Tyrosinemia Type I

Mendelian MONDO:0010161 Pathograph 36 Inborn Error of Metabolism

Tyrosinemia type I (HT-1) is an autosomal recessive inborn error of tyrosine metabolism caused by deficiency of fumarylacetoacetate hydrolase (FAH), the terminal enzyme in the tyrosine catabolic pathway. FAH deficiency leads to accumulation of toxic intermediates including fumarylacetoacetate (FAA), maleylacetoacetate (MAA), and succinylacetone (SA). FAA directly injures hepatocytes through mitochondrial cytochrome c release with caspase-mediated apoptosis. SA inhibits delta-aminolevulinic acid dehydratase, causing porphyria-like neurovisceral crises. Untreated disease leads to acute liver failure, cirrhosis, hepatocellular carcinoma, renal tubular dysfunction, and neurological crises. Nitisinone (NTBC) combined with dietary tyrosine and phenylalanine restriction is the standard of care, dramatically improving survival, though residual risk of hepatocellular carcinoma persists even under continuous therapy. Global incidence is approximately 1 in 100,000.

Ask OpenScientist

Ask a research question about Tyrosinemia Type I. OpenScientist will conduct autonomous deep research using the Disorder Mechanisms Knowledge Base and PubMed literature (typically 10-30 minutes).

Submitting...

Do not include personal health information in your question. Questions and results are cached in your browser's local storage.

7
Pathophys.
16
Phenotypes
36
Pathograph
1
Genes
7
Treatments
1
References
1
Deep Research
⚙

Pathophysiology

7
Fumarylacetoacetate hydrolase deficiency
Loss of FAH activity blocks the terminal enzymatic step of tyrosine catabolism.
hepatocyte link
FAH link
tyrosine catabolic process link ↓ DECREASED
fumarylacetoacetase activity link ↓ DECREASED
liver link
Downstream
Toxic fumarylacetoacetate and maleylacetoacetate accumulation FAH block causes upstream toxic tyrosine-pathway metabolites to accumulate.
Tyrosine Defective tyrosine catabolism contributes to elevated tyrosine, particularly during HPD inhibition with nitisinone.
Show evidence (1 reference)
PMID:38505790 SUPPORT Human Clinical
"Hepatorenal tyrosinemia type 1 (HT-1) is a rare autosomal recessive disease that results from a deficiency of fumaryl acetoacetate hydrolase (FAH), a critical enzyme in the catabolic pathway for tyrosine."
Directly supports FAH deficiency as the initiating molecular defect.
Toxic fumarylacetoacetate and maleylacetoacetate accumulation
FAH deficiency causes accumulation of fumarylacetoacetate (FAA) and maleylacetoacetate (MAA), with secondary formation of succinylacetone (SA). These toxic tyrosine-pathway metabolites damage the liver, kidneys, and nervous system, and FAA directly triggers mitochondrial cytochrome c release in hepatocytes.
hepatocyte link
cellular response to toxic substance link ↑ INCREASED
liver link
Downstream
Fumarylacetoacetate (FAA) FAH deficiency directly increases the toxic substrate fumarylacetoacetate.
Succinylacetone (SA) Toxic tyrosine intermediates produce the pathognomonic metabolite succinylacetone.
FAA-induced mitochondrial apoptosis in hepatocytes FAA reactivity drives mitochondrial injury and caspase-mediated hepatocyte apoptosis.
Succinylacetone inhibition of heme biosynthesis Succinylacetone accumulation perturbs ALAD-linked heme biosynthesis and contributes to porphyria-like crises.
Renal proximal tubule toxic injury Tyrosine-pathway metabolite toxicity causes renal tubular injury and Fanconi-like tubulopathy.
Neurocognitive impairment Toxic metabolite effects on the nervous system and long-term treatment factors contribute to neurocognitive risk.
Persistent hepatocarcinogenic programs under NTBC therapy Residual FAH deficiency leaves chronic pro-oncogenic hepatic stress despite upstream metabolic blockade by NTBC.
Show evidence (1 reference)
PMID:38505790 SUPPORT Human Clinical
"This leads to the accumulation of toxic metabolites such as fumaryl and maleylacetoacetate, which can damage the liver, kidneys, and nervous system."
Directly supports toxic-metabolite accumulation downstream of FAH deficiency.
FAA-induced mitochondrial apoptosis in hepatocytes
Fumarylacetoacetate directly triggers mitochondrial outer membrane permeabilization with release of cytochrome c, activating the caspase cascade and inducing hepatocyte apoptosis. Caspase inhibitors were shown to prevent liver failure in FAH-deficient mouse models, confirming the causal role of the intrinsic apoptotic pathway.
hepatocyte link
intrinsic apoptotic signaling pathway link
mitochondrion link
Downstream
Acute liver failure Caspase-mediated hepatocyte death causes acute hepatic failure in severe or untreated HT-1.
Coagulopathy Acute hepatic failure impairs coagulation factor synthesis.
Hepatomegaly Hepatic injury and regenerative stress can present with enlarged liver.
Show evidence (2 references)
PMID:9689118 SUPPORT Model Organism
"Cytochrome c was released from mitochondria prior to liver failure in the Fah-/- Hpd-/- double-mutant mice after the administration of HGA. In a cell-free system, the addition of fumarylacetoacetate induced the release of cytochrome c from the mitochondria."
Demonstrates that FAA directly induces mitochondrial cytochrome c release in tyrosinemia model.
PMID:9689118 SUPPORT Model Organism
"We also found that caspase inhibitors were highly effective in preventing the liver failure induced by HGA in the double-mutant mice."
Proves caspase-mediated apoptosis is the mechanism of hepatocyte injury in tyrosinemia.
Renal proximal tubule toxic injury
Accumulated tyrosine-pathway metabolites injure kidney tissue, especially the proximal tubule, causing a Fanconi-like renal phenotype with phosphate wasting. This renal tubular mechanism explains renal tubular dysfunction and secondary hypophosphatemic rickets in HT-1.
proximal tubule epithelial cell link
cellular response to toxic substance link
proximal tubule link
Downstream
Renal tubular dysfunction Toxic injury to proximal tubule epithelium produces Fanconi-like renal tubular dysfunction.
Rickets Renal Fanconi syndrome causes phosphate wasting and secondary rickets.
Show evidence (1 reference)
PMID:38505790 SUPPORT Human Clinical
"This leads to the accumulation of toxic metabolites such as fumaryl and maleylacetoacetate, which can damage the liver, kidneys, and nervous system."
Directly links toxic metabolite accumulation to kidney injury in HT-1.
Chronic hepatic injury and regeneration
Untreated or late-treated HT-1 produces chronic hepatic injury with regeneration, fibrosis, cirrhosis, and malignant transformation risk. Continuous NTBC reduces acute toxicity but does not restore FAH activity, so residual liver-disease and HCC-associated programs can persist.
hepatocyte link
liver regeneration link
liver link
Downstream
Hepatic fibrosis Chronic hepatic injury in untreated HT-1 produces fibrosis.
Hepatic cirrhosis Chronic hepatic injury and fibrosis can progress to cirrhosis.
Hepatocellular carcinoma Chronic liver injury and regeneration increase HCC risk.
Failure to thrive Chronic liver disease and metabolic instability impair growth.
Edema Advanced hepatic disease can cause peripheral edema or ascites.
Show evidence (2 references)
PMID:38132825 SUPPORT Human Clinical
"Undiagnosed and untreated tyrosinemia type 1 (TT1) individuals carry a significant risk for developing liver fibrosis, cirrhosis and hepatocellular carcinoma (HCC)."
Directly links untreated HT-1 to fibrosis, cirrhosis, and HCC.
PMID:36980965 SUPPORT Model Organism
"The differentially expressed genes were enriched in toxicological gene classes related to liver disease, liver damage, liver regeneration and liver cancer, in particular HCC."
Mouse transcriptomics supports persistent hepatic injury, regeneration, and HCC-related programs under NTBC.
Succinylacetone inhibition of heme biosynthesis
Succinylacetone (SA) is a competitive inhibitor of delta-aminolevulinic acid dehydratase (ALAD), blocking the heme biosynthetic pathway and causing accumulation of delta-aminolevulinic acid (ALA). This produces porphyria-like neurovisceral crises with neuropathy, similar to acute intermittent porphyria or lead poisoning.
hepatocyte link
ALAD link
heme biosynthetic process link ↓ DECREASED
Downstream
Delta-aminolevulinic acid (ALA) ALAD inhibition increases ALA accumulation.
Peripheral neuropathy Porphyria-like crises in HT-1 can include peripheral neuropathy.
Abdominal pain Porphyria-like neurologic crises in HT-1 can include abdominal pain.
Encephalopathy Porphyria-like neurologic crises in HT-1 can include altered mental status.
Respiratory failure Severe neurologic crises in HT-1 can include respiratory failure.
Show evidence (3 references)
PMID:6826727 SUPPORT In Vitro
"Our data indicate that succinylacetone is an extremely potent competitive inhibitor of ALA dehydratase in human as well as in animal tissues."
Biochemical evidence directly supports succinylacetone inhibition of ALA dehydratase.
PMID:6826727 SUPPORT Human Clinical
"patients with this hereditary disease excrete excessive amounts of delta-aminolevulinic acid (ALA) in urine and that certain patients have an accompanying clinical syndrome resembling that of acute intermittent porphyria (AIP)."
Patient observations connect HT-1 to ALA accumulation and porphyria-like neurovisceral crises.
PMID:6826727 SUPPORT In Vitro
"In cultured hepatocytes, succinylacetone also inhibited ALA dehydratase activity, decreased the cellular content of heme and cytochrome P-450"
Supports reduced heme-biosynthesis output downstream of succinylacetone-mediated ALAD inhibition.
Persistent hepatocarcinogenic programs under NTBC therapy
Although nitisinone prevents acute toxicity by blocking upstream toxic metabolite formation, it does not restore FAH activity. Transcriptomic analysis in FAH-deficient mice under continuous NTBC revealed persistent enrichment of genes related to liver disease, liver regeneration, and hepatocellular carcinoma. This supports the ongoing HCC risk even in treated patients.
hepatocyte link
liver regeneration link
Downstream
Hepatocellular carcinoma Residual hepatic disease programs under NTBC support sustained HCC risk.
Alpha-fetoprotein (AFP) Persistent HCC risk motivates AFP surveillance in HT-1.
Elevated alpha-fetoprotein AFP elevation is tracked as a marker of disease activity and malignant transformation risk.
Show evidence (2 references)
PMID:36980965 SUPPORT Model Organism
"The differentially expressed genes were enriched in toxicological gene classes related to liver disease, liver damage, liver regeneration and liver cancer, in particular HCC."
Demonstrates persistent HCC-related gene expression under NTBC therapy in mouse model.
PMID:36980965 SUPPORT Model Organism
"NTBC does not restore the enzymatic defects inflicted by the disease nor does it cure HT1."
Confirms NTBC does not cure the underlying enzymatic deficiency.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Tyrosinemia Type I Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

16
Blood 1
Coagulopathy Abnormality of coagulation (HP:0001928)
Show evidence (1 reference)
PMID:28771246 SUPPORT Human Clinical
"Tyrosinemia type I (hepatorenal tyrosinemia, HT-1) is an autosomal recessive condition resulting in hepatic failure"
Coagulopathy is a direct consequence of hepatic failure in HT-1.
Digestive 5
Acute liver failure Acute hepatic failure (HP:0006554)
Show evidence (2 references)
PMID:28771246 SUPPORT Human Clinical
"Tyrosinemia type I (hepatorenal tyrosinemia, HT-1) is an autosomal recessive condition resulting in hepatic failure with comorbidities involving the renal and neurologic systems"
Directly supports hepatic failure as a primary manifestation.
PMID:38505790 SUPPORT Human Clinical
"Patients failing medical treatment (eg, due to non-adherence), and who develop acute liver failure (ALF), have HCC or evidence of histologically proven dysplastic liver nodule(s)"
Confirms acute liver failure as an indication for liver transplantation in HT-1.
Hepatic fibrosis Hepatic fibrosis (HP:0001395)
Show evidence (1 reference)
PMID:38132825 SUPPORT Human Clinical
"Undiagnosed and untreated tyrosinemia type 1 (TT1) individuals carry a significant risk for developing liver fibrosis, cirrhosis and hepatocellular carcinoma (HCC)."
Directly lists liver fibrosis as a significant risk in untreated HT-1.
Hepatic cirrhosis Cirrhosis (HP:0001394)
Show evidence (2 references)
PMID:38132825 SUPPORT Human Clinical
"A nine-year-old boy presented with HCC in a cirrhotic liver."
Documents cirrhosis in a missed NBS case of HT-1.
PMID:39050308 SUPPORT Human Clinical
"A liver biopsy confirmed mixed nodular cirrhosis, and a subsequent whole exome sequencing revealed autosomal recessive inheritance of tyrosinemia type 1."
Confirms cirrhosis in a late-presenting HT-1 patient.
Hepatocellular carcinoma Hepatocellular carcinoma (HP:0001402)
Show evidence (1 reference)
PMID:38505790 SUPPORT Human Clinical
"NTBC combined with dietary therapy, if initiated early, can provide liver transplant (LT) free survival and reduce the risk of hepatocellular carcinoma (HCC)."
Confirms HCC as a recognized risk requiring monitoring.
Hepatomegaly Hepatomegaly (HP:0002240)
Show evidence (1 reference)
PMID:39050308 SUPPORT Human Clinical
"We present a case of HT-1 in a three-year-old female child characterized by abdominal distension, facial edema, lower limb edema, and an enlarged liver with parenchymal disease."
Documents hepatomegaly in a late-presenting HT-1 patient.
Genitourinary 1
Renal tubular dysfunction Renal Fanconi syndrome (HP:0001994)
Show evidence (2 references)
PMID:38505790 SUPPORT Human Clinical
"This leads to the accumulation of toxic metabolites such as fumaryl and maleylacetoacetate, which can damage the liver, kidneys, and nervous system."
Confirms kidney damage from toxic metabolite accumulation.
PMID:28771246 SUPPORT Human Clinical
"Tyrosinemia type I (hepatorenal tyrosinemia, HT-1) is an autosomal recessive condition resulting in hepatic failure with comorbidities involving the renal and neurologic systems"
Renal involvement is a defining feature of hepatorenal tyrosinemia.
Metabolism 2
Elevated alpha-fetoprotein Elevated circulating alpha-fetoprotein concentration (HP:0006254)
Show evidence (1 reference)
PMID:17008115 SUPPORT Human Clinical
"A rise of alpha-fetoprotein (AFP) is an indicator of liver cancer."
Directly supports AFP elevation as a clinically important HT-1 surveillance finding.
Edema Edema (HP:0000969)
Show evidence (1 reference)
PMID:39050308 SUPPORT Human Clinical
"We present a case of HT-1 in a three-year-old female child characterized by abdominal distension, facial edema, lower limb edema, and an enlarged liver with parenchymal disease."
Directly documents edema in an HT-1 patient with liver disease.
Musculoskeletal 1
Rickets Rickets (HP:0002748)
Show evidence (1 reference)
PMID:20301688 SUPPORT Other
"liver dysfunction and renal tubular dysfunction associated with growth failure and rickets."
GeneReviews directly lists rickets in association with renal tubular dysfunction in untreated HT-1.
Nervous System 3
Peripheral neuropathy Peripheral neuropathy (HP:0009830)
Show evidence (2 references)
PMID:20301688 SUPPORT Other
"neurologic crises lasting one to seven days that can include change in mental status, abdominal pain, peripheral neuropathy, and/or respiratory failure"
GeneReviews directly lists peripheral neuropathy during HT-1 neurologic crises.
PMID:28771246 SUPPORT Human Clinical
"Tyrosinemia type I (hepatorenal tyrosinemia, HT-1) is an autosomal recessive condition resulting in hepatic failure with comorbidities involving the renal and neurologic systems"
Neurologic system involvement includes neuropathic crises.
Encephalopathy Encephalopathy (HP:0001298)
Show evidence (1 reference)
PMID:20301688 SUPPORT Other
"neurologic crises lasting one to seven days that can include change in mental status, abdominal pain, peripheral neuropathy, and/or respiratory failure"
GeneReviews directly lists change in mental status during HT-1 neurologic crises.
Neurocognitive impairment Cognitive impairment (HP:0100543)
Show evidence (1 reference)
PMID:38505790 SUPPORT Human Clinical
"They are also at risk of long-term neurocognitive impairment, which highlights the need for neurocognitive assessment and therapy."
Directly states neurocognitive impairment as a long-term risk in HT-1.
Respiratory 1
Respiratory failure Respiratory failure (HP:0002878)
Show evidence (1 reference)
PMID:20301688 SUPPORT Other
"neurologic crises lasting one to seven days that can include change in mental status, abdominal pain, peripheral neuropathy, and/or respiratory failure"
GeneReviews directly lists respiratory failure during HT-1 neurologic crises.
Constitutional 1
Abdominal pain Abdominal pain (HP:0002027)
Show evidence (1 reference)
PMID:20301688 SUPPORT Other
"neurologic crises lasting one to seven days that can include change in mental status, abdominal pain, peripheral neuropathy, and/or respiratory failure"
GeneReviews directly lists abdominal pain during HT-1 neurologic crises.
Growth 1
Failure to thrive Failure to thrive (HP:0001508)
Show evidence (2 references)
PMID:20301688 SUPPORT Other
"liver dysfunction and renal tubular dysfunction associated with growth failure and rickets."
GeneReviews directly supports growth failure in untreated HT-1.
PMID:39050308 SUPPORT Human Clinical
"We present a case of HT-1 in a three-year-old female child characterized by abdominal distension, facial edema, lower limb edema, and an enlarged liver with parenchymal disease."
Case demonstrates growth and nutritional compromise in untreated HT-1.
🧬

Genetic Associations

1
FAH deficiency
Autosomal recessive
Show evidence (2 references)
PMID:38505790 SUPPORT Human Clinical
"Hepatorenal tyrosinemia type 1 (HT-1) is a rare autosomal recessive disease that results from a deficiency of fumaryl acetoacetate hydrolase (FAH), a critical enzyme in the catabolic pathway for tyrosine."
Directly describes FAH deficiency as the genetic cause of HT-1.
CGGV:assertion_39c50699-f422-4bae-89ac-af13ef7cb8cc-2020-06-29T174149.440Z SUPPORT Other
"FAH | HGNC:3579 | tyrosinemia type I | MONDO:0010161 | AR | Definitive"
ClinGen classifies the FAH-tyrosinemia type I gene-disease relationship as definitive with autosomal recessive inheritance.
💊

Treatments

7
Nitisinone (NTBC) therapy
Action: Pharmacotherapy NCIT:C15986
Agent: nitisinone ↗
Nitisinone (2-[2-nitro-4-trifluoromethylbenzoyl]-1,3-cyclohexanedione) is a potent inhibitor of 4-hydroxyphenylpyruvate dioxygenase (HPD), the second enzyme in tyrosine degradation. By blocking HPD, NTBC prevents formation of the toxic downstream metabolites FAA, MAA, and SA. Early initiation of NTBC, ideally before symptom onset via NBS identification, provides greater than 90% survival and dramatically reduces the need for liver transplantation.
Mechanism Target:
INHIBITS Toxic fumarylacetoacetate and maleylacetoacetate accumulation — Nitisinone inhibits HPD upstream of FAH, reducing formation of FAA, MAA, and succinylacetone.
Show evidence (1 reference)
PMID:36980965 SUPPORT Model Organism
"Nitisinone (NTBC), a potent inhibitor of the 4-hydroxyphenylpyruvate dioxygenase (HPD) enzyme, rescues HT1 patients from severe illness and death."
Directly supports upstream HPD inhibition as the therapeutic mechanism that prevents severe HT-1 illness.
Target Phenotypes: Acute hepatic failure ↗ Hepatocellular carcinoma ↗
Show evidence (2 references)
PMID:38505790 SUPPORT Human Clinical
"has significantly improved the management of HT-1, particularly when initiated before the onset of symptoms."
Supports NTBC as the transformative therapy for HT-1.
PMID:36980965 PARTIAL Model Organism
"Nitisinone (NTBC), a potent inhibitor of the 4-hydroxyphenylpyruvate dioxygenase (HPD) enzyme, rescues HT1 patients from severe illness and death. However, despite its demonstrated benefits, HT1 patients under continuous NTBC therapy are at risk to develop HCC"
Confirms NTBC efficacy but notes residual HCC risk.
Dietary tyrosine and phenylalanine restriction
Action: dietary intervention MAXO:0000088
Low-tyrosine, low-phenylalanine diet is essential in combination with NTBC therapy, since NTBC causes upstream accumulation of tyrosine. Specialized medical formulas provide essential amino acids while restricting tyrosine and phenylalanine intake.
Mechanism Target:
MODULATES Toxic fumarylacetoacetate and maleylacetoacetate accumulation — Dietary restriction reduces tyrosine and phenylalanine substrate flux and helps control upstream tyrosine accumulation during NTBC therapy.
Show evidence (1 reference)
PMID:28771246 SUPPORT Human Clinical
"There was strong consensus in favor of NBS for HT-1, using blood succinylacetone as a marker, followed by diagnostic confirmation and early treatment with NTBC and diet."
Consensus guidance supports diet as part of early HT-1 treatment after diagnosis.
Show evidence (2 references)
PMID:28771246 SUPPORT Human Clinical
"There was strong consensus in favor of NBS for HT-1, using blood succinylacetone as a marker, followed by diagnostic confirmation and early treatment with NTBC and diet."
Consensus recommendation for combined NTBC and dietary therapy.
PMID:38505790 SUPPORT Human Clinical
"NTBC combined with dietary therapy, if initiated early, can provide liver transplant (LT) free survival and reduce the risk of hepatocellular carcinoma (HCC)."
Confirms dietary therapy as part of the standard treatment combination.
Liver transplantation
Action: organ transplantation MAXO:0010039
Liver transplantation is curative for the hepatic manifestations of HT-1 but does not correct renal FAH deficiency, and residual SA production by the kidneys may persist. Indications include acute liver failure, HCC or dysplastic nodules, or failure of medical management.
Mechanism Target:
RESTORES Fumarylacetoacetate hydrolase deficiency — Liver transplantation replaces FAH-deficient liver tissue, correcting hepatic manifestations while leaving extrahepatic FAH deficiency uncorrected.
Show evidence (1 reference)
PMID:38505790 SUPPORT Human Clinical
"Patients failing medical treatment (eg, due to non-adherence), and who develop acute liver failure (ALF), have HCC or evidence of histologically proven dysplastic liver nodule(s), or experience poor quality of life secondary to severe dietary restrictions are currently indicated for LT."
HT-1 liver transplantation is reserved for hepatic failure, HCC, dysplastic nodules, or failed medical management.
Target Phenotypes: Acute hepatic failure ↗ Hepatocellular carcinoma ↗
Show evidence (2 references)
PMID:38505790 SUPPORT Human Clinical
"Patients failing medical treatment (eg, due to non-adherence), and who develop acute liver failure (ALF), have HCC or evidence of histologically proven dysplastic liver nodule(s), or experience poor quality of life secondary to severe dietary restrictions are currently indicated for LT."
Lists specific indications for liver transplantation in HT-1.
PMID:39050308 SUPPORT Human Clinical
"The patient is currently undergoing treatment with capsule nitisinone 5 mg, which inhibits the second step of tyrosine degradation to prevent tyrosinemia, along with a restricted protein diet, while awaiting liver transplantation."
Confirms liver transplantation as a treatment option for severe cases.
Newborn screening
Action: disease screening MAXO:0000124
NBS for HT-1 using dried blood spot succinylacetone measurement is recommended, as it is superior to tyrosine-based screening. Early identification enables pre-symptomatic NTBC initiation for optimal long-term outcomes.
Target Phenotypes: Acute hepatic failure ↗ Hepatocellular carcinoma ↗
Show evidence (3 references)
PMID:28771246 SUPPORT Human Clinical
"Newborn screening (NBS) utilizing blood succinylacetone as the NBS marker is superior to observing tyrosine levels as a way of identifying neonates with HT-1."
Strong consensus supporting SA-based NBS for HT-1.
PMID:39728402 SUPPORT Human Clinical
"Overall positive predictive values were 27.3% for SUAC, 1.2% for Tyr solely, and 90.1% for Tyr + SUAC."
Provides worldwide performance data for NBS strategies.
PMID:38132825 PARTIAL Human Clinical
"While SA was long considered to be elevated in every TT1 patient, here we present a recent false-negative SA TT1 screen."
Highlights that NBS can have rare false negatives requiring protocol optimization.
Supportive care
Action: supportive care MAXO:0000950
Acute and chronic supportive management includes correction of coagulopathy, electrolyte management for renal tubular dysfunction, vitamin D and phosphate supplementation for rickets, and monitoring of liver and renal function.
Target Phenotypes: Renal Fanconi syndrome ↗ Rickets ↗ Abnormality of coagulation ↗ Edema ↗
Show evidence (1 reference)
PMID:38505790 SUPPORT Human Clinical
"Children with HT-1 require frequent monitoring of liver and renal function to assess disease progression and treatment compliance."
Supports ongoing monitoring and supportive care in HT-1 management.
Genetic counseling
Action: genetic counseling MAXO:0000079
Genetic counseling for affected families, including discussion of autosomal recessive inheritance, 25% recurrence risk, carrier testing, and prenatal or preimplantation genetic diagnosis options.
Show evidence (1 reference)
PMID:28771246 SUPPORT Human Clinical
"Tyrosinemia type I (hepatorenal tyrosinemia, HT-1) is an autosomal recessive condition"
Autosomal recessive inheritance pattern supports the role of genetic counseling.
Neurocognitive assessment and therapy
Action: supportive care MAXO:0000950
Long-term neurocognitive assessment is recommended for HT-1 patients, as they are at risk for neurocognitive impairment even under NTBC therapy. Early intervention and educational support may improve outcomes.
Target Phenotypes: Cognitive impairment ↗
Show evidence (1 reference)
PMID:38505790 SUPPORT Human Clinical
"They are also at risk of long-term neurocognitive impairment, which highlights the need for neurocognitive assessment and therapy."
Directly recommends neurocognitive assessment and therapy for HT-1 patients.
🌍

Environmental Factors

1
Catabolic and dietary stress
Excess dietary protein, protein malnutrition, prolonged fasting, intercurrent catabolic illness, and inadequate calories during procedures or other stressors should be avoided because they can worsen metabolic instability.
Show evidence (1 reference)
PMID:20301688 SUPPORT Other
"Agents/circumstances to avoid: Excessive dietary protein or protein malnutrition inducing catabolic state; prolonged fasting; catabolic illness (intercurrent infection, brief febrile illness post vaccination); inadequate caloric provision during other stressors, especially when fasting is..."
GeneReviews directly lists dietary and catabolic circumstances to avoid in HT-1.
🔬

Biochemical Markers

5
Succinylacetone (SA) (INCREASED)
Context: Succinylacetone is the pathognomonic metabolite for HT-1, elevated in blood and urine. It is the primary biomarker for newborn screening (NBS) with a pooled median cut-off of 1.50 umol/L in dried blood spots. SA is both a toxic metabolite and a highly sensitive and specific diagnostic marker.
Pathograph Readouts
Readout Of Toxic fumarylacetoacetate and maleylacetoacetate accumulation Positive Diagnostic
Elevated succinylacetone reports the toxic tyrosine-intermediate branch and is the pathognomonic HT-1 screening marker.
Show evidence (1 reference)
PMID:38132825 SUPPORT Human Clinical
"Elevated succinylacetone (SA) is pathognomonic for TT1 and therefore often used as marker for TT1 newborn screening (NBS)."
Establishes succinylacetone as the diagnostic readout of HT-1 toxic-metabolite accumulation.
Readout Of Succinylacetone inhibition of heme biosynthesis Positive Diagnostic
Succinylacetone presence reports the ALAD-inhibition branch that drives ALA accumulation and porphyria-like crises.
Show evidence (1 reference)
PMID:6826727 SUPPORT In Vitro
"Our data indicate that succinylacetone is an extremely potent competitive inhibitor of ALA dehydratase in human as well as in animal tissues."
Shows that succinylacetone is the biochemical driver and readout of the heme-biosynthesis inhibition mechanism.
Show evidence (2 references)
PMID:38132825 SUPPORT Human Clinical
"Elevated succinylacetone (SA) is pathognomonic for TT1 and therefore often used as marker for TT1 newborn screening (NBS)."
Directly states SA is pathognomonic and the key NBS marker.
PMID:39728402 SUPPORT Human Clinical
"Most used biomarkers were DBS SUAC (78.9%), DBS Tyrosine (Tyr; 5.3%), or DBS Tyr with second tier SUAC (15.8%). The pooled median cut-off for SUAC was 1.50 µmol/L (range 0.3-7.0 µmol/L)."
Provides worldwide NBS data on SA cut-off values and usage.
Tyrosine (INCREASED)
Context: Plasma tyrosine is elevated, particularly after NTBC treatment which blocks upstream catabolism. Dietary tyrosine and phenylalanine restriction is required to control tyrosine levels during NTBC therapy.
Pathograph Readouts
Correlates With Fumarylacetoacetate hydrolase deficiency Threshold Dependent Diagnostic
Tyrosine is a less specific screening signal for HT-1 than succinylacetone, so its interpretation is threshold- and assay-dependent.
Show evidence (1 reference)
PMID:28771246 SUPPORT Human Clinical
"Newborn screening (NBS) utilizing blood succinylacetone as the NBS marker is superior to observing tyrosine levels as a way of identifying neonates with HT-1."
Consensus review supports tyrosine as an identifiable but inferior biochemical screening readout.
Show evidence (1 reference)
PMID:28771246 SUPPORT Human Clinical
"Newborn screening (NBS) utilizing blood succinylacetone as the NBS marker is superior to observing tyrosine levels as a way of identifying neonates with HT-1."
Confirms elevated tyrosine as a recognized but less specific marker in HT-1.
Alpha-fetoprotein (AFP) (INCREASED)
Context: AFP is markedly elevated in untreated HT-1 and serves as a biomarker for disease activity and HCC surveillance. AFP should decline after NTBC therapy; failure to decline or subsequent rise raises suspicion for HCC or non-adherence.
Pathograph Readouts
Predicts Persistent hepatocarcinogenic programs under NTBC therapy Positive Prognostic
Rising, slowly decreasing, or non-normalizing AFP tracks residual HCC-risk biology during NTBC-treated HT-1.
Show evidence (1 reference)
PMID:17008115 SUPPORT Human Clinical
"Apart from a rise of AFP, a slow AFP decrease, and never normalizing levels of AFP are important predictors of liver cancer development in further life."
Patient AFP trajectories predict later liver cancer risk in NTBC-treated HT-1.
Predicts Hepatocellular carcinoma Positive Monitoring
AFP is monitored because a rise or persistently abnormal decline pattern predicts liver cancer in HT-1.
Show evidence (1 reference)
PMID:17008115 SUPPORT Human Clinical
"A rise of alpha-fetoprotein (AFP) is an indicator of liver cancer."
Establishes AFP rise as a monitoring readout for liver cancer in HT-1.
Show evidence (1 reference)
PMID:17008115 SUPPORT Human Clinical
"Apart from a rise of AFP, a slow AFP decrease, and never normalizing levels of AFP are important predictors of liver cancer development in further life."
Establishes AFP trajectory as a biomarker for liver cancer risk in NTBC-treated HT-1.
Delta-aminolevulinic acid (ALA) (INCREASED)
Context: ALA accumulates due to succinylacetone-mediated inhibition of ALAD in the heme biosynthetic pathway. Elevated urinary ALA is associated with porphyria-like neurovisceral crises.
Pathograph Readouts
Readout Of Succinylacetone inhibition of heme biosynthesis Positive Diagnostic
Urinary ALA accumulation reports succinylacetone-mediated ALAD inhibition in the heme-biosynthesis branch.
Show evidence (1 reference)
PMID:6826727 SUPPORT Human Clinical
"patients with this hereditary disease excrete excessive amounts of delta-aminolevulinic acid (ALA) in urine"
Patient urinary ALA excess directly reports the ALAD-inhibition mechanism.
Show evidence (1 reference)
PMID:6826727 SUPPORT Human Clinical
"patients with this hereditary disease excrete excessive amounts of delta-aminolevulinic acid (ALA) in urine"
Directly supports increased ALA excretion in hereditary tyrosinemia.
Fumarylacetoacetate (FAA) (INCREASED)
Context: FAA is the direct toxic substrate accumulating due to FAH deficiency. It directly induces mitochondrial cytochrome c release and caspase activation in hepatocytes.
Pathograph Readouts
Readout Of Toxic fumarylacetoacetate and maleylacetoacetate accumulation Positive Diagnostic
FAA accumulation reports the proximal toxic-metabolite block downstream of FAH deficiency.
Show evidence (1 reference)
PMID:38505790 SUPPORT Human Clinical
"This leads to the accumulation of toxic metabolites such as fumaryl and maleylacetoacetate, which can damage the liver, kidneys, and nervous system."
Human clinical review directly links FAH deficiency to accumulation of fumaryl/maleylacetoacetate toxic metabolites.
Predicts FAA-induced mitochondrial apoptosis in hepatocytes Positive Diagnostic
FAA is the chemical substrate whose accumulation predicts the mitochondrial apoptosis branch in HT-1 models.
Show evidence (1 reference)
PMID:9689118 SUPPORT In Vitro
"the addition of fumarylacetoacetate induced the release of cytochrome c from the mitochondria."
Cell-free evidence connects FAA directly to mitochondrial cytochrome c release, the initiating event in this apoptosis branch.
Show evidence (2 references)
PMID:38505790 SUPPORT Human Clinical
"This leads to the accumulation of toxic metabolites such as fumaryl and maleylacetoacetate, which can damage the liver, kidneys, and nervous system."
Supports increased fumaryl/fumarylacetoacetate-pathway toxic metabolites due to FAH deficiency.
PMID:9689118 SUPPORT In Vitro
"the addition of fumarylacetoacetate induced the release of cytochrome c from the mitochondria."
Demonstrates direct cell-free toxicity of FAA at the mitochondrial level.
{ }

Source YAML

click to show 
name: Tyrosinemia Type I
category: Mendelian
creation_date: '2025-06-12T20:16:27Z'
updated_date: '2026-05-21T13:02:01Z'
synonyms:
- Hepatorenal tyrosinemia
- HT-1
- TT1
- Tyrosinemia type 1
- FAH deficiency
- Fumarylacetoacetase deficiency
description: 'Tyrosinemia type I (HT-1) is an autosomal recessive inborn error of tyrosine metabolism caused by deficiency of fumarylacetoacetate hydrolase (FAH), the terminal enzyme in the tyrosine catabolic pathway. FAH deficiency leads to accumulation of toxic intermediates including fumarylacetoacetate (FAA), maleylacetoacetate (MAA), and succinylacetone (SA). FAA directly injures hepatocytes through mitochondrial cytochrome c release with caspase-mediated apoptosis. SA inhibits delta-aminolevulinic acid dehydratase, causing porphyria-like neurovisceral crises. Untreated disease leads to acute liver failure, cirrhosis, hepatocellular carcinoma, renal tubular dysfunction, and neurological crises. Nitisinone (NTBC) combined with dietary tyrosine and phenylalanine restriction is the standard of care, dramatically improving survival, though residual risk of hepatocellular carcinoma persists even under continuous therapy. Global incidence is approximately 1 in 100,000.

  '
disease_term:
  preferred_term: tyrosinemia type I
  term:
    id: MONDO:0010161
    label: tyrosinemia type I
parents:
- Inborn Error of Metabolism
prevalence:
- notes: Global incidence is approximately 1 in 100,000 newborns. NBS survey data show incidence ranging from 1/13,636 to 1/750,000 across worldwide programs. Higher prevalence is found in the Saguenay-Lac-Saint-Jean region of Quebec, Canada.
pathophysiology:
- name: Fumarylacetoacetate hydrolase deficiency
  description: 'Loss of FAH activity blocks the terminal enzymatic step of tyrosine catabolism.

    '
  genes:
  - preferred_term: FAH
    term:
      id: hgnc:3579
      label: FAH
  molecular_functions:
  - preferred_term: fumarylacetoacetase activity
    term:
      id: GO:0004334
      label: fumarylacetoacetase activity
    modifier: DECREASED
  biological_processes:
  - preferred_term: tyrosine catabolic process
    term:
      id: GO:0006572
      label: L-tyrosine catabolic process
    modifier: DECREASED
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  evidence:
  - reference: PMID:38505790
    reference_title: "Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Hepatorenal tyrosinemia type 1 (HT-1) is a rare autosomal recessive disease that results from a deficiency of fumaryl acetoacetate hydrolase (FAH), a critical enzyme in the catabolic pathway for tyrosine.
    explanation: Directly supports FAH deficiency as the initiating molecular defect.
  downstream:
  - target: Toxic fumarylacetoacetate and maleylacetoacetate accumulation
    causal_link_type: DIRECT
    description: FAH block causes upstream toxic tyrosine-pathway metabolites to accumulate.
    evidence:
    - reference: PMID:38505790
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: This leads to the accumulation of toxic metabolites such as fumaryl and maleylacetoacetate, which can damage the liver, kidneys, and nervous system.
      explanation: Clinical review evidence directly links FAH deficiency to toxic fumaryl and maleylacetoacetate accumulation.
  - target: Tyrosine
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Impaired terminal tyrosine catabolism and nitisinone treatment both increase tyrosine-pathway substrate burden.
    description: Defective tyrosine catabolism contributes to elevated tyrosine, particularly during HPD inhibition with nitisinone.
    evidence:
    - reference: PMID:28771246
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Newborn screening (NBS) utilizing blood succinylacetone as the NBS marker is superior to observing tyrosine levels as a way of identifying neonates with HT-1.
      explanation: Consensus review supports tyrosine as a measurable but less-specific biochemical signal in HT-1.
- name: Toxic fumarylacetoacetate and maleylacetoacetate accumulation
  description: 'FAH deficiency causes accumulation of fumarylacetoacetate (FAA) and maleylacetoacetate (MAA), with secondary formation of succinylacetone (SA). These toxic tyrosine-pathway metabolites damage the liver, kidneys, and nervous system, and FAA directly triggers mitochondrial cytochrome c release in hepatocytes.

    '
  biological_processes:
  - preferred_term: cellular response to toxic substance
    term:
      id: GO:0097237
      label: cellular response to toxic substance
    modifier: INCREASED
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  chemical_entities:
  - preferred_term: fumarylacetoacetate
    term:
      id: CHEBI:18034
      label: 4-fumarylacetoacetate(2-)
    modifier: INCREASED
  - preferred_term: succinylacetone
    term:
      id: CHEBI:87897
      label: 4,6-dioxoheptanoic acid
    modifier: INCREASED
  evidence:
  - reference: PMID:38505790
    reference_title: "Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: This leads to the accumulation of toxic metabolites such as fumaryl and maleylacetoacetate, which can damage the liver, kidneys, and nervous system.
    explanation: Directly supports toxic-metabolite accumulation downstream of FAH deficiency.
  downstream:
  - target: Fumarylacetoacetate (FAA)
    causal_link_type: DIRECT
    description: FAH deficiency directly increases the toxic substrate fumarylacetoacetate.
    evidence:
    - reference: PMID:38505790
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: This leads to the accumulation of toxic metabolites such as fumaryl and maleylacetoacetate, which can damage the liver, kidneys, and nervous system.
      explanation: Clinical review evidence supports fumaryl/fumarylacetoacetate-pathway metabolite accumulation downstream of FAH deficiency.
  - target: Succinylacetone (SA)
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Accumulated fumarylacetoacetate and maleylacetoacetate generate succinylacetone through alternative routes.
    description: Toxic tyrosine intermediates produce the pathognomonic metabolite succinylacetone.
    evidence:
    - reference: PMID:38132825
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Elevated succinylacetone (SA) is pathognomonic for TT1 and therefore often used as marker for TT1 newborn screening (NBS).
      explanation: Human screening evidence supports succinylacetone as the pathognomonic toxic-metabolite readout of TT1.
  - target: FAA-induced mitochondrial apoptosis in hepatocytes
    causal_link_type: DIRECT
    description: FAA reactivity drives mitochondrial injury and caspase-mediated hepatocyte apoptosis.
    evidence:
    - reference: PMID:9689118
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: the addition of fumarylacetoacetate induced the release of cytochrome c from the mitochondria.
      explanation: Cell-free biochemical evidence directly links FAA to mitochondrial cytochrome c release in the apoptosis branch.
  - target: Succinylacetone inhibition of heme biosynthesis
    causal_link_type: DIRECT
    description: Succinylacetone accumulation perturbs ALAD-linked heme biosynthesis and contributes to porphyria-like crises.
    evidence:
    - reference: PMID:6826727
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Our data indicate that succinylacetone is an extremely potent competitive inhibitor of ALA dehydratase in human as well as in animal tissues.
      explanation: Biochemical evidence directly supports succinylacetone as the ALAD inhibitor linking toxic metabolite accumulation to heme-biosynthesis disruption.
  - target: Renal proximal tubule toxic injury
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Toxic tyrosine-pathway metabolites damage renal tissue as well as liver.
    description: Tyrosine-pathway metabolite toxicity causes renal tubular injury and Fanconi-like tubulopathy.
    evidence:
    - reference: PMID:38505790
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: This leads to the accumulation of toxic metabolites such as fumaryl and maleylacetoacetate, which can damage the liver, kidneys, and nervous system.
      explanation: Clinical review evidence directly links toxic tyrosine metabolites to kidney damage.
  - target: Neurocognitive impairment
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Toxic metabolite effects on the nervous system and long-term treatment factors contribute to neurocognitive risk.
    evidence:
    - reference: PMID:38505790
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: They are also at risk of long-term neurocognitive impairment, which highlights the need for neurocognitive assessment and therapy.
      explanation: Clinical review evidence supports long-term neurocognitive impairment as an HT-1 risk.
  - target: Persistent hepatocarcinogenic programs under NTBC therapy
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Residual FAH deficiency leaves hepatic stress and regenerative programs despite upstream HPD blockade.
    description: Residual FAH deficiency leaves chronic pro-oncogenic hepatic stress despite upstream metabolic blockade by NTBC.
    evidence:
    - reference: PMID:36980965
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: NTBC does not restore the enzymatic defects inflicted by the disease nor does it cure HT1.
      explanation: Continuous-NTBC model evidence supports residual FAH-defect biology despite upstream pharmacologic blockade.
- name: FAA-induced mitochondrial apoptosis in hepatocytes
  description: 'Fumarylacetoacetate directly triggers mitochondrial outer membrane permeabilization with release of cytochrome c, activating the caspase cascade and inducing hepatocyte apoptosis. Caspase inhibitors were shown to prevent liver failure in FAH-deficient mouse models, confirming the causal role of the intrinsic apoptotic pathway.

    '
  biological_processes:
  - preferred_term: intrinsic apoptotic signaling pathway
    term:
      id: GO:0097193
      label: intrinsic apoptotic signaling pathway
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: mitochondrion
    term:
      id: GO:0005739
      label: mitochondrion
  evidence:
  - reference: PMID:9689118
    reference_title: "Hepatocyte injury in tyrosinemia type 1 is induced by fumarylacetoacetate and is inhibited by caspase inhibitors."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Cytochrome c was released from mitochondria prior to liver failure in the Fah-/- Hpd-/- double-mutant mice after the administration of HGA. In a cell-free system, the addition of fumarylacetoacetate induced the release of cytochrome c from the mitochondria.
    explanation: Demonstrates that FAA directly induces mitochondrial cytochrome c release in tyrosinemia model.
  - reference: PMID:9689118
    reference_title: "Hepatocyte injury in tyrosinemia type 1 is induced by fumarylacetoacetate and is inhibited by caspase inhibitors."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: We also found that caspase inhibitors were highly effective in preventing the liver failure induced by HGA in the double-mutant mice.
    explanation: Proves caspase-mediated apoptosis is the mechanism of hepatocyte injury in tyrosinemia.
  downstream:
  - target: Acute liver failure
    causal_link_type: DIRECT
    description: Caspase-mediated hepatocyte death causes acute hepatic failure in severe or untreated HT-1.
    evidence:
    - reference: PMID:9689118
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: We also found that caspase inhibitors were highly effective in preventing the liver failure induced by HGA in the double-mutant mice.
      explanation: Mouse-model evidence supports caspase-mediated hepatocyte injury as causal for liver failure.
  - target: Coagulopathy
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Hepatocyte apoptosis causes hepatic synthetic failure.
    description: Acute hepatic failure impairs coagulation factor synthesis.
    evidence:
    - reference: PMID:28771246
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Tyrosinemia type I (hepatorenal tyrosinemia, HT-1) is an autosomal recessive condition resulting in hepatic failure
      explanation: Clinical consensus supports hepatic failure as a core HT-1 manifestation, providing the clinical basis for downstream coagulopathy.
    - reference: PMID:20301688
      supports: SUPPORT
      evidence_source: OTHER
      snippet: routine coagulation tests, liver enzymes, and bilirubin concentrations should be measured per age-related recommendations.
      explanation: GeneReviews surveillance guidance explicitly includes routine coagulation testing in HT-1 liver-disease monitoring.
  - target: Hepatomegaly
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Hepatic injury and regenerative stress can present with enlarged liver.
    evidence:
    - reference: PMID:39050308
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: We present a case of HT-1 in a three-year-old female child characterized by abdominal distension, facial edema, lower limb edema, and an enlarged liver with parenchymal disease.
      explanation: Human case evidence documents enlarged liver with parenchymal disease in late-presenting HT-1.
- name: Renal proximal tubule toxic injury
  description: 'Accumulated tyrosine-pathway metabolites injure kidney tissue, especially the proximal tubule, causing a Fanconi-like renal phenotype with phosphate wasting. This renal tubular mechanism explains renal tubular dysfunction and secondary hypophosphatemic rickets in HT-1.

    '
  biological_processes:
  - preferred_term: cellular response to toxic substance
    term:
      id: GO:0097237
      label: cellular response to toxic substance
  cell_types:
  - preferred_term: proximal tubule epithelial cell
    term:
      id: CL:0002306
      label: epithelial cell of proximal tubule
  locations:
  - preferred_term: proximal tubule
    term:
      id: UBERON:0004134
      label: proximal tubule
  evidence:
  - reference: PMID:38505790
    reference_title: "Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: This leads to the accumulation of toxic metabolites such as fumaryl and maleylacetoacetate, which can damage the liver, kidneys, and nervous system.
    explanation: Directly links toxic metabolite accumulation to kidney injury in HT-1.
  downstream:
  - target: Renal tubular dysfunction
    causal_link_type: DIRECT
    description: Toxic injury to proximal tubule epithelium produces Fanconi-like renal tubular dysfunction.
    evidence:
    - reference: PMID:28771246
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Tyrosinemia type I (hepatorenal tyrosinemia, HT-1) is an autosomal recessive condition resulting in hepatic failure with comorbidities involving the renal and neurologic systems
      explanation: Clinical consensus directly supports renal-system involvement in HT-1.
  - target: Rickets
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Proximal tubular phosphate wasting causes hypophosphatemic rickets.
    description: Renal Fanconi syndrome causes phosphate wasting and secondary rickets.
    evidence:
    - reference: PMID:20301688
      supports: SUPPORT
      evidence_source: OTHER
      snippet: liver dysfunction and renal tubular dysfunction associated with growth failure and rickets.
      explanation: GeneReviews directly links renal tubular dysfunction with growth failure and rickets in untreated HT-1.
- name: Chronic hepatic injury and regeneration
  description: 'Untreated or late-treated HT-1 produces chronic hepatic injury with regeneration, fibrosis, cirrhosis, and malignant transformation risk. Continuous NTBC reduces acute toxicity but does not restore FAH activity, so residual liver-disease and HCC-associated programs can persist.

    '
  biological_processes:
  - preferred_term: liver regeneration
    term:
      id: GO:0097421
      label: liver regeneration
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  evidence:
  - reference: PMID:38132825
    reference_title: "A False-Negative Newborn Screen for Tyrosinemia Type 1-Need for Re-Evaluation of Newborn Screening with Succinylacetone."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Undiagnosed and untreated tyrosinemia type 1 (TT1) individuals carry a significant risk for developing liver fibrosis, cirrhosis and hepatocellular carcinoma (HCC).
    explanation: Directly links untreated HT-1 to fibrosis, cirrhosis, and HCC.
  - reference: PMID:36980965
    reference_title: "Hereditary Tyrosinemia Type 1 Mice under Continuous Nitisinone Treatment Display Remnants of an Uncorrected Liver Disease Phenotype."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: The differentially expressed genes were enriched in toxicological gene classes related to liver disease, liver damage, liver regeneration and liver cancer, in particular HCC.
    explanation: Mouse transcriptomics supports persistent hepatic injury, regeneration, and HCC-related programs under NTBC.
  downstream:
  - target: Hepatic fibrosis
    causal_link_type: DIRECT
    description: Chronic hepatic injury in untreated HT-1 produces fibrosis.
    evidence:
    - reference: PMID:38132825
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Undiagnosed and untreated tyrosinemia type 1 (TT1) individuals carry a significant risk for developing liver fibrosis, cirrhosis and hepatocellular carcinoma (HCC).
      explanation: Human evidence directly supports liver fibrosis as a risk of untreated TT1.
  - target: Hepatic cirrhosis
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Progressive fibrosis remodels hepatic architecture.
    description: Chronic hepatic injury and fibrosis can progress to cirrhosis.
    evidence:
    - reference: PMID:38132825
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Undiagnosed and untreated tyrosinemia type 1 (TT1) individuals carry a significant risk for developing liver fibrosis, cirrhosis and hepatocellular carcinoma (HCC).
      explanation: Human evidence supports cirrhosis as part of the chronic untreated TT1 liver-disease spectrum.
  - target: Hepatocellular carcinoma
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Chronic hepatocyte injury and regeneration create pro-oncogenic stress.
    description: Chronic liver injury and regeneration increase HCC risk.
    evidence:
    - reference: PMID:38132825
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Undiagnosed and untreated tyrosinemia type 1 (TT1) individuals carry a significant risk for developing liver fibrosis, cirrhosis and hepatocellular carcinoma (HCC).
      explanation: Human evidence supports HCC as a complication of the chronic untreated TT1 hepatic-injury branch.
  - target: Failure to thrive
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Chronic liver disease and metabolic instability impair growth.
    evidence:
    - reference: PMID:20301688
      supports: SUPPORT
      evidence_source: OTHER
      snippet: liver dysfunction and renal tubular dysfunction associated with growth failure and rickets.
      explanation: GeneReviews supports growth failure in the context of liver and renal tubular dysfunction in untreated HT-1.
  - target: Edema
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Liver synthetic dysfunction and portal-hypertensive physiology can cause fluid retention.
    description: Advanced hepatic disease can cause peripheral edema or ascites.
    evidence:
    - reference: PMID:39050308
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: We present a case of HT-1 in a three-year-old female child characterized by abdominal distension, facial edema, lower limb edema, and an enlarged liver with parenchymal disease.
      explanation: Human case evidence documents edema in a patient with HT-1 liver disease.
- name: Succinylacetone inhibition of heme biosynthesis
  description: 'Succinylacetone (SA) is a competitive inhibitor of delta-aminolevulinic acid dehydratase (ALAD), blocking the heme biosynthetic pathway and causing accumulation of delta-aminolevulinic acid (ALA). This produces porphyria-like neurovisceral crises with neuropathy, similar to acute intermittent porphyria or lead poisoning.

    '
  biological_processes:
  - preferred_term: heme biosynthetic process
    term:
      id: GO:0006783
      label: heme biosynthetic process
    modifier: DECREASED
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  genes:
  - preferred_term: ALAD
    term:
      id: hgnc:395
      label: ALAD
  chemical_entities:
  - preferred_term: succinylacetone
    term:
      id: CHEBI:87897
      label: 4,6-dioxoheptanoic acid
    modifier: INCREASED
  - preferred_term: delta-aminolevulinic acid
    term:
      id: CHEBI:17549
      label: 5-aminolevulinic acid
    modifier: INCREASED
  - preferred_term: heme
    term:
      id: CHEBI:30413
      label: heme
    modifier: DECREASED
  evidence:
  - reference: PMID:6826727
    reference_title: "Hereditary tyrosinemia and the heme biosynthetic pathway. Profound inhibition of delta-aminolevulinic acid dehydratase activity by succinylacetone."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Our data indicate that succinylacetone is an extremely potent competitive inhibitor of ALA dehydratase in human as well as in animal tissues.
    explanation: Biochemical evidence directly supports succinylacetone inhibition of ALA dehydratase.
  - reference: PMID:6826727
    reference_title: "Hereditary tyrosinemia and the heme biosynthetic pathway. Profound inhibition of delta-aminolevulinic acid dehydratase activity by succinylacetone."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: patients with this hereditary disease excrete excessive amounts of delta-aminolevulinic acid (ALA) in urine and that certain patients have an accompanying clinical syndrome resembling that of acute intermittent porphyria (AIP).
    explanation: Patient observations connect HT-1 to ALA accumulation and porphyria-like neurovisceral crises.
  - reference: PMID:6826727
    reference_title: "Hereditary tyrosinemia and the heme biosynthetic pathway. Profound inhibition of delta-aminolevulinic acid dehydratase activity by succinylacetone."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: In cultured hepatocytes, succinylacetone also inhibited ALA dehydratase activity, decreased the cellular content of heme and cytochrome P-450
    explanation: Supports reduced heme-biosynthesis output downstream of succinylacetone-mediated ALAD inhibition.
  downstream:
  - target: Delta-aminolevulinic acid (ALA)
    causal_link_type: DIRECT
    description: ALAD inhibition increases ALA accumulation.
    evidence:
    - reference: PMID:6826727
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: patients with this hereditary disease excrete excessive amounts of delta-aminolevulinic acid (ALA) in urine
      explanation: Human biochemical evidence supports ALA accumulation downstream of succinylacetone-mediated ALAD inhibition.
  - target: Peripheral neuropathy
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - ALA accumulation produces porphyria-like neurovisceral crises.
    description: Porphyria-like crises in HT-1 can include peripheral neuropathy.
    evidence:
    - reference: PMID:20301688
      supports: SUPPORT
      evidence_source: OTHER
      snippet: neurologic crises lasting one to seven days that can include change in mental status, abdominal pain, peripheral neuropathy, and/or respiratory failure
      explanation: GeneReviews directly lists peripheral neuropathy during HT-1 neurologic crises.
  - target: Abdominal pain
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - ALA accumulation produces porphyria-like neurovisceral crises.
    description: Porphyria-like neurologic crises in HT-1 can include abdominal pain.
    evidence:
    - reference: PMID:20301688
      supports: SUPPORT
      evidence_source: OTHER
      snippet: neurologic crises lasting one to seven days that can include change in mental status, abdominal pain, peripheral neuropathy, and/or respiratory failure
      explanation: GeneReviews directly lists abdominal pain during HT-1 neurologic crises.
  - target: Encephalopathy
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - ALA accumulation produces porphyria-like neurovisceral crises.
    description: Porphyria-like neurologic crises in HT-1 can include altered mental status.
    evidence:
    - reference: PMID:20301688
      supports: SUPPORT
      evidence_source: OTHER
      snippet: neurologic crises lasting one to seven days that can include change in mental status, abdominal pain, peripheral neuropathy, and/or respiratory failure
      explanation: GeneReviews directly lists change in mental status during HT-1 neurologic crises.
  - target: Respiratory failure
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - ALA accumulation produces porphyria-like neurovisceral crises.
    description: Severe neurologic crises in HT-1 can include respiratory failure.
    evidence:
    - reference: PMID:20301688
      supports: SUPPORT
      evidence_source: OTHER
      snippet: neurologic crises lasting one to seven days that can include change in mental status, abdominal pain, peripheral neuropathy, and/or respiratory failure
      explanation: GeneReviews directly lists respiratory failure during HT-1 neurologic crises.
- name: Persistent hepatocarcinogenic programs under NTBC therapy
  description: 'Although nitisinone prevents acute toxicity by blocking upstream toxic metabolite formation, it does not restore FAH activity. Transcriptomic analysis in FAH-deficient mice under continuous NTBC revealed persistent enrichment of genes related to liver disease, liver regeneration, and hepatocellular carcinoma. This supports the ongoing HCC risk even in treated patients.

    '
  biological_processes:
  - preferred_term: liver regeneration
    term:
      id: GO:0097421
      label: liver regeneration
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  evidence:
  - reference: PMID:36980965
    reference_title: "Hereditary Tyrosinemia Type 1 Mice under Continuous Nitisinone Treatment Display Remnants of an Uncorrected Liver Disease Phenotype."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: The differentially expressed genes were enriched in toxicological gene classes related to liver disease, liver damage, liver regeneration and liver cancer, in particular HCC.
    explanation: Demonstrates persistent HCC-related gene expression under NTBC therapy in mouse model.
  - reference: PMID:36980965
    reference_title: "Hereditary Tyrosinemia Type 1 Mice under Continuous Nitisinone Treatment Display Remnants of an Uncorrected Liver Disease Phenotype."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: NTBC does not restore the enzymatic defects inflicted by the disease nor does it cure HT1.
    explanation: Confirms NTBC does not cure the underlying enzymatic deficiency.
  downstream:
  - target: Hepatocellular carcinoma
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Persistent liver-disease and HCC-associated transcriptional programs remain under NTBC.
    description: Residual hepatic disease programs under NTBC support sustained HCC risk.
    evidence:
    - reference: PMID:36980965
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: The differentially expressed genes were enriched in toxicological gene classes related to liver disease, liver damage, liver regeneration and liver cancer, in particular HCC.
      explanation: Continuous-NTBC mouse transcriptomics supports persistent HCC-related liver-disease programs.
  - target: Alpha-fetoprotein (AFP)
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - AFP is used as a marker of hepatic disease activity and HCC surveillance.
    description: Persistent HCC risk motivates AFP surveillance in HT-1.
    evidence:
    - reference: PMID:17008115
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: A rise of alpha-fetoprotein (AFP) is an indicator of liver cancer.
      explanation: Patient AFP data support AFP as a surveillance readout tied to liver cancer risk in HT-1.
  - target: Elevated alpha-fetoprotein
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Hepatic injury and HCC risk drive AFP monitoring.
    description: AFP elevation is tracked as a marker of disease activity and malignant transformation risk.
    evidence:
    - reference: PMID:17008115
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Apart from a rise of AFP, a slow AFP decrease, and never normalizing levels of AFP are important predictors of liver cancer development in further life.
      explanation: Human AFP trajectory data support elevated or non-normalizing AFP as a biomarker of HT-1 liver cancer risk.
phenotypes:
- name: Acute liver failure
  description: 'Acute hepatic decompensation is a hallmark of untreated or severe HT-1, driven by FAA-mediated oxidative damage and caspase-dependent apoptosis of hepatocytes. In untreated acute-form HT-1, liver failure typically presents in the first months of life.

    '
  phenotype_term:
    preferred_term: Acute hepatic failure
    term:
      id: HP:0006554
      label: Acute hepatic failure
  evidence:
  - reference: PMID:28771246
    reference_title: "Diagnosis and treatment of tyrosinemia type I: a US and Canadian consensus group review and recommendations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Tyrosinemia type I (hepatorenal tyrosinemia, HT-1) is an autosomal recessive condition resulting in hepatic failure with comorbidities involving the renal and neurologic systems
    explanation: Directly supports hepatic failure as a primary manifestation.
  - reference: PMID:38505790
    reference_title: "Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Patients failing medical treatment (eg, due to non-adherence), and who develop acute liver failure (ALF), have HCC or evidence of histologically proven dysplastic liver nodule(s)
    explanation: Confirms acute liver failure as an indication for liver transplantation in HT-1.
- name: Hepatic fibrosis
  description: 'Progressive liver fibrosis and cirrhosis develop in untreated or late-treated HT-1. Even false-negative NBS cases have presented with cirrhosis years later.

    '
  phenotype_term:
    preferred_term: Hepatic fibrosis
    term:
      id: HP:0001395
      label: Hepatic fibrosis
  evidence:
  - reference: PMID:38132825
    reference_title: "A False-Negative Newborn Screen for Tyrosinemia Type 1-Need for Re-Evaluation of Newborn Screening with Succinylacetone."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Undiagnosed and untreated tyrosinemia type 1 (TT1) individuals carry a significant risk for developing liver fibrosis, cirrhosis and hepatocellular carcinoma (HCC).
    explanation: Directly lists liver fibrosis as a significant risk in untreated HT-1.
- name: Hepatic cirrhosis
  description: 'Cirrhosis develops progressively in untreated HT-1 as a consequence of chronic hepatocyte injury and regeneration. A case of false-negative NBS presented at age 9 with HCC in a cirrhotic liver.

    '
  phenotype_term:
    preferred_term: Cirrhosis
    term:
      id: HP:0001394
      label: Cirrhosis
  evidence:
  - reference: PMID:38132825
    reference_title: "A False-Negative Newborn Screen for Tyrosinemia Type 1-Need for Re-Evaluation of Newborn Screening with Succinylacetone."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: A nine-year-old boy presented with HCC in a cirrhotic liver.
    explanation: Documents cirrhosis in a missed NBS case of HT-1.
  - reference: PMID:39050308
    reference_title: "Hereditary Tyrosinemia Type-1 With Late Presentation: A Case Report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: A liver biopsy confirmed mixed nodular cirrhosis, and a subsequent whole exome sequencing revealed autosomal recessive inheritance of tyrosinemia type 1.
    explanation: Confirms cirrhosis in a late-presenting HT-1 patient.
- name: Hepatocellular carcinoma
  description: 'HCC is the most feared long-term complication of HT-1. Risk persists even under NTBC therapy, necessitating lifelong surveillance with alpha-fetoprotein monitoring and liver imaging.

    '
  phenotype_term:
    preferred_term: Hepatocellular carcinoma
    term:
      id: HP:0001402
      label: Hepatocellular carcinoma
  evidence:
  - reference: PMID:38505790
    reference_title: "Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: NTBC combined with dietary therapy, if initiated early, can provide liver transplant (LT) free survival and reduce the risk of hepatocellular carcinoma (HCC).
    explanation: Confirms HCC as a recognized risk requiring monitoring.
- name: Renal tubular dysfunction
  description: 'Proximal renal tubular dysfunction with a Fanconi-like syndrome is a core manifestation, resulting from toxic metabolite damage to renal tubular epithelial cells. May manifest as aminoaciduria, phosphaturia, glycosuria, and renal tubular acidosis.

    '
  phenotype_term:
    preferred_term: Renal Fanconi syndrome
    term:
      id: HP:0001994
      label: Renal Fanconi syndrome
  evidence:
  - reference: PMID:38505790
    reference_title: "Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: This leads to the accumulation of toxic metabolites such as fumaryl and maleylacetoacetate, which can damage the liver, kidneys, and nervous system.
    explanation: Confirms kidney damage from toxic metabolite accumulation.
  - reference: PMID:28771246
    reference_title: "Diagnosis and treatment of tyrosinemia type I: a US and Canadian consensus group review and recommendations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Tyrosinemia type I (hepatorenal tyrosinemia, HT-1) is an autosomal recessive condition resulting in hepatic failure with comorbidities involving the renal and neurologic systems
    explanation: Renal involvement is a defining feature of hepatorenal tyrosinemia.
- name: Rickets
  description: 'Hypophosphatemic rickets develops secondary to renal tubular phosphate wasting in the context of Fanconi-like tubulopathy.

    '
  phenotype_term:
    preferred_term: Rickets
    term:
      id: HP:0002748
      label: Rickets
  evidence:
  - reference: PMID:20301688
    reference_title: "Tyrosinemia Type I."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: liver dysfunction and renal tubular dysfunction associated with growth failure and rickets.
    explanation: GeneReviews directly lists rickets in association with renal tubular dysfunction in untreated HT-1.
- name: Peripheral neuropathy
  description: 'Porphyria-like neurovisceral crises with peripheral neuropathy result from succinylacetone-mediated inhibition of ALAD and accumulation of delta-aminolevulinic acid. Episodes mimic acute intermittent porphyria.

    '
  phenotype_term:
    preferred_term: Peripheral neuropathy
    term:
      id: HP:0009830
      label: Peripheral neuropathy
  evidence:
  - reference: PMID:20301688
    reference_title: "Tyrosinemia Type I."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: neurologic crises lasting one to seven days that can include change in mental status, abdominal pain, peripheral neuropathy, and/or respiratory failure
    explanation: GeneReviews directly lists peripheral neuropathy during HT-1 neurologic crises.
  - reference: PMID:28771246
    reference_title: "Diagnosis and treatment of tyrosinemia type I: a US and Canadian consensus group review and recommendations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Tyrosinemia type I (hepatorenal tyrosinemia, HT-1) is an autosomal recessive condition resulting in hepatic failure with comorbidities involving the renal and neurologic systems
    explanation: Neurologic system involvement includes neuropathic crises.
- name: Abdominal pain
  description: 'Porphyria-like neurologic crises in HT-1 can include abdominal pain, linking succinylacetone-mediated heme-biosynthesis inhibition to an acute neurovisceral manifestation.

    '
  phenotype_term:
    preferred_term: Abdominal pain
    term:
      id: HP:0002027
      label: Abdominal pain
  evidence:
  - reference: PMID:20301688
    reference_title: "Tyrosinemia Type I."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: neurologic crises lasting one to seven days that can include change in mental status, abdominal pain, peripheral neuropathy, and/or respiratory failure
    explanation: GeneReviews directly lists abdominal pain during HT-1 neurologic crises.
- name: Encephalopathy
  description: 'Neurologic crises in HT-1 can include change in mental status, captured here as encephalopathy in the porphyria-like crisis branch.

    '
  phenotype_term:
    preferred_term: Change in mental status
    term:
      id: HP:0001298
      label: Encephalopathy
  evidence:
  - reference: PMID:20301688
    reference_title: "Tyrosinemia Type I."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: neurologic crises lasting one to seven days that can include change in mental status, abdominal pain, peripheral neuropathy, and/or respiratory failure
    explanation: GeneReviews directly lists change in mental status during HT-1 neurologic crises.
- name: Respiratory failure
  description: 'Severe neurologic crises in HT-1 can include respiratory failure, consistent with the acute porphyria-like neurovisceral branch.

    '
  phenotype_term:
    preferred_term: Respiratory failure
    term:
      id: HP:0002878
      label: Respiratory failure
  evidence:
  - reference: PMID:20301688
    reference_title: "Tyrosinemia Type I."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: neurologic crises lasting one to seven days that can include change in mental status, abdominal pain, peripheral neuropathy, and/or respiratory failure
    explanation: GeneReviews directly lists respiratory failure during HT-1 neurologic crises.
- name: Neurocognitive impairment
  description: 'Long-term neurocognitive impairment is a recognized risk in HT-1 patients, even those treated early with NTBC. Neurocognitive assessment and therapy are recommended in clinical follow-up.

    '
  phenotype_term:
    preferred_term: Cognitive impairment
    term:
      id: HP:0100543
      label: Cognitive impairment
  evidence:
  - reference: PMID:38505790
    reference_title: "Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: They are also at risk of long-term neurocognitive impairment, which highlights the need for neurocognitive assessment and therapy.
    explanation: Directly states neurocognitive impairment as a long-term risk in HT-1.
- name: Failure to thrive
  description: 'Poor growth and failure to thrive occur in untreated or poorly controlled HT-1 due to chronic liver disease, renal dysfunction, and metabolic instability.

    '
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:20301688
    reference_title: "Tyrosinemia Type I."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: liver dysfunction and renal tubular dysfunction associated with growth failure and rickets.
    explanation: GeneReviews directly supports growth failure in untreated HT-1.
  - reference: PMID:39050308
    reference_title: "Hereditary Tyrosinemia Type-1 With Late Presentation: A Case Report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We present a case of HT-1 in a three-year-old female child characterized by abdominal distension, facial edema, lower limb edema, and an enlarged liver with parenchymal disease.
    explanation: Case demonstrates growth and nutritional compromise in untreated HT-1.
- name: Hepatomegaly
  description: 'Liver enlargement is common in HT-1 due to hepatocellular injury, regeneration nodules, and progressive liver disease.

    '
  phenotype_term:
    preferred_term: Hepatomegaly
    term:
      id: HP:0002240
      label: Hepatomegaly
  evidence:
  - reference: PMID:39050308
    reference_title: "Hereditary Tyrosinemia Type-1 With Late Presentation: A Case Report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We present a case of HT-1 in a three-year-old female child characterized by abdominal distension, facial edema, lower limb edema, and an enlarged liver with parenchymal disease.
    explanation: Documents hepatomegaly in a late-presenting HT-1 patient.
- name: Coagulopathy
  description: 'Hepatic synthetic dysfunction leads to coagulopathy, which is one of the earliest signs of liver failure in acute-form HT-1.

    '
  phenotype_term:
    preferred_term: Abnormality of coagulation
    term:
      id: HP:0001928
      label: Abnormality of coagulation
  evidence:
  - reference: PMID:28771246
    reference_title: "Diagnosis and treatment of tyrosinemia type I: a US and Canadian consensus group review and recommendations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Tyrosinemia type I (hepatorenal tyrosinemia, HT-1) is an autosomal recessive condition resulting in hepatic failure
    explanation: Coagulopathy is a direct consequence of hepatic failure in HT-1.
- name: Elevated alpha-fetoprotein
  description: 'Alpha-fetoprotein (AFP) is markedly elevated in HT-1 and serves as both a diagnostic and monitoring biomarker. AFP should decrease after NTBC initiation; rising or persistently elevated AFP raises suspicion for hepatocellular carcinoma or treatment non-adherence.

    '
  phenotype_term:
    preferred_term: Elevated circulating alpha-fetoprotein concentration
    term:
      id: HP:0006254
      label: Elevated circulating alpha-fetoprotein concentration
  evidence:
  - reference: PMID:17008115
    reference_title: "Tyrosinemia type I treated by NTBC: how does AFP predict liver cancer?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: A rise of alpha-fetoprotein (AFP) is an indicator of liver cancer.
    explanation: Directly supports AFP elevation as a clinically important HT-1 surveillance finding.
- name: Edema
  description: 'Peripheral edema and ascites may occur due to hepatic synthetic failure with hypoalbuminemia.

    '
  phenotype_term:
    preferred_term: Edema
    term:
      id: HP:0000969
      label: Edema
  evidence:
  - reference: PMID:39050308
    reference_title: "Hereditary Tyrosinemia Type-1 With Late Presentation: A Case Report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We present a case of HT-1 in a three-year-old female child characterized by abdominal distension, facial edema, lower limb edema, and an enlarged liver with parenchymal disease.
    explanation: Directly documents edema in an HT-1 patient with liver disease.
biochemical:
- name: Succinylacetone (SA)
  presence: INCREASED
  context: 'Succinylacetone is the pathognomonic metabolite for HT-1, elevated in blood and urine. It is the primary biomarker for newborn screening (NBS) with a pooled median cut-off of 1.50 umol/L in dried blood spots. SA is both a toxic metabolite and a highly sensitive and specific diagnostic marker.

    '
  biomarker_term:
    preferred_term: succinylacetone
    term:
      id: CHEBI:87897
      label: 4,6-dioxoheptanoic acid
  readouts:
  - target: Toxic fumarylacetoacetate and maleylacetoacetate accumulation
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Elevated succinylacetone reports the toxic tyrosine-intermediate branch and is the pathognomonic HT-1 screening marker.
    evidence:
    - reference: PMID:38132825
      reference_title: "A False-Negative Newborn Screen for Tyrosinemia Type 1-Need for Re-Evaluation of Newborn Screening with Succinylacetone."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Elevated succinylacetone (SA) is pathognomonic for TT1 and therefore often used as marker for TT1 newborn screening (NBS).
      explanation: Establishes succinylacetone as the diagnostic readout of HT-1 toxic-metabolite accumulation.
  - target: Succinylacetone inhibition of heme biosynthesis
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Succinylacetone presence reports the ALAD-inhibition branch that drives ALA accumulation and porphyria-like crises.
    evidence:
    - reference: PMID:6826727
      reference_title: "Hereditary tyrosinemia and the heme biosynthetic pathway. Profound inhibition of delta-aminolevulinic acid dehydratase activity by succinylacetone."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Our data indicate that succinylacetone is an extremely potent competitive inhibitor of ALA dehydratase in human as well as in animal tissues.
      explanation: Shows that succinylacetone is the biochemical driver and readout of the heme-biosynthesis inhibition mechanism.
  evidence:
  - reference: PMID:38132825
    reference_title: "A False-Negative Newborn Screen for Tyrosinemia Type 1-Need for Re-Evaluation of Newborn Screening with Succinylacetone."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Elevated succinylacetone (SA) is pathognomonic for TT1 and therefore often used as marker for TT1 newborn screening (NBS).
    explanation: Directly states SA is pathognomonic and the key NBS marker.
  - reference: PMID:39728402
    reference_title: "Evaluation of Neonatal Screening Programs for Tyrosinemia Type 1 Worldwide."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Most used biomarkers were DBS SUAC (78.9%), DBS Tyrosine (Tyr; 5.3%), or DBS Tyr with second tier SUAC (15.8%). The pooled median cut-off for SUAC was 1.50 µmol/L (range 0.3-7.0 µmol/L).
    explanation: Provides worldwide NBS data on SA cut-off values and usage.
- name: Tyrosine
  presence: INCREASED
  context: 'Plasma tyrosine is elevated, particularly after NTBC treatment which blocks upstream catabolism. Dietary tyrosine and phenylalanine restriction is required to control tyrosine levels during NTBC therapy.

    '
  biomarker_term:
    preferred_term: tyrosine
    term:
      id: CHEBI:18186
      label: tyrosine
  readouts:
  - target: Fumarylacetoacetate hydrolase deficiency
    relationship: CORRELATES_WITH
    direction: THRESHOLD_DEPENDENT
    endpoint_context: DIAGNOSTIC
    interpretation: Tyrosine is a less specific screening signal for HT-1 than succinylacetone, so its interpretation is threshold- and assay-dependent.
    evidence:
    - reference: PMID:28771246
      reference_title: "Diagnosis and treatment of tyrosinemia type I: a US and Canadian consensus group review and recommendations."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Newborn screening (NBS) utilizing blood succinylacetone as the NBS marker is superior to observing tyrosine levels as a way of identifying neonates with HT-1.
      explanation: Consensus review supports tyrosine as an identifiable but inferior biochemical screening readout.
  evidence:
  - reference: PMID:28771246
    reference_title: "Diagnosis and treatment of tyrosinemia type I: a US and Canadian consensus group review and recommendations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Newborn screening (NBS) utilizing blood succinylacetone as the NBS marker is superior to observing tyrosine levels as a way of identifying neonates with HT-1.
    explanation: Confirms elevated tyrosine as a recognized but less specific marker in HT-1.
- name: Alpha-fetoprotein (AFP)
  presence: INCREASED
  context: 'AFP is markedly elevated in untreated HT-1 and serves as a biomarker for disease activity and HCC surveillance. AFP should decline after NTBC therapy; failure to decline or subsequent rise raises suspicion for HCC or non-adherence.

    '
  biomarker_term:
    preferred_term: Alpha-Fetoprotein
    term:
      id: NCIT:C16278
      label: Alpha-Fetoprotein
  readouts:
  - target: Persistent hepatocarcinogenic programs under NTBC therapy
    relationship: PREDICTS
    direction: POSITIVE
    endpoint_context: PROGNOSTIC
    interpretation: Rising, slowly decreasing, or non-normalizing AFP tracks residual HCC-risk biology during NTBC-treated HT-1.
    evidence:
    - reference: PMID:17008115
      reference_title: "Tyrosinemia type I treated by NTBC: how does AFP predict liver cancer?"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Apart from a rise of AFP, a slow AFP decrease, and never normalizing levels of AFP are important predictors of liver cancer development in further life.
      explanation: Patient AFP trajectories predict later liver cancer risk in NTBC-treated HT-1.
  - target: Hepatocellular carcinoma
    relationship: PREDICTS
    direction: POSITIVE
    endpoint_context: MONITORING
    interpretation: AFP is monitored because a rise or persistently abnormal decline pattern predicts liver cancer in HT-1.
    evidence:
    - reference: PMID:17008115
      reference_title: "Tyrosinemia type I treated by NTBC: how does AFP predict liver cancer?"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: A rise of alpha-fetoprotein (AFP) is an indicator of liver cancer.
      explanation: Establishes AFP rise as a monitoring readout for liver cancer in HT-1.
  evidence:
  - reference: PMID:17008115
    reference_title: "Tyrosinemia type I treated by NTBC: how does AFP predict liver cancer?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Apart from a rise of AFP, a slow AFP decrease, and never normalizing levels of AFP are important predictors of liver cancer development in further life.
    explanation: Establishes AFP trajectory as a biomarker for liver cancer risk in NTBC-treated HT-1.
- name: Delta-aminolevulinic acid (ALA)
  presence: INCREASED
  context: 'ALA accumulates due to succinylacetone-mediated inhibition of ALAD in the heme biosynthetic pathway. Elevated urinary ALA is associated with porphyria-like neurovisceral crises.

    '
  biomarker_term:
    preferred_term: 5-aminolevulinic acid
    term:
      id: CHEBI:17549
      label: 5-aminolevulinic acid
  readouts:
  - target: Succinylacetone inhibition of heme biosynthesis
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Urinary ALA accumulation reports succinylacetone-mediated ALAD inhibition in the heme-biosynthesis branch.
    evidence:
    - reference: PMID:6826727
      reference_title: "Hereditary tyrosinemia and the heme biosynthetic pathway. Profound inhibition of delta-aminolevulinic acid dehydratase activity by succinylacetone."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: patients with this hereditary disease excrete excessive amounts of delta-aminolevulinic acid (ALA) in urine
      explanation: Patient urinary ALA excess directly reports the ALAD-inhibition mechanism.
  evidence:
  - reference: PMID:6826727
    reference_title: "Hereditary tyrosinemia and the heme biosynthetic pathway. Profound inhibition of delta-aminolevulinic acid dehydratase activity by succinylacetone."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: patients with this hereditary disease excrete excessive amounts of delta-aminolevulinic acid (ALA) in urine
    explanation: Directly supports increased ALA excretion in hereditary tyrosinemia.
- name: Fumarylacetoacetate (FAA)
  presence: INCREASED
  context: 'FAA is the direct toxic substrate accumulating due to FAH deficiency. It directly induces mitochondrial cytochrome c release and caspase activation in hepatocytes.

    '
  biomarker_term:
    preferred_term: fumarylacetoacetate
    term:
      id: CHEBI:18034
      label: 4-fumarylacetoacetate(2-)
  readouts:
  - target: Toxic fumarylacetoacetate and maleylacetoacetate accumulation
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: FAA accumulation reports the proximal toxic-metabolite block downstream of FAH deficiency.
    evidence:
    - reference: PMID:38505790
      reference_title: "Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: This leads to the accumulation of toxic metabolites such as fumaryl and maleylacetoacetate, which can damage the liver, kidneys, and nervous system.
      explanation: Human clinical review directly links FAH deficiency to accumulation of fumaryl/maleylacetoacetate toxic metabolites.
  - target: FAA-induced mitochondrial apoptosis in hepatocytes
    relationship: PREDICTS
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: FAA is the chemical substrate whose accumulation predicts the mitochondrial apoptosis branch in HT-1 models.
    evidence:
    - reference: PMID:9689118
      reference_title: "Hepatocyte injury in tyrosinemia type 1 is induced by fumarylacetoacetate and is inhibited by caspase inhibitors."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: the addition of fumarylacetoacetate induced the release of cytochrome c from the mitochondria.
      explanation: Cell-free evidence connects FAA directly to mitochondrial cytochrome c release, the initiating event in this apoptosis branch.
  evidence:
  - reference: PMID:38505790
    reference_title: "Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: This leads to the accumulation of toxic metabolites such as fumaryl and maleylacetoacetate, which can damage the liver, kidneys, and nervous system.
    explanation: Supports increased fumaryl/fumarylacetoacetate-pathway toxic metabolites due to FAH deficiency.
  - reference: PMID:9689118
    reference_title: "Hepatocyte injury in tyrosinemia type 1 is induced by fumarylacetoacetate and is inhibited by caspase inhibitors."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: the addition of fumarylacetoacetate induced the release of cytochrome c from the mitochondria.
    explanation: Demonstrates direct cell-free toxicity of FAA at the mitochondrial level.
genetic:
- name: FAH deficiency
  gene_term:
    preferred_term: FAH
    term:
      id: hgnc:3579
      label: FAH
  inheritance:
  - name: Autosomal recessive
    description: 'HT-1 follows autosomal recessive inheritance. Carrier parents have a 25% recurrence risk per pregnancy.

      '
    evidence:
    - reference: PMID:28771246
      reference_title: "Diagnosis and treatment of tyrosinemia type I: a US and Canadian consensus group review and recommendations."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Tyrosinemia type I (hepatorenal tyrosinemia, HT-1) is an autosomal recessive condition
      explanation: Directly states autosomal recessive inheritance pattern.
    - reference: PMID:39050308
      reference_title: "Hereditary Tyrosinemia Type-1 With Late Presentation: A Case Report."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: With an autosomal recessive inheritance pattern, it is an uncommon genetic condition.
      explanation: Confirms autosomal recessive inheritance in a clinical case report.
  variants:
  - name: FAH pathogenic variants
    description: 'Over 100 pathogenic variants in FAH have been reported worldwide. The IVS12+5G>A splice site mutation is the most common variant in the French-Canadian population of Quebec. Various missense, nonsense, splice-site, and frameshift mutations have been identified across diverse ethnic groups.

      '
  features: 'HT-1 is caused by biallelic pathogenic variants in the FAH gene encoding fumarylacetoacetate hydrolase, the terminal enzyme in tyrosine catabolism. Complete loss of FAH function produces the severe acute form with neonatal presentation, while residual enzyme activity may allow later presentation with chronic liver disease. Genotype- phenotype correlations are imperfect due to modifier effects and environmental factors.

    '
  evidence:
  - reference: PMID:38505790
    reference_title: "Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Hepatorenal tyrosinemia type 1 (HT-1) is a rare autosomal recessive disease that results from a deficiency of fumaryl acetoacetate hydrolase (FAH), a critical enzyme in the catabolic pathway for tyrosine.
    explanation: Directly describes FAH deficiency as the genetic cause of HT-1.
  - reference: CGGV:assertion_39c50699-f422-4bae-89ac-af13ef7cb8cc-2020-06-29T174149.440Z
    reference_title: "FAH / tyrosinemia type I (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "FAH | HGNC:3579 | tyrosinemia type I | MONDO:0010161 | AR | Definitive"
    explanation: ClinGen classifies the FAH-tyrosinemia type I gene-disease relationship as definitive with autosomal recessive inheritance.
environmental:
- name: Catabolic and dietary stress
  notes: >
    Excess dietary protein, protein malnutrition, prolonged fasting,
    intercurrent catabolic illness, and inadequate calories during procedures or
    other stressors should be avoided because they can worsen metabolic
    instability.
  evidence:
  - reference: PMID:20301688
    reference_title: "Tyrosinemia Type I."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Agents/circumstances to avoid: Excessive dietary protein or protein
      malnutrition inducing catabolic state; prolonged fasting; catabolic illness
      (intercurrent infection, brief febrile illness post vaccination);
      inadequate caloric provision during other stressors, especially when
      fasting is involved (surgery or procedure requiring fasting/anesthesia).
    explanation: GeneReviews directly lists dietary and catabolic circumstances to avoid in HT-1.
treatments:
- name: Nitisinone (NTBC) therapy
  description: 'Nitisinone (2-[2-nitro-4-trifluoromethylbenzoyl]-1,3-cyclohexanedione) is a potent inhibitor of 4-hydroxyphenylpyruvate dioxygenase (HPD), the second enzyme in tyrosine degradation. By blocking HPD, NTBC prevents formation of the toxic downstream metabolites FAA, MAA, and SA. Early initiation of NTBC, ideally before symptom onset via NBS identification, provides greater than 90% survival and dramatically reduces the need for liver transplantation.

    '
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: nitisinone
      term:
        id: CHEBI:50378
        label: nitisinone
  evidence:
  - reference: PMID:38505790
    reference_title: "Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: has significantly improved the management of HT-1, particularly when initiated before the onset of symptoms.
    explanation: Supports NTBC as the transformative therapy for HT-1.
  - reference: PMID:36980965
    reference_title: "Hereditary Tyrosinemia Type 1 Mice under Continuous Nitisinone Treatment Display Remnants of an Uncorrected Liver Disease Phenotype."
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: Nitisinone (NTBC), a potent inhibitor of the 4-hydroxyphenylpyruvate dioxygenase (HPD) enzyme, rescues HT1 patients from severe illness and death. However, despite its demonstrated benefits, HT1 patients under continuous NTBC therapy are at risk to develop HCC
    explanation: Confirms NTBC efficacy but notes residual HCC risk.
  target_phenotypes:
  - preferred_term: Acute hepatic failure
    term:
      id: HP:0006554
      label: Acute hepatic failure
  - preferred_term: Hepatocellular carcinoma
    term:
      id: HP:0001402
      label: Hepatocellular carcinoma
  target_mechanisms:
  - target: Toxic fumarylacetoacetate and maleylacetoacetate accumulation
    treatment_effect: INHIBITS
    description: Nitisinone inhibits HPD upstream of FAH, reducing formation of FAA, MAA, and succinylacetone.
    evidence:
    - reference: PMID:36980965
      reference_title: "Hereditary Tyrosinemia Type 1 Mice under Continuous Nitisinone Treatment Display Remnants of an Uncorrected Liver Disease Phenotype."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: Nitisinone (NTBC), a potent inhibitor of the 4-hydroxyphenylpyruvate dioxygenase (HPD) enzyme, rescues HT1 patients from severe illness and death.
      explanation: Directly supports upstream HPD inhibition as the therapeutic mechanism that prevents severe HT-1 illness.
- name: Dietary tyrosine and phenylalanine restriction
  description: 'Low-tyrosine, low-phenylalanine diet is essential in combination with NTBC therapy, since NTBC causes upstream accumulation of tyrosine. Specialized medical formulas provide essential amino acids while restricting tyrosine and phenylalanine intake.

    '
  treatment_term:
    preferred_term: dietary intervention
    term:
      id: MAXO:0000088
      label: dietary intervention
  evidence:
  - reference: PMID:28771246
    reference_title: "Diagnosis and treatment of tyrosinemia type I: a US and Canadian consensus group review and recommendations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: There was strong consensus in favor of NBS for HT-1, using blood succinylacetone as a marker, followed by diagnostic confirmation and early treatment with NTBC and diet.
    explanation: Consensus recommendation for combined NTBC and dietary therapy.
  - reference: PMID:38505790
    reference_title: "Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: NTBC combined with dietary therapy, if initiated early, can provide liver transplant (LT) free survival and reduce the risk of hepatocellular carcinoma (HCC).
    explanation: Confirms dietary therapy as part of the standard treatment combination.
  target_mechanisms:
  - target: Toxic fumarylacetoacetate and maleylacetoacetate accumulation
    treatment_effect: MODULATES
    description: Dietary restriction reduces tyrosine and phenylalanine substrate flux and helps control upstream tyrosine accumulation during NTBC therapy.
    evidence:
    - reference: PMID:28771246
      reference_title: "Diagnosis and treatment of tyrosinemia type I: a US and Canadian consensus group review and recommendations."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: There was strong consensus in favor of NBS for HT-1, using blood succinylacetone as a marker, followed by diagnostic confirmation and early treatment with NTBC and diet.
      explanation: Consensus guidance supports diet as part of early HT-1 treatment after diagnosis.
- name: Liver transplantation
  description: 'Liver transplantation is curative for the hepatic manifestations of HT-1 but does not correct renal FAH deficiency, and residual SA production by the kidneys may persist. Indications include acute liver failure, HCC or dysplastic nodules, or failure of medical management.

    '
  treatment_term:
    preferred_term: organ transplantation
    term:
      id: MAXO:0010039
      label: organ transplantation
  evidence:
  - reference: PMID:38505790
    reference_title: "Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Patients failing medical treatment (eg, due to non-adherence), and who develop acute liver failure (ALF), have HCC or evidence of histologically proven dysplastic liver nodule(s), or experience poor quality of life secondary to severe dietary restrictions are currently indicated for LT.
    explanation: Lists specific indications for liver transplantation in HT-1.
  - reference: PMID:39050308
    reference_title: "Hereditary Tyrosinemia Type-1 With Late Presentation: A Case Report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The patient is currently undergoing treatment with capsule nitisinone 5 mg, which inhibits the second step of tyrosine degradation to prevent tyrosinemia, along with a restricted protein diet, while awaiting liver transplantation.
    explanation: Confirms liver transplantation as a treatment option for severe cases.
  target_phenotypes:
  - preferred_term: Acute hepatic failure
    term:
      id: HP:0006554
      label: Acute hepatic failure
  - preferred_term: Hepatocellular carcinoma
    term:
      id: HP:0001402
      label: Hepatocellular carcinoma
  target_mechanisms:
  - target: Fumarylacetoacetate hydrolase deficiency
    treatment_effect: RESTORES
    description: Liver transplantation replaces FAH-deficient liver tissue, correcting hepatic manifestations while leaving extrahepatic FAH deficiency uncorrected.
    evidence:
    - reference: PMID:38505790
      reference_title: "Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Patients failing medical treatment (eg, due to non-adherence), and who develop acute liver failure (ALF), have HCC or evidence of histologically proven dysplastic liver nodule(s), or experience poor quality of life secondary to severe dietary restrictions are currently indicated for LT.
      explanation: HT-1 liver transplantation is reserved for hepatic failure, HCC, dysplastic nodules, or failed medical management.
- name: Newborn screening
  description: 'NBS for HT-1 using dried blood spot succinylacetone measurement is recommended, as it is superior to tyrosine-based screening. Early identification enables pre-symptomatic NTBC initiation for optimal long-term outcomes.

    '
  treatment_term:
    preferred_term: disease screening
    term:
      id: MAXO:0000124
      label: disease screening
  evidence:
  - reference: PMID:28771246
    reference_title: "Diagnosis and treatment of tyrosinemia type I: a US and Canadian consensus group review and recommendations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Newborn screening (NBS) utilizing blood succinylacetone as the NBS marker is superior to observing tyrosine levels as a way of identifying neonates with HT-1.
    explanation: Strong consensus supporting SA-based NBS for HT-1.
  - reference: PMID:39728402
    reference_title: "Evaluation of Neonatal Screening Programs for Tyrosinemia Type 1 Worldwide."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Overall positive predictive values were 27.3% for SUAC, 1.2% for Tyr solely, and 90.1% for Tyr + SUAC.
    explanation: Provides worldwide performance data for NBS strategies.
  - reference: PMID:38132825
    reference_title: "A False-Negative Newborn Screen for Tyrosinemia Type 1-Need for Re-Evaluation of Newborn Screening with Succinylacetone."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: While SA was long considered to be elevated in every TT1 patient, here we present a recent false-negative SA TT1 screen.
    explanation: Highlights that NBS can have rare false negatives requiring protocol optimization.
  target_phenotypes:
  - preferred_term: Acute hepatic failure
    term:
      id: HP:0006554
      label: Acute hepatic failure
  - preferred_term: Hepatocellular carcinoma
    term:
      id: HP:0001402
      label: Hepatocellular carcinoma
- name: Supportive care
  description: 'Acute and chronic supportive management includes correction of coagulopathy, electrolyte management for renal tubular dysfunction, vitamin D and phosphate supplementation for rickets, and monitoring of liver and renal function.

    '
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
  evidence:
  - reference: PMID:38505790
    reference_title: "Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Children with HT-1 require frequent monitoring of liver and renal function to assess disease progression and treatment compliance.
    explanation: Supports ongoing monitoring and supportive care in HT-1 management.
  target_phenotypes:
  - preferred_term: Renal Fanconi syndrome
    term:
      id: HP:0001994
      label: Renal Fanconi syndrome
  - preferred_term: Rickets
    term:
      id: HP:0002748
      label: Rickets
  - preferred_term: Abnormality of coagulation
    term:
      id: HP:0001928
      label: Abnormality of coagulation
  - preferred_term: Edema
    term:
      id: HP:0000969
      label: Edema
- name: Genetic counseling
  description: 'Genetic counseling for affected families, including discussion of autosomal recessive inheritance, 25% recurrence risk, carrier testing, and prenatal or preimplantation genetic diagnosis options.

    '
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: MAXO:0000079
      label: genetic counseling
  evidence:
  - reference: PMID:28771246
    reference_title: "Diagnosis and treatment of tyrosinemia type I: a US and Canadian consensus group review and recommendations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Tyrosinemia type I (hepatorenal tyrosinemia, HT-1) is an autosomal recessive condition
    explanation: Autosomal recessive inheritance pattern supports the role of genetic counseling.
- name: Neurocognitive assessment and therapy
  description: 'Long-term neurocognitive assessment is recommended for HT-1 patients, as they are at risk for neurocognitive impairment even under NTBC therapy. Early intervention and educational support may improve outcomes.

    '
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
  evidence:
  - reference: PMID:38505790
    reference_title: "Decoding hepatorenal tyrosinemia type 1: Unraveling the impact of early detection, NTBC, and the role of liver transplantation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: They are also at risk of long-term neurocognitive impairment, which highlights the need for neurocognitive assessment and therapy.
    explanation: Directly recommends neurocognitive assessment and therapy for HT-1 patients.
  target_phenotypes:
  - preferred_term: Cognitive impairment
    term:
      id: HP:0100543
      label: Cognitive impairment
notes: 'HT-1 is classified into acute (presentation before 6 months), subacute (6-12 months), and chronic (after 12 months) forms based on age of presentation. The acute form, presenting with liver failure in early infancy, carries the worst prognosis without treatment. With universal newborn screening and early NTBC therapy, the natural history has been dramatically altered. However, long-term HCC risk persists even with optimal medical management, and liver transplantation remains necessary for a subset of patients. Residual SA production by the kidneys continues after liver transplantation, requiring ongoing monitoring.

  '
references:
- reference: PMID:20301688
  tags:
  - GeneReviews
📚

References & Deep Research

References

1
No top-level findings curated for this source.

Deep Research

1
Falcon ▸
Disease Pathophysiology Research Template
Edison Scientific Literature 19 citations 2026-02-23T23:26:11.786406

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on: 1. Key concepts and definitions with current understanding 2. Recent developments and latest research (prioritize 2023-2024 sources) 3. Current applications and real-world implementations 4. Expert opinions and analysis from authoritative sources 5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available. Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Disease Pathophysiology Research Template

Target Disease

  • Disease Name: Tyrosinemia Type I
  • MONDO ID: (if available)
  • Category: Genetic

Research Objectives

Please provide a comprehensive research report on the pathophysiology of Tyrosinemia Type I. Focus on the molecular and cellular mechanisms underlying disease progression.

Required Information

1. Core Pathophysiology

  • What are the primary pathophysiological mechanisms?
  • What molecular pathways are dysregulated?
  • What cellular processes are affected?

2. Key Molecular Players

  • Genes/Proteins: Which genes are causally involved or implicated?
  • Chemical Entities: What metabolites, drugs, or small molecules are relevant?
  • Cell Types: Which cell types are primarily affected?
  • Anatomical Locations: Which tissues/organs are involved?

3. Biological Processes (for GO annotation)

  • What biological processes (GO terms) are disrupted?
  • Consider: signaling pathways, metabolic processes, cellular responses, transport, etc.

4. Cellular Components

  • Where in the cell do key processes occur?
  • Consider: organelles, membrane compartments, extracellular space, etc.

5. Disease Progression

  • What is the sequence of events from initial trigger to clinical manifestation?
  • Are there distinct stages or phases?

6. Phenotypic Manifestations

  • What are the key clinical phenotypes?
  • How do they relate to the underlying mechanisms?

Citation Requirements

  • Cite primary literature (PMID preferred) for all mechanistic claims
  • Prioritize recent reviews and landmark papers
  • Include direct quotes where possible to support key statements

Output Format

Structure your response as a narrative that could be used to populate a disease knowledge base entry with: - Pathophysiology description - Gene/protein annotations with ontology terms (HGNC, GO) - Phenotype associations (HP terms) - Cell type involvement (CL terms) - Anatomical locations (UBERON terms) - Chemical entities (CHEBI terms) - Evidence items with PMIDs

Title: Pathophysiology Research Report—Tyrosinemia Type I (HT1)

Target disease - Disease: Tyrosinemia type I (hepatorenal tyrosinemia) - MONDO: MONDO_0010161 (Open Targets disease mapping) () - Category: Genetic (autosomal recessive inborn error of metabolism)

  1. Key concepts and current understanding (core definitions)

1.1 Definition and primary biochemical defect Tyrosinemia type I (HT1/TT1) is caused by deficiency of fumarylacetoacetate hydrolase (FAH), the terminal enzyme of tyrosine catabolism, leading to accumulation of toxic intermediates. Recent newborn-screening review language is explicit that FAH deficiency “disrupts the catabolic pathway of tyrosine (Tyr). Consequently, toxic metabolites, including fumarylacetoacetate and succinylacetone (SUAC), accumulate” with major hepatic and renal consequences (published 16 Dec 2024) (kuypers2024evaluationofneonatal pages 1-2). The causative gene–disease association is strongly supported in Open Targets, where FAH is the sole top-associated target for MONDO_0010161 with multiple literature evidences ().

1.2 Pathognomonic metabolite and diagnostic concept Succinylacetone (SA; SUAC in dried blood spots) is central to both pathophysiology and diagnostics. A 2023 Dutch newborn-screening case report states: “Elevated succinylacetone (SA) is pathognomonic for TT1 and therefore often used as marker for TT1 newborn screening (NBS)” (published 4 Dec 2023) (dijkstra2023afalsenegativenewborn pages 1-2). Kehar et al. (Feb 2024) similarly note that accumulating fumarylacetoacetate ultimately forms SA, which is “a highly sensitive and specific marker” (kehar2024decodinghepatorenaltyrosinemia pages 2-4).

  1. Core pathophysiology (molecular and cellular mechanisms)

2.1 Metabolic block → accumulation of reactive/mutagenic metabolites FAH loss causes accumulation of maleylacetoacetate (MAA) and fumarylacetoacetate (FAA), with formation of SA through alternative routes (illustrated schematically for liver tyrosine degradation and NTBC block) (neuckermans2023hereditarytyrosinemiatype media 50dfa151). Kehar et al. describe FAA as “highly reactive,” “mutagenic,” and able to cause “oxidative damage to cells by reacting with glutathione and sulfhydryl groups of proteins” (kehar2024decodinghepatorenaltyrosinemia pages 2-4). This provides a mechanistic bridge from a metabolic lesion to oxidative stress and macromolecular damage.

2.2 Hepatocellular injury: mitochondrial cytochrome c release → caspase cascade → apoptosis (primary evidence) A landmark mechanistic study (Kubo et al., PNAS, Aug 1998; URL: https://doi.org/10.1073/pnas.95.16.9552) demonstrated that FAA can directly trigger mitochondrial apoptotic signaling. They report that in FAH-deficient mice, “Cytochrome c was released from mitochondria prior to liver failure” and that “in a cell-free system, the addition of fumarylacetoacetate induced the release of cytochrome c from the mitochondria” (kubo1998hepatocyteinjuryin pages 1-2). The same paper states “caspase inhibitors were highly effective in preventing the liver failure induced by HGA” (a precursor that generates FAA in their model) (kubo1998hepatocyteinjuryin pages 1-2). Together, these data support a causal chain: toxic tyrosine intermediates → mitochondrial outer membrane permeabilization → caspase activation → hepatocyte apoptosis.

  1. Dysregulated pathways and cellular processes (beyond the metabolic block)

3.1 Persistent pro-carcinogenic liver programs even under nitisinone (NTBC) Although nitisinone substantially prevents acute toxicity, it does not reconstitute FAH activity. Neuckermans et al. (Genes, 11 Mar 2023; URL: https://doi.org/10.3390/genes14030693) emphasize that “NTBC does not restore the enzymatic defects inflicted by the disease nor does it cure HT1” (neuckermans2023hereditarytyrosinemiatype pages 1-2). Their mouse transcriptome study found enrichment of differentially expressed genes in “toxicological gene classes related to liver disease, liver damage, liver regeneration and liver cancer, in particular HCC,” and they interpret their results as showing that “NTBC therapy does not completely resolves HT1-driven liver disease and supports the sustained risk to develop HCC over time” (neuckermans2023hereditarytyrosinemiatype pages 1-2). Visual evidence from their pathway/toxicology analyses and gene signatures under continuous NTBC is available in extracted figures/tables (neuckermans2023hereditarytyrosinemiatype media 0fafe895).

3.2 Porphyria-like crises: SA inhibition of ALAD → ALA accumulation → neurovisceral crises HT1 includes episodic “porphyria crises with neuropathy” in modern screening reviews (kuypers2024evaluationofneonatal pages 1-2). A 2023 nitisinone-focused dissertation/review synthesizes a mechanistic explanation: SA is a competitive inhibitor of δ-aminolevulinic acid dehydratase (ALAD), causing δ-aminolevulinic acid (ALA) accumulation with downstream mitochondrial, hepatic, and neuropsychiatric toxicity and “neurological crises … similar to porphyria/lead poisoning” (rudebeck2023nitisinonetreatmentfor pages 16-21). Kehar et al. include 5-aminolevulinic acid (5-ALA) as a relevant biochemical entity in HT1 clinical workups (kehar2024decodinghepatorenaltyrosinemia pages 2-4), consistent with heme-pathway involvement.

3.3 Renal tubular dysfunction and Fanconi-like phenotype Renal tubular dysfunction is a core multi-organ manifestation: TT1 toxic metabolites “accumulate, resulting in … renal tubular dysfunction” (kuypers2024evaluationofneonatal pages 1-2), and Dijkstra et al. list renal tubular dysfunction among classic outcomes of untreated disease (dijkstra2023afalsenegativenewborn pages 1-2). A 2024 clinical report summarizes cohort frequencies of tubulopathy-related findings (aminoaciduria, hypercalciuria, tubular acidosis, nephromegaly, nephrocalcinosis, reduced GFR), reflecting proximal tubular injury consistent with a Fanconi-like syndrome (ilyaz2024hereditarytyrosinemiatype1 pages 4-5).

  1. Key molecular players (knowledge-base style)

4.1 Genes / proteins - FAH (fumarylacetoacetate hydrolase; causal gene). Open Targets identifies FAH as the associated target for MONDO_0010161 with multiple supporting studies/literature (). - HPD / 4-hydroxyphenylpyruvate dioxygenase (4HPPD): upstream enzyme pharmacologically inhibited by nitisinone (NTBC) to prevent formation of toxic downstream metabolites (kehar2024decodinghepatorenaltyrosinemia pages 2-4, neuckermans2023hereditarytyrosinemiatype pages 1-2). - Caspase cascade components / mitochondrial apoptosis machinery: cytochrome c release and caspase involvement shown in FAH-deficiency injury model (kubo1998hepatocyteinjuryin pages 1-2). - ALAD (δ-aminolevulinic acid dehydratase): inhibited by SA, linking HT1 to porphyria-like neurovisceral crises via ALA accumulation (rudebeck2023nitisinonetreatmentfor pages 16-21).

4.2 Chemical entities (metabolites, drugs, biomarkers) - Tyrosine (substrate; elevated upstream of NTBC block) - Fumarylacetoacetate (FAA): reactive, mutagenic; triggers oxidative damage via glutathione/protein sulfhydryls (kehar2024decodinghepatorenaltyrosinemia pages 2-4); induces cytochrome c release (kubo1998hepatocyteinjuryin pages 1-2) - Maleylacetoacetate (MAA): upstream toxic intermediate (neuckermans2023hereditarytyrosinemiatype media 50dfa151) - Succinylacetone (SA/SUAC): toxic and diagnostic metabolite; “pathognomonic” marker for NBS (dijkstra2023afalsenegativenewborn pages 1-2) - δ-aminolevulinic acid (ALA/5-ALA): accumulates via ALAD inhibition in porphyria-like crises (rudebeck2023nitisinonetreatmentfor pages 16-21, kehar2024decodinghepatorenaltyrosinemia pages 2-4) - Nitisinone (NTBC; 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione): 4HPPD inhibitor; blocks toxic metabolite formation (kehar2024decodinghepatorenaltyrosinemia pages 2-4, kuypers2024evaluationofneonatal pages 1-2) - Alpha-fetoprotein (AFP): biomarker of metabolic derangement and HCC risk; AFP decreases after NTBC, and abnormal AFP kinetics can raise suspicion for HCC or nonadherence (kehar2024decodinghepatorenaltyrosinemia pages 2-4)

4.3 Cell types and anatomical locations - Primary affected tissues: liver and kidney; pathophysiologic damage occurs in hepatic and renal cells (kuypers2024evaluationofneonatal pages 1-2, neuckermans2023hereditarytyrosinemiatype pages 1-2). - Key cell types: hepatocytes (site of most severe organ pathology and carcinogenic transformation risk) (neuckermans2023hereditarytyrosinemiatype pages 1-2); renal tubular epithelial cells/proximal tubule cells (tubulopathy/Fanconi-like syndrome) (ilyaz2024hereditarytyrosinemiatype1 pages 4-5). - Nervous system involvement: porphyria-like crises with neuropathy (kuypers2024evaluationofneonatal pages 1-2, dijkstra2023afalsenegativenewborn pages 1-2).

  1. Biological processes and cellular components (GO-style narrative)

5.1 Disrupted biological processes (examples of GO terms) - Tyrosine catabolic process (disrupted at FAH; upstream pathway blockade with NTBC) (kuypers2024evaluationofneonatal pages 1-2, kehar2024decodinghepatorenaltyrosinemia pages 2-4) - Response to oxidative stress / glutathione metabolism and thiol-dependent redox homeostasis (FAA reacting with glutathione/protein sulfhydryls) (kehar2024decodinghepatorenaltyrosinemia pages 2-4) - Intrinsic apoptotic signaling pathway / caspase activation (FAA-induced cytochrome c release; caspase inhibitors protective) (kubo1998hepatocyteinjuryin pages 1-2) - Heme biosynthetic process (functional inhibition via SA→ALAD inhibition; porphyria-like crises through ALA accumulation) (rudebeck2023nitisinonetreatmentfor pages 16-21) - Renal tubular transport (renal tubular dysfunction; Fanconi-like phenotype) (kuypers2024evaluationofneonatal pages 1-2, ilyaz2024hereditarytyrosinemiatype1 pages 4-5) - Liver regeneration and carcinogenesis programs (persistent enrichment of liver-damage/regeneration/cancer gene classes under NTBC in murine model) (neuckermans2023hereditarytyrosinemiatype pages 1-2, neuckermans2023hereditarytyrosinemiatype media 0fafe895)

5.2 Cellular components (examples of GO CC) - Cytosol (accumulation of intermediates and cytochrome c release measured in cytosolic fractions) (kubo1998hepatocyteinjuryin pages 2-4) - Mitochondrial intermembrane space/outer membrane (cytochrome c release as key event) (kubo1998hepatocyteinjuryin pages 1-2) - Hepatocyte cytosol (tyrosine catabolism described as present in liver cytosol) (neuckermans2023hereditarytyrosinemiatype pages 1-2)

  1. Disease progression (sequence of events)

6.1 Initiation (genetic trigger) Biallelic pathogenic variants in FAH cause FAH deficiency (kehar2024decodinghepatorenaltyrosinemia pages 2-4), blocking the terminal step of tyrosine catabolism.

6.2 Early biochemical stage Toxic intermediates accumulate (FAA/MAA) and SA is formed/accumulates early in blood and urine; Kehar et al. note that “Marked SA elevation occurs early in blood and urine” (kehar2024decodinghepatorenaltyrosinemia pages 2-4). This biochemical stage underpins newborn screening and early confirmatory testing.

6.3 Cellular injury and organ dysfunction - Liver: FAA-driven oxidative stress and mitochondrial apoptosis contribute to acute hepatic decompensation, progressive liver damage, and predisposition to malignant transformation (kehar2024decodinghepatorenaltyrosinemia pages 2-4, kubo1998hepatocyteinjuryin pages 1-2). - Kidney: renal tubular dysfunction develops, manifesting as tubulopathy/Fanconi-like syndrome and rickets in many patients (kuypers2024evaluationofneonatal pages 1-2, ilyaz2024hereditarytyrosinemiatype1 pages 4-5). - Nervous system: metabolic decompensation can trigger porphyria-like neurovisceral crises via heme-pathway disruption (kuypers2024evaluationofneonatal pages 1-2, rudebeck2023nitisinonetreatmentfor pages 16-21).

6.4 Chronic stage and malignancy risk HT1 carries prominent risk for hepatocellular carcinoma (HCC); even under continuous NTBC, transcriptomic signals associated with liver cancer can persist in model systems (neuckermans2023hereditarytyrosinemiatype pages 1-2, neuckermans2023hereditarytyrosinemiatype media 0fafe895).

  1. Phenotypic manifestations (mechanism-linked)

Key clinical phenotypes noted in recent screening and management literature include: - Hepatic: acute liver failure, fibrosis, cirrhosis, hepatocellular carcinoma and hepatoblastoma (kuypers2024evaluationofneonatal pages 1-2, dijkstra2023afalsenegativenewborn pages 1-2) - Renal: renal tubular dysfunction with downstream growth/bone disease (rickets) (kuypers2024evaluationofneonatal pages 1-2, ilyaz2024hereditarytyrosinemiatype1 pages 4-5) - Neurologic: porphyria crises with neuropathy; neurocognitive impairment risk highlighted in management review (kuypers2024evaluationofneonatal pages 1-2, kehar2024decodinghepatorenaltyrosinemia pages 1-2) Mechanistic mapping: FAA reactivity and apoptotic signaling align with liver failure/cirrhosis; SA-mediated ALAD inhibition aligns with porphyria-like crises; renal tubular injury aligns with Fanconi-like findings and rickets (kehar2024decodinghepatorenaltyrosinemia pages 2-4, kubo1998hepatocyteinjuryin pages 1-2, rudebeck2023nitisinonetreatmentfor pages 16-21, ilyaz2024hereditarytyrosinemiatype1 pages 4-5).

  1. Recent developments and latest research (prioritizing 2023–2024)

8.1 Newborn screening optimization (2023–2024) A 2024 worldwide evaluation of NBS programs reported that “TT1 incidence ranged from 1/13,636 to 1/750,000,” with most programs using DBS SUAC (78.9%) and a “pooled median cut-off for SUAC … 1.50 µmol/L (range 0.3–7.0 µmol/L)” (published 16 Dec 2024; URL: https://doi.org/10.3390/ijns10040082) (kuypers2024evaluationofneonatal pages 1-2). In the same report, overall positive predictive values were “27.3% for SUAC” and “90.1% for Tyr + SUAC,” and false negatives were reported for both SUAC and Tyr-based strategies (kuypers2024evaluationofneonatal pages 1-2). A 2023 Dutch report provides real-world evidence that SUAC-based screening can be falsely negative near cut-off thresholds (SUAC 1.08 µmol/L vs Dutch cut-off 1.20 µmol/L), reinforcing the need for protocol re-evaluation (published 4 Dec 2023; URL: https://doi.org/10.3390/ijns9040066) (dijkstra2023afalsenegativenewborn pages 1-2).

8.2 Persistent residual disease biology under NTBC (2023) Neuckermans et al. (published 11 Mar 2023) used transcriptomics in Fah/Hgd-deficient mice to identify that NTBC does not fully normalize liver disease programs and identified a 25-gene set related to liver disease and HCC development that differs between HT1 and a reference tyrosine disorder (AKU) under NTBC (neuckermans2023hereditarytyrosinemiatype pages 1-2). Extracted pathway/toxicology figures provide visual support for these claims (neuckermans2023hereditarytyrosinemiatype media 0fafe895).

  1. Current applications and real-world implementation

9.1 Standard-of-care therapy: NTBC + diet Kehar et al. describe NTBC as a “potent inhibitor” of 4-hydroxyphenylpyruvate dioxygenase (second enzyme in tyrosine degradation) and state that it “prevents the formation of toxic metabolites” with “greater than 90% survival rate” when combined with dietary therapy (kehar2024decodinghepatorenaltyrosinemia pages 2-4). Their extracted figure/table includes dietary therapy targets (tyrosine and phenylalanine ranges) used in practice (kehar2024decodinghepatorenaltyrosinemia media e8fe4339).

9.2 Monitoring for cancer risk AFP kinetics are used clinically for both metabolic control and HCC suspicion: AFP should fall after NTBC; abnormal decline or rising AFP suggests HCC or poor adherence (kehar2024decodinghepatorenaltyrosinemia pages 2-4).

9.3 Liver transplantation Liver transplantation is described as curative for HT1 liver disease but does not correct renal FAH deficiency; Kehar et al. note that post-transplant “LT does not correct renal FAH deficiency, and residual SA production by the kidney remains” (kehar2024decodinghepatorenaltyrosinemia pages 2-4). Indications include acute liver failure, HCC/dysplastic nodules, or failure of medical management (kehar2024decodinghepatorenaltyrosinemia pages 1-2).

  1. Relevant statistics and data (recent)

  2. Global incidence: ~1 in 100,000 newborns worldwide (reported in 2023 review) (neuckermans2023hereditarytyrosinemiatype pages 1-2).

  3. NBS survey incidence range: 1/13,636 to 1/750,000 (2024 worldwide survey) (kuypers2024evaluationofneonatal pages 1-2).
  4. Screening cut-offs (SUAC): pooled median 1.50 µmol/L (range 0.3–7.0 µmol/L) (kuypers2024evaluationofneonatal pages 1-2).
  5. Screening performance: PPV 27.3% for SUAC vs 90.1% for Tyr+SUAC (kuypers2024evaluationofneonatal pages 1-2).

  6. Clinical outcomes with early NTBC: Quebec cohort example—mortality 36% in non-NTBC-treated children (10/28) vs 0 deaths among children receiving NTBC before 1 month; none of early-treated Quebec cases developed HCC (Kehar 2024; publication Feb 2024; URL: https://doi.org/10.3138/canlivj-2023-0018) (kehar2024decodinghepatorenaltyrosinemia pages 2-4).

  7. Expert opinions / authoritative analysis (interpretive synthesis)

  8. Early detection + early NTBC is the major modifiable determinant of outcome: Kehar et al. explicitly frame this as “EARLY DIAGNOSIS AND THERAPY SAVES LIVES” and link pre-symptomatic NTBC to improved outcomes and reduced transplant need (kehar2024decodinghepatorenaltyrosinemia pages 2-4).

  9. Residual long-term risk (especially HCC) remains a key unmet need: both clinical reviews and transcriptomic models support continued surveillance, because NTBC blocks toxic metabolite formation but does not restore FAH function and does not fully normalize liver disease biology (neuckermans2023hereditarytyrosinemiatype pages 1-2, kehar2024decodinghepatorenaltyrosinemia pages 2-4).

  10. Knowledge-base-ready annotation blocks

12.1 Pathophysiology description (narrative) HT1 results from FAH deficiency, causing accumulation of reactive tyrosine-catabolic intermediates (notably FAA/MAA) and formation of SA. FAA is described as mutagenic and capable of oxidative damage via glutathione/protein thiol reactions, and primary evidence indicates FAA can directly induce mitochondrial cytochrome c release, activating caspase-dependent apoptosis in hepatocytes. SA contributes to systemic manifestations and is pathognomonic diagnostically; mechanistically, SA inhibits ALAD, leading to ALA accumulation and porphyria-like neurovisceral crises. Chronic liver injury and regeneration pressures create a high risk for hepatocellular carcinoma; emerging 2023 transcriptomic evidence suggests that even under continuous NTBC, residual dysregulation of liver-disease and HCC-related gene programs persists, aligning with the need for long-term surveillance.

12.2 Gene/protein annotations (HGNC; selected GO suggestions) - FAH (HGNC:3375): causal gene for HT1/TT1 (MONDO_0010161). GO suggestions: tyrosine catabolic process; cellular detoxification; response to oxidative stress (kuypers2024evaluationofneonatal pages 1-2). - HPD/4HPPD: pharmacologic target of nitisinone; GO: tyrosine catabolic process (kehar2024decodinghepatorenaltyrosinemia pages 2-4). - ALAD: inhibited by SA; GO: heme biosynthetic process; porphobilinogen synthase activity (rudebeck2023nitisinonetreatmentfor pages 16-21). - Apoptosis effectors (cytochrome c release; caspase cascade): GO: intrinsic apoptotic signaling; mitochondrial outer membrane permeabilization (kubo1998hepatocyteinjuryin pages 1-2).

12.3 Phenotype associations (HPO term names) - Liver failure; liver fibrosis; cirrhosis; hepatocellular carcinoma; hepatoblastoma; elevated AFP (kuypers2024evaluationofneonatal pages 1-2, dijkstra2023afalsenegativenewborn pages 1-2, kehar2024decodinghepatorenaltyrosinemia pages 2-4) - Renal tubular dysfunction; Fanconi syndrome-like tubulopathy; rickets; nephrocalcinosis; reduced GFR (kuypers2024evaluationofneonatal pages 1-2, ilyaz2024hereditarytyrosinemiatype1 pages 4-5) - Porphyria-like crises; neuropathy; neurocognitive impairment (kuypers2024evaluationofneonatal pages 1-2, rudebeck2023nitisinonetreatmentfor pages 16-21, kehar2024decodinghepatorenaltyrosinemia pages 1-2)

12.4 Cell types (CL term names) - Hepatocyte (primary site of injury and carcinogenesis) (neuckermans2023hereditarytyrosinemiatype pages 1-2) - Renal proximal tubule epithelial cell (tubulopathy/Fanconi-like syndrome) (ilyaz2024hereditarytyrosinemiatype1 pages 4-5)

12.5 Anatomical locations (UBERON term names) - Liver; kidney; nervous system (neuropathy crises) (kuypers2024evaluationofneonatal pages 1-2, dijkstra2023afalsenegativenewborn pages 1-2)

12.6 Chemicals (CHEBI names) - Tyrosine; fumarylacetoacetate; maleylacetoacetate; succinylacetone; δ-aminolevulinic acid; nitisinone (kuypers2024evaluationofneonatal pages 1-2, kehar2024decodinghepatorenaltyrosinemia pages 2-4, rudebeck2023nitisinonetreatmentfor pages 16-21)

  1. Evidence items with PMIDs (where available in retrieved full text)
  2. Kubo et al. PNAS 1998 (Hepatocyte injury … induced by fumarylacetoacetate … inhibited by caspase inhibitors). PMID not present in extracted text; DOI provided: 10.1073/pnas.95.16.9552 (kubo1998hepatocyteinjuryin pages 1-2).

Note on PMID coverage: Several 2023–2024 open-access clinical/review sources used here (MDPI journals; Canadian Liver Journal) and the dissertation-style text excerpts did not display PMIDs in the extracted full text. Where PMIDs were not retrievable from the provided content, DOI/URL and publication date are provided, and mechanistic claims are tied to direct quotations from the accessible text.

Key URLs (recent prioritized) - Kuypers et al., “Evaluation of Neonatal Screening Programs for Tyrosinemia Type 1 Worldwide” (Published 16 Dec 2024): https://doi.org/10.3390/ijns10040082 (kuypers2024evaluationofneonatal pages 1-2) - Kehar et al., “Decoding hepatorenal tyrosinemia type 1 …” (Feb 2024): https://doi.org/10.3138/canlivj-2023-0018 (kehar2024decodinghepatorenaltyrosinemia pages 2-4) - Dijkstra et al., “A False-Negative Newborn Screen for Tyrosinemia Type 1 …” (Published 4 Dec 2023): https://doi.org/10.3390/ijns9040066 (dijkstra2023afalsenegativenewborn pages 1-2) - Neuckermans et al., “Hereditary Tyrosinemia Type 1 Mice under Continuous Nitisinone Treatment …” (Published 11 Mar 2023): https://doi.org/10.3390/genes14030693 (neuckermans2023hereditarytyrosinemiatype pages 1-2) - Kubo et al., PNAS (Aug 1998): https://doi.org/10.1073/pnas.95.16.9552 (kubo1998hepatocyteinjuryin pages 1-2)

References

  1. (kuypers2024evaluationofneonatal pages 1-2): Allysa M. Kuypers, Marelle J. Bouva, J. Gerard Loeber, Anita Boelen, Eugenie Dekkers, Konstantinos Petritis, C. Austin Pickens, Francjan J. van Spronsen, and M. Rebecca Heiner-Fokkema. Evaluation of neonatal screening programs for tyrosinemia type 1 worldwide. International Journal of Neonatal Screening, 10:82, Dec 2024. URL: https://doi.org/10.3390/ijns10040082, doi:10.3390/ijns10040082. This article has 4 citations.

  2. (dijkstra2023afalsenegativenewborn pages 1-2): Allysa M. Dijkstra, Kimber Evers-van Vliet, M. Rebecca Heiner-Fokkema, Frank A. J. A. Bodewes, Dennis K. Bos, József Zsiros, Koen J. van Aerde, Klaas Koop, Francjan J. van Spronsen, and Charlotte M. A. Lubout. A false-negative newborn screen for tyrosinemia type 1—need for re-evaluation of newborn screening with succinylacetone. International Journal of Neonatal Screening, 9:66, Dec 2023. URL: https://doi.org/10.3390/ijns9040066, doi:10.3390/ijns9040066. This article has 14 citations.

  3. (kehar2024decodinghepatorenaltyrosinemia pages 2-4): Mohit Kehar, Moinak Sen Sarma, Jayendra Seetharaman, Carolina Jimenez Rivera, and Pranesh Chakraborty. Decoding hepatorenal tyrosinemia type 1: unraveling the impact of early detection, ntbc, and the role of liver transplantation. Canadian Liver Journal, 7:54-63, Feb 2024. URL: https://doi.org/10.3138/canlivj-2023-0018, doi:10.3138/canlivj-2023-0018. This article has 5 citations.

  4. (neuckermans2023hereditarytyrosinemiatype media 50dfa151): Jessie Neuckermans, Sien Lequeue, Paul Claes, Anja Heymans, Juliette H. Hughes, Haaike Colemonts-Vroninks, Lionel Marcélis, Georges Casimir, Philippe Goyens, Geert A. Martens, James A. Gallagher, Tamara Vanhaecke, George Bou-Gharios, and Joery De Kock. Hereditary tyrosinemia type 1 mice under continuous nitisinone treatment display remnants of an uncorrected liver disease phenotype. Genes, 14:693, Mar 2023. URL: https://doi.org/10.3390/genes14030693, doi:10.3390/genes14030693. This article has 6 citations.

  5. (kubo1998hepatocyteinjuryin pages 1-2): Shuji Kubo, Maosen Sun, Michio Miyahara, Kazuhiro Umeyama, Ken-ichi Urakami, Tetsuro Yamamoto, Cornelis Jakobs, Ichiro Matsuda, and Fumio Endo. Hepatocyte injury in tyrosinemia type 1 is induced by fumarylacetoacetate and is inhibited by caspase inhibitors. Proceedings of the National Academy of Sciences of the United States of America, 95 16:9552-7, Aug 1998. URL: https://doi.org/10.1073/pnas.95.16.9552, doi:10.1073/pnas.95.16.9552. This article has 102 citations and is from a highest quality peer-reviewed journal.

  6. (neuckermans2023hereditarytyrosinemiatype pages 1-2): Jessie Neuckermans, Sien Lequeue, Paul Claes, Anja Heymans, Juliette H. Hughes, Haaike Colemonts-Vroninks, Lionel Marcélis, Georges Casimir, Philippe Goyens, Geert A. Martens, James A. Gallagher, Tamara Vanhaecke, George Bou-Gharios, and Joery De Kock. Hereditary tyrosinemia type 1 mice under continuous nitisinone treatment display remnants of an uncorrected liver disease phenotype. Genes, 14:693, Mar 2023. URL: https://doi.org/10.3390/genes14030693, doi:10.3390/genes14030693. This article has 6 citations.

  7. (neuckermans2023hereditarytyrosinemiatype media 0fafe895): Jessie Neuckermans, Sien Lequeue, Paul Claes, Anja Heymans, Juliette H. Hughes, Haaike Colemonts-Vroninks, Lionel Marcélis, Georges Casimir, Philippe Goyens, Geert A. Martens, James A. Gallagher, Tamara Vanhaecke, George Bou-Gharios, and Joery De Kock. Hereditary tyrosinemia type 1 mice under continuous nitisinone treatment display remnants of an uncorrected liver disease phenotype. Genes, 14:693, Mar 2023. URL: https://doi.org/10.3390/genes14030693, doi:10.3390/genes14030693. This article has 6 citations.

  8. (rudebeck2023nitisinonetreatmentfor pages 16-21): M Rudebeck. Nitisinone treatment for inherited disorders of tyrosine metabolism–investigating long-term outcomes, optimal monitoring, and new treatment options and indications. Unknown journal, 2023.

  9. (ilyaz2024hereditarytyrosinemiatype1 pages 4-5): Md Ilyaz, Renuka S Jadhav, Vineeta Pande, Shailaja V Mane, and Pranavi Mokkarala. Hereditary tyrosinemia type-1 with late presentation: a case report. Cureus, Jun 2024. URL: https://doi.org/10.7759/cureus.62990, doi:10.7759/cureus.62990. This article has 3 citations.

  10. (kubo1998hepatocyteinjuryin pages 2-4): Shuji Kubo, Maosen Sun, Michio Miyahara, Kazuhiro Umeyama, Ken-ichi Urakami, Tetsuro Yamamoto, Cornelis Jakobs, Ichiro Matsuda, and Fumio Endo. Hepatocyte injury in tyrosinemia type 1 is induced by fumarylacetoacetate and is inhibited by caspase inhibitors. Proceedings of the National Academy of Sciences of the United States of America, 95 16:9552-7, Aug 1998. URL: https://doi.org/10.1073/pnas.95.16.9552, doi:10.1073/pnas.95.16.9552. This article has 102 citations and is from a highest quality peer-reviewed journal.

  11. (kehar2024decodinghepatorenaltyrosinemia pages 1-2): Mohit Kehar, Moinak Sen Sarma, Jayendra Seetharaman, Carolina Jimenez Rivera, and Pranesh Chakraborty. Decoding hepatorenal tyrosinemia type 1: unraveling the impact of early detection, ntbc, and the role of liver transplantation. Canadian Liver Journal, 7:54-63, Feb 2024. URL: https://doi.org/10.3138/canlivj-2023-0018, doi:10.3138/canlivj-2023-0018. This article has 5 citations.

  12. (kehar2024decodinghepatorenaltyrosinemia media e8fe4339): Mohit Kehar, Moinak Sen Sarma, Jayendra Seetharaman, Carolina Jimenez Rivera, and Pranesh Chakraborty. Decoding hepatorenal tyrosinemia type 1: unraveling the impact of early detection, ntbc, and the role of liver transplantation. Canadian Liver Journal, 7:54-63, Feb 2024. URL: https://doi.org/10.3138/canlivj-2023-0018, doi:10.3138/canlivj-2023-0018. This article has 5 citations.