein intake, your provider might recommend using specialized infant formula instead of human milk.
You can’t prevent urea cycle disorder since it’s a genetic condition. If you plan on becoming pregnant and want to understand the risks of having a child with a genetic condition, talk to your provider about genetic testing.
Treatment will begin immediately if your provider diagnoses you with urea cycle disorder to reduce the amount of ammonia in your blood. Newborns diagnosed with the condition will receive immediate treatment after birth to prevent complications. Once treatment begins, your provider will check your blood ammonia levels until your blood ammonia reaches a safe level.
Your condition will need lifelong monitoring and a special diet that is low in protein. Eating too much protein can trigger your symptoms.
Severe cases of hyperammonemia can cause irreversible brain damage, which leads to coma or death. Talk to your provider about how you can manage your condition or your newborn’s condition to avoid these life-threatening complications.
Your outlook depends on the severity of your symptoms. If you receive an early diagnosis with treatment and lifelong management, your life expectancy could be normal. If the condition is untreated or undiagnosed, it could be fatal.
Visit your provider if you have symptoms of the condition, especially if you’re extremely tired or unable to eat.
It’s important to monitor your child’s developmental milestones as they grow to make sure they’re meeting expectations for their age. If your child doesn’t meet their developmental milestones, visit your healthcare provider.
Visit the emergency room if you or your newborn has a seizure or has trouble breathing.
A note from Cleveland Clinic
It may be overwhelming to learn that you or your newborn has a rare genetic condition. Your provider will help you manage your baby’s diagnosis or your diagnosis if you experience symptoms as an adult. Eating a diet low in protein reduces the way that the condition affects your body, which could minimize your symptoms so you can feel better. If you feel tired all the time, have trouble eating or experience changes to your behavior that aren’t normal, visit your provider.
Last reviewed by a Cleveland Clinic medical professional on 07/11/2022.
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