Conditions Tyrosinemia, Type III

Tyrosinemia, type III (TYR III) is an inherited condition in which the body is unable to break down certain building blocks of proteins, known as amino acids. It is considered an amino acid condition because people with this condition are unable to break down the amino acid tyrosine. TYR III can cause learning problems, seizures, and loss of balance. However, detecting TYR III early and beginning treatment can prevent some of the serious outcomes of the condition.

Tyrosinemia is a condition with multiple forms, which each have different outcomes and treatment. Tyrosinemia, type III is only one form of the condition. Click on these links to read about the different forms of the condition: tyrosinemia type I or tyrosinemia type II.

Condition Type

Amino Acid Disorders


Tyrosinemia, type III (TYR III) is a very rare condition. Only a few cases of TYR III have been reported.

Also known as

  • Tyrosinemia due to 4-hydroxyphenylpyruvate dioxygenase deficiency
  • Tyrosinemia due to 4-hydroxyphenylpyruvic acid oxidase deficiency
  • Tyrosinemia due to HPD deficiency
  • Tyrosinemia type III

Follow-Up Testing

Your baby’s doctor may ask you if your baby is showing any of the signs of TYR III (see Early Signs below). If your baby has certain signs, your baby’s doctor may suggest starting immediate treatment.

If your baby’s newborn screening result for tyrosinemia, type III (TYR III) was out of the normal range, your baby’s doctor or the state screening program will contact you to arrange for your baby to have additional testing. It is important to remember that an out-of-range screening result does not necessarily mean that your child has the condition. An out-of-range result may occur because the initial blood sample was too small or the test was performed too early. However, as a few babies do have the condition, it is very important that you go to your follow-up appointment for a confirmatory test. Because the harmful effects of untreated TYR III can occur soon after birth, follow-up testing must be completed as soon as possible to determine whether or not your baby has the condition.

Follow-up testing will involve checking your baby’s urine and blood samples for signs of TYR III. Harmful levels of certain substances build up in the body when a child has an amino acid condition, so measuring the amounts of these substances in your baby’s body can help doctors determine if your baby has a condition. A high amount of tyrosine in the blood might indicate that your baby has TYR III.

About Tyrosinemia, Type III

Early Signs

There are three types of tyrosinemia (I, II, and III); tyrosinemia, type III (TYR III) is the least common type, with fewer than twenty reported cases. Signs of TYR III are highly variable and not yet well known. Signs of TYR III may include:

  • Poor coordination and balance
  • Seizures (Epilepsy)

These signs may occur when your baby eats foods that their body cannot break down. They can be triggered by long periods of time without eating, illnesses, and infections.

If your baby shows any of these signs, be sure to contact your baby’s doctor immediately.


Although the signs and symptoms of tyrosinemia, type III (TYR III) are not well known, treatment is still recommended to try to avoid any possible health complications for your child.

Dietary Treatments

Your baby may need to be on a restricted diet in order to avoid certain proteins that their body cannot break down. Babies with TYR III may need to limit certain amino acids (phenylalanine, tyrosine, and methionine) in their diet. Amino acids are the building blocks of protein. These are all found in many proteins, and phenylalanine is also found in artificial sweeteners.

Special foods and formulas for children with TYR III are available. These formulas will likely need to continue through adulthood.


Your baby’s doctor might prescribe a medication called NTBC. NTBC helps lower amino acid levels in the blood. Everyone has some amino acids in their blood, but the high levels associated with TYR III can be toxic.

Expected Outcomes

Babies who are treated early for tyrosinemia, type III (TYR III) may never develop any signs. This is why newborn screening for TYR III is so important.

Children with TYR III do have a risk of having an intellectual disability, but this risk is lower when the child receives treatment.


When we eat food, enzymes help break it down. Some enzymes help break down proteins into their building blocks, called amino acids. Other enzymes break down these amino acids into their base molecules. In tyrosinemia, type III (TYR III), the enzyme 4-hydrocyphenylpyruvate dioxygenase (HPD) is not working correctly.

HPD’s job is to break down the amino acid tyrosine. Babies with TYR III do not make enough HPD. When HPD is not working correctly, the body cannot break down tyrosine. This causes tyrosine and other amino acids (methionine and phenylalanine) to build up in the body, which can be toxic. When HPD cannot break down tyrosine correctly, tyrosine may be converted into a harmful acid called homogentisic acid. If homogentisic acid builds up in the body, it can be dangerous. Everyone has some acid and amino acids in their blood, but the high levels associated with TYR III can be toxic.

TYR III is an autosomal recessive genetic condition. This means that a child must inherit two copies of the non-working gene for TYR III, one from each parent, in order to have the condition. The parents of a child with an autosomal recessive condition each carry one copy of the non-working gene, but they typically do not show signs and symptoms of the condition. While having a child with TYR III is rare, when both parents are carriers, they can have more than one child with the condition. Learn more about autosomal recessive inheritance.

Support for Tyrosinemia, Type III

Support Services

Support groups can help connect families who have a child or other family member affected with tyrosinemia, type III with a supportive community of people who have experience and expertise in living with the condition. These organizations offer resources for families, affected individuals, health care providers, and advocates:

Accessing Care

Work with your baby’s doctor to determine the next steps for your baby’s care. Your baby’s doctor may help you coordinate care with a doctor specializing in metabolism, a dietician who can help plan your child’s specialized diet, and other medical resources in your community. Depending on the symptoms your baby experiences, your baby’s doctor may work with other physicians who specialize in the brain and nervous system. Some children with tyrosinemia, type III (TYR III) have developmental delays. If you think that your baby is not meeting their developmental milestones, ask your baby's health care provider about the next steps in accessing a developmental evaluation and care.

Because TYR III is a genetic condition, you may want to talk with a genetics specialist. A genetic counselor or geneticist can help you understand the causes of the condition, discuss genetic testing for TYR III, and understand what this diagnosis means for other family members and future pregnancies. Speak with your baby’s doctor about getting a referral. The Clinic Services Search Engine offered by the American College of Medical Genetics and Genomics (ACMG) and the Find a Genetic Counselor tool on the National Society of Genetic Counselors (NSGC) website are two good resources for you or your baby's health care provider to use to identify local specialists.

Families' Experiences

At this time we have not located a family story for this particular condition. If your family is affected by tyrosinemia, type III (TYR III) and you would like to share your story, please contact us so other families may benefit from your experience.

References & Sources

Visit OrphaNet for more information on tyrosinemia, type III

Visit MedlinePlus Genetics for more condition information

Visit Genetic and Rare Diseases Information Center (GARD) for more information on tyrosinemia, type III

Visit Genetics Home Reference from the National Library of Medicine for more information on the HBD gene

Read this fact sheet prepared by the Iowa Department of Public Health for more information

Visit West Virginia's Office of Maternal and Child Health website for more information on tyrosinemia

Visit Genetics Home Reference from the National Library of Medicine for more information on the TAT gene

ACT Sheets

Healthcare professionals can learn more about confirmatory testing by reading the American College of Medical Genetics and Genomics' Algorithm for Diagnosis and ACT Sheet, a guide for follow-up after newborn screening. You can visit this page of the ACMG website here.

Was this Helpful?

Your input helps us improve the site for parents and practitioners. Leave us feedback about this page.

Was this page helpful?

Was this Helpful? - Feedback

Your input helps us improve the site for parents and practitioners. Leave us feedback about this page.

We're sorry to hear that. How can we do to improve it?

This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.