Hereditary Tyrosinaemia (HT)

Feeding your possible with HT

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What is HT1 and HT2 (Hereditary Tyrosinaemia type 1 and 2)?

Hereditary Tyrosinaemia (HT) is the name given to a group of rare inherited metabolic conditions. Across Australia and New Zealand, only one or two babies are born with HT each year. People with HT are born with a simple change in one of their genes, inherited from both parents. This gene change results in an enzyme deficiency, which means people with HT have trouble breaking down an amino acid called tyrosine (Tyr) in the protein that they eat. There are two forms of the condition. Hereditary Tyrosinaemia Type 1 (HT1) is caused by a deficiency in an enzyme called fumarylacetoacetate hydrolase (FAH) while Hereditary Tyrosinaemia Type 2 (HT2) is caused by a deficiency in a different enzyme called tyrosine aminotransferase (TAT). If people with HT eat too much protein, Tyr and harmful breakdown products can build up in the body and cause problems. That’s why following a low protein diet is very important for you to reach your health potential and live your best life with HT.

We call this “Feeding Your Possible”

Why should you feed your possible?

A low protein diet is the gold standard in the management of HT. People with HT1 follow a low protein diet in combination with a medication prescribed to them by their doctor. In a person without HT, Tyr would be broken down into metabolites and then into substances the body can use, by enzymes, including FAH and TAT. HT1 and HT2 are simply enzyme deficiencies at different points in the Tyr breakdown process. People with HT2 cannot break Tyr down into metabolites, and people with HT1 cannot break down metabolites into useful substances. This means Tyr and metabolites can build up in the body to high levels. In HT1, a buildup of metabolites and Tyr can cause serious damage to the liver, kidneys and brain, and increase the risk of liver cancer. In HT2, crystals of Tyr can build up in the eyes and skin, causing painful inflammation.

Medication works in people with HT1 by stopping the breakdown of Tyr into harmful metabolites, but it doesn’t lower the levels of Tyr. This medication is not effective in people with HT2 because their bodies can’t break Tyr down into metabolites.

A low protein diet means people with HT can stay healthy and be the best version of themselves.

Hereditary Tyrosinaemia (HT)
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How is HT diagnosed?

These days, all babies born in Australia and New Zealand are tested for HT a few days after birth, through the Newborn Screening Program. There are a number of conditions that can cause high Tyr levels on this test, so if levels are high, more testing is done to work out whether this is caused by HT or a different condition. The newborn screening test is highly effective in detecting HT2, but does not detect all people with HT1, so some people with the condition may have a false negative result. In these people, diagnosis usually occurs in infancy, when people with untreated HT1 may develop symptoms like slow growth, liver problems or liver failure, cancer of the liver or problems with the kidneys.

As soon as an HT diagnosis is confirmed, management is started with a supplement that lowers Tyr levels. Starting a low protein diet, supplements and medication early, and continuing through life is the best way to manage HT.

How is HT1 managed?

Following a low protein diet is the gold standard in HT management, in combination with prescribed medication for people with HT1. Everyone has specific and individual dietary needs, whether they have HT or not, and reach their full potential by eating the food their bodies need. HT is really no different. Many people in Australia and New Zealand living with HT feed their possible by following an individualised diet that includes low protein food, and an HT nutritional supplement, keeping an eye on their Tyr levels, and regularly checking in with their metabolic team.

There are many ways you can feed your possible at Low Protein Connect. Get inspired by our low protein recipes, discover flavour and variety in the online store where you’ll find a wide range of PKU supplements and low protein foods, and take time out for your wellbeing with our low protein lifestyle tips.

Reference sources:

The Australian Society for Inborn Errors of Metabolism (ASIEM). The ASIEM Low Protein Handbook for Tyrosinaemia. Available at: https://www.hgsa.org.au/resources/asiem-resources-for-parents-and-families/asiem-dietary-handbooks. Accessed January 2021.

Angileri F et al. JIMD Rep 2015;19:43–58.

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