Health A-Z

Who Gets Them?

UCDs affect about 1 in 35,000 newborns.

There are eight types. They’re named after what’s missing from the urea cycle. You’ll also hear doctors call them by their initials:

• ARG1 deficiency -- Arginase
• ASL deficiency -- Argininosuccinate lyase
• ASS1 deficiency -- Argininosuccinate synthase 1
• Citrin deficiency -- Citrin
• CPSI deficiency -- Carbamoyl phosphate synthetase I
• NAGS deficiency -- N-acetylglutamate synthase
• ORNT1 deficiency -- Ornithine translocase
• OTC deficiency -- Ornithine transcarbamylase

  Parents pass these diseases down to their children through defective genes. We all inherit two copies of our genes, one from each parent. With most UCDs, you must get a defective gene from both parents to get the disease. The genes tell your child’s body how to break down protein.

  One UCD, called ornithine transcarbamylase (OTC) deficiency, is what doctors call a sex-linked disorder. Mothers carry the gene on their X chromosome, and they mostly pass it to their sons.

Symptoms

UCDs fall into two groups:

Complete UCD: This means your baby has a severe or total lack of the enzyme. You’ll notice symptoms in the first couple of days:

• Fussy
• Sleepy or sluggish
• Can’t feed
• Vomits
• Low body temperature
• Problems with posture
• Seizures
• Fast breathing that becomes slow
• Coma

  Partial UCD: Your baby can make some of the enzyme, but not as much as they need. You may not spot symptoms for months or even years.

  A buildup of ammonia (you may hear the doctor call it hyperammonemia) can happen from illness, injury, stress, or quick weight loss.

  Symptoms are usually less severe than in babies with complete UCD. They include:

• Avoiding foods high in protein or a dislike of meat
• Loss of appetite
• Nausea or vomiting
• Behavior problems, including hyperactivity
• Mental problems (confusion, delusions, hallucinations, psychosis)

UCDs are life-threatening. Don’t wait to get treatment.

A team of health professionals will care for your child. They will first do these three treatments at the same time:

• Dialysis to remove ammonia from their blood
• Feeding them supplements of sugars, fats, and amino acids
• Medicines to remove extra nitrogen

Long-term treatment can manage UCD symptoms. Your child will need frequent blood tests throughout their life to check ammonia levels. Stresses on their body -- like illness, injury, or surgery -- can cause their levels to rise. During those times, you’ll need to give them extra calories so their body has plenty of fuel.

Long-term treatment will include:

• A low protein, high-calorie diet
• Medications to remove nitrogen
• Supplements of amino acids
• Drinking plenty of water

A liver transplant can reverse the symptoms of a urea cycle disorder.

Diagnosis

Most newborns in the U.S. are tested for ASS1 and ASL, but how well the tests work is different in each state. Many states test for arginase and citrin deficiencies. A handful also test for OTC and CPS1 deficiencies.

If your baby starts to show symptoms after you get home, the doctor will do a physical exam. They’ll ask about your family history and do tests. They’ll look for ammonia in your child’s blood and amino acid in their blood and urine. The doctor can take a tiny piece of their liver through a process called biopsy. They’ll test it for enzymes. Genetic tests will usually confirm the diagnosis.