TYR overview

Types of TYR and causes

Symptoms of TYR

TYR dietary management and treatment

Living with TYR

TYR overview

What is Tyrosinemia (TYR)?

Tyrosinaemia (TYR) is a hereditary metabolic disorder diagnosed through newborn screening in some forms. People with TYR cannot properly metabolise the amino acid tyrosine. When tyrosine is not broken down correctly by the liver, toxic by-products build up in the body. If untreated, this can cause developmental delay, liver and kidney problems, and neurological complications.

There is no cure, but TYR can be managed with a low-protein diet and specialised medical nutrition, which help control blood tyrosine levels and prevent complications.

Types of TYR and causes

TYR is an inherited genetic condition that is present from birth. Every cell in the body contains DNA, half inherited from the mother and half from the father. DNA carries genes that provide instructions for how the body functions. In TYR, both parents usually carry a changed (mutated) gene that affects one of the enzymes responsible for breaking down tyrosine. 

If a child inherits the changed gene from both parents, tyrosine and its by-products accumulate in the body, leading to symptoms. When both parents are carriers, there is a 1 in 4 (25%) chance with each pregnancy that their child will have TYR. When both parents are carriers, there is a 1 in 4 (25%) chance with each pregnancy that their child will have PKU. Because this gene change is uncommon, the overall chance of a child being born with TYR is low.

Types of Tyrosinaemia

There are three main types of TYR, each caused by a different enzyme deficiency:

• Type I (TYR I): The most severe form, which can lead to liver and kidney failure. Treatment may include a low-protein diet, medical nutrition, medication, and sometimes a liver transplant.
• Type II (TYR II): Affects the eyes and skin, and can cause light sensitivity, eye pain, and skin lesions, along with possible learning difficulties.
• Type III (TYR III): A rare form that mainly affects the nervous system, potentially causing seizures and developmental delay.

Newborn screening can detect tyrosinaemia type I, allowing early treatment. Types II and III are not identified through screening and are usually diagnosed after symptoms appear.

Symptoms of TYR

Symptoms of TYR vary depending on the type but can include

• growth delay
• fatigue
• weakness
• enlarged liver and spleen
• neurological problems
• seizures
• skin or eye issues (particularly in TYR II)

Without treatment, liver failure, kidney damage, and developmental problems may occur.

TYR dietary management and treatment

Managing TYR requires lifelong adherence to a strict low-protein diet, with medically prescribed amino acid supplements to ensure adequate nutrition while controlling tyrosine levels. Early and consistent treatment helps prevent serious complications and supports normal growth and development.

The role of Foods for Special Medical Purposes and protein substitutes

A low-protein diet is essential for people with tyrosinaemia (TYR) and other metabolic disorders. The diet is specifically designed to limit the intake of tyrosine, helping to keep blood levels within a safe range and preventing the harmful effects of its accumulation. The TYR diet mainly consists of protein-restricted foods, supplemented with specialised amino acid preparations to ensure the body receives enough of the other essential amino acids needed for growth and health. Strict adherence to this diet is crucial for normal development and long-term wellbeing.

Beyond adhering to a low-protein diet, TYR is managed with a variety of supplementary amino acids and protein substitutes that supply essential nutrients according to tyrosine tolerance levels and nutritional needs.

Medical intervention

Medical treatments for TYR may include nitisinone (NTBC), a medication that blocks the formation of toxic tyrosine by-products. This treatment is effective in reducing complications and improving quality of life in people with tyrosinaemia type I (TYR I). In some cases, a liver transplant may be necessary and can lead to excellent outcomes and improved long-term health.

TYR diet and foods to avoid

The TYR diet focuses on limiting the intake of both tyrosine and phenylalanine. This involves eating mainly low-protein foods, such as fruits, most vegetables, and specially manufactured low-protein products and protein substitutes that are free from tyrosine and phenylalanine. Tracking tyrosine intake carefully is essential to maintain safe levels.

Foods high in protein—and therefore high in tyrosine and phenylalanine—should be avoided. These include meat, fish, eggs, dairy products, nuts, and soya.

Living with TYR

Living with TYR requires ongoing commitment to a low-protein diet and regular medical check-ups. Ongoing support from a dietitian specialising in metabolic disorders is essential to ensure the correct amount of protein substitute is prescribed and that nutritional needs are met.

TYR presents different challenges throughout life. The needs and experiences of someone with TYR will vary from infancy through adulthood. For example, babies need a special low-tyrosine infant formula alongside breast milk or standard formula; children learn to manage dietary restrictions; teenagers may face social pressures; and adults must balance dietary control with the demands of daily life.

Regular follow-ups with a doctor and dietitian are vital to ensure effective management as the body’s needs change over time. By following a low-protein diet and adhering to medical guidance, people with TYR can live healthy, active, and fulfilling lives.

For ideas and inspiration, visit our low protein recipes page for a selection of delicious meals.