Introduction
Tyrosinemia type II is a genetic condition characterized by high blood levels of the amino acid tyrosine, a component of most proteins. This disorder may have an impact on intellectual growth, the skin, and the eyes. Tyrosine aminotransferase (TAT) is one of the enzymes necessary for the multi-step process that breaks down tyrosine, and its loss results in tyrosinemia type II. Genetic alterations in the TAT gene are the root cause of this enzyme deficiency. This condition is inherited in an autosomal recessive manner. The signs and symptoms of the condition may develop if the damage is not treated.
What Are the Synonyms of Tyrosinemia Type II?
Several other names for Tyrosinemia type II include the following:
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TYR II.
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TAT deficiency.
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Richner Hanhart syndrome.
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Oregon type tyrosinemia.
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Tyrosine transaminase deficiency.
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Keratosis palmoplantar with corneal dystrophy.
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Hypertyrosinemia type II.
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Tyrosine aminotransferase deficiency.
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Oculocutaneous tyrosinemia.
What Happens in Tyrosinemia Type II?
Tyrosine aminotransferase (TAT) is a hepatic pyridoxine-dependent enzyme that causes type II tyrosinemia. As a result, tyrosine accumulates in plasma, urine, and tissues due to this deficiency. Furthermore, other substances are generated due to the high tyrosine concentrations, such as tyrosine derivatives (tyramine) and p-OH-phenylpyruvate derivatives.
What Causes Tyrosinemia Type II?
Tyrosinemia II is caused by a mutation (stable and hereditary change) in the TAT gene. It gives the body instructions for making the enzyme tyrosine aminotransferase. This enzyme is part of the first step in breaking 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. It causes tyrosine and other amino acids (methionine and phenylalanine) to build up in the body, which can be toxic. It can cause damage to the body.
Tyrosinemia type II is an autosomal recessive genetic disorder. To have this condition, a kid must inherit two copies of the non-working TYR II gene, one from each parent. Therefore, a parent who does not exhibit the signs and symptoms of this condition carries one copy of the defective gene. While it is uncommon to have more than one kid with TYR II, this is possible when both parents are carriers.
What Are the Signs and Symptoms of Tyrosinemia Type II?
Tyrosinemia comes in three forms (I, II, and III). Eyes and skin are usually affected by type II tyrosinemia. TYR II symptoms and signs typically appear during the first year of life. These signs and symptoms include:
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Increased tear production.
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Sensitivity to light (called photophobia).
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Behavior changes.
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Eye redness.
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Poor coordination.
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Skin lesions on the hands and feet.
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Developmental delay.
Many of these symptoms could manifest if the baby consumes foods the body cannot process. In addition, it can be induced by fasting for extended periods, diseases, and infections. Contact the baby's pediatrician right away if any of these symptoms appear.
How Is Type II Tyrosinemia Diagnosed?
The diagnosis is made based on clinical suspicion and is verified by an analysis of the amino acids in the plasma and urine, which reveals increased levels of tyrosine. In addition, there may be a modest rise in phenylalanine. Organic acid study shows a high excretion of tyrosine and p-OH-phenylpyruvate derivatives in the absence of succinylacetone. Expanded newborn screening enables the early identification of tyrosinemia II before the onset of the first clinical signs and symptoms. A liver biopsy is unnecessary to show an enzyme deficit because TAT is only expressed in the liver. As a result, genetic studies confirm the diagnosis.
What Is the Type II Tyrosinemia Screening Test?
A small amount of blood is collected from the baby's heels to screen for tyrosinemia type II. Tyrosine levels in the baby's blood are measured using a specialized device during the screening. Tyrosinemia type II may be present in newborns with elevated tyrosine levels.
What Happens After an Out-of-Range Screening Result?
If the baby's tyrosinemia type II blood spot test result is abnormal, the baby's healthcare professional will inform you. An abnormal screening result does not indicate that the infant has the disease. It implies that the infant requires additional follow-up testing. Following an abnormal screening result, children can need the following tests:
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Urine and blood tests.
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A genetic test using a blood sample.
This disorder can produce false-positive neonatal screening results. Premature babies may have out-of-range outcomes. Infants with developing liver conditions or jaundice may also experience false-positive results. In some instances, newborns have elevated tyrosine levels that reduce over time. This condition is known as newborn transitory tyrosinemia. It is a benign condition rather than a genetic disease like tyrosinemia types I, II, and III that persists throughout life.
What Is the Treatment for Tyrosinemia Type II?
It is essential to discuss with the healthcare practitioner which treatments are appropriate for the baby. The main purpose of treatment is to prevent the health concerns produced by this condition. Children with tyrosinemia type II who get early, and continued treatment can have average growth and development. The following are the possible treatments:
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Diet Low in Protein- A restricted diet may be necessary for the baby to prevent specific proteins their body cannot digest. Babies with type II tyrosinemia may need to limit their intake of particular amino acids like phenylalanine, tyrosine, and methionine. Proteins are the building components of amino acids. All of them are present in large numbers of proteins, and phenylalanine is also present in artificial sweeteners.
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Special Foods and Formulas- Special diets and formulas are necessary for kids with TYR II. These formulations will probably need to be used till adulthood.
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Medications- Physicians may provide NTBC (Nitisinone), a drug that helps lower amino acid levels in the blood. Everyone's blood contains specific amino acids, but the excessive levels linked to TYRII can be harmful.
What Is the Outcome of Type II Tyrosinemia?
Children who undergo early and continued treatment for tyrosinemia type II can have average growth and development. This is why it is essential to screen newborns for TYR II. In addition, approximately half of those diagnosed with TYR II have intellectual impairments. Early treatment can lower the chances of developing intellectual impairments.
Conclusion
The diagnosis must be made as quickly as feasible, and the appropriate treatment must be initiated. Preventing tyrosine buildup is the primary goal of therapy. It will be accomplished by limiting natural dietary proteins because they contain precursor amino acids. However, amino acids are necessary to create the proteins that make up the baby's body. Type II tyrosinemia is a hereditary condition with severe consequences if left untreated. However, if the disease is detected and treated promptly, clinical symptoms are avoided, and affected children have a high quality of life.
