Natural Protein Tolerance and Metabolic Control in Patients with Hereditary Tyrosinaemia Type 1

In a longitudinal retrospective study, we aimed to assess natural protein (NP) tolerance and metabolic control in a cohort of 20 Hereditary Tyrosinaemia type I (HTI) patients. Their median age was 12 years ([3.2-17.7 years], n = 11 female, n = 8 Caucasian, n = 8 Asian origin, n = 2 Arabic and n = 2 Indian). All were on nitisinone (NTBC) with a median dose of 0.7 g/kg/day (range 0.4-1.5 g/kg/day) and were prescribed a tyrosine (Tyr)/phenylalanine (Phe)-restricted diet supplemented with Tyr/Phe-free L-amino acids. Data were collected on clinical signs at presentation, medical history, annual dietary prescriptions, and blood Phe and Tyr levels from diagnosis until transition to the adult service (aged 16-18 years) or liver transplantation (if it preceded transition). The median age of diagnosis was 2 months (range: 0 to 24 months), with n = 1 diagnosed by newborn screening, n = 3 following phenylketonuria (PKU) screening and n = 7 by sibling screening. Five patients were transplanted (median age 6.3 years), and one died due to liver cancer. The median follow-up was 10 years (3-16 years), and daily prescribed NP intake increased from a median of 5 to 24 g/day. Lifetime median blood Tyr (370 µmol/L, range 280-420 µmol/L) and Phe (50 µmol/L, 45-70 µmol/L) were maintained within the target recommended ranges. This cohort of HTI patients were able to increase the daily NP intake with age while maintaining good metabolic control. Extra NP may improve lifelong adherence to the diet.