The Role of Genetics in Urea Cycle Disorders

Urea cycle disorders (UCDs) are inherited genetic traits. This means they're usually passed down from parents to children. UCDs can also be caused by an unexpected genetic change. If you have a UCD in your family, your children may or may not be born with it. In most cases, it depends on the mix of genes that they get from each parent.

Some people may not realize they can have a UCD gene in their bodies. A carrier is someone who has the gene but may not be showing signs or symptoms.

The X factor

A person's sex (male or female) is decided by his or her chromosomes. Each pair of chromosomes carries genes that decide which traits are passed from parent to child, such as hair and eye color. There are 2 types of sex chromosomes: X chromosomes and Y chromosomes. A female has 2 X chromosomes and a male has 1 X and 1 Y chromosome.

The most common type of UCD is ornithine transcarbamylase (OTC) deficiency. OTC deficiency is passed from mother to child through her X chromosome. A mother who has a UCD gene may not know she is a carrier, but also may often experience subtle signs and symptoms of a UCD and may need to be treated. In rare cases, the UCD gene may be passed from a father to his daughter.

If you are a carrier of a UCD gene, at some point, you may also show symptoms yourself. These symptoms may include headaches, confusion, or trouble concentrating. If you have any of these symptoms, you should speak with your child's doctor to find out if you should be treated for a UCD, too.

When both parents have a UCD gene (Autosomal Recessive Inheritance)

For all other urea cycle disorders except OTC, both parents carry a gene that doesn't work. Review the graphic below to see how a urea cycle disorder is passed from parent to child.

When both parents have a UCD gene:
Chances of having a child with a UCD

UCD hereditary distribution chart UCD hereditary distribution chart

Father Carrier

Mother Carrier

25%

A 25% chance that their child will develop a UCD by receiving a gene that doesn’t work from each parent

50%

A 50% chance that their child will get one gene that doesn't work from one parent. This child is a carrier

25%

A 25% chance that their child will receive both normal genes and be unaffected

A blood test can find out if you have a UCD gene. If the test shows you have a gene, it means that you could pass it on to your children.

Different UCD genes cause different types of UCDs

The urea cycle is controlled by a series of proteins (enzymes and transporters) that help chemical reactions take place in your body. Eight of these proteins have the job of removing ammonia from the blood stream. In people with urea cycle disorders, one of these proteins is not working correctly. This prevents ammonia from being processed properly so it can safely leave the body.

Different UCD genes cause different types of UCDs. There are 8 types of urea cycle defects. The name of each one identifies the protein that is not working in the urea cycle:

  • Argininosuccinate synthetase (ASSD)
  • Arginase deficiency (hyperargininemia, ARG1)
  • Argininosuccinic aciduria (ASL)
  • Carbamylphosphate synthetase I deficiency (CPS1)
  • Citrullinemia type 1 (ASS1)
  • N-acetylglutamate synthetase deficiency (NAGS)*
  • Ornithine transcarbamylase deficiency (OTC) — the most common UCD
  • Ornithine translocase (ORNT1)

*Important Limitation of Use:

It is not known if RAVICTI® (glycerol phenylbutyrate) is safe and effective for the treatment of NAGS deficiency.

UCD Family icon

Who Should Get Tested for UCDs?

Other family members could be at risk

Find out why
UCD Family icon
Patricia, UCD patient and caregiver
Patricia, UCD patient and caregiver

Real Patients. Real Stories.

"I learned I had a urea cycle disorder when my son was diagnosed."
– Patricia | Caregiver and Patient

Talk to someone who's been there

APPROVED USES and IMPORTANT SAFETY INFORMATION for RAVICTI
What is the most important safety information I should know about RAVICTI?
RAVICTI may cause serious side effects, including: Nervous system side effects (Neurotoxicity).
 The breakdown of RAVICTI produces the byproduct phenylacetate (PAA), which may cause nervous system side effects.

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What is RAVICTI?

RAVICTI (glycerol phenylbutyrate) Oral Liquid is a prescription medicine used for long-term management of high blood levels of ammonia (hyperammonemia) caused by a condition called a urea cycle disorder (UCD). RAVICTI should be used if the UCD cannot be managed with a low-protein diet and dietary supplements alone. RAVICTI must be used along with a low-protein diet and in some cases, dietary supplements.

RAVICTI is not used to treat extremely high levels of ammonia in the blood (hyperammonemic crisis) in people with UCDs.

It is not known if RAVICTI is safe and effective for the treatment ofN-acetylglutamate synthase (NAGS) deficiency.

IMPORTANT SAFETY INFORMATION

What is the most important safety information I should know about RAVICTI?

RAVICTI may cause serious side effects, including:

Nervous system side effects (Neurotoxicity). The breakdown of RAVICTI produces the byproduct phenylacetate (PAA), which may cause nervous system side effects.

Call your doctor or get medical help right away if you have any of these symptoms while taking RAVICTI:

  • sleepiness
  • lightheadedness
  • change in taste
  • problems with hearing
  • confusion
  • problems with memory
  • worsening of numbness, tingling, or burning in your hands or feet
  • headache
  • feeling very tired (fatigue)
  • nausea
  • vomiting

Who should not take RAVICTI?

Do not take RAVICTI if you are allergic to phenylbutyrate. Call your doctor or go to the nearest hospital emergency room if you experience any of the following symptoms of an allergic reaction while taking RAVICTI:

  • wheezing
  • shortness of breath
  • cough
  • low blood pressure
  • flushing
  • nausea
  • skin rash

What should I tell my doctor before taking RAVICTI?

Tell your doctor about any medical conditions and if you:

  • Have liver or kidney problems.
  • Have pancreas or bowel (intestine) problems.
  • Are pregnant or plan to become pregnant. It is not known if RAVICTI will harm your unborn baby.
    • Pregnancy Registry: There is a Pregnancy Registry for women who take RAVICTI just before becoming pregnant or who become pregnant during treatment with RAVICTI. The purpose of this registry is to collect information about the health of you and your baby. Talk to your doctor about how you can join the Pregnancy Registry. For more information about this registry, call 1-855-823-2595 or visit www.ucdregistry.com.
  • Are breastfeeding or plan to breastfeed. It is not known if RAVICTI passes into your breast milk. Breastfeeding is not recommended during treatment with RAVICTI. Talk to your doctor about the best way to feed your baby if you take RAVICTI.

What are possible side effects of RAVICTI?

RAVICTI may cause serious side effects, including:

  • See "What is the most important information I should know about RAVICTI?"

The most common side effects of RAVICTI in adults include:

  • diarrhea
  • gas
  • headache
  • abdomen (stomach) pain
  • vomiting
  • tiredness
  • decreased appetite
  • indigestion or heartburn

The most common side effects of RAVICTI in children 2 years to 17 years of age include:

  • upper abdomen (stomach) pain
  • rash
  • nausea
  • vomiting
  • diarrhea
  • decreased appetite
  • headache

The most common side effects of RAVICTI in children 2 months to less than 2 years of age include:

  • low white blood cell count (neutropenia)
  • vomiting
  • diarrhea
  • fever
  • reduced food intake
  • cough
  • stuffy nose
  • runny nose
  • skin rash
  • small round bumps on the skin

The most common side effects of RAVICTI in children less than 2 months of age include:

  • vomiting
  • rash
  • gastroesophageal reflux
  • increased levels of liver enzymes in the blood
  • decreased appetite and reduced food intake
  • low red blood cell count (anemia)
  • cough
  • loss of too much body fluid (dehydration)
  • too much acid in the blood (acidosis)
  • high blood platelet count (thrombocytosis)
  • low blood platelet count (thrombocytopenia)
  • low blood neutrophil count (type of white blood cell) (neutropenia)
  • high white blood cell count (lymphocytosis)
  • diarrhea
  • gas
  • constipation
  • fever
  • drowsiness (lethargy)
  • irritability
  • agitation

These are not all of the possible side effects of RAVICTI. Call your doctor for medical advice about side effects.

For additional important safety information, click here for the Full Prescribing Information and Medication Guide and discuss with your doctor.

You are encouraged to report negative side effects of prescription drugs to the FDA. Visit http://www.fda.gov/medwatch or call 1-800-FDA-1088.

What is RAVICTI?

RAVICTI (glycerol phenylbutyrate) Oral Liquid is a prescription medicine used for long-term management of high blood levels of ammonia (hyperammonemia) caused by a condition called a urea cycle disorder (UCD). RAVICTI should be used if the UCD cannot be managed with a low-protein diet and dietary supplements alone. RAVICTI must be used along with a low-protein diet and in some cases, dietary supplements.

RAVICTI is not used to treat extremely high levels of ammonia in the blood (hyperammonemic crisis) in people with UCDs.

It is not known if RAVICTI is safe and effective for the treatment ofN-acetylglutamate synthase (NAGS) deficiency.

IMPORTANT SAFETY INFORMATION

What is the most important safety information I should know about RAVICTI?

RAVICTI may cause serious side effects, including:

Nervous system side effects (Neurotoxicity). The breakdown of RAVICTI produces the byproduct phenylacetate (PAA), which may cause nervous system side effects.

Call your doctor or get medical help right away if you have any of these symptoms while taking RAVICTI:

  • sleepiness
  • lightheadedness
  • change in taste
  • problems with hearing
  • confusion
  • problems with memory
  • worsening of numbness, tingling, or burning in your hands or feet
  • headache
  • feeling very tired (fatigue)
  • nausea
  • vomiting

Who should not take RAVICTI?

Do not take RAVICTI if you are allergic to phenylbutyrate. Call your doctor or go to the nearest hospital emergency room if you experience any of the following symptoms of an allergic reaction while taking RAVICTI:

  • wheezing
  • shortness of breath
  • cough
  • low blood pressure
  • flushing
  • nausea
  • skin rash

What should I tell my doctor before taking RAVICTI?

Tell your doctor about any medical conditions and if you:

  • Have liver or kidney problems.
  • Have pancreas or bowel (intestine) problems.
  • Are pregnant or plan to become pregnant. It is not known if RAVICTI will harm your unborn baby.
    • Pregnancy Registry: There is a Pregnancy Registry for women who take RAVICTI just before becoming pregnant or who become pregnant during treatment with RAVICTI. The purpose of this registry is to collect information about the health of you and your baby. Talk to your doctor about how you can join the Pregnancy Registry. For more information about this registry, call 1-855-823-2595 or visit www.ucdregistry.com.
  • Are breastfeeding or plan to breastfeed. It is not known if RAVICTI passes into your breast milk. Breastfeeding is not recommended during treatment with RAVICTI. Talk to your doctor about the best way to feed your baby if you take RAVICTI.

What are possible side effects of RAVICTI?

RAVICTI may cause serious side effects, including:

  • See "What is the most important information I should know about RAVICTI?"

The most common side effects of RAVICTI in adults include:

  • diarrhea
  • gas
  • headache
  • abdomen (stomach) pain
  • vomiting
  • tiredness
  • decreased appetite
  • indigestion or heartburn

The most common side effects of RAVICTI in children 2 years to 17 years of age include:

  • upper abdomen (stomach) pain
  • rash
  • nausea
  • vomiting
  • diarrhea
  • decreased appetite
  • headache

The most common side effects of RAVICTI in children 2 months to less than 2 years of age include:

  • low white blood cell count (neutropenia)
  • vomiting
  • diarrhea
  • fever
  • reduced food intake
  • cough
  • stuffy nose
  • runny nose
  • skin rash
  • small round bumps on the skin

The most common side effects of RAVICTI in children less than 2 months of age include:

  • vomiting
  • rash
  • gastroesophageal reflux
  • increased levels of liver enzymes in the blood
  • decreased appetite and reduced food intake
  • low red blood cell count (anemia)
  • cough
  • loss of too much body fluid (dehydration)
  • too much acid in the blood (acidosis)
  • high blood platelet count (thrombocytosis)
  • low blood platelet count (thrombocytopenia)
  • low blood neutrophil count (type of white blood cell) (neutropenia)
  • high white blood cell count (lymphocytosis)
  • diarrhea
  • gas
  • constipation
  • fever
  • drowsiness (lethargy)
  • irritability
  • agitation

These are not all of the possible side effects of RAVICTI. Call your doctor for medical advice about side effects.

For additional important safety information, click here for the Full Prescribing Information and Medication Guide and discuss with your doctor.

You are encouraged to report negative side effects of prescription drugs to the FDA. Visit http://www.fda.gov/medwatch or call 1-800-FDA-1088.