Tyrosinaemia Type II

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TYR II stands for Tyrosinaemia Type II. It is an inherited metabolic condition. In TYR II there is too much tyrosine in the blood. Abnormal chemicals are also found in the urine.  

TYR II affects the way your body breaks down protein. Many foods contain protein. The body needs protein for growth and repair. 

Protein is broken down into amino acids (building blocks of protein) by enzymes (which are like chemical scissors). Enzymes then further break the amino acids into smaller parts. 

Metabolism refers to the chemical processes that occur inside the cells of the body. 

In TYR II, the body lacks an enzyme called tyrosine aminotransferase (TAT). This means that the body is unable to break down an amino acid called tyrosine. As a result, tyrosine builds up in the blood. 

This disorder is rare with less than 150 cases reported so far. The disease appears to be more common in Arab and Mediterranean populations.

Signs of TYR II usually begin in the first year of life but can occur at any age. Signs may include: 

• Sensitivity to light (called photophobia) 
• Eye redness 
• Skin lesions on the hands and feet 
• Behaviour problems 
• Learning difficulties 

TYR II is diagnosed by high levels of tyrosine in the blood and abnormal chemicals in the urine. The diagnosis is confirmed by finding the mutation in the TAT gene. 

TYR II is managed with the following special diet: 

• Limited high protein foods 
• Measured amounts of tyrosine (protein) containing foods 
• A protein substitute. Sometimes extra phenylalanine is needed 
• Low protein foods 

 These foods are high in tyrosine (protein) and must be avoided: 

• meat 
• fish 
• eggs 
• cheese 
• bread 
• pasta 
• nuts 
• seeds 
• soya 
• Quorn  
• tofu 

In babies, a restricted amount of tyrosine (protein) is given from breast milk or measured amounts of infant formula. The amount given will be monitored regularly by your specialist metabolic dietitian. 

Protein substitute is essential for metabolic control. It will help to meet your child’s protein, energy, vitamin and mineral requirements. It is available on prescription. 

There are many low protein foods. These include fruit, many vegetables and low protein foods such as bread and pasta which are available on prescription. They provide a source of energy and variety in the diet. 

During any childhood illness, catabolism or protein breakdown occurs, causing blood tyrosine levels to increase. It is important to continue with the usual diet as much as possible.  

This condition is monitored by: 

• Frequent blood tests to check tyrosine and phenylalanine  
• Height and weight 
• Developmental checks 

Diet is adjusted according to age, weight and blood tests. 

Take Home Messages: 

• TYR II is a serious inherited metabolic disorder that can lead to eye and skin problems and affect intellectual ability. 

• Damage can be prevented with a diet low in tyrosine and a protein substitute 
• Remember to give the correct amount of protein exchanges and protein substitute as prescribed by your metabolic centre 

Helpful Hints: 

• Always ensure you have a good supply of your dietary products and medicines and that they are in date. 

• Your dietary products and medicines are prescribed by your GP. These are obtained via a pharmacy or home delivery. 
• Always ensure you have sufficient blood testing equipment and send samples on a regular basis. 
• Medications to control fever should be given as normally recommended – always keep supplies available. 

Humans have chromosomes composed of DNA 

Genes are pieces of DNA that carry the genetic instruction. Each chromosome may have several thousand genes. The word mutation means a change or error in the genetic instruction. 

We inherit particular chromosomes from the egg of the mother and sperm of the father. 

The genes on those chromosomes carry the instruction that determines characteristics, which are a combination of the parents. 

TYR II is an inherited condition. There is nothing that could have been done to prevent your baby from having TYR II. 

Everyone has a pair of genes that make the tyrosine aminotransferase enzyme. In children with TYR II, neither of these genes works correctly. These children inherit one non-working TYR II gene from each parent. 

Parents of children with TYR II are carriers of the condition. Carriers do not have TYR II because the other gene of this pair is working correctly. 

When both parents are carriers, in each pregnancy the risk to the baby is as follows: 

• 25% chance (1 in 4) of TYR II 
• 50% chance (1 in 2) for the baby to be a carrier of TYR II 

• 25% chance (1 in 4) for the baby to have two working genes and neither have TYR II or be a carrier 

References are available on request. Please contact Helen Morris by phoning 0845 241 2173 or emailing contact@metabolicsupportuk.org [Resource Library No: TAP021].