Hereditary tyrosinaemia: screening and treatment

When we eat protein, the body breaks it into smaller parts called amino acids. Enzymes then break the amino acids down further so they can be used. In HT1, an enzyme called fumarylacetoacetate hydratase is missing, so the body cannot process an amino acid called tyrosine properly.

The result is a high level of tyrosine and a build-up of a harmful substance called succinylacetone, or SUAC. This is what the newborn blood spot test measures. The condition is caused by changes in both copies of the FAH gene.

This page covers type 1, because it is the form that UK newborn screening looks for and the one described in the NHS England screening information. Other forms of tyrosinaemia exist but are not covered here.

Screening aims to find HT1 before a baby becomes unwell, but some babies are already ill when the result comes back. NHS England lists the signs that may appear if HT1 is not detected: failure to gain weight, jaundice, diarrhoea and vomiting, fever, a swollen tummy caused by an enlarged liver, and bleeding and bruising.

If a baby shows these signs, particularly poor weight gain with yellowing of the skin and eyes, or unusual bleeding, they need prompt medical assessment. Call NHS 111, or 999 if a baby is very unwell, floppy or difficult to wake.

The NHS says the newborn blood spot test checks for 10 rare but serious conditions, and HT1 is one of them. A midwife or health professional pricks the baby's heel, usually at 5 days old, and collects a few drops of blood on a card. Parents get results by the time the baby is 6 weeks old, or sooner depending on the result.

The test is recommended for all babies, but it is the parents' choice. If the SUAC level is high, the result is called screen positive, or condition suspected. This does not yet confirm HT1.

NHS England says that if a baby is screen positive, the family is contacted by the local hospital or a metabolic centre and seen the same day by a specialist team of a metabolic doctor, dietitian and nurse specialist. Blood and urine tests confirm whether the baby has HT1, and a sample is taken for genetic testing with consent.

Diagnostic results take about seven working days, and the genetic result may take several months. Treatment is started immediately based on the screening and early test results, because HT1 can be life-threatening if left untreated. Some babies turn out not to have HT1. That is called a false positive and treatment is not needed.

The metabolic team starts a medicine called nitisinone, which helps prevent the build-up of SUAC. They also start a restricted protein feed plan that limits intake of tyrosine and phenylalanine.

The baby has two types of feed to meet nutritional needs: a limited daily volume of breast milk or infant formula, and a special infant formula free of tyrosine and phenylalanine. Supplements may be needed. Parents learn to take blood spot tests at home and post them to the metabolic laboratory, and levels are checked weekly in the first year.

A metabolic dietitian advises on feed volumes based on the results and weight. The GP is asked to prescribe the special formula and supplement. Follow-up with the metabolic team continues throughout childhood.

NHS England says that with regular medication, good diet and well-controlled blood tyrosine and SUAC levels, most children with HT1 have a very good outcome and avoid long-term health problems. Following the dietetic and treatment instructions is described as very important for the child's health.

Because the condition needs lifelong specialist input, regular outpatient appointments are a normal part of life. Metabolic Support UK and the British Inherited Metabolic Diseases Group provide information for families, including a booklet on tyrosinaemia.

HT1 is inherited when both parents carry a faulty copy of the gene. NHS England says each child of the same parents has a 1 in 4 chance of having HT1. Brothers and sisters who were never screened may be at risk even if they have shown no symptoms, so it is important they are tested. The metabolic team can arrange this.

If the parents have another pregnancy, they should tell the midwife and GP about the family history and inform the metabolic team early. The team writes a birth plan that includes an early screening test for the new baby, taken between 24 and 48 hours after birth, in addition to the routine blood spot test.

HT1 care in the UK is delivered mainly through NHS specialist metabolic centres, reached through the screening programme or a paediatric referral. The medicines, special formula and monitoring are coordinated by that team.

Because the condition is rare and treatment is highly specialised, private care is unlikely to replace this pathway. Families sometimes use private genetic counselling or second opinions. Ask the metabolic team about this, and keep one clear point of contact for results.