Guidance

Hereditary tyrosinaemia type 1 (HT1): detailed information

Published 29 September 2025

Applies to England

In this information, the word ‘we’ refers to the NHS service that provides screening.

This information is for parents if their baby is suspected of having hereditary tyrosinaemia type 1 (HT1) or has been diagnosed with HT1 following their newborn blood spot screening test. It will help you and your healthcare professionals to talk through the next stages of your baby’s care.

1. About tyrosinaemia

Hereditary tyrosinaemia (pronounced tie-roh-sin-ee-me-uh) type 1 (HT1), is a rare but treatable inherited metabolic disorder that prevents the normal breakdown of protein. Babies with the condition inherit 2 faulty copies of the gene for HT1, called FAH, one from each parent.

When we eat, our body breaks down protein in food into smaller parts called amino acids. Enzymes, which are chemicals found naturally in our body, then break down the amino acids further so they can be used.

In HT1, an enzyme called fumarylacetoacetate hydratase is missing, which leads to problems breaking down an amino acid called tyrosine. This causes a high level of tyrosine and a build-up in the body of a harmful substance called succinylacetone (SUAC).

If not detected through newborn screening, babies with HT1 may show signs such as:

• failure to gain weight
• jaundice (yellowing of the skin and eyes)
• diarrhoea and vomiting
• fever
• abdominal swelling caused by an enlarged liver
• bleeding and bruising

If untreated HT1 can cause long-term health problems, including liver and kidney disease.  Newborn screening allows an early diagnosis and treatment which can improve their long-term outcome.

2. Screening and diagnosis of HT1

Newborn blood spot

When your baby was about 5 days old, your midwife or health professional took some blood from your baby’s heel for their newborn blood spot screening test. The test measures the amount of SUAC in the blood. A high level of SUAC suggests your baby may have HT1. This is called a screen positive or condition suspected result, which you can read more about at NHS screening - NHS (www.nhs.uk)

Diagnostic tests

If your baby has a screen positive result, you will be contacted by either your local hospital or a metabolic centre and will be seen on the same day. You will be seen by the specialist team (metabolic doctor, dietitian and nurse specialist) at the metabolic centre. Blood and urine tests will be carried out to confirm if your baby has HT1 and a sample will be taken for genetic testing, with your consent.

Although your baby may not seem unwell, many screen positive babies will already have other biochemical changes. You will need to wait about seven working days to get all the diagnostic test results. However, management will be started immediately based on the screening result and some initial blood test results, as HT1 can be life threatening if left untreated. It may take several months to get the genetic test result.

Some babies may have diagnostic test results showing they do not have HT1. These results are called a false positive and treatment for HT1 will not be needed. Your metabolic team will discuss if any further testing is needed to exclude any other conditions.

3. Treatment

If your baby does have HT1, the metabolic team will:

• explain the condition in detail and answer any questions you might have

• start your baby on medical treatment which includes:

  • a medicine called nitisinone which helps to prevent the build-up of SUAC in the blood
  • a restricted protein feed plan to limit intake of the amino acids, tyrosine and phenylalanine
• teach you how to do blood spot tests on your baby when you are at home. These will be posted to the metabolic laboratory to monitor the tyrosine and phenylalanine levels in the blood. These results are used to decide the amount of protein to give your baby
• provide you with written information and contact details for the metabolic team
• arrange regular out-patient follow-up appointments with the metabolic team who will see you regularly throughout your child’s life.

The aim of the restricted protein feed plan is to prevent the build-up of tyrosine and harmful substances, mainly SUAC. Your baby will need to be on two different types of feed to provide all the nutrition they need for growth and development.

These are:

• a limited daily volume of breastmilk feeds (breast feeds or expressed breast milk) or infant formula
• a tyrosine and phenylalanine free infant formula

Supplements may also be needed.

The level of tyrosine and phenylalanine in your baby’s blood will be monitored by weekly tests during the first year. Your metabolic dietitian will advise you on how much of each feed to give based on these blood test results and your baby’s weight. Following the dietetic instructions is very important for your baby’s health.

The blood levels of SUAC and dose of nitisinone will also be monitored. The frequency of monitoring will depend on previous results and will be decided by the metabolic team.  

Your GP will be asked to prescribe the tyrosine and phenylalanine free infant formula and the phenylalanine supplement. You will continue to have regular appointments with a metabolic dietitian who will advise on dietary management throughout the various stages of childhood.

4. Long-term outlook

With regular medication, good dietary treatment and well controlled blood tyrosine and SUAC levels, most children with HT1 have a very good outcome and avoid long-term health problems.

5. Your other children

At-risk siblings

Children from the same parents have a 1 in 4 chance of also having HT1. If you have other children, they may be at risk of HT1 even if they have never shown any symptoms. It is therefore very important to get them tested if they have never been screened for HT1. Your metabolic team can arrange this testing.

Future children

A new baby from the same parents will also have a 1 in 4 chance of having HT1. If you become pregnant again, you should tell your midwife and GP there is a family history of HT1. You should also inform your metabolic team early in the pregnancy.

The metabolic team will write a birth plan for you. This will include advice on an early screening test for your new baby, which should be taken between 24 and 48 hours after birth. This blood test will be taken in addition to the routine newborn blood spot screening test. The team will give you the birth plan and share it with your local midwifery and medical teams.

You should notify your metabolic team once you have given birth so they can ensure the correct blood tests are taken and sent to the screening laboratory without delay.

6. Confidentiality

The NHS screening programmes use personal information from your NHS records to invite you for screening at the right time and to ensure you receive high quality care and to improve the screening programmes. Find out more about how your information is used and protected, and your options at www.gov.uk/phe/screening-data.

7. More information and support

The metabolic team will be happy to discuss any queries you may have.

Further information can be found from Metabolic Support UK at www.metabolicsupportuk.org. The Metabolic Support UK team can be contacted at:

• Phone: 0845 241 2173 or 0800 652 3181

• Email: contact@metabolicsupportuk.org

The British Inherited Metabolic Diseases Group (BIMDG) website has a booklet about HT1 at www.bimdg.org.uk/education/temple  

NHS.UK has information about newborn blood spot screening at www.nhs.uk/conditions/baby/newborn-screening/blood-spot-test.