A metabolic genetic disease characterized by abnormally high levels of amino acid tyrosine in blood (hypertyrosinemia) and urine (tyrosinuria) due to deficiency of an enzyme called fumarylacetoacetic hydrolase, the last enzyme in the tyrosine pathway. Tyrosinemia type I is inherited as an autosomal recessive disorder.
The disease causes cirrhosis of the liver before 6 months of age and, untreated, leads to death from liver failure. A more chronic form is characterized by progressive cirrhosis of the liver, a renal syndrome (with loss of phosphate into the urine causing rickets of renal origin and growth failure) and recurring neurologic crises. Untreated, it usually leads to death by age 10 from liver failure or hepatocarcinoma (cancer of the liver ).
A diet with a special formula that lacks the amino acids phenylalanine and tyrosine can slow the inevitable progression of the disorder. Liver transplantation provides a better long-term outcome than diet alone. A drug called NTBC that inhibits the tyrosine metabolic pathway can reverse the symptoms of tyrosinemia and help the liver and kidney tissue to return to normal.
The usual treatment of tyrosinemia today is NTBC plus diet. This permits greater than 90% survival. Infants with tyrosinemia and cancer of the liver need a liver transplant to survive.
- Tyrosinemia type II
A metabolic genetic disease due to deficiency of the enzyme tyrosine transaminase. The disease is characterized by the deposition of crystals of tyrosine in the skin and eyes. Thickened areas (keratoses) on the palms and soles become painful and ulcers develop in the cornea. There is often mental retardation in tyrosinemia type II. It is […]
- Tzanck test
The examination of fluid from a bulla (a blister) in search of Tzanck cells characteristic of varicella (chickenpox), herpes zoster, herpes simplex, and pemphigus vulgaris. Named for a Russian dermatologist Arnault Tzanck (1886-1954).
- Tumor, ear
Benign (noncancerous) bumps on the pinna of the ear (the external ear) or within the external ear canal. Most of these lumps and bumps are just harmless cysts and tumors. However, some of the bumps are bony overgrowths (known as exostoses or osteomas). If they are large and interfere with hearing, they can be surgically […]
- Tumor, carcinoid
surgery (to take out the cancer); radiation therapy (using high-dose x-rays to kill the cancer cells); biological therapy (using the body’s natural immune system to fight the cancer); and chemotherapy (using drugs to kill cancer cells). Carcinoid tumors are considered a type of endocrine tumor since they secrete a hormone (serotonin). They can occur as […]
- Tumor suppressor gene
A protective gene that normally limits the growth of tumors. When a tumor suppressor gene is mutated (altered), it may fail to keep a cancer from growing. BRCA1, an example of a tumor suppressor gene, was the first breast cancer gene to be identified; mutated forms of this gene are responsible for some cases of […]