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Urea Cycle Disorder

Urea Cycle Disorder



Overview

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:

Arginine.

Ornithine.

Citrulline.

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).

What are the types of urea cycle disorders?

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:

N-acetylglutamate synthase (NAGS) deficiency.

Carbamoylphosphate synthetase I (CPS1) deficiency.

Ornithine transcarbamylase (OTC) deficiency.

Argininosuccinate synthase 1 (ASS1) deficiency or Citrullinemia type I.

Citrin deficiency or Citrullinemia type II.

Argininosuccinic lyase (ASL) deficiency.

Arginase (ARG) deficiency.

Ornithine translocase deficiency.

Symptoms

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:

Lethargy or feeling tired.

Fussiness in babies.

Nausea or vomiting.

Can’t eat or feed.

Breathing too fast or too slow.

Confusion.

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:

Problems with cognitive development and intellectual challenges.

Behavioral changes.

Developmental delays.

The buildup of fluid around your brain (cerebral edema).

Tight muscles (spasticity).

Seizures.

Coma.

Symptoms that affect your brain can be life-threatening.

Causes

A genetic mutation causes urea cycle disorder. There’s a different genetic mutation that causes each type including:

N-acetylglutamate synthase caused by a NAGS gene mutation.

Carbamoylphosphate synthetase I caused by a CPS1 gene mutation.

Ornithine transcarbamylase caused by an OTC gene mutation.

Argininosuccinate synthase 1 caused by an ASS1 gene mutation.

Citrin deficiency caused by an SLC25A13 gene mutation.

Argininosuccinic lyase caused by an ASL gene mutation.

Arginase caused by an ARG gene mutation.

Ornithine translocase caused by an SLC25A15 gene mutation.

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.

Diagnosis

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:

Amino acid profile or analysis: Your provider will test a small sample of your blood or urine to measure the amino acids that your body processes (metabolizes).

Liver biopsy: Your provider will remove a very small piece of your liver to examine it under a microscope to look for enzymes associated with the condition.

Genetic test: Your provider will examine a small sample of your blood to look for genetic changes that cause your symptoms.

Treatment

Treatment for urea cycle disorder focuses on lowering the amount of ammonia in your blood, which could include:

Eating a diet low in protein.

Dialysis to clean your blood of toxins (hemodialysis).

Taking medicine that includes sodium phenylacetate and sodium benzoate (Ammonul ®) to remove ammonia from your blood.

Taking amino acid supplements (arginine or citrulline) to encourage your body to complete the urea cycle.

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.

What foods should I avoid if I have urea cycle disorder?

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:

Fish.

Chicken.

Eggs.

Beef.

Beans.

Tofu or soy-based foods.

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.

Type of Doctor Department : A metabolic geneticist or biochemical geneticist.

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