Hereditary Tyrosinemia

The Québec NTBC Study Group, Fernando Alvarez, Suzanne Atkinson, Manon Bouchard, Catherine Brunel-Guitton, Daniela Buhas, Jean-François Bussières, Josée Dubois, Daphna Fenyves, Paul Goodyer, Martyne Gosselin, Ugur Halac, Patrick Labbé, Rachel Laframboise, Bruno Maranda, Serge Melançon, Aicha Merouani, Grant A. Mitchell, John Mitchell, Guy Parizeault, Luc Pelletier, Véronique Phan, Jean-François Turcotte

In this chapter we describe the current Quebec NTBC Study protocol. Quebec's unique characteristics have influenced the development of the protocol, including a high prevalence of hepatorenal tyrosinemia (HT1), universal newborn screening for HT1, availability of treatment with nitisinone (NTBC) and special diet, a large territory, where HT1 treatment is coordinated by a small number of centers. Screened newborns are seen within 3 weeks of birth. Patients with liver dysfunction (prolonged prothrombin time and/or international normalized ratio (INR) provide sensitive, rapidly available indicators) are treated by NTBC and special diet. The specific diagnosis is confirmed by diagnostic testing for succinylacetone (SA) in plasma and urine samples obtained before treatment. After an initial period of frequent surveillance, stable patients are followed every 3 months by assay of plasma amino acids and NTBC and plasma and urine SA. Abdominal ultrasound is done every 6 months. Patients have an annual visit to the coordinating center that includes multidisciplinary evaluations in metabolic genetics, hepatology, imaging (for abdominal ultrasound and magnetic resonance imaging) and other specialties as necessary. If hepatocellular carcinoma is suspected by imaging and/or because of progressive elevation of alphafetoprotein, liver transplantation is discussed. To date, no patient in whom treatment was started before 1 month of age has developed hepatocellular carcinoma, after surveillance for up to 20 years in some. This patient group is the largest in the world that has been treated rapidly following newborn screening. The protocol continues to evolve to adapt to the challenges of long term surveillance.