Tyrosinemia type I (the term “tyrosinemia” refers to tyrosinemia type I*) is an inherited, genetic disorder. Tyrosinemia occurs due to a deficiency of the enzyme fumarylacetoacetic hydrolase (FAH). A deficiency of FAH interferes with the breakdown of an amino acid called tyrosine. Tyrosine is one of 20 amino acids that make up the protein that is found in our bodies and the food we eat. Digestion breaks protein down into individual amino acids. The body can convert another amino acid, phenylalanine, to tyrosine.
If tyrosinemia is not treated, toxins such as succinylacetone build up and cause serious medical problems in the liver, kidneys and brain. If tyrosinemia type 1 is not diagnosed early and treated, most infants will die from liver failure. A milder form may lead to liver disease, kidney problems, rickets, growth failure and neurologic problems.
Finding out that your child has tyrosinemia can be overwhelming. Fortunately, nutrition management is available to help prevent many of these problems. Take comfort in knowing that your metabolic healthcare team can provide you with the best advice to help manage tyrosinemia.
*There are other types of tyrosinemia (types II and III). These have different, less severe symptoms and different treatment approaches.
Incidence, Genetics and Newborn Screening
Tyrosinemia is a rare disorder that is occurs in about 1 in every 100,000 births in the United States and Europe. Tyrosinemia occurs more often in Norway, Finland and in the province of
Tyrosinemia is a “recessive disorder.” In recessive disorders, both the mother and father are “carriers,” and they do not have any symptoms of the disorder (see diagram). With each pregnancy there is a 1 in 4 (25%) chance that the infant will be affected. A genetic counselor can help explain the inheritance of tyrosinemia and the risks to future infants.
Tyrosinemia can be screened for at birth through a simple blood test. For more details on newborn screening (NBS) in the US, visit https://newbornscreening.hrsa.gov/your-state; for information on NBS in Canada, see https://www.raredisorders.ca/.
There is no cure for tyrosinemia, but it can be managed with a modified diet, medication, and special medical formulas specifically designed for persons with tyrosinemia. The modified diet for tyrosinemia is low in tyrosine (TYR) and phenylalanine (PHE). It is important that an individual with tyrosinemia remains on treatment for life. Another medical option for some patients with tyrosinemia is a liver transplant. Your metabolic physician will discuss the options that are best.
A medical formula is a very important part of the diet for tyrosinemia. The protein source in tyrosinemia medical formulas is individual amino acids, but TYR and PHE are left out. This allows a person with tyrosinemia to get enough protein without the parts of protein that can be harmful. Medical formulas may also provide calories, vitamins and minerals the body needs for normal growth.
To provide just enough TYR and PHE that a person with tyrosinemia needs, a limited amount of natural protein-containing foods are allowed in the diet. For infants, breast milk or regular infant formula is given in precise amounts. As the baby grows and can eat solid foods, the breast milk or regular infant formula will be removed from the diet and the TYR and PHE will come from foods instead.
Since all foods with protein contain TYR and PHE, individuals with tyrosinemia must limit their intake of foods high in protein. These include milk and dairy products, meat, poultry, fish, eggs, beans, nuts and peanut butter. Regular breads and pastas may be allowed, but special low-protein versions of these foods are often used instead to allow for more choices in the diet and less concern for eating too much protein. Vegetables and fruit are allowed in small amounts. Foods are usually weighed or measured to ensure that extra protein is not eaten.
Nutricia North America provides a range of medical formulas as well as low protein foods. Please contact us for more information. Your dietitian will help you decide which products are best.
Nitisinone is a drug designed to help manage tyrosinemia. It blocks the formation of fumarylacetoacetate and succinylacetone. Studies of the drug have had good results. Your metabolic physician will discuss nitisinone with you.
|The Network of Tyrosinemia Advocates (N.O.T.A.)|
|Genetics Home Reference - Tyrosinemia|
|NewbornScreening.Info (Screening Technologies and Research in Genetics)|
|Newborn Screening in Your State (US)|
|Canadian Organization for Rare Disorders|
Nutricia North America would like to thank Beth Ogata, MS, RD, University of Washington, Seattle for her consultation.
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