Last Reviewed June 2, 2009
Symptoms & Characteristics
Tyrosinemia is a genetic condition in which the body is can't process tyrosine, a building block of most proteins. If left untreated, tyrosine and its byproducts build up in tissues and organs causing damage.
Different enzymes are required for the multistep process that breaks down tyrosine. There are three types of tyrosinemia depending on which of these enzymes is deficient. Each type has different symptoms.
Type I tyrosinemia is caused by a deficiency in the enzyme fumarylacetoacetate hydrolase and is the most severe type. Symptoms typically appear in the newborn period and may include:
- failure to gain weight and grow (called failure to thrive)
- yellowing of the skin and whites of the eyes (called jaundice)
- increased tendency to bleed (especially nosebleeds)
If left untreated, symptoms can lead to:
- problems affecting the nervous system
Type II tyrosinemia is caused by a deficiency of the enzyme tyrosine aminotransferase. Symptoms often begin in early childhood and may include:
- abnormal sensitivity to light (called photophobia)
- painful skin lesions on the palms of hands and soles of feet
- abnormalities in mental development
Type III tyrosinemia is caused by a deficiency of the enzyme 4-hydroxyphenylpyruvate dioxygenase. Symptoms may include:
- periodic loss of balance and coordination (called intermittent ataxia)
Treatment
There is currently no cure for tyrosinemia. Treatments may include a diet low in phenylalanine, methionine and tyrosine, medications, and liver transplantation.
How Common Is It?
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Type I tyrosinemia affects about 1 in 100,000 people worldwide and is more common in Quebec, Canada.
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Type II tyrosinemia affects less than 1 in 250,000 people worldwide.
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Type III tyrosinemia is very rare.
Genetics & Inheritance
The different types of tyrosinemia are caused by mutations in different genes.
We all have two copies of each of these genes - one from each parent. In the different types of tyrosinemia, it is necessary to have two mutations, one in each copy, to be affected. This is called autosomal recessive inheritance.
Both parents of an affected person are always both obligate carriers (each have only one mutation). Two carriers have a 25% chance with each pregnancy to have an affected child, but do not have symptoms themselves.
A genetic consultation with a trained genetic professional is important for a complete evaluation, accurate diagnosis, as well as discussion of the benefits and limitations of testing and recurrence risk.
Genetic Testing
Clinical genetic testing for tyrosinemia can be
broken down into two categories: diagnostic testing and carrier testing.
- Diagnostic testing may be used to confirm or rule out a diagnosis in a person suspected to have the disorder. A clinical diagnosis is often made by special biochemical testing peformed on blood and/or urine samples.
- Carrier testing is typically offered after a clinical diagnosis and/or mutations have already been identified in an affected family member(s). Carrier testing usually involves DNA testing for the known familial mutations or if not available, the most common mutations. Biochemical testing cannot be used for carrier testing purposes.
Clinical genetic testing for tyrosinemia is available through an in person genetic consultation for people who are considered at risk. Use our find a genetic professional directory to locate a trained
genetic professional in your area.
Many state newborn screening programs include screening for type 1 tyrosinemia as well.
Support & More Information
More information can be
found at:
Support can be found at:
Alternative Names
- Hereditary Tyrosinemias
- Hypertyrosinemia