Tyrosinaemia Type 1

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In HT1 there is too much succinyl acetone and tyrosine in the blood and too much succinyl acetone in the urine. 

HT1 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 HT1, the body lacks an enzyme called fumarylacetoacetate hydrolyase. This means that the body is unable to break down an amino acid called tyrosine. As a result, a harmful chemical called succinyl acetone builds up in the blood. 

When untreated HT1 can cause liver failure and lead to liver cancer. Some children may have lower school achievement. 

HT1 is estimated to affect approximately 1 in every 100,000 births. However, reports have ranged between 1 in every 1,846 to 1 in every 781,144. The incidence is higher in Quebec, Canada and in Asian children in the West Midlands of the UK, and in North Africa and the Middle East. 

Most babies become unwell in the first few months of life. Symptoms include: 

• Poor weight gain 

• Liver failure 

Other children have a gradual onset of symptoms such as: 

• Large liver 
• Rickets 
• Kidney problems 

Some children may develop liver cancer. 

HT1 is a serious inherited metabolic disorder that can lead to severe liver problems. 

Damage can be prevented with nitisinone, a diet low in tyrosine and a protein substitute. 

It is important that blood levels of tyrosine and phenylalanine are regularly checked. 

Remember, during illness, it is imperative that nitisinone is still given. 

HT1 is diagnosed by high levels of succinyl acetone in the blood and urine. 

HT1 is managed with a drug called nitisinone. This medication is also called NTBC. Your child will start taking NTBC/nitisinone as soon as possible. 

NTBC/nitisinone helps prevent liver and kidney damage and lowers the risk of liver cancer 

HT1 is managed with the following 

• special diet and medication: 

• Nitisinone medication 
• 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 baby’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. The drug nitisinone should be given at all times including illness. 

This condition is monitored by: 

• Frequent blood tests to check tyrosine, phenylalanine and other chemical levels 
• Height and weight 
• Developmental checks 

Diet and medication are adjusted according to age, weight and blood tests. 

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. 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. 

Everyone has a pair of genes that make the fumarylacetoacetate hydrolase enzyme. In children with 

HT1, neither of these genes works correctly. These children inherit one non-working HT1 gene from each parent. 

Parents of children with HT1 are carriers of the condition. Carriers do not have HT1 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 HT1 
• 50% chance (1 in 2) for the baby to be a carrier of HT1 

• 25% chance (1 in 4) for the baby to have two working genes and neither have HT1 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: TAP020].