General Condition Information
Other Names
- FAH Deficiency
- Fumarylacetoacetase Deficiency
- Fumarylacetoacetate Hydrolase Deficiency
- Tyrosinemia
- Tyrosinemia I
- Tyrosinemia type 1
- Tyrosinemia type I (Hepatorenal)
- Tyrosinemia, type 1
- Tyrosinemia, type I
Condition Type
Birth Prevalence
- It is estimated that fewer than 40 babies are born with this condition each year in the United States.
- Visit GeneReviews to learn more about how often this condition occurs.
Screening Finding
What is tyrosinemia type i
Tyrosinemia type I is an inherited (genetic) condition that prevents the body from processing proteins correctly. Your body breaks down the protein that you eat into amino acids. Your body then uses those amino acids to make other proteins that it needs to function.
There are several enzymes in your body that break down an amino acid called tyrosine. The process of breaking down tyrosine happens in multiple steps. Each step needs a specific enzyme. In tyrosinemia, one of these enzymes is not working well. Either the body does not make enough enzyme, or does not make the enzyme correctly. People with tyrosinemia have trouble with the process of breaking down tyrosine.
There are different types of tyrosinemia: type I, type II, and type III. The type of tyrosinemia that your baby has depends on which step in the breakdown process is not working.
In tyrosinemia type I, the enzyme fumarylacetoacetate hydrolase (FAH) is not working. Without working FAH, the last step of breaking down tyrosine slows or shuts down. When the last step of breaking down tyrosine slows down or stops, a toxin called succinylacetone can form.
Without treatment, high levels of succinylacetone can damage the liver and kidneys. This damage can lead to the signs and symptoms of the condition.
There are two forms of tyrosinemia type I: acute and chronic. The form your baby has depends on how well their body can break down tyrosine. The acute form is more severe and shows up earlier in life. In severe cases, this condition can lead to serious health problems or death if not treated early.
Newborn Screening and Follow-Up
Newborn screening for tyrosinemia type I is done using a small amount of blood collected from your baby’s heel. To learn more about this process, visit the Blood Spot Screening page.
During screening, a special machine measures how much tyrosine and succinylacetone are in your baby’s blood. Babies with high levels of tyrosine and succinylacetone might have tyrosinemia type I.
If your baby’s blood spot screening result for tyrosinemia type I is out-of-range, your baby’s health care provider will contact you. Together, you will discuss next steps and follow-up plans.
An out-of-range screening result does not mean that your baby definitely has the condition. It does mean that your baby needs more follow-up testing. To learn more about screening results, visit the Blood Spot Screening Results page.
Your baby may need the following tests after an out-of-range screening result:
- Blood and urine tests
- Genetic testing using a blood sample
You should complete any recommended follow-up testing as soon as possible. Babies with this condition can have serious health problems in the first few months of life if they are not diagnosed and treated quickly.
False-positive newborn screening results for this condition are rare. Typically, elevations of succinylacetone are only seen with tyrosinemia type I.
Condition Details
Newborn screening helps babies lead healthier lives. If your baby has an out-of-range result, follow up with your health care provider quickly. It is important to follow their instructions. Your baby may need to get treatment right away, even if they are not showing signs or symptoms. In some cases, your baby’s health care provider may decide it is best to watch (monitor) your baby to decide next steps. Careful monitoring and early treatment will help your baby stay as healthy as possible.
Signs of tyrosinemia type I can vary widely, but typically develop within the first few months. These signs may be triggered by eating foods or milk that the body cannot break down or by going long periods without eating. The symptoms can also be caused by illnesses or infections. Milder forms of tyrosinemia type I may not appear until later in childhood or adulthood.
Signs of the condition may include the following:
The condition is caused by a change in the FAH gene. The FAH gene gives the body instructions for making the enzyme fumarylacetoacetate hydrolase (FAH). FAH helps break down the amino acid tyrosine.
Without a working FAH gene, FAH cannot break down enough tyrosine. As a result, tyrosine and related toxins like succinylacetone can build up and become toxic to their body.
Tyrosinemia type I is a genetic condition. Babies inherit it from their biological (birth) parents. To learn more about genetic conditions, visit MedlinePlus Genetics.
- Tyrosinemia type I is an autosomal recessive condition. Babies inherit the condition when each parent passes down a nonworking FAH gene to their baby. Only babies with two nonworking FAH genes—one from the mom and one from the dad—have this condition.
- People with one working copy and one nonworking copy of the FAH gene are called carriers.
- Carriers do not have or develop the condition. However, they may pass down a nonworking copy of the gene to their children.
- If two parents are carriers of a nonworking copy of the FAH gene, they have a 1 in 4 chance of having a child with tyrosinemia type I.
- Carriers for tyrosinemia type I often do not know they are carriers before having a child with the condition. In most cases, families have no history of the condition until the birth of a child with tyrosinemia type I.
- Parents who already have a child with tyrosinemia type I still have a 1 in 4 chance of having another child with tyrosinemia type I. This 1 in 4 chance stays the same for all future children.
- Genetic counselors and medical geneticists can help families learn about this condition and the chance of having children with it. Visit the National Society of Genetic Counselors to find a genetic counselor and the American College of Medical Genetics and Genomics to find a medical geneticist.
Treatment and Management
It is important to talk to your health care provider about which treatment(s) are best for your baby. The goal of treatment is to prevent the health problems caused by this condition.
Treatments may include the following:
- Diet low in protein
- Special formulas and foods
- Medication called nitisinone that helps stop succinylacetone from building up
- Vitamin D and carnitine supplementation in some cases
Children who receive early intervention and treatment for tyrosinemia type I can have healthy growth and development. Treatment is very important for lowering the chance of liver and kidney problems.