Tyrosinemia (TYR) overview

What is Tyrosinemia (TYR)?

Tyrosinemia, abbreviated as TYR, is a rare hereditary metabolic disorder often diagnosed via neonatal screening. People with TYR cannot metabolize the amino acid tyrosine (Tyr). When the liver does not correctly process tyrosine, the by-products of the malfunctioning protein breakdown process accumulate to toxic levels in the body. Left untreated, this toxic build-up can lead to severe health complications such as developmental delays, neurological challenges, and permanent brain damage. There is no cure for TYR. However, the disorder can be managed with a tailored low-protein diet, and tyrosine blood levels can be controlled, preventing serious health complications and enabling a better quality of life.

Types of Tyrosinemia (TYR) and causes

TYR is an inherited disorder and is present from birth. Every cell contains DNA, half of which comes from the mother and half from the father. DNA contains genes that give instructions to the body; sometimes, genes contain an error.

If both parents are carriers of this genetic anomaly, that affects the which degrades tyrosine, there is a 1 in 4 (25%) chance with each pregnancy that their child will have TYR. However, because the gene change is uncommon, the overall chance of a child being born with TYR is low.

Tyrosinemia is characterised by different enzymes malfunctioning in each type, leading to the body's inability to break down tyrosine. This results in the accumulation of tyrosine and its harmful by-products, detectable in blood or urine.

There are three main types of tyrosinemia:

  • Type I Tyrosinemia (TYR1)*: This is the most severe form and can lead to liver and kidney failure. It requires a combination of a low-protein diet, specialised medical nutrition, medicine and sometimes a liver transplant.
  • Type II Tyrosinemia (TYR2)**: This type mainly affects the eyes and nervous system, potentially leading to light sensitivity and intellectual disabilities.
  • Type III Tyrosinemia (TYR3)**: This rare form primarily affects the nervous system and can lead to intellectual disabilities and epilepsy.

*Neonatal screening helps detect hereditary disorders such as Tyrosinemia type I as early as possible, allowing for prompt dietary treatment.
**Tyrosinemia types II and III are not detected through neonatal screening, requiring hospital investigations when symptoms appear. Once diagnosed, low-protein dietary therapy begins.

Symptoms of Tyrosinemia (TYR)

Without dietary treatment, symptoms of TYR can be severe and varied. Common symptoms include:

  • Intellectual disabilities
  • Enlarged liver and spleen
  • Growth delays
  • Fatigue and weakness
  • Epileptic seizures
  • Increased risk of liver cancer
  • Skin and eye problems (especially in TYR2)

The importance of recognising early signs for timely treatment is crucial. Potential complications include liver failure, kidney issues, and developmental delays.

TYR dietary management and treatment

Managing TYR requires lifelong adherence to a strict low-protein diet and the intake of medically prescribed amino acid supplements.

The role of Food for Special Medical Purposes and protein substitutes

A low-protein diet is crucial for people with TYR and other metabolic disorders. The diet is specially designed to limit the intake of tyrosine, which helps keep levels low in the blood and prevent the harmful effects of their accumulation. The diet consists mainly of protein-restricted foods, supplemented with specialised amino acid preparations to ensure the body receives enough of the other essential amino acids. Precisely following this diet is critical for proper development.

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 interventions for TYR include medications like nitisinone (NTBC) that block production of toxic tyrosine metabolites. These medications are effective in reducing complications and improving quality of life. In severe Type 1 Tyrosinemia cases, liver transplantation may be considered necessary, with successful outcomes and improvements in patient well-being.

TYR diet and foods to avoid

The TYR diet focuses on limiting tyrosine and phenylalanine intake. This means consuming a diet mainly of low-protein natural foods such as fruits, vegetablesand specially manufactured low-protein products, and protein substitutes free from tyrosine and phenylalanine. It is crucial to track tyrosine intake diligently.

A comprehensive list of foods high in tyrosine should be avoided, including those rich in protein like meat, fish, dairy, and nuts.

Living with Tyrosinemia (TYR)

Living with TYR requires constant vigilance and commitment to a low-protein diet supported by regular medical check-ups. It's essential to have ongoing support from a dietician specialising in metabolic disorders to help manage a low-protein diet and ensure the correct amount of protein substitute is prescribed to ensure protein requirements are still met.

TYR presents different challenges throughout life. As a baby, child, teenager, and adult, the needs and experiences of a person diagnosed with TYR will vary. For example, babies need a special infant feed, in addition to breast milk and/or standard infant formula, children must learn to cope with dietary restrictions, teenagers may face social pressure, and adults must manage their diet while living an independent, busy lifestyle.

Regular check-ups with a doctor and/or dietitian are crucial to ensure ongoing effective management of the disorder as the body's needs change over time. By following a low-protein diet and appending medical protocols, people with TYR can live healthy and full lives. For inspiration, delicious low-protein recipes are available

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Disclaimer
The opinions/views presented are solely those of the person themselves and do not necessarily represent those of Nutricia. This article does not constitute medical advice or professional services. Consult your doctor and dietitian before making any changes to your diet or protein intake to ensure the right nutrition to support your unique needs.

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