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Tyrosinemia is a genetic disorder characterized by elevated blood levels of the amino acid tyrosine, a building block of most proteins. Tyrosinemia is caused by the shortage (deficiency) of one of the enzymes required for the multistep process that breaks down tyrosine. If untreated, tyrosine and its byproducts build up in tissues and organs, which leads to serious medical problems.
There are three types of tyrosinemia, each with distinctive symptoms and caused by the deficiency of a different enzyme. Type I tyrosinemia is the most severe form of this disorder and is caused by a shortage of the enzyme fumarylacetoacetate hydrolase. Symptoms usually appear in the first few months of life and include failure to gain weight and grow at the expected rate (failure to thrive), diarrhea, vomiting, yellowing of the skin and whites of the eyes (jaundice), cabbagelike odor, and increased tendency to bleed (particularly nosebleeds). Type I tyrosinemia can lead to liver and kidney failure, problems affecting the nervous system, and an increased risk of liver cancer.
Type II tyrosinemia is caused by a deficiency of the enzyme tyrosine aminotransferase. This form of the disorder can affect the eyes, skin, and mental development. Symptoms often begin in early childhood and include excessive tearing, abnormal sensitivity to light (photophobia), eye pain and redness, and painful skin lesions on the palms and soles. About half of individuals with type II tyrosinemia are also mentally retarded.
Type III tyrosinemia is a rare disorder caused by a deficiency of the enzyme 4-hydroxyphenylpyruvate dioxygenase. Characteristic features include mild mental retardation, seizures, and periodic loss of balance and coordination (intermittent ataxia).
About 10 percent of newborns have temporarily elevated levels of tyrosine. In these cases, the cause is not genetic. The most likely causes are vitamin C deficiency or immature liver enzymes due to premature birth.
Worldwide, type I tyrosinemia affects about 1 person in 100,000. This type of tyrosinemia is much more common in Quebec, Canada. The overall incidence in Quebec is about 1 in 16,000 individuals. In the Saguenay-Lac St. Jean region of Quebec, type 1 tyrosinemia affects 1 person in 1,846.
Type 2 tyrosinemia occurs in fewer than 1 in 250,000 individuals. Type 3 tyrosinemia is very rare; only a few cases have been reported.
Mutations in the FAH, HPD, and TAT genes cause tyrosinemia.
In the liver, tyrosine is broken down in a five-step process to harmless molecules that are either excreted by the kidneys or used in reactions that produce energy. Mutations in the FAH, HPD, or TAT gene cause a shortage of one of the enzymes in this multistep process. The resulting enzyme deficiency leads to a toxic accumulation of tyrosine and its byproducts, which can damage the liver, kidneys, nervous system, or other tissues.
This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. Most often, the parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but do not show signs and symptoms of the condition.
'''Tyrosinemia''' is an error of metabolism, usually inborn, in which the body can not effectively break down the amino acid tyrosine, found in most animal and plant proteins. Tyrosinemia is caused by an absence of the enzyme fumarylacetoacetate hydrolase (FAH) which is essential in the metabolism of tyrosine, which takes place primarily in the liver. The absence of FAH leads to an accumulation of toxic metabolic products in various body tissues, which in turn results in progressive damage to the liver and kidneys. Treatment varies depending on the specific type. A low protein diet may be required in the management of tyrosinemia. [ Read More ]
National Library of Medicine - The synonyms of Tyrosinemia 11, a summary and major features.
Tyrosinemia - For all people interested in connecting with others with this disease.
NORD: Tyrosinemia, Hereditary - Offers the synonyms, a general discussion and further resources.