The Pillars of Care: Nitisinone and the Metabolic Diet

Managing Tyrosinemia Type 1 (HT1) requires a dedicated, lifelong commitment to two main treatments that work in tandem: a medication called nitisinone and a specialized low-protein diet. Together, these have transformed HT1 from a life-threatening illness into a manageable chronic condition ^[1][2].

Nitisinone (NTBC): The Vital Blockade

Before the discovery of nitisinone (NTBC), the body would break down protein until it reached the “broken” part of the assembly line, creating the toxin succinylacetone ^[2].

Nitisinone works by moving the “blockade” further up the line. It inhibits an enzyme called 4-HPPD, which is several steps before the toxic build-up happens ^[3][4]. By stopping the process earlier, nitisinone prevents the production of the toxins that cause liver cancer, liver failure, and kidney damage ^[2][5].

Administration of Nitisinone

Nitisinone is taken by mouth and is available in capsules or as a liquid suspension ^[3]. For infants and small children, capsules can be opened and mixed into a small amount of water, medical formula, or applesauce to make it easier to take. Your medical team will instruct you on the correct dosage and administration method based on your child’s weight and age ^[2].

The Importance of Adherence

Nitisinone has a long half-life, meaning it stays in the body for a while ^[3]. A single slightly delayed dose will not instantly cause a severe crisis. However, consistent adherence is critical. If medication is repeatedly missed or discontinued over time, the body will begin producing toxins again ^[6]. Over days or weeks, this can trigger a neurovisceral crisis—a severe medical emergency characterized by extreme abdominal pain, vomiting, high blood pressure, and nerve issues like weakness or seizures ^[6][7][8]. If you realize you have missed a dose, contact your metabolic team for instructions rather than panicking.

Sick Day Protocols

When a child with a metabolic disorder gets a common illness like a stomach bug, it can quickly become serious if they vomit their medication or refuse their medical formula ^[6]. You must have a clear “Sick Day Protocol” from your care team. If your child cannot keep their medication down or is not getting enough calories, you may need to go to the emergency room for intravenous (IV) fluids and medical support to prevent their body from breaking down its own muscle for energy (a state called catabolism) ^[2].

The Medical Diet: Managing the Side Effect

While nitisinone stops the toxins, it causes the “raw material” (tyrosine) to back up in the blood ^[9][3]. This is known as secondary hypertyrosinemia.

If tyrosine levels get too high (typically above 400–500 µmol/L), it can cause harmful side effects, most notably corneal crystals (keratopathy) ^[10][11]. Photophobia (extreme sensitivity to light) is an early warning sign. If you notice your child squinting, tearing up constantly, or trying to avoid bright lights, contact your team immediately ^[9][12].

To prevent this, children must follow a protein-restricted diet ^[13]:

1. Low-Protein Foods: Natural protein (found in meat, dairy, beans, and nuts) must be strictly limited because it contains tyrosine and phenylalanine (which the body turns into tyrosine) ^[14][15].
2. Medical Formula: To ensure your child gets enough protein for growth without the harmful amino acids, they must drink a specialized metabolic formula that is tyrosine-free and phenylalanine-free ^[16].

Interestingly, because the diet is so restrictive, some children’s phenylalanine levels may drop too low, which can also cause growth issues. In these cases, the dietitian may prescribe a specific phenylalanine supplement ^[15].

When is Liver Transplantation Needed?

While nitisinone and diet are the gold standard, there are rare cases where a liver transplant is necessary ^[17]:

• Late Diagnosis: If the liver was already severely damaged or developed cancer (HCC) before treatment started ^[2][18].
• Non-Response: In very rare instances where a child does not respond well to medical therapy or cannot tolerate the treatment ^[17].
• Suspicious Growths: If imaging shows nodules in the liver that the medical team suspects could be cancerous despite treatment ^[2].

A transplant “cures” the liver disease because the new liver has the working FAH enzyme, but it is a major surgery with its own lifelong requirements, so medical management is always the first choice ^[19].