Early Treatment Transforms Tyrosinemia Type I From Fatal to Manageable
Newborn screening plus nitisinone therapy has raised survival rates above 90%, preventing liver failure, neurologic crises, and early death.
Summary
Tyrosinemia Type I is a rare inherited metabolic disorder caused by mutations in the FAH gene, leading to toxic buildup of tyrosine byproducts that devastate the liver, kidneys, and nervous system. Without treatment, most children die before age ten from liver failure or hepatocellular carcinoma. The introduction of newborn screening and the drug nitisinone, combined with a low-tyrosine diet, has dramatically changed outcomes. Survival now exceeds 90%, with patients achieving normal growth, preserved liver function, and prevention of cirrhosis. This GeneReviews entry provides comprehensive clinical guidance covering diagnosis via succinylacetone biomarkers or FAH genetic testing, targeted and supportive therapies, surveillance protocols, and genetic counseling for families — offering a definitive clinical reference for physicians managing this condition.
Detailed Summary
Tyrosinemia Type I is a rare autosomal recessive disorder arising from biallelic pathogenic variants in the FAH gene, which encodes fumarylacetoacetase — an enzyme critical to tyrosine catabolism. Without functional FAH, toxic metabolites including succinylacetone accumulate, causing progressive and often fatal damage to the liver, kidneys, and peripheral nervous system.
Untreated, the disease presents in two patterns: severe acute liver failure in early infancy, or a more insidious course with liver dysfunction, renal tubular acidosis, growth failure, and rickets emerging later in the first year of life. Recurrent neurologic crises — involving abdominal pain, mental status changes, peripheral neuropathy, and sometimes respiratory failure — frequently go unrecognized. Death typically occurs before age ten from liver failure, neurologic crisis, or hepatocellular carcinoma.
The clinical landscape has been transformed by universal newborn screening and combination therapy with nitisinone (an HPPD inhibitor that blocks upstream tyrosine catabolism) alongside a low-phenylalanine, low-tyrosine diet. Survival rates now exceed 90%, with treated patients showing normal growth trajectories, restored liver function, prevention of cirrhosis, correction of renal tubular acidosis, and reduced hepatocellular carcinoma risk. Liver transplantation remains an option for those with severe presentation or malignant hepatic changes unresponsive to nitisinone.
Diagnosis relies on elevated succinylacetone in blood or urine, or molecular confirmation of FAH variants. Ongoing surveillance is extensive, including metabolic panels, liver imaging for carcinoma, renal function tests, developmental assessments, and neuropsychological evaluations.
Caveats include limited data on nitisinone safety during pregnancy, the need for lifelong dietary vigilance, and the complexity of managing acute neurologic crises. As a GeneReviews entry, this is a curated clinical summary rather than a novel primary research study.
Key Findings
- Nitisinone plus low-tyrosine diet achieves greater than 90% survival, compared to near-universal early death when untreated.
- Untreated children face liver failure, hepatocellular carcinoma, and neurologic crises, typically dying before age ten.
- Diagnosis confirmed by elevated succinylacetone in blood/urine or biallelic FAH pathogenic variants on genetic testing.
- Liver transplantation is reserved for nitisinone non-responders or those with malignant hepatic transformation.
- Autosomal recessive inheritance gives each sibling a 25% risk; prenatal and preimplantation genetic testing are available.
Methodology
This is a GeneReviews clinical summary entry, not a primary research study. It synthesizes published literature and expert consensus to provide evidence-based guidance on diagnosis, management, and genetic counseling for Tyrosinemia Type I. The entry is periodically updated, with the most recent revision in November 2025.
Study Limitations
As a GeneReviews summary, this entry reflects synthesized expert consensus rather than presenting new primary data. Evidence on nitisinone use during pregnancy is limited to only a few reported cases. Long-term outcomes data in adults treated from birth remain sparse given the relatively recent introduction of newborn screening programs.
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