Secondary rickets from phosphaturia and vitamin D dysregulation
Neurologic damage
ALA-mediated peripheral neuropathy
Autonomic dysfunction during neurologic crises
Demyelination in peripheral nerves
Nitisinone mechanism of action
Inhibits 4-hydroxyphenylpyruvate dioxygenase (HPD) — upstream in tyrosine catabolism
Prevents formation of FAA, MAA, and succinylacetone
Causes upstream accumulation of tyrosine (requires dietary restriction to prevent toxicity)
Net effect: stops toxic metabolite production while requiring dietary tyrosine management
Does not correct the underlying FAH deficiency
Gene therapy approaches under investigation
Therapeutic Considerations
Nitisinone therapy principles
Early initiation is critical — initiating nitisinone before 6 months dramatically improves HCC outcomes
Pre-symptomatic treatment via NBS is the ideal
Evidence: US/Canadian consensus and GeneReviews support immediate initiation on positive screen
Monitoring framework
Plasma nitisinone trough: target 40-60 µmol/L
Succinylacetone: target undetectable
Plasma tyrosine: target 300-600 µmol/L; must be <500 µmol/L
Plasma phenylalanine: target 20-80 µmol/L
AFP and liver imaging: every 6 months AFP and ultrasound; annual MRI
HCC risk on nitisinone — key evidence
HCC can still develop even on long-term nitisinone therapy
Late initiation (>1 year of age) carries OR 12.7 for HCC
Lifelong surveillance is required regardless of metabolic control
Liver transplantation considerations
Transplantation corrects hepatic FAH deficiency but does not cure renal or neurologic disease
Post-transplant low-dose nitisinone (0.1 mg/kg/day) recommended to protect residual renal and neurologic function
German-speaking countries consensus 2025 recommendation
Transplantation indications have narrowed with nitisinone era
Now reserved for nitisinone-unresponsive liver failure or HCC
Gene therapy
Investigational for HT1 — ex vivo hepatocyte FAH gene correction approaches
No approved gene therapy as of 2025
Ongoing clinical trials
Patient Discharge Instructions
copy discharge instructions
Tyrosinemia Type I — Instructions for Home
Your medications
Nitisinone (Orfadin): take every dose as prescribed — do not skip or stop without speaking to your metabolic doctor
Missing doses can cause a serious crisis with abdominal pain, weakness, and breathing problems
Store nitisinone in the refrigerator
Your diet
Follow the low-tyrosine, low-phenylalanine diet exactly as instructed by your dietitian
Take your specialized amino acid formula at every prescribed time
Do not give your child high-protein foods (meat, regular dairy, legumes) beyond what your dietitian allows
Never skip meals or allow prolonged fasting — this can cause dangerous low blood sugar
Monitoring at home
Follow your scheduled blood and urine test dates
Your liver ultrasound and AFP (blood marker) must be done every 6 months
Your liver MRI must be done every year
Return immediately to the emergency department if:
Abdominal pain combined with arm or leg weakness
Difficulty breathing or rapid breathing
New or worsening yellowing of the skin or eyes
Seizures
Confusion or unusual sleepiness
Bleeding that does not stop
Eye pain or sudden vision changes
Vomiting that prevents giving medications or formula
Emergency protocol
Carry your emergency letter from the metabolic team to all hospital visits
Inform any new doctor or emergency provider about your diagnosis before treatment
If admitted elsewhere, contact your metabolic genetics team immediately
Expected course
With nitisinone and diet, most children grow normally and the liver and kidneys improve
Lifelong monitoring is required because cancer risk in the liver remains even with excellent control
Regular developmental assessments are part of your care plan
References
Guidelines and key sources
Ficicioglu C. Tyrosinemia Type I. GeneReviews Internet. Updated 2025 Nov 20. National Center for Biotechnology Information. PMID: NBK1487
Primary GeneReviews reference for HT1 clinical presentation, diagnosis, and management
Evidence basis for nitisinone dosing, monitoring targets, and dietary recommendations
Chinsky JM, Singh R, Ficicioglu C, et al. Diagnosis and Treatment of Tyrosinemia Type I: A US and Canadian Consensus Group Review and Recommendations. Genetics in Medicine. 2017;19:1380-1395
US/Canadian expert consensus on NBS, nitisinone initiation, monitoring, and HCC surveillance
Class I consensus recommendation supporting nitisinone as first-line treatment
Das AM, Ballhausen D, Haas D, et al. Diagnosis, Treatment, Management and Monitoring of Patients With Tyrosinaemia Type 1: Consensus Group Recommendations From the German-Speaking Countries. Journal of Inherited Metabolic Disease. 2025;48:e12802
2025 European consensus on HT1 management including post-transplant nitisinone and simplified dietary approaches
Joshi D, Nayagam J, Clay L, et al. UK guideline on the transition and management of childhood liver diseases in adulthood. Alimentary Pharmacology and Therapeutics. 2024
Adult transition and long-term management guidance; HCC surveillance recommendations
Squires JE, Alonso EM, Ibrahim SH, et al. NASPGHAN Position Paper on Pediatric Acute Liver Failure. Journal of Pediatric Gastroenterology and Nutrition. 2022
Diagnostic criteria and disposition guidance for pediatric acute liver failure including HT1
Squires RH, Ng V, Romero R, et al. Evaluation of the Pediatric Patient for Liver Transplantation: AASLD/AST/NASPGHAN Practice Guideline. Hepatology. 2014;60:362-398
PELD scoring guidance and transplant evaluation framework for pediatric liver failure
Orfadin (nitisinone). FDA Drug Label. Updated 2025-12-18. NDA 021232
Official dosing, safety, and monitoring information for nitisinone (NTBC)
El-Karaksy H, Abdullatif HM, Ghobrial CM, et al. Clinical Experience With Hepatorenal Tyrosinemia From a Single Egyptian Center. PLoS One. 2022
Epidemiologic data on consanguinity (87%) and presenting features (abdominal distension 52.6%)
Basan H, Bilginer Gürbüz B, Gürbüz F, et al. Management of Porphyria-Like Syndrome in Tyrosinemia Type 1. Journal of Pediatric Endocrinology and Metabolism. 2026
Guidance on IV hemin use and management of neurologic crisis
De Jesús VR, Adam BW, Mandel D, Cuthbert CD, Matern D. Succinylacetone as Primary Marker to Detect Tyrosinemia Type I in Newborns. Molecular Genetics and Metabolism. 2014
Evidence supporting succinylacetone-first NBS approach and near-100% detection sensitivity
Bayzaei Z, Dehghani SM, Geramizadeh B. Tyrosinemia Type II. GeneReviews Internet. Updated 2024 Oct 24
Type II differential diagnosis; ICD-10 E70.21 classification
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.