Conditions Tyrosinemia, Type II
Tyrosinemia, type II (TYR II) is a condition that can affect the eyes, skin, and intellectual development. It is considered an amino acid condition because people with TYR II are unable to break down an amino acid, a small molecule that makes up proteins, known as tyrosine. Detecting TYR II early and beginning treatment can prevent some of the severe outcomes of the condition.
Amino Acid Disorders
How common is TYR II?
Tyrosinemia, type II (TYR II) affects fewer than one in 250,000 individuals. The condition may be more common in Arab and Mediterranean regions.
Also known as
- TYR II
- Hypertyrosinemia type II
- Keratosis palmoplantaris - corneal dystrophy
- Oculocutaneous tyrosinemia
- Richner-Hanhart syndrome
- Tyrosinemia due to TAT deficiency
- Tyrosinemia due to tyrosine aminotransferase deficiency
Your baby’s doctor may ask you if your baby is showing any of the signs of TYR II (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 II (TYR II) 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 II 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 II. 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 very high amount of tyrosine in the blood might indicate that your baby has TYR II.
About Tyrosinemia, Type II
There are three types of tyrosinemia (I, II, and III). Tyrosinemia, type II (TYR II) tends to affect the skin and eyes. Signs of TYR II usually begin in the first year of life. These signs include:
- Increased tear production
- Sensitivity to light (called photophobia)
- Eye redness
- Skin lesions on the hands and feet
- Behavior changes
- Poor coordination
Many of these signs may occur when your baby eats foods that his or her 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.
Your baby may need to be on a restricted diet in order to avoid certain proteins that his or her body cannot break down. Babies with tyrosinemia, type II (TYR II) 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 II are available. These formulas will likely need to be continued through adulthood.
Your baby’s doctor might prescribe a drug called NTBC. NTBC helps lower amino acid levels in the blood. Everyone has some amino acids in his or her blood, but the high levels associated with TYRII can be toxic.
Children who receive early and ongoing treatment for tyrosinemia, type II (TYR II) can have healthy growth and development. This is why newborn screening for TYR II is so important.
About half of the individuals who have been diagnosed with TYR II have intellectual disabilities. Early treatment can reduce the risk of developing intellectual disabilities.
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. In tyrosinemia, type II (TYR II), the enzyme tyrosine aminotransferase (TAT) is not working correctly.
TAT’s job is to break down the amino acid tyrosine. Babies with TYR II either make non-working or do not make enough TAT. When TAT 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.
TYR II is an autosomal recessive genetic condition. This means that a child must inherit two copies of the non-working gene for TYR II, 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 II 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 II
Support groups can help connect families who have a child or other family member affected with tyrosinemia, type II 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.
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 who specializes 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, baby’s doctor may work with other doctors who specialize in treating the eyes or skin. Some children with tyrosinemia, type II (TYR II) have developmental delays. If you think that your baby is not meeting his or her developmental milestones, ask your baby’s doctor about the next steps in accessing a developmental evaluation and care.
Because TYR II 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 II, 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 National Coordinating Center for the Regional Genetic and Newborn Screening Service Collaboratives 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.
References & Sources
http://www.orpha.net/consor/cgi-bin/OC_Exp.php?Expert=28378Visit Genetics Home Reference from the National Library of Medicine for more condition informationhttp://ghr.nlm.nih.gov/condition/tyrosinemiaRead this fact sheet prepared by the Iowa Department of Public Health for more informationhttp://www.idph.state.ia.us/genetics/common/pdf/tyr.pdfVisit Genetic and Rare Diseases Information Center (GARD) for more information on tyrosinemia, type II
http://rarediseases.info.nih.gov/GARD/Condition/3105/Tyrosinemia_type_2.aspxVisit West Virginia's Office of Maternal and Child Health website for more information on tyrosinemiattp://www.wvdhhr.org/nbms/diseases/Tyrosinemia.aspVisit Genetics Home Reference from the National Library of Medicine for more information on the TAT gene