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Tyrosinemia

Tyrosinemia (or "Tyrosinaemia") 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 inherited in an autosomal recessive pattern. There are three types of tyrosinemia, each with distinctive symptoms and caused by the deficiency of a different enzyme. more...

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Medicines

Types

Type I tyrosinemia

Type I tyrosinemia (OMIM 276700) is the most severe form of this disorder and is caused by a shortage of the enzyme fumarylacetoacetate hydrolase (EC 3.7.1.2), encoded by the gene FAH. Fumarylacetoacetate hydrolase is the last in a series of five enzymes needed to break down tyrosine. Symptoms of type I tyrosinemia 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.

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 II tyrosinemia

Type II tyrosinemia (OMIM 276600) is caused by a deficiency of the enzyme tyrosine aminotransferase (EC 2.6.1.5), encoded by the gene TAT. Tyrosine aminotransferase is the first in a series of five enzymes that converts tyrosine to smaller molecules, which are excreted by the kidneys or used in reactions that produce energy. 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 II tyrosinemia occurs in fewer than 1 in 250,000 individuals.

Type III tyrosinemia

Type III tyrosinemia (OMIM 276710) is a rare disorder caused by a deficiency of the enzyme 4-hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27), encoded by the gene HPD. This enzyme is abundant in the liver, and smaller amounts are found in the kidneys. It is one of a series of enzymes needed to break down tyrosine. Specifically, 4-hydroxyphenylpyruvate dioxygenase converts a tyrosine byproduct called 4-hydroxyphenylpyruvate to homogentisic acid. Characteristic features of type III tyrosinemia include mild mental retardation, seizures, and periodic loss of balance and coordination (intermittent ataxia). Type III tyrosinemia is very rare; only a few cases have been reported.

Treatment

Treatment varies depending on the specific type. A low protein diet may be required in the management of tyrosinemia.

Read more at Wikipedia.org


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Drug to treat rare pediatric liver disease - Updates - Brief Article
From FDA Consumer, 3/1/02

A drug to treat hereditary tyrosinemia type I (HT-1), a rare disease causing progressive liver failure and liver cancer in young children, was approved by the FDA.

The drug, Orfadin (nitisinone) capsules, is an orphan drug. Orphan products are developed to treat rare diseases or conditions that affect less than 200,000 people in the United States. The Orphan Drug Act provides a seven-year period of exclusive marketing to the first sponsor who obtains marketing approval for a designated orphan drug.

Fewer than 100 children in the United States are affected by HT-1. Children with HT-1 rarely survive into their 20s without a liver transplant. However, for children treated early enough with Orfadin, liver failure and liver cancer occur at much-reduced rates.

Orfadin was studied in more than 180 children with a median age of 9 months at the start of therapy. When the drug was combined with a restricted diet, the four-year survival rate of children under 2 months of age at the time of diagnosis was 88 percent. Historical data for children treated with dietary restrictions alone indicates a survival rate of 29 percent for the same time period.

Orfadin must be combined with a diet restricted in the amino acids tyrosine and phenylalanine. The most common side effects of the drug were related to high tyrosine levels due to deviation from the restricted diet, as well as rare cases of mild reductions in platelet and white blood cell counts. High tyrosine levels may be toxic to eyes, skin and the nervous system.

Orfadin should be prescribed by physicians experienced in treating HT-1. Doses must be adjusted and monitored for each child according to specific tests.

Orfadin is a product of Swedish Orphan International AB, of Stockholm, Sweden, and is distributed in the United States by Rare Disease Therapeutics Inc., of Nashville, Tenn.

COPYRIGHT 2002 U.S. Government Printing Office
COPYRIGHT 2004 Gale Group

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