The Role of Genetics in Urea Cycle Disorders (UCDs)

UCDs are caused by a genetic disorder

UCDs are usually passed down from parents to their children. In rare cases, UCDs can also be caused by an unexpected genetic change, also called a random mutation. To find out if you have a UCD, a doctor can order a genetic test. If the genetic test shows you have a UCD, it means that you could pass it on to your children. Learn more about how the UCD gene can be passed down through families below.

What are chromosomes?
Chart showing how a female has 2 X chromosomes and a male has 1 X and 1 Y chromosome. Chart showing how a female has 2 X chromosomes and a male has 1 X and 1 Y chromosome. Chart showing how a female has 2 X chromosomes and a male has 1 X and 1 Y chromosome.

A person’s sex (male or female) is decided by their chromosomes. Each pair of chromosomes carries genes that define which traits are passed from parent to child, such as hair and eye color. There are 2 types of chromosomes which determine your sex at birth: X chromosomes and Y chromosomes. A female has 2 X chromosomes and a male has 1 X and 1 Y chromosome. When someone passes a UCD down through a gene that’s located on the X chromosome, they are called X-linked carriers. 

What does autosomal recessive mean?

Autosomal recessive is when both parents have a UCD gene. When this happens, see the chances of having a child with a UCD:

UCD hereditary distribution chart. UCD hereditary distribution chart. UCD hereditary distribution chart.

For all other UCDs except ornithine transcarbamylase (OTC) deficiency, both parents carry a gene that doesn’t work.

There are different types of UCDs

Different UCD genes cause different types of UCDs. In people with UCDs, ammonia cannot leave the body because it is not processed correctly. See how the urea cycle works. 

There are 8 types of urea cycle disorders. They are named after the protein in the urea cycle that is not working correctly:

  • Arginase deficiency (hyperargininemia, ARG)
  • Hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome
  • Citrullinemia II (CTLN2)
  • N-acetylglutamate synthase (NAGS) deficiency*

*Important Limitation of Use: It is not known if RAVICTI is safe and effective for the treatment of N-acetylglutamate synthase (NAGS) deficiency.  

If you or your child has been diagnosed with a UCD, it’s important to pay attention to other relatives, especially children, who may have similar signs and symptoms.

Mya lives with OTC.Mya lives with OTC.

MYA

lives with OTC

MYA lives with OTC

OTC, the most common UCD type

OTC deficiency is most commonly passed from a mother to her child through her X chromosome. Some mothers who are carriers may not know they have the OTC gene until their child is diagnosed. Mothers who are OTC carriers may have subtle signs and symptoms, which should not be ignored. Those subtle symptoms can include headaches, confusion, and trouble concentrating. If you experience these symptoms, you should talk with your doctor to see if you may need treatment.

More about OTC

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Use and 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) Phenylacetate (PAA), a breakdown product of RAVICTI, may cause nervous system side effects.

Use and 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) Phenylacetate (PAA), a breakdown product of RAVICTI, 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

Your doctor may do blood tests to measure the amount of PAA in your blood during your treatment with RAVICTI.

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 for the acute treatment of hyperammonemia in people with UCD.
  • It is not known if RAVICTI is safe and effective for the treatment of N-acetylglutamate synthase (NAGS) deficiency.

Do not take RAVICTI if you are allergic to phenylbutyrate. Call your doctor or go to the nearest hospital emergency room if you have wheezing, shortness of breath, cough, low blood pressure, flushing, nausea or a rash while taking RAVICTI.

Before taking RAVICTI, tell your doctor about all of your medical conditions, including 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. If you become pregnant during treatment with RAVICTI, call Horizon at 1‐866‐479‐6742 to report the pregnancy.
  • 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
  • constipation
  • 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. You may report side effects to FDA at 1-800-FDA-1088.

For additional Important Safety Information, click here for the Medication Guide and discuss with your doctor.

Use and 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) Phenylacetate (PAA), a breakdown product of RAVICTI, may cause nervous system side effects.

Use and 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) Phenylacetate (PAA), a breakdown product of RAVICTI, 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

Your doctor may do blood tests to measure the amount of PAA in your blood during your treatment with RAVICTI.

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 for the acute treatment of hyperammonemia in people with UCD.
  • It is not known if RAVICTI is safe and effective for the treatment of N-acetylglutamate synthase (NAGS) deficiency.

Do not take RAVICTI if you are allergic to phenylbutyrate. Call your doctor or go to the nearest hospital emergency room if you have wheezing, shortness of breath, cough, low blood pressure, flushing, nausea or a rash while taking RAVICTI.

Before taking RAVICTI, tell your doctor about all of your medical conditions, including 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. If you become pregnant during treatment with RAVICTI, call Horizon at 1‐866‐479‐6742 to report the pregnancy.
  • 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
  • constipation
  • 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. You may report side effects to FDA at 1-800-FDA-1088.

For additional Important Safety Information, click here for the Medication Guide and discuss with your doctor.