Hereditary tyrosinemia type 1

Hereditary tyrosinemia type 1 is one of the most common recessive genetic disorders in some regions of Québec:

• Saguenay–Lac-Saint-Jean
• Charlevoix
• Haute-Côte-Nord

Hereditary tyrosinemia type 1 is a liver disease caused by an enzyme deficiency, in this case the enzyme fumarylacetoacetate hydrolase (FAH). This enzyme is necessary to break down tyrosine, an amino acid present in several animal and plant proteins contained in food. For example, meat, dairy products, fish, eggs, legumes, nuts and tofu contain tyrosine.

Because of FAH deficiency, metabolic waste cannot be broken down. It then accumulates in the body, damaging the liver, kidneys and central nervous system (nerves).

A child with untreated hereditary tyrosinemia type 1 generally presents with the following symptoms:

• failure to thrive (poor growth)
• vomiting
• bleeding (such as nose bleeds)
• in some children: irritability, pains in the limbs in the first few months of life
• progressive deterioration of the kidneys and especially the liver.

Treatment for hereditary tyrosinemia type 1 includes a combination of a low-tyrosine diet and the medication nitisinone, or NTBC.

• The diet is low in animal and plant proteins. People with hereditary tyrosinemia type 1 must follow this diet throughout their lives. They can obtain low-tyrosine products free of charge under a program funded by the Ministère de la Santé et des Services sociaux (MSSS).
• NTBC is a medication that acts on the digestion of tyrosine and prevents the accumulation of metabolic waste that can damage the liver, kidneys and nerves. 

If this disorder is left untreated, children die most often in their first years of life from cirrhosis (liver disease) or liver cancer.

Treatment combining NTBC and a low-tyrosine diet helps manage the progression of hereditary tyrosinemia type 1, but does not cure it. To date, children following this treatment have developed normally. However, the long-term effects of NTBC are not yet known because this medication has been available only since 1994.

If the child’s health declines despite this treatment, a liver transplantation may be required. The transplantation helps cure the disease, but the child must take a medication for the rest of their life to ensure the long-term success of the transplantation

Teams of professionals in the health and social services system provide therapy and care for affected children. These teams are composed of geneticists, pediatricians, dietitians and nurses.

Hereditary tyrosinemia type 1 is a recessive genetic disorder.

For more information, see the page Transmission d’une maladie héréditaire récessive.

Carrier screening

It is impossible to prevent hereditary tyrosinemia type 1 in newborns who have received a copy of the defective gene from each of their two parents. However, the defective gene responsible for this disorder can be detected through a simple, quick and inexpensive screening test.

The Ministère de la Santé et des Services sociaux and the Centre intégré universitaire de santé et de services sociaux (CIUSSS) du Saguenay–Lac-Saint-Jean offer screening tests to detect the carriers of this disorder.

These tests are offered to anyone who:

• is over the age of 18 years
• wants children
• has at least one biological grandparent born in one of the following three regions:
  • Saguenay–Lac-Saint-Jean
  • Charlevoix
  • Haute-Côte-Nord

In these regions, 1 in 1500 newborns has hereditary tyrosinemia type 1. Furthermore, 1 in 19 people carries the defective gene responsible for this disorder.

To learn more about carrier screening, see the page Offre de tests de porteur pour 4 maladies héréditaires récessives chez les personnes originaires des régions du Saguenay–Lac-Saint-Jean, de Charlevoix et de la Haute-Côte-Nord.

Neonatal screening

Hereditary tyrosinemia type 1 is one of the diseases screened within a few hours of the birth of all newborns in Québec. This screening is provided under the Québec Neonatal Screening Program. Thanks to screening, an affected child can be treated quickly and maintain a good quality of life. Early treatment also allows the family to better handle their child’s disorder.

For help or more information on hereditary tyrosinemia type 1, please visit the following links:

• Groupe d’aide aux enfants tyrosinémiques du Québec 
• Corporation de recherche et d’action sur les maladies héréditaires