Children and Youth with Special Health Needs (CYSHN)
Tyrosinemia Type I (TYR-I)
On this page...
- What is TYR-1?
- What causes TYR-1?
- What causes the FAH enzyme to be absent or not working correctly?
- How is TYR-1 inherited?
- Is genetic testing available?
- What other testing is available?
- Can you test during pregnancy?
- Can other members of the family have TYR-1 or be carriers?
- Can other family members be tested?
- How many people have TYR-1?
- Does TYR-1 happen more frequently n a certain ethnic group?
- Does TYR-1 go by any other names?
- What is the treatment for TYR-1?
- What happens when TYR-1 is treated?
- If TYR-1 is not treated, what problems occur?
This fact sheet has general information about tyrosinemia type I (TYR-I). Every child is different and some of these facts may not apply to your child specifically. Certain treatments may be recommended for some children but not others. Children with TYR-I should be followed by a metabolic doctor in addition to their primary doctor.
What is TYR-I?
TYR-I is one type of amino acid disorders. People with TYR-I have problems breaking down an amino acid called tyrosine from the food they eat. If not treated, the condition causes severe liver disease and other serious health problems.
|Amino Acid Disorders:
Amino acid disorders (AAs) are a group of rare inherited conditions. They are caused by enzymes that do not work properly.
Protein is made up of smaller building blocks called amino acids. A number of different enzymes are needed to process these amino acids for use by the body. Because of missing or non-working enzymes, people with amino acid disorders cannot process certain amino acids. These amino acids, along with other toxic substances, then build up in the body and cause problems.
The symptoms and treatment vary between different amino acid disorders. They can also vary from person to person with the same amino acid disorder. See the fact sheets for each specific amino acid disorder.
Amino acid disorders are inherited in an autosomal recessive manner and affect both males and females.
What causes TYR-I?
In order for the body to use protein from the food we eat, it is broken down into smaller parts called amino acids. Special enzymes then make changes to the amino acids so the body can use them.
TYR-I occurs when an enzyme, called fumarylacetoacetase (FAH), is either missing or not working properly. When FAH is not working, it cannot break down tyrosine. Tyrosine and other harmful substances then build up in the blood. One of these substances is called succinylacetone. When it builds up in the blood, it causes serious liver and kidney damage. It may also cause episodes of weakness or pain.
Genes tell the body to make various enzymes. People with TYR-I have a pair of genes that do not work correctly. Because of the changes in this pair of genes, the FAH enzyme either does not work properly or is not made at all.
How is TYR-I inherited?
TYR-I is inherited in an autosomal recessive manner. It affects both boys and girls equally.
Everyone has a pair of genes that make the FAH enzyme. In children with TYR-I, neither of these genes works correctly. These children inherit one non-working gene for the condition from each parent.
Parents of children with TYR-I rarely have the disorder. Instead, each parent has a single non-working gene for TYR-I. They are called carriers. Carriers do not have the condition because the other gene of this pair is working correctly.
When both parents are carriers, there is a 25% chance in each pregnancy for the child to have TYR-I. There is a 50% chance for the child to be a carrier, just like the parents. And, there is a 25% chance for the child to have two working genes.
Genetic counseling is available to families who have children with TYR-I. Genetic counselors can answer your questions about how the condition is inherited, choices during future pregnancies, and how to test other family members. Ask your doctor about a referral to a genetic counselor.
Is there genetic testing available?
Genetic testing for TYR-I can be done on a blood sample. Genetic testing, also called DNA testing, looks for changes in the pair of genes that causes this condition.
DNA testing is not necessary to diagnose your child. It can be helpful for carrier testing below.
What other testing is available?
This condition can be confirmed by measuring the amount of succinylacetone in the urine or by an enzyme test on blood, skin or liver samples. Talk to your metabolic doctor if you have questions about these tests.
Can you test during pregnancy?
If both gene changes have been found in the child with TYR-I, DNA testing can be done during future pregnancies. The sample needed for this test is obtained by either CVS or amniocentesis. CVS stands for Chorionic Villus Sampling, which is a special test done early in pregnancy. During CVS, a small sample of the placenta is removed for genetic testing.
Parents may choose to have testing during pregnancy or wait until birth to have the baby tested. A genetic counselor can talk to you about your choices and answer questions about prenatal testing or testing your baby after birth.
Can other members of the family have TYR-I or be carriers?
The brothers and sisters of a baby with TYR-I are unlikely to be affected. However, finding out whether other children in the family have this condition may be important because early treatment may prevent serious health problems. Ask your metabolic doctor whether your other children should be tested.
Brothers and sisters who do not have TYR-I still have a chance to be carriers like their parents. Except in special cases, carrier testing should only be done in people over 18 years of age.
Each of the parents' brothers and sisters has a 50% chance to be a carrier. It is important for other family members to be told that they could be carriers. There is a small chance they are also at risk to have children with TYR-I.
When both parents are carriers, newborn screening results are not sufficient to rule out the condition in a newborn baby. In this case, special diagnostic testing should be done in addition to newborn screening.
Can other family members be tested?
If there is a concern, diagnostic testing can be done on brothers and sisters. Talk to your metabolic doctor if you have questions about testing other family members.
If both gene changes have been found in your child, other family members can have DNA testing to see if they are carriers.
How many people have TYR-I?
About one in every 100,000 babies in the United States is born with TYR-I.
Does TYR-I happen more often in a certain ethnic group?
This condition occurs in all ethnic groups around the world. It is found more often in people of French-Canadian background, especially in the Saguenay Lac Saint-Jean region of Quebec. About 1 in 20 French-Canadians in this region are carriers. About one in every 2000 babies in this population is born with the condition.
Does TYR-I go by any other names?
TYR-I is sometimes also called:
- Hereditary Infantile tyrosinemia
- Hepatorenal tyrosinemia
- Fumarylacetoacetase deficiency
- Fumarylacetoacetate hydrolase deficiency
- FAH deficiency
- Hereditary tyrosinemia type 1
What is the treatment for TYR-I?
Your baby’s doctor will work with a metabolic doctor and dietician to care for your child. Lifelong treatment is usually needed to prevent liver and kidney problems.
Treatment consists of medication and a diet low in tyrosine and another amino acid called phenylalanine (phe). The low-tyrosine/phenylalanine diet is made up of a special medical formula and carefully chosen foods. You must start the treatment as soon as you know your child has the condition.
The following treatments are often recommended for children with TYR-I:
Nitisinone will increase the level of tyrosine in your child’s blood. So, a low-tyrosine diet is a very important part of treatment.
Vitamin D is sometimes used to treat children who have rickets.
Do not take any medication without talking with your doctor.
The special medical formula gives babies and children the nutrients and protein they need while helping keep their tyrosine levels within a safe range. Your metabolic doctor and dietician will tell you what type of formula is best and how much to use.
Low-tyrosine / phenylalanine diet:
Many vegetables and fruits have only small amounts of phenylalanine and tyrosine and can be eaten regularly in carefully measured amounts.
There are other medical foods such as special flours, pastas, and rice that are made especially for people with TYR-I. Some states offer help with payment, or require private insurance coverage for formula and other special medical foods.
Your metabolic doctor and dietician will decide on the best food plan for your child. The exact plan will depend on many things such as your child’s age, weight, general health, and how well the medication is working. Your dietician will fine-tune your child’s diet over time.
Blood, urine and other tests Your child will have regular blood and urine tests to
These tests help your doctor and dietician figure out whether any changes to the medication or diet are needed.
Some experts suggest that children with TYR-I have a CT or MRI scan of their liver once a year to check for scarring or cancer.
Liver transplantation is still an option for those children that show signs of liver cancer or liver failure. If you have questions, talk to your metabolic doctor or doctor about the benefits and risks of transplantation.
What happens when TYR-I is treated?
When treatment is started early, severe liver, kidney, and neurologic symptoms can be prevented. Children who are treated usually have normal growth and intelligence.
If treatment is not started right away, children may have some liver or kidney damage. Rickets may already be present and need to be treated. Delays in growth and development may also be present. The effects of delayed treatment vary from child to child.
If TYR-I is not treated, what problems occur?
The symptoms can vary a great deal from person to person. There are two types of TYR-I. The more common form happens in infants. The less common form is seen in older children and adults.
TYR-I in infants:
Babies usually show effects of the condition within the first few months of life. Some of the first symptoms may be:
- diarrhea and bloody stools
- poor weight gain
- extreme sleepiness
- “cabbage-like” odor to the skin or urine
Liver problems are common. They can lead to:
- enlarged liver
- yellowing of the ski
- tendency to bleed and bruise easily
- swelling of the legs and abdomen
Kidney problems also happen and can lead to:
- rickets, a bone thinning condition
- delays in walking
Without prompt and careful treatment, babies with severe liver and kidney problems usually die.
Some babies also have episodes that include:
- pain or weakness, especially in the legs
- breathing problems
- rapid heartbeat
- coma, sometimes leading to death
TYR-I in children (“chronic” form): Children with the chronic form usually start having symptoms after two months of age. Some of the first signs may be trouble gaining weight and episodes of vomiting and diarrhea. Over time, the condition can cause liver, kidney and nerve problems.
- Liver: If the condition is not treated, a rare type of liver scarring called nodular cirrhosis can happen. This gets worse over time and can lead to liver failure. If not treated, many children develop liver failure or liver cancer before the age of 10. Medication, when started early, can prevent liver failure in most children.
- Kidneys: Serious kidney problems can occur in untreated children. When the kidneys are not working properly, episodes of vomiting, weakness and fever can happen. Rickets, a bone thinning condition, may happen in children with kidney damage. Medication can prevent kidney problems in most children.
- Neurologic crises: Some children have episodes of weakness, pain or numbness in their arms, legs or other parts of the body. Breathing problems and rapid heartbeat may also happen. Some children have seizures that can lead to coma. Medication can stop episodes of neurologic crisis in most children.
- Other: A small number of children have had heart problems. Some have had high blood pressure.
Where can I find more information?
Medically Prescribed Formula: a table that provides a list of commonly prescribed medical foods and formulas and /or medication for this disorder.
National Library of Medicine Genetics Home Reference: Tyrosinemia
National Urea Cycle Disorders Foundation
CLIMB (Children Living with Inherited Metabolic Disorders)
For additional genetics information and resources:
- Genetic Alliance
- Region 4 Genetics Collaborative
- Partnering with your Doctor The Medical Home Approach: A guide for families with children who have genetic conditions - The Guide is intended to be a user-friendly, hands-on tool to support families of children who have genetic conditions to move forward in obtaining and providing a medical home for their children. The guide provides definitions, examples and tools for families to use when working with the doctor to develop a medical home.
More help available from Children and Youth with Special Health Needs (CYSHN):
- Resources: Financial and Other
- Early Childhood Intervention
- Resources for Children and Families
- Youth and Young Adults - Planning for the Future
- Emergency Planning
- Medical Home
We would like to acknowledge the Star G Project. The information on the fact sheet was obtained from the Star G Project. For the most up-to-date information on the disorder please visit their web site at http://www.newbornscreening.info. Each fact sheet was extensively reviewed by family support groups, metabolic specialists across the country and the Star G steering committee.
THIS INFORMATION DOES NOT PROVIDE MEDICAL ADVICE. All content, including text, graphics, images and information are for general informational purposes only. You are encouraged to confer with your doctor or other health care professional with regard to information contained on this information sheet. After reading this information sheet, you are encouraged to review the information carefully with your doctor or other healthcare provider. The Content is not intended to be a substitute for professional medical advice, diagnosis or treatment. NEVER DISREGARD PROFESSIONAL MEDICAL ADVICE, OR DELAY IN SEEKING IT, BECAUSE OF SOMETHING YOU HAVE READ ON THIS INFORMATION SHEET.
|Updated Wednesday, 25-Jul-2012 16:46:43 CDT|