Tyrosinemia Type I. Metabolic disorder

Tyrosinemia type I is a metabolic disorder in which an enzyme critical for the breakdown of the amino acid tyrosine is missing. This allows abnormal amounts of tyrosine to accumulate in the body and act like a poison causing damage, especially in the liver.

Tyrosinemia is an inherited disorder of chromosome 15 which affects males and females equally. In the United States it occurs in 1 of every 100,000 babies born. In one region of Quebec, Canada, the disorder occurs in 1 of every 1,850 babies born, because many people there carry the gene for it. It is an autosomal recessive disorder, meaning that an infant must receive two copies of the defective gene for the disorder, one from each parent, in order to develop tyrosinemia type I.

Symptoms
Different babies may have different symptoms of tyrosinemia type I. Some may show symptoms within the first few months of life (acute form); others may develop symptoms around 1 year of age (chronic form). Some symptoms may be:

Acute form
• poor appetite and failure to grow normally
• vomiting
• diarrhea, bloody stools
• a cabbage-like odor
• jaundice (yellow skin and whites of eyes)
• swollen liver
• irritability
• lethargy (overwhelming tiredness)

Chronic form
• cirrhosis of the liver
• pain, numbness, and tingling in parts of the body (polyneuropathy)
• kidney problems
• episodes of intense abdominal pain
• heart muscle weakness

Both forms of tyrosinemia type I may cause the liver to shut down (liver failure) and/or develop liver cancer.

Diagnosis
The symptoms the infant has, especially the liver problems, usually suggest a diagnosis of tyrosinemia type I. Blood tests of liver function will abnormal. A urine test for succinylacetone is done; if it is present, it confirms the diagnosis.

Treatment
There are three ways to treat the disorder.

1. Diet
The first thing done when a baby is diagnosed with tyrosinemia type I is to restrict the amount of tyrosine and another amino acid, phenylalanine, in the baby's food. There are special baby formulas that can meet this need. A dietary specialist helps families learn which foods are permitted and which are not.

2. Medication
Nitisinone (Orfadin, sometimes called NTBC) reduces the toxic effects of tyrosine in the body. The medication, when used along with the dietary restrictions, has been successful in reducing the symptoms of tyrosinemia type I and thus allowing children to be healthy and grow normally.

3. Liver transplant
In the past, a child with tyrosinemia type I would almost certainly need a liver transplant. Now, thanks to nitisinone, surgery is reserved for severe cases of liver damage or cancer. Transplantation carries many risks with it, including the rejection of the new liver by the body.

Overall, early diagnosis and treatment provide the greatest benefits for the child with tyrosinemia type I.

Sources
- The Pediatrician's Guide to Tyrosinemia Type I. National Organization for Rare Disorders, 2001.
- Roth, Karl S. "Tyrosinemia." eMedicine 03 Apr 2006 09 Feb 2007 .