Tyrosinemia Type III

Mendelian MONDO:0010162 Pathograph 16 Show in embeddings browser Disorder of Tyrosine Metabolism Inborn Error of Metabolism

Tyrosinemia type III is the rarest of the three genetic tyrosinemias, an autosomal recessive inborn error caused by biallelic loss-of-function variants in HPD encoding 4-hydroxyphenylpyruvate dioxygenase, the second enzyme of the tyrosine catabolic pathway. Loss of HPD activity blocks conversion of 4-hydroxyphenylpyruvate to homogentisate, producing hypertyrosinemia and massive urinary excretion of 4-hydroxyphenyl organic acids. Because the block sits upstream of the maleylacetoacetate and fumarylacetoacetate steps, no succinylacetone or other hepatotoxic intermediate is generated, and reported patients have had normal liver and renal function and no eye or skin disease — the distinction that separates this entry mechanistically from tyrosinemia type I (FAH) and type II (TAT). The clinical spectrum is dominated by variable neurodevelopmental manifestations (developmental delay, intellectual impairment, ataxia, seizures, ADHD), but the causal route from tyrosine elevation to neurological injury is unresolved: plasma tyrosine levels do not correlate with phenotype and biochemically affected individuals with normal development have been reported. Management is a phenylalanine- and tyrosine-restricted low-protein diet; nitisinone, which is therapeutic in tyrosinemia type I, is an HPD inhibitor and therefore pharmacologically reproduces rather than corrects this lesion.

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1
Mappings
1
Inheritance
4
Pathophys.
7
Phenotypes
3
Gaps
16
Pathograph
1
Genes
2
Variants
2
Medical Actions
2
Models
15
References
2
Deep Research
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Mappings

MONDO
MONDO:0010162 tyrosinemia type III
skos:exactMatch OMIM:276710
MONDO:0010162 (tyrosinemia type III) cross-references OMIM:276710 and Orphanet:69723 and records HPD (HGNC:5147) as its causal gene via RO:0004003, matching the HPD-deficiency entity curated here.
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Inheritance

1
Autosomal recessive HP:0000007
Tyrosinemia type III is caused by biallelic pathogenic HPD variants; affected individuals have been homozygous or compound heterozygous, and heterozygous carriers are unaffected.
Autosomal recessive inheritance
Show evidence (2 references)
PMID:10942115 SUPPORT Human Clinical
"Tyrosinemia type III (OMIM 276710) is an autosomal recessive disorder caused by the deficiency of 4-hydroxyphenylpyruvate dioxygenase (HPD), the second enzyme in the tyrosine catabolic pathway."
States the autosomal recessive inheritance and the causal enzyme deficiency.
PMID:37817461 SUPPORT Human Clinical
"Hereditary tyrosinemia type III (HT III) is an extremely rare form of tyrosinemia, characterized by autosomal recessive inheritance and biallelic mutations in the HPD gene."
Confirms autosomal recessive inheritance with biallelic HPD variants.
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Discussions and Knowledge Gaps

3
If hypertyrosinemia is the only established biochemical abnormality in tyrosinemia type III, why does neither the severity of the HPD lesion nor the plasma tyrosine concentration predict the neurological phenotype, and what actually mediates the neurodevelopmental injury?
KNOWLEDGE GAP OPEN tyrosinemia_iii_tyrosine_neurotoxicity_unresolved
Attached to
pathophysiology#Hypertyrosinemia and phenolic metabolite accumulation pathophysiology#Neurodevelopmental dysfunction
The pathograph edge from the metabolic block to neurodevelopmental dysfunction is the only edge in this entry that cannot be curated as DIRECT. Three independent observations refuse a simple dose-response model: the first mutation survey found no correlation between mutation severity, residual enzyme activity, mental function, or tyrosine level; an 11-year-old girl with serum tyrosine of 425-535 micromol/L had no symptoms and normal mental development; and newborn-screened patients on mild protein restriction have had normal psychomotor development. Candidate explanations that the literature has not discriminated between include a critical early developmental window, a downstream phenolic metabolite rather than tyrosine itself, and ascertainment bias inflating the neurological association in a disorder historically found by investigating neurological symptoms.
Proposed experiments
Systematic neurodevelopmental follow-up of newborn-screened cohorts
exp_ht3_screened_cohort_neurodevelopmental_followup
Prospective, standardized neurocognitive assessment of all screening-ascertained HPD-deficient individuals, stratified by age at dietary initiation and by time-integrated tyrosine exposure, to separate ascertainment bias from a genuine exposure-response relationship.
Decision criterion
A monotonic relationship between time-integrated tyrosine exposure and neurocognitive score would support tyrosine itself as the mediator; normal outcomes across the full exposure range would refute it and redirect the search to a downstream phenolic metabolite or to ascertainment bias.
Show evidence (2 references)
PMID:10942115 SUPPORT Human Clinical
"No correlation of the severity of the mutation and enzyme deficiency and mental function has been found; neither do the recorded tyrosine levels correlate with the clinical phenotype."
The absence of a genotype-, enzyme-, or metabolite-phenotype correlation is the primary basis for the gap.
PMID:28649543 SUPPORT Human Clinical
"Presented case may suggest that high tyrosine concentration itself does not participate directly in neuronal damage described in patients with tyrosinemia type 3."
A biochemically affected, neurologically normal patient supports the gap and argues against direct tyrosine neurotoxicity.
Nitisinone is a pharmacological HPD inhibitor, so patients treated with it for tyrosinemia type I or alkaptonuria carry an acquired HPD block and develop tyrosine-driven corneal keratopathy and skin lesions. Why do genetically HPD-deficient patients not?
OPEN QUESTION OPEN tyrosinemia_iii_vs_nitisinone_phenocopy
Attached to
pathophysiology#4-Hydroxyphenylpyruvate dioxygenase deficiency pathophysiology#Hypertyrosinemia and phenolic metabolite accumulation
This is a direct, testable discrepancy between a genetic lesion and its pharmacological phenocopy at the same enzyme. Reported tyrosinemia type III patients have had no skin or eye abnormalities, whereas nitisinone-induced hypertyrosinemia in alkaptonuria causes skin issues and sight-threatening corneal keratopathy. Possible explanations that the literature has not resolved include a higher absolute tyrosine level reached under pharmacological blockade than under most reported genetic deficiency, residual HPD activity in hypomorphic genotypes, differences in the tissue distribution of the block, and the older age and longer exposure of nitisinone-treated adults. Resolving it would inform whether the ocular surveillance mandated for nitisinone-treated patients should extend to tyrosinemia type III.
Show evidence (2 references)
PMID:11916315 SUPPORT Human Clinical
"All have had normal liver and renal function and none has skin or eye abnormalities."
Establishes the absence of oculocutaneous disease in genetic HPD deficiency.
PMID:39290064 SUPPORT Human Clinical
"NTBC treatment of alkaptonuria (AKU) leads to increased blood tyrosine levels, causing skin issues and potentially sight-threatening corneal keratopathy."
Establishes the contrasting oculocutaneous toxicity of pharmacological HPD blockade.
Mouse strain III carries a null Hpd allele and lifelong hypertyrosinemia yet was reported as apparently healthy, while the dominant consequence of the human disorder is neurodevelopmental. Is the mouse genuinely spared, or has the phenotype simply never been looked for with an assay capable of detecting it?
HUMAN MODEL MISMATCH OPEN tyrosinemia_iii_mouse_model_neurodevelopmental_silence
Attached to
pathophysiology#Neurodevelopmental dysfunction
The strain is a high-fidelity model of the two upstream nodes of this entry: hepatic HPD activity and protein are absent with the flanking pathway enzymes intact, and the biochemical signature — persistent hypertyrosinemia, increased urinary 4-hydroxyphenyl derivatives, no succinylacetone — reproduces the human one including its discriminating negative. That fidelity is exactly what makes the third node's silence hard to read. If the mouse is truly unaffected, that is evidence against tyrosine itself as the neurotoxic agent and would strengthen the alternative explanations already curated in the tyrosine-neurotoxicity knowledge gap: a downstream phenolic metabolite, a human-specific critical developmental window, or ascertainment bias in a disorder historically found by investigating neurological symptoms. But the only reported phenotypic assessment is gross observation of general health plus hepatorenal chemistry. The human phenotype — mild intellectual impairment, developmental delay, ADHD, intermittent ataxia — is detected by developmental and neurocognitive assessment, not by inspection of an animal, and one reported human patient with serum tyrosine of 425-535 micromol/L was herself entirely asymptomatic. Absence of an overt murine phenotype is therefore not yet a measurement, and the model must not be cited as evidence that hypertyrosinemia is neurologically harmless. The Ttc36-null mouse is the direct contrast that settles the reading: a mouse whose hepatic HPD is lowered post-translationally, and which was given actual learning and memory testing, shows hippocampal neuronal damage and cognitive deficits. Reduced HPD with tyrosinemia is therefore not inherently silent in mouse, and the difference between the two strains is most parsimoniously a difference in what was measured rather than in what happened — though the two models also differ in genetic architecture, completeness of the block, and the confound of TTC36's other substrates, so the comparison motivates the experiment below rather than substituting for it.
Proposed experiments
Standardized neurobehavioural phenotyping of the Hpd-null mouse strain
exp_ht3_mouse_strain_iii_neurobehavioural_phenotyping
Battery-based neurobehavioural and neurodevelopmental assessment of homozygous strain III mice against littermate controls — learning and memory, motor coordination, activity and attention-analogous measures — paired with brain histology and myelination assessment, and with time-integrated plasma tyrosine measured so murine exposure can be placed on the human scale.
Decision criterion
A measurable deficit that tracks tyrosine exposure would support tyrosine or a proximal metabolite as the mediator and make the strain usable for intervention studies. A negative battery in animals whose exposure overlaps the human range would be genuine evidence of a human-specific mechanism and would redirect the search away from tyrosine itself. A negative battery at sub-human exposure would resolve nothing, which is the current state.
Show evidence (4 references)
PMID:2014797 SUPPORT Model Organism
"All the animals were apparently healthy, and there was no evidence of hepatorenal dysfunction."
The sole reported phenotypic assessment of the strain, and the observation the mismatch turns on.
PMID:2014797 SUPPORT Model Organism
"These features are similar to type III tyrosinemia in humans."
Establishes the biochemical fidelity that makes the absent neurological phenotype worth flagging rather than dismissing.
PMID:35707594 SUPPORT Human Clinical
"Although the clinical spectrum of the disease is not fully known, most patients present with neurodevelopmental symptoms."
States the human phenotype that the model does not display, which is the other half of the mismatch.
+ 1 more reference
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Pathophysiology

4
4-Hydroxyphenylpyruvate dioxygenase deficiency
Biallelic loss-of-function HPD variants reduce 4-hydroxyphenylpyruvate dioxygenase activity, blocking the second step of tyrosine catabolism, which converts 4-hydroxyphenylpyruvate to homogentisate. The enzyme is expressed principally in liver and kidney.
HPD hgnc:5147 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves HPD (hgnc:5147). hgnc:5147 is a gene from the HUGO Gene Nomenclature Committee.
L-tyrosine catabolic process GO:0006572 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased L-tyrosine catabolic process (GO:0006572). GO:0006572 is a biological process from the Gene Ontology. ↓ DECREASED
4-hydroxyphenylpyruvate dioxygenase activity GO:0003868 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased 4-hydroxyphenylpyruvate dioxygenase activity (GO:0003868). GO:0003868 is a molecular function from the Gene Ontology. ↓ DECREASED
liver UBERON:0002107 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in liver (UBERON:0002107). UBERON:0002107 is an anatomical location from the Uberon multi-species anatomy ontology. kidney UBERON:0002113 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in kidney (UBERON:0002113). UBERON:0002113 is an anatomical location from the Uberon multi-species anatomy ontology.
Animal models
Mouse strain III (spontaneous Hpd-null mouse) Mouse recapitulates Enzymatically and immunologically null for hepatic 4-hydroxyphenylpyruvate dioxygenase, with the neighbouring enzymes of the pathway intact, so the block sits at the same step as the human lesion.
Ttc36-null mouse (post-translational HPD depletion) Mouse partially recapitulates Reaches the same end state as the human lesion — reduced hepatic HPD protein — by an entirely different route: loss of a chaperone that normally blocks STK33/PELI1-driven degradation of the enzyme.
Downstream
Hypertyrosinemia and phenolic metabolite accumulation Loss of the second catabolic step prevents disposal of tyrosine and its transamination product, so tyrosine and 4-hydroxyphenyl derivatives accumulate.
Show evidence (2 references)
PMID:11073718 SUPPORT Human Clinical
"The enzyme 4-hydroxyphenylpyruvic acid dioxygenase (HPD) catalyzes the reaction of 4-hydroxyphenylpyruvic acid to homogentisic acid in the tyrosine catabolism pathway."
Defines the biochemical reaction that the causal lesion blocks.
PMID:10942115 SUPPORT Human Clinical
"We have identified four presumed pathogenic mutations (two missense and two nonsense mutations) in the HPD gene in three unrelated families encompassing four homozygous individuals and one compound heterozygous individual with tyrosinemia type III."
Patient-allele sequencing establishes HPD variants as the molecular cause.
Hypertyrosinemia and phenolic metabolite accumulation
The enzymatic block raises blood tyrosine and drives accumulation of the 4-hydroxyphenyl organic acids proximal to the block. Unlike tyrosinemia type I, the block lies upstream of maleylacetoacetate and fumarylacetoacetate, so succinylacetone is not produced and there is no hepatorenal toxicity.
Animal models
Mouse strain III (spontaneous Hpd-null mouse) Mouse recapitulates Reproduces the full biochemical signature of the human disorder, including the discriminating negative: persistent hypertyrosinemia with increased urinary 4-hydroxyphenyl derivatives and no succinylacetone.
Downstream
Hypertyrosinemia Persistently elevated blood tyrosine is the clinical expression of this node and the finding on which newborn-screening ascertainment rests.
Urinary excretion of 4-hydroxyphenyl organic acids Accumulated 4-hydroxyphenyl derivatives proximal to the enzymatic block are excreted in urine, where they are detected as organic acids.
Neurodevelopmental dysfunction Neurological and cognitive manifestations are the dominant clinical consequence, but no intermediate mechanism has been established, and tyrosine concentration does not track phenotype severity.
Show evidence (2 references)
PMID:11073718 SUPPORT Human Clinical
"A deficiency in the catalytic activity of HPD may lead to tyrosinemia type III, an autosomal recessive disorder characterized by elevated levels of blood tyrosine and massive excretion of tyrosine derivatives into urine."
States the defining biochemical phenotype of raised blood tyrosine with urinary derivative excretion.
PMID:9343288 SUPPORT Human Clinical
"The biochemical phenotype shows hypertyrosinemia and elevated urinary excretion of 4-hydroxyphenyl derivatives."
Independently confirms the two-component biochemical phenotype.
Urinary excretion of 4-hydroxyphenyl organic acids
Massive urinary excretion of tyrosine derivatives — 4-hydroxyphenylpyruvate, 4-hydroxyphenyllactate, and 4-hydroxyphenylacetate — is the diagnostic organic-acid signature and, together with hypertyrosinemia in the absence of succinylacetone, distinguishes this disorder from tyrosinemia type I.
Show evidence (1 reference)
PMID:28649543 SUPPORT Human Clinical
"The disorder is characterized by tyrosine accumulation in body fluids and massive excretion of tyrosine derivatives into urine"
States the urinary derivative excretion that defines the readout.
Neurodevelopmental dysfunction
The clinical burden of the disorder, spanning developmental delay, intellectual impairment, intermittent ataxia, seizures, and attention deficit hyperactivity disorder. Expression is highly variable and includes biochemically affected individuals with entirely normal development, so the node is curated as a consequence with an unresolved upstream route rather than as a direct toxic effect of tyrosine.
Animal models
Mouse strain III (spontaneous Hpd-null mouse) Mouse fails to recapitulate Despite lifelong hypertyrosinemia from a null HPD allele, the mutant animals were reported as apparently healthy with no evidence of hepatorenal dysfunction. No overt disease counterpart of the human neurodevelopmental phenotype was described.
Ttc36-null mouse (post-translational HPD depletion) Mouse partially recapitulates The one rodent result pairing reduced HPD and tyrosinemia with a measured neurological outcome: hippocampal neuronal damage with learning and memory deficits.
Downstream
Intellectual disability Cognitive impairment is the most frequently reported expression of the neurodevelopmental node, spanning mild impairment to severe intellectual disability with neurological abnormalities.
Global developmental delay Developmental delay is a common presenting expression of the node and, in one reported patient, the reason the disorder was investigated at all.
Ataxia Intermittent ataxia is part of the neurological spectrum attributed to this node.
Seizure Seizures are part of the neurological spectrum attributed to this node and may be severe.
Attention deficit hyperactivity disorder Attention deficit and hyperactivity are part of the behavioural expression of the node and have preceded the metabolic diagnosis.
Show evidence (2 references)
PMID:35707594 SUPPORT Human Clinical
"Although the clinical spectrum of the disease is not fully known, most patients present with neurodevelopmental symptoms."
Establishes neurodevelopmental symptoms as the predominant clinical consequence.
PMID:28649543 SUPPORT Human Clinical
"Presented case may suggest that high tyrosine concentration itself does not participate directly in neuronal damage described in patients with tyrosinemia type 3."
A biochemically affected but neurologically normal patient argues against tyrosine concentration as the direct neurotoxic agent.
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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 III Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

7
Nervous System 6
Intellectual disability HP:0001249 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Intellectual disability (HP:0001249). HP:0001249 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:9343288 SUPPORT Human Clinical
"We report the clinical and biochemical findings and the results of long-term follow-up in a new patient with this disorder presenting with severe mental retardation and neurological abnormalities."
Documents severe cognitive impairment with long-term follow-up in an individual patient.
PMID:32520295 SUPPORT Human Clinical
"Despite initiating a dietetic treatment, her behavior did not improve, and she has a mild intellectual impairment."
Documents mild intellectual impairment at the other end of the reported severity range.
Global developmental delay HP:0001263 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Global developmental delay (HP:0001263). HP:0001263 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37817461 SUPPORT Human Clinical
"The clinical presentation of HT III is variable and poorly understood, with symptoms ranging from developmental delay and intellectual impairment to seizures and intermittent ataxia."
Lists developmental delay within the reported clinical spectrum.
Ataxia HP:0001251 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ataxia (HP:0001251). HP:0001251 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:16602095 SUPPORT Other
"Tyrosinemia Type III is an extremely rare disorder caused by a deficiency of 4-hydroxyphenylpyruvic dioxygenase. It has been associated with ataxia and mild mental retardation."
Review associates ataxia with tyrosinemia type III.
Seizure HP:0001250 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:29456978 SUPPORT Human Clinical
"We present a case, who was admitted to the hospital at the age of 4 months for recurrent seizures. Two months later, she was admitted again with status epilepticus."
Documents a seizure presentation progressing to status epilepticus.
Attention deficit hyperactivity disorder HP:0007018 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Attention deficit hyperactivity disorder (HP:0007018). HP:0007018 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32520295 SUPPORT Human Clinical
"The neurological involvement varies, including intellectual impairment and attention deficit disorder with hyperactivity (ADHD)."
Names ADHD as part of the neurological involvement.
Ventriculomegaly HP:0002119 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ventriculomegaly (HP:0002119). HP:0002119 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:35707594 SUPPORT Human Clinical
"The girl had a novel splice-site mutation in the HPD gene and ventriculomegaly in cranial imaging, which was not previously associated with tyrosinemia type III."
Single-patient report; the source itself flags the finding as novel and unreplicated, so the evidence is PARTIAL.
Other 1
Hypertyrosinemia HP:0003231 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypertyrosinemia (HP:0003231). HP:0003231 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:11073718 SUPPORT Human Clinical
"A deficiency in the catalytic activity of HPD may lead to tyrosinemia type III, an autosomal recessive disorder characterized by elevated levels of blood tyrosine and massive excretion of tyrosine derivatives into urine."
Elevated blood tyrosine is stated as a defining characteristic.
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Genetic Associations

1
HPD deficiency
Gene: HPD hgnc:5147 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is HPD (hgnc:5147). hgnc:5147 is a gene from the HUGO Gene Nomenclature Committee.
Autosomal recessive
Show evidence (2 references)
PMID:11073718 SUPPORT Human Clinical
"These findings support the hypothesis that alterations in the structure and activity of HPD are causally related to two different metabolic disorders, tyrosinemia type III and hawkinsinuria."
Establishes that HPD underlies two distinct disease entities, motivating separate dismech entries.
PMID:11073718 SUPPORT Human Clinical
"A heterozygous missense mutation predicting an Ala to Thr change at codon 33 (A33T) was found in the same HPD gene in the two patients with hawkinsinuria."
Identifies the distinct heterozygous allele associated with the dominant sibling disorder.
Variants (2)
HPD missense and nonsense variants
Two missense and two nonsense variants were identified across three unrelated families in the first mutation survey; a homozygous A268V missense change was reported in a separate patient, and a compound heterozygous p.A244V/p.T219M genotype in another.
Show evidence (3 references)
PMID:10942115 SUPPORT Human Clinical
"We have identified four presumed pathogenic mutations (two missense and two nonsense mutations) in the HPD gene in three unrelated families encompassing four homozygous individuals and one compound heterozygous individual with tyrosinemia type III."
Documents the first characterized pathogenic HPD allele set.
PMID:11073718 SUPPORT Human Clinical
"A homozygous missense mutation predicting an Ala to Val change at codon 268 (A268V) in the HPD gene was found in the patient with tyrosinemia type III."
Documents a specific homozygous missense allele in an affected patient.
PMID:37817461 SUPPORT Human Clinical
"The genetic analysis of the proband revealed compound heterozygous mutations in the HPD gene such as c.731C>T (p.A244V) and c.656C>T (p.T219M)."
Documents a compound heterozygous genotype including a previously unreported allele.
HPD splice-site variants
Splice variants also cause the disorder: a homozygous IVS11+1G>A splice donor change in intron 11 was found in a newborn-screened boy, and a further novel splice-site variant was reported in a patient with developmental delay.
Show evidence (2 references)
PMID:23036342 SUPPORT Human Clinical
"We report the case of a boy with tyrosinemia Type III detected using neonatal screening, who is homozygous for the splice donor mutation IVS11+1G>A in intron 11 of the HPD gene."
Documents a homozygous splice donor allele.
PMID:35707594 SUPPORT Human Clinical
"The girl had a novel splice-site mutation in the HPD gene and ventriculomegaly in cranial imaging, which was not previously associated with tyrosinemia type III."
Documents a second, novel splice-site allele.
💊

Medical Actions

2
Dietary phenylalanine and tyrosine restriction
Action: dietary interventionNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is dietary intervention (NCIT:C15447). NCIT:C15447 is a clinical intervention from the NCI Thesaurus. Ontology label: Dietary Intervention NCIT:C15447
Platform: Behavioral / lifestyle
A low-protein diet restricting phenylalanine and tyrosine, with a tyrosine-free amino acid substitute, is the standard management for all genetic tyrosinemias and lowers plasma tyrosine in this disorder. Whether it alters the neurological natural history is unresolved; the strongest supporting observation is that earlier initiation was associated with better neurological and behavioural outcome in an affected sibling pair.
Mechanism Target:
INHIBITS Hypertyrosinemia and phenolic metabolite accumulation — Restricting the dietary precursors of tyrosine reduces substrate delivery to the blocked step and lowers the circulating tyrosine burden.
Show evidence (1 reference)
PMID:29456978 SUPPORT Human Clinical
"She was treated with a diet low in tyrosine and phenylalanine and anamix formula that leading to catch-up growth and improvement of her symptoms. Plasma tyrosine level dropped to normal values."
Human treatment response supports dietary restriction lowering the accumulating metabolite.
Show evidence (3 references)
PMID:16602095 SUPPORT Other
"Therapy consists of a diet low in phenylalanine and tyrosine for each of the tyrosinemias and 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) for tyrosinemia Type I."
Establishes dietary restriction as the therapy common to all tyrosinemias and confines NTBC to type I.
PMID:32520295 SUPPORT Human Clinical
"This is the first case report describing siblings with HT III who underwent nutritional treatment with a low-protein diet in different phases of life, with a better neurological and behavioral evaluation in the patient who started treatment earlier."
Within-family comparison suggesting benefit from earlier dietary initiation, but from a single sibling pair.
PMID:11916315 SUPPORT Human Clinical
"It is not clear whether a strict low tyrosine diet alters the natural history of tyrosinaemia type III, although there remains a suspicion that treatment may be important, at least in infancy."
Explicitly limits the disease-modifying claim for dietary therapy.
Developmental and neurological supportive care
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
Developmental, educational, and antiseizure support according to the individual neurological phenotype; one patient reported subjective gains in social skills and language after dietary therapy alongside falling tyrosine.
Show evidence (1 reference)
PMID:35707594 SUPPORT Human Clinical
"Our patient had mild subjective improvement in social skills and language development after dietary therapy was started and her tyrosine levels decreased."
Single-patient, subjectively assessed developmental improvement; supports supportive developmental follow-up rather than a treatment effect.
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Biochemical Markers

2
Plasma tyrosine (INCREASED)
Context: Blood tyrosine is persistently elevated and is both the screening analyte and the monitoring parameter under dietary therapy. In one asymptomatic 11-year-old girl serum tyrosine ranged from 425 to 535 micromol/L against a 29-86 micromol/L reference interval; in a symptomatic infant, plasma tyrosine fell to normal values on a tyrosine- and phenylalanine-restricted diet.
Show evidence (2 references)
PMID:9343288 SUPPORT Human Clinical
"The biochemical phenotype shows hypertyrosinemia and elevated urinary excretion of 4-hydroxyphenyl derivatives."
Establishes hypertyrosinemia as the core biochemical marker.
PMID:29456978 SUPPORT Human Clinical
"She was treated with a diet low in tyrosine and phenylalanine and anamix formula that leading to catch-up growth and improvement of her symptoms. Plasma tyrosine level dropped to normal values."
Demonstrates that the marker is dietarily modifiable.
Urinary 4-hydroxyphenyl organic acids (INCREASED)
Context: Urine organic acid analysis shows elevated p-hydroxyphenyl organic acids. The discriminating negative is succinylacetone, which is absent here and pathognomonic for tyrosinemia type I.
Show evidence (1 reference)
PMID:16602095 SUPPORT Other
"Urine organic acids show elevated p-hydroxy-phenyl organic acids in each type of tyrosinemia, and the pathognomic succinylacetone in tyrosinemia Type I."
Supports both the positive urinary finding and the succinylacetone discriminator.
🔬

Diagnosis

3
Plasma amino acid and urine organic acid analysis
Diagnosis rests on elevated plasma tyrosine with characteristic p-hydroxyphenyl organic acids on urine organic acid analysis, and on the absence of succinylacetone, which excludes tyrosinemia type I.
laboratory procedure NCIT:C25294 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:16602095 SUPPORT Other
"These disorders are diagnosed by observing elevated tyrosine by plasma amino acid chromatography and characteristic tyrosine metabolites by urine organic acid analysis."
States the biochemical diagnostic approach for the genetic tyrosinemias.
HPD molecular genetic testing
Identification of biallelic pathogenic HPD variants confirms the diagnosis; targeted next-generation sequencing has been used in a newborn-screened proband.
genetic testing NCIT:C15709 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:37817461 SUPPORT Human Clinical
"A 3-year-old girl, identified through newborn screening, was diagnosed with HT III using targeted next-generation sequencing."
Documents molecular confirmation by targeted sequencing.
Newborn screening for elevated tyrosine
Newborn screening for hypertyrosinemia is the route by which asymptomatic patients are ascertained.
Show evidence (1 reference)
PMID:23036342 SUPPORT Human Clinical
"We report the case of a boy with tyrosinemia Type III detected using neonatal screening, who is homozygous for the splice donor mutation IVS11+1G>A in intron 11 of the HPD gene."
Documents ascertainment through neonatal screening.
📈

Progression

2
Newborn-screening ascertainment
Age: Neonatal period
Individuals detected by newborn screening for elevated tyrosine may be asymptomatic at diagnosis; one screened boy homozygous for an HPD splice donor variant had normal growth and psychomotor development at 30 months on mild protein restriction.
Show evidence (1 reference)
PMID:23036342 SUPPORT Human Clinical
"At the age of 30 months, the boy's outcome under mild protein restriction was characterized by normal growth and psychomotor development."
Documents a normal early course after newborn-screening ascertainment and early dietary management.
Symptomatic neurological presentation
Age: Infancy through childhood
Most historically reported patients came to attention after the neonatal period with neurological symptoms; presentations have included recurrent seizures and status epilepticus in infancy and severe intellectual disability with neurological abnormalities on long-term follow-up.
Show evidence (2 references)
PMID:11916315 SUPPORT Human Clinical
"The majority of the nine previously reported patients have presented with neurological symptoms after the neonatal period, while others detected by neonatal screening have been asymptomatic."
Establishes the bimodal ascertainment pattern between symptomatic and screened patients.
PMID:29456978 SUPPORT Human Clinical
"We present a case, who was admitted to the hospital at the age of 4 months for recurrent seizures. Two months later, she was admitted again with status epilepticus."
Documents a severe infantile seizure presentation.
📊

Prevalence

1
Worldwide, published case literature
Cases In Literature <1 in 1,000,000
No population-based rate has been established. As of the 2022 review, only 19 patients with biallelic HPD variants had been reported worldwide, and contemporary reviews continue to describe the disorder as extremely rare and the rarest of the genetic tyrosinemias. The prevalence_class is recorded as the coarse ultra-rare band on that basis rather than from a measured rate.
Show evidence (2 references)
PMID:35707594 SUPPORT Human Clinical
"Tyrosinemia type III is an extremely rare autosomal recessive disease, with only 19 patients yet reported."
Provides the published-case count that the ultra-rare band is derived from.
PMID:32520295 SUPPORT Human Clinical
"Tyrosinemia type III (HT III) is the rarest form of tyrosinemia, and the full clinical spectrum of this disorder is still unknown."
Confirms it is the rarest of the genetic tyrosinemias.
⚖️

Clinical Burden

Moderate
Reported burden is confined to the neurodevelopmental domain — developmental delay, intellectual impairment, ataxia, seizures, and attention deficit hyperactivity disorder — with normal liver and renal function and no ocular or cutaneous disease. Burden is highly variable: individuals ascertained by newborn screening have been asymptomatic with normal psychomotor development, while late-presenting patients have had severe intellectual disability or status epilepticus. Whether diet modifies that outcome is not established, which is itself part of the burden.
Show evidence (2 references)
PMID:11916315 SUPPORT Human Clinical
"All have had normal liver and renal function and none has skin or eye abnormalities."
Bounds the burden to the neurological domain by excluding hepatic, renal, ocular, and cutaneous disease.
PMID:37817461 SUPPORT Human Clinical
"The clinical presentation of HT III is variable and poorly understood, with symptoms ranging from developmental delay and intellectual impairment to seizures and intermittent ataxia."
Describes the range of neurological severity underlying the moderate, highly variable burden.
🐁

Animal Models

2
Mouse strain III (spontaneous Hpd-null mouse)
A spontaneously arising inbred mouse strain with autosomal recessive hypertyrosinemia, characterised in 1991 as the murine counterpart of human tyrosinemia type III. Hepatic 4-hydroxyphenylpyruvate dioxygenase activity is virtually absent and the enzyme subunit is undetectable on immunoblot, while fumarylacetoacetase and both tyrosine aminotransferase isoforms are normal — so the lesion is confined to the same single step of tyrosine catabolism as the human disease. Blood tyrosine is persistently high with increased urinary 4-hydroxyphenylpyruvic acid derivatives and no succinylacetone, reproducing the biochemical discriminant that separates type III from type I. The causal allele was resolved in 1995 as a nonsense substitution in exon 7 of Hpd that additionally causes skipping of that constitutive exon in most transcripts.
Species
Mouse
Genotype
Hpd exon 7 nonsense mutation, homozygous (spontaneous)
Publication
PMID:2014797
Pathograph links
4-Hydroxyphenylpyruvate dioxygenase deficiency recapitulates fidelity: high Enzymatically and immunologically null for hepatic 4-hydroxyphenylpyruvate dioxygenase, with the neighbouring enzymes of the pathway intact, so the block sits at the same step as the human lesion.
Limitations: The causal allele is a spontaneous murine exon-7 nonsense substitution acting partly through exon skipping, not one of the human patient alleles, so it models complete loss of function and cannot speak to the hypomorphic missense genotypes that make up much of the human series. Enzyme activity and protein were assayed in liver only; the human enzyme is also expressed in kidney, and this model says nothing about residual extrahepatic activity.
Readouts
Hepatic 4-hydroxyphenylpyruvate dioxygenase activity
Enzyme assay of hepatic tyrosine-pathway enzymes in mutant versus control mice, with fumarylacetoacetase and both tyrosine aminotransferase isoforms measured as internal specificity controls.
Direction: DECREASED
Interpretation: Loss of activity restricted to HPD, with the flanking pathway enzymes normal, is what makes this a model of the HPD step rather than of hypertyrosinemia generally.
Show evidence (1 reference)
PMID:2014797 SUPPORT Model Organism
"4-hydroxyphenylpyruvic acid dioxygenase activity was virtually absent, while fumarylacetoacetase and tyrosine aminotransferases (cytosolic and mitochondrial forms) were normal in these mutant mice"
Reports the enzyme measurement and its specificity controls.
Hepatic HPD subunit protein on immunoblot
Immunoblot for the 4-hydroxyphenylpyruvate dioxygenase subunit in liver from mutant mice.
Direction: ABOLISHED
Interpretation: Absence of the protein, not merely of activity, establishes the lesion as loss of the enzyme rather than inhibition of it.
Show evidence (1 reference)
PMID:2014797 SUPPORT Model Organism
"Immunoblot analysis of 4-hydroxyphenylpyruvic acid dioxygenase protein in the liver indicated that the subunit protein of the enzyme was absent."
Reports the protein-level measurement underlying this readout.
Show evidence (1 reference)
PMID:7774914 SUPPORT Model Organism
"We report a nucleotide substitution that generates a termination codon in exon 7 of the 4-hydroxyphenylpyruvic acid dioxygenase gene in III mice."
Establishes that the strain's defect is a lesion in Hpd itself, which is what licenses treating it as informative for this node.
Hypertyrosinemia and phenolic metabolite accumulation recapitulates fidelity: high Reproduces the full biochemical signature of the human disorder, including the discriminating negative: persistent hypertyrosinemia with increased urinary 4-hydroxyphenyl derivatives and no succinylacetone.
Limitations: Absolute tyrosine concentrations in the mutant strain are not directly comparable with human plasma values, and the reported metabolite panel is qualitative; the model therefore supports the pattern of accumulation but not the exposure levels the human neurotoxicity question turns on.
Readouts
Blood tyrosine and urinary 4-hydroxyphenylpyruvic acid derivatives
Blood amino acid and urinary organic acid analysis in the mutant strain.
Direction: INCREASED
Interpretation: The two-component biochemical phenotype curated on this node - hypertyrosinemia plus urinary 4-hydroxyphenyl derivative excretion - is reproduced in the mouse.
Show evidence (1 reference)
PMID:2014797 SUPPORT Model Organism
"The blood tyrosine level was persistently high, and increased amounts of 4-hydroxyphenylpyruvic acid and its derivatives were excreted into the urine."
Reports both measurements behind this readout.
Urinary succinylacetone
Urinary succinylacetone assay in the mutant strain, the discriminant against a block at fumarylacetoacetase (tyrosinemia type I).
Direction: UNCHANGED
Interpretation: A deliberate negative result. Absence of succinylacetone confirms the block lies upstream of fumarylacetoacetate, matching the human type III biochemistry and the absence of hepatorenal disease that follows from it.
Show evidence (1 reference)
PMID:2014797 SUPPORT Model Organism
"Succinylacetone was not detected in urine samples from these mice."
Reports the negative succinylacetone measurement.
Show evidence (1 reference)
PMID:2014797 SUPPORT Model Organism
"We have characterized a new mutant strain of mouse that has hypertyrosinemia."
Establishes hypertyrosinemia as the defining phenotype of the strain, which is the node this link attaches to.
Neurodevelopmental dysfunction fails to recapitulate fidelity: low Despite lifelong hypertyrosinemia from a null HPD allele, the mutant animals were reported as apparently healthy with no evidence of hepatorenal dysfunction. No overt disease counterpart of the human neurodevelopmental phenotype was described.
Limitations: This is a negative on gross observation, not a measured absence. The characterising report describes no standardized neurobehavioural or neurodevelopmental testing, no neuropathology, and no cognitive or motor endpoints, so "apparently healthy" cannot exclude a phenotype that in humans is detected by developmental assessment rather than by inspection. Absolute tyrosine exposure in the strain is also not calibrated against the human range. The model therefore cannot currently adjudicate the tyrosine-neurotoxicity knowledge gap in either direction - see the tyrosinemia_iii_mouse_model_neurodevelopmental_silence discussion.
Readouts
Overt disease on gross observation
General health assessment of the mutant animals, reported alongside hepatic and renal function testing.
Direction: UNCHANGED
Interpretation: No gross phenotype accompanied the biochemical abnormality; the human disorder's dominant clinical consequence has no reported counterpart in this strain.
Show evidence (1 reference)
PMID:2014797 SUPPORT Model Organism
"All the animals were apparently healthy, and there was no evidence of hepatorenal dysfunction."
The only reported phenotypic assessment of the strain, and the basis for the negative claim.
Show evidence (1 reference)
PMID:2014797 SUPPORT Model Organism
"All the animals were apparently healthy, and there was no evidence of hepatorenal dysfunction."
Substantiates the negative claim that the model does not display an overt counterpart of the human neurodevelopmental consequence.
The strain predates targeted mutagenesis and arose spontaneously; the 1991 paper characterises the biochemistry and the 1995 paper resolves the allele. No later study appears to have subjected it to neurobehavioural phenotyping, which is why its bearing on the tyrosine-neurotoxicity question is recorded as a HUMAN_MODEL_MISMATCH rather than as evidence against neurotoxicity. The Ttc36-null mouse below is the informative contrast: reduced hepatic HPD assessed with learning and memory testing rather than by inspection.
Show evidence (2 references)
PMID:2014797 SUPPORT Model Organism
"These features are similar to type III tyrosinemia in humans."
The characterising study concludes the strain's biochemical phenotype matches human tyrosinemia type III.
PMID:7774914 SUPPORT Model Organism
"Mouse strain III is a model for human tyrosinemia type 3 (McKusick 276710), and this strain together with recently established models for tyrosinemia type 1 will facilitate studies of hereditary tyrosinemias."
Identifies the causal Hpd allele and states the strain's status as the model for this disorder.
Ttc36-null mouse (post-translational HPD depletion)
A knockout of the liver-enriched chaperone TTC36, which normally shields HPD from STK33-mediated T382 phosphorylation and subsequent PELI1-mediated polyubiquitylation and proteasomal degradation. Losing TTC36 therefore lowers hepatic HPD protein post-translationally, with no lesion in Hpd itself, and the animals develop tyrosinemia together with hippocampal neuronal damage and deficits of learning and memory. This is not a model of tyrosinemia type III — the genetic architecture is different and the route to low HPD is regulatory rather than allelic — but it is the only reported rodent in which reduced HPD and hypertyrosinemia have been paired with actual neurobehavioural testing, which is what makes it the necessary counterweight to the silence of the Hpd-null strain III.
Species
Mouse
Genotype
Ttc36 knockout, homozygous
Publication
PMID:31537781
Pathograph links
4-Hydroxyphenylpyruvate dioxygenase deficiency partially recapitulates fidelity: low Reaches the same end state as the human lesion — reduced hepatic HPD protein — by an entirely different route: loss of a chaperone that normally blocks STK33/PELI1-driven degradation of the enzyme.
Limitations: There is no variant in Hpd. The reduction is post-translational and partial rather than a biallelic loss-of-function null, so residual enzyme remains and the degree of block is not comparable to the human genotypes. TTC36 loss also has HPD-independent consequences that this entry does not curate, so any phenotype in these animals may be only partly attributable to the HPD reduction.
Readouts
Hepatic HPD protein abundance
Immunoblot of HPD in liver and in primary hepatocytes from Ttc36-null versus wild-type mice, with ubiquitylation and cycloheximide-chase assays establishing the degradative mechanism.
Direction: DECREASED
Interpretation: Confirms the model arrives at reduced HPD protein, the same node state as the human enzyme deficiency, without an Hpd allele.
Show evidence (1 reference)
PMID:31537781 SUPPORT Model Organism
"deficiency or depletion of TTC36 results in enhanced STK33-mediated HPD T382 phosphorylation and binding of PELI1 to HPD and subsequent PELI1-mediated HPD downregulation"
States the measured mechanism and direction of the HPD reduction.
Show evidence (1 reference)
PMID:31537781 SUPPORT Model Organism
"Ttc36-/- mice have reduced HPD expression in the"
Supports treating the model as informative for reduced HPD, while the absence of an Hpd lesion is why the link is PARTIALLY_RECAPITULATES at LOW fidelity.
Neurodevelopmental dysfunction partially recapitulates fidelity: low The one rodent result pairing reduced HPD and tyrosinemia with a measured neurological outcome: hippocampal neuronal damage with learning and memory deficits.
Limitations: The route to low HPD is regulatory, not allelic, so the phenotype cannot be attributed to HPD reduction alone — TTC36 has other substrates and the knockout is whole-body. The readout is adult rodent hippocampal learning and memory, which is not the human phenotype of childhood developmental delay, intellectual impairment, ataxia and ADHD, and the animals' tyrosine exposure is not calibrated against the human range. This model therefore does not establish that hypertyrosinemia causes the human neurodevelopmental phenotype; it establishes only that reduced HPD with tyrosinemia is not inherently neurologically silent in mouse.
Readouts
Hippocampal neuronal integrity and learning and memory performance
Hippocampal neuropathology together with behavioural learning and memory testing in Ttc36-null versus wild-type mice.
Direction: DECREASED
Interpretation: A positive neurological result in a low-HPD, tyrosinemic mouse, obtained with assays the Hpd-null strain III was never given. It is the direct contrast that makes strain III's "apparently healthy" reading a question about assay sensitivity rather than a finding of safety.
Show evidence (1 reference)
PMID:31537781 SUPPORT Model Organism
"and exhibit tyrosinemia, damage to hippocampal neurons, and deficits of learning and memory."
Reports both the neuropathological and the behavioural measurement behind this readout.
Show evidence (1 reference)
PMID:31537781 SUPPORT Model Organism
"highlight the physiological significance of TTC36-STK33-PELI1-regulated HPD expression in tyrosinemia and tyrosinemia-associated neurological disorders"
The authors frame the result as bearing on tyrosinemia-associated neurological disease, which is the node this link attaches to; PARTIAL because the genetic architecture is not that of tyrosinemia type III.
Surfaced by the independent Falcon deep-research pass rather than by the original curation, and verified against the cached abstract before use. It is deliberately curated as a model of the low-HPD state and not as a model of this disease.
Show evidence (1 reference)
PMID:31537781 SUPPORT Model Organism
"and exhibit tyrosinemia, damage to hippocampal neurons, and deficits of learning and memory."
Establishes the model's tyrosinemia-plus-neurological phenotype. Marked PARTIAL because the mice are Ttc36-null rather than Hpd-mutant, so the model is informative for the consequences of low HPD but is not a genetic model of this disease.
{ }

Source YAML

click to show 
name: Tyrosinemia Type III
category: Mendelian
creation_date: '2026-08-21T00:00:00Z'
synonyms:
- Hereditary tyrosinemia type III
- HT III
- 4-Hydroxyphenylpyruvate dioxygenase deficiency
- HPD deficiency
- Tyrosinemia due to 4-hydroxyphenylpyruvate dioxygenase deficiency
- TYRSN3
description: >
  Tyrosinemia type III is the rarest of the three genetic tyrosinemias, an
  autosomal recessive inborn error caused by biallelic loss-of-function variants
  in HPD encoding 4-hydroxyphenylpyruvate dioxygenase, the second enzyme of the
  tyrosine catabolic pathway. Loss of HPD activity blocks conversion of
  4-hydroxyphenylpyruvate to homogentisate, producing hypertyrosinemia and
  massive urinary excretion of 4-hydroxyphenyl organic acids. Because the block
  sits upstream of the maleylacetoacetate and fumarylacetoacetate steps, no
  succinylacetone or other hepatotoxic intermediate is generated, and reported
  patients have had normal liver and renal function and no eye or skin disease
  — the distinction that separates this entry mechanistically from tyrosinemia
  type I (FAH) and type II (TAT). The clinical spectrum is dominated by variable
  neurodevelopmental manifestations (developmental delay, intellectual
  impairment, ataxia, seizures, ADHD), but the causal route from tyrosine
  elevation to neurological injury is unresolved: plasma tyrosine levels do not
  correlate with phenotype and biochemically affected individuals with normal
  development have been reported. Management is a phenylalanine- and
  tyrosine-restricted low-protein diet; nitisinone, which is therapeutic in
  tyrosinemia type I, is an HPD inhibitor and therefore pharmacologically
  reproduces rather than corrects this lesion.
disease_term:
  preferred_term: tyrosinemia type III
  term:
    id: MONDO:0010162
    label: tyrosinemia type III
parents:
- Disorder of Tyrosine Metabolism
- Inborn Error of Metabolism
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0010162
      label: tyrosinemia type III
    mapping_predicate: skos:exactMatch
    mapping_source: OMIM:276710
    mapping_justification: >
      MONDO:0010162 (tyrosinemia type III) cross-references OMIM:276710 and
      Orphanet:69723 and records HPD (HGNC:5147) as its causal gene via
      RO:0004003, matching the HPD-deficiency entity curated here.
inheritance:
- name: Autosomal recessive
  description: >
    Tyrosinemia type III is caused by biallelic pathogenic HPD variants;
    affected individuals have been homozygous or compound heterozygous, and
    heterozygous carriers are unaffected.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:10942115
    reference_title: "Mutations in the 4-hydroxyphenylpyruvate dioxygenase gene (HPD) in patients with tyrosinemia type III."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Tyrosinemia type III (OMIM 276710) is an autosomal recessive disorder caused by the deficiency of 4-hydroxyphenylpyruvate dioxygenase (HPD), the second enzyme in the tyrosine catabolic pathway."
    explanation: States the autosomal recessive inheritance and the causal enzyme deficiency.
  - reference: PMID:37817461
    reference_title: "Novel HPD mutation p.A244V compound with p.T219M causing tyrosinemia type III in a Chinese girl and review of the genotype-phenotype spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hereditary tyrosinemia type III (HT III) is an extremely rare form of tyrosinemia, characterized by autosomal recessive inheritance and biallelic mutations in the HPD gene."
    explanation: Confirms autosomal recessive inheritance with biallelic HPD variants.
prevalence:
- population: Worldwide, published case literature
  measure_type: CASES_IN_LITERATURE
  prevalence_class: BELOW_1_IN_1000000
  notes: >
    No population-based rate has been established. As of the 2022 review, only
    19 patients with biallelic HPD variants had been reported worldwide, and
    contemporary reviews continue to describe the disorder as extremely rare and
    the rarest of the genetic tyrosinemias. The prevalence_class is recorded as
    the coarse ultra-rare band on that basis rather than from a measured rate.
  evidence:
  - reference: PMID:35707594
    reference_title: "Novel Cranial Imaging Findings and a Splice-Site Variant in a Patient with Tyrosinemia Type III, and a Summary of Published Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Tyrosinemia type III is an extremely rare autosomal recessive disease, with only 19 patients yet reported."
    explanation: Provides the published-case count that the ultra-rare band is derived from.
  - reference: PMID:32520295
    reference_title: "TYROSINEMIA TYPE III: A CASE REPORT OF SIBLINGS AND LITERATURE REVIEW."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Tyrosinemia type III (HT III) is the rarest form of tyrosinemia, and the full clinical spectrum of this disorder is still unknown."
    explanation: Confirms it is the rarest of the genetic tyrosinemias.
clinical_burden:
  burden_level: MODERATE
  rationale: >
    Reported burden is confined to the neurodevelopmental domain — developmental
    delay, intellectual impairment, ataxia, seizures, and attention deficit
    hyperactivity disorder — with normal liver and renal function and no ocular
    or cutaneous disease. Burden is highly variable: individuals ascertained by
    newborn screening have been asymptomatic with normal psychomotor
    development, while late-presenting patients have had severe intellectual
    disability or status epilepticus. Whether diet modifies that outcome is not
    established, which is itself part of the burden.
  evidence:
  - reference: PMID:11916315
    reference_title: "Outcome of tyrosinaemia type III."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All have had normal liver and renal function and none has skin or eye abnormalities."
    explanation: Bounds the burden to the neurological domain by excluding hepatic, renal, ocular, and cutaneous disease.
  - reference: PMID:37817461
    reference_title: "Novel HPD mutation p.A244V compound with p.T219M causing tyrosinemia type III in a Chinese girl and review of the genotype-phenotype spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The clinical presentation of HT III is variable and poorly understood, with symptoms ranging from developmental delay and intellectual impairment to seizures and intermittent ataxia."
    explanation: Describes the range of neurological severity underlying the moderate, highly variable burden.
progression:
- phase: Newborn-screening ascertainment
  age_range: Neonatal period
  notes: >
    Individuals detected by newborn screening for elevated tyrosine may be
    asymptomatic at diagnosis; one screened boy homozygous for an HPD splice
    donor variant had normal growth and psychomotor development at 30 months on
    mild protein restriction.
  evidence:
  - reference: PMID:23036342
    reference_title: "Tyrosinemia Type III detected via neonatal screening: management and outcome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At the age of 30 months, the boy's outcome under mild protein restriction was characterized by normal growth and psychomotor development."
    explanation: Documents a normal early course after newborn-screening ascertainment and early dietary management.
- phase: Symptomatic neurological presentation
  age_range: Infancy through childhood
  notes: >
    Most historically reported patients came to attention after the neonatal
    period with neurological symptoms; presentations have included recurrent
    seizures and status epilepticus in infancy and severe intellectual
    disability with neurological abnormalities on long-term follow-up.
  evidence:
  - reference: PMID:11916315
    reference_title: "Outcome of tyrosinaemia type III."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The majority of the nine previously reported patients have presented with neurological symptoms after the neonatal period, while others detected by neonatal screening have been asymptomatic."
    explanation: Establishes the bimodal ascertainment pattern between symptomatic and screened patients.
  - reference: PMID:29456978
    reference_title: "A Case of Tyrosinemia Type III with Status Epilepticus and Mental Retardation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We present a case, who was admitted to the hospital at the age of 4 months for recurrent seizures. Two months later, she was admitted again with status epilepticus."
    explanation: Documents a severe infantile seizure presentation.
pathophysiology:
- name: 4-Hydroxyphenylpyruvate dioxygenase deficiency
  role: trigger
  biological_scale: MOLECULAR
  description: >
    Biallelic loss-of-function HPD variants reduce 4-hydroxyphenylpyruvate
    dioxygenase activity, blocking the second step of tyrosine catabolism, which
    converts 4-hydroxyphenylpyruvate to homogentisate. The enzyme is expressed
    principally in liver and kidney.
  genes:
  - preferred_term: HPD
    term:
      id: hgnc:5147
      label: HPD
  molecular_functions:
  - preferred_term: 4-hydroxyphenylpyruvate dioxygenase activity
    term:
      id: GO:0003868
      label: 4-hydroxyphenylpyruvate dioxygenase activity
    modifier: DECREASED
  biological_processes:
  - preferred_term: L-tyrosine catabolic process
    term:
      id: GO:0006572
      label: L-tyrosine catabolic process
    modifier: DECREASED
  chemical_entities:
  - preferred_term: homogentisate
    term:
      id: CHEBI:16169
      label: homogentisate
    modifier: DECREASED
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  - preferred_term: kidney
    term:
      id: UBERON:0002113
      label: kidney
  evidence:
  - reference: PMID:11073718
    reference_title: "Mutations in the 4-hydroxyphenylpyruvic acid dioxygenase gene are responsible for tyrosinemia type III and hawkinsinuria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The enzyme 4-hydroxyphenylpyruvic acid dioxygenase (HPD) catalyzes the reaction of 4-hydroxyphenylpyruvic acid to homogentisic acid in the tyrosine catabolism pathway."
    explanation: Defines the biochemical reaction that the causal lesion blocks.
  - reference: PMID:10942115
    reference_title: "Mutations in the 4-hydroxyphenylpyruvate dioxygenase gene (HPD) in patients with tyrosinemia type III."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We have identified four presumed pathogenic mutations (two missense and two nonsense mutations) in the HPD gene in three unrelated families encompassing four homozygous individuals and one compound heterozygous individual with tyrosinemia type III."
    explanation: Patient-allele sequencing establishes HPD variants as the molecular cause.
  downstream:
  - target: Hypertyrosinemia and phenolic metabolite accumulation
    description: >
      Loss of the second catabolic step prevents disposal of tyrosine and its
      transamination product, so tyrosine and 4-hydroxyphenyl derivatives
      accumulate.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:10942115
      reference_title: "Mutations in the 4-hydroxyphenylpyruvate dioxygenase gene (HPD) in patients with tyrosinemia type III."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The enzyme deficiency results in an accumulation and increased excretion of tyrosine and phenolic metabolites."
      explanation: Directly links the enzyme deficiency to metabolite accumulation.
- name: Hypertyrosinemia and phenolic metabolite accumulation
  role: central_effector
  biological_scale: ORGANISM
  description: >
    The enzymatic block raises blood tyrosine and drives accumulation of the
    4-hydroxyphenyl organic acids proximal to the block. Unlike tyrosinemia type
    I, the block lies upstream of maleylacetoacetate and fumarylacetoacetate, so
    succinylacetone is not produced and there is no hepatorenal toxicity.
  chemical_entities:
  - preferred_term: L-tyrosine
    term:
      id: CHEBI:17895
      label: L-tyrosine
    modifier: INCREASED
  - preferred_term: 4-hydroxyphenylpyruvate
    term:
      id: CHEBI:15999
      label: 4-hydroxyphenylpyruvic acid
    modifier: INCREASED
  evidence:
  - reference: PMID:11073718
    reference_title: "Mutations in the 4-hydroxyphenylpyruvic acid dioxygenase gene are responsible for tyrosinemia type III and hawkinsinuria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A deficiency in the catalytic activity of HPD may lead to tyrosinemia type III, an autosomal recessive disorder characterized by elevated levels of blood tyrosine and massive excretion of tyrosine derivatives into urine."
    explanation: States the defining biochemical phenotype of raised blood tyrosine with urinary derivative excretion.
  - reference: PMID:9343288
    reference_title: "Tyrosinemia type III: diagnosis and ten-year follow-up."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The biochemical phenotype shows hypertyrosinemia and elevated urinary excretion of 4-hydroxyphenyl derivatives."
    explanation: Independently confirms the two-component biochemical phenotype.
  downstream:
  - target: Hypertyrosinemia
    description: >
      Persistently elevated blood tyrosine is the clinical expression of this
      node and the finding on which newborn-screening ascertainment rests.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:11073718
      reference_title: "Mutations in the 4-hydroxyphenylpyruvic acid dioxygenase gene are responsible for tyrosinemia type III and hawkinsinuria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "A deficiency in the catalytic activity of HPD may lead to tyrosinemia type III, an autosomal recessive disorder characterized by elevated levels of blood tyrosine and massive excretion of tyrosine derivatives into urine."
      explanation: Names raised blood tyrosine as the defining manifestation of the enzyme block, which is what this edge asserts.
  - target: Urinary excretion of 4-hydroxyphenyl organic acids
    description: >
      Accumulated 4-hydroxyphenyl derivatives proximal to the enzymatic block
      are excreted in urine, where they are detected as organic acids.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:16602095
      reference_title: "The genetic tyrosinemias."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Urine organic acids show elevated p-hydroxy-phenyl organic acids in each type of tyrosinemia, and the pathognomic succinylacetone in tyrosinemia Type I."
      explanation: Supports urinary p-hydroxyphenyl organic acid excretion, and separates it from the succinylacetone that is specific to type I.
  - target: Neurodevelopmental dysfunction
    description: >
      Neurological and cognitive manifestations are the dominant clinical
      consequence, but no intermediate mechanism has been established, and
      tyrosine concentration does not track phenotype severity.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:16602095
      reference_title: "The genetic tyrosinemias."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Tyrosinemia Type III is an extremely rare disorder caused by a deficiency of 4-hydroxyphenylpyruvic dioxygenase. It has been associated with ataxia and mild mental retardation."
      explanation: Supports the association while its hedged wording matches the unresolved causal route.
    - reference: PMID:10942115
      reference_title: "Mutations in the 4-hydroxyphenylpyruvate dioxygenase gene (HPD) in patients with tyrosinemia type III."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "No correlation of the severity of the mutation and enzyme deficiency and mental function has been found; neither do the recorded tyrosine levels correlate with the clinical phenotype."
      explanation: Qualifies the edge — genotype, residual enzyme activity, and tyrosine level all fail to predict the neurological outcome, which is why the link is curated with unknown intermediates.
- name: Urinary excretion of 4-hydroxyphenyl organic acids
  role: biomarker
  biological_scale: ORGANISM
  description: >
    Massive urinary excretion of tyrosine derivatives — 4-hydroxyphenylpyruvate,
    4-hydroxyphenyllactate, and 4-hydroxyphenylacetate — is the diagnostic
    organic-acid signature and, together with hypertyrosinemia in the absence of
    succinylacetone, distinguishes this disorder from tyrosinemia type I.
  chemical_entities:
  - preferred_term: 4-hydroxyphenylacetate
    term:
      id: CHEBI:18101
      label: 4-hydroxyphenylacetic acid
    modifier: INCREASED
  evidence:
  - reference: PMID:28649543
    reference_title: "Tyrosinemia type III in an asymptomatic girl."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The disorder is characterized by tyrosine accumulation in body fluids and massive excretion of tyrosine derivatives into urine"
    explanation: States the urinary derivative excretion that defines the readout.
- name: Neurodevelopmental dysfunction
  role: consequence
  biological_scale: ORGANISM
  description: >
    The clinical burden of the disorder, spanning developmental delay,
    intellectual impairment, intermittent ataxia, seizures, and attention
    deficit hyperactivity disorder. Expression is highly variable and includes
    biochemically affected individuals with entirely normal development, so the
    node is curated as a consequence with an unresolved upstream route rather
    than as a direct toxic effect of tyrosine.
  evidence:
  - reference: PMID:35707594
    reference_title: "Novel Cranial Imaging Findings and a Splice-Site Variant in a Patient with Tyrosinemia Type III, and a Summary of Published Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Although the clinical spectrum of the disease is not fully known, most patients present with neurodevelopmental symptoms."
    explanation: Establishes neurodevelopmental symptoms as the predominant clinical consequence.
  - reference: PMID:28649543
    reference_title: "Tyrosinemia type III in an asymptomatic girl."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Presented case may suggest that high tyrosine concentration itself does not participate directly in neuronal damage described in patients with tyrosinemia type 3."
    explanation: A biochemically affected but neurologically normal patient argues against tyrosine concentration as the direct neurotoxic agent.
  downstream:
  - target: Intellectual disability
    description: >
      Cognitive impairment is the most frequently reported expression of the
      neurodevelopmental node, spanning mild impairment to severe intellectual
      disability with neurological abnormalities.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:9343288
      reference_title: "Tyrosinemia type III: diagnosis and ten-year follow-up."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We report the clinical and biochemical findings and the results of long-term follow-up in a new patient with this disorder presenting with severe mental retardation and neurological abnormalities."
      explanation: A long-followed patient in whom the neurodevelopmental burden of the disorder presented as severe cognitive impairment.
  - target: Global developmental delay
    description: >
      Developmental delay is a common presenting expression of the node and, in
      one reported patient, the reason the disorder was investigated at all.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:35707594
      reference_title: "Novel Cranial Imaging Findings and a Splice-Site Variant in a Patient with Tyrosinemia Type III, and a Summary of Published Cases."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We report on a 20-month-old patient who was investigated due to developmental delay and dysmorphic features."
      explanation: Developmental delay is the presenting neurodevelopmental manifestation in this reported patient.
  - target: Ataxia
    description: >
      Intermittent ataxia is part of the neurological spectrum attributed to
      this node.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:37817461
      reference_title: "Novel HPD mutation p.A244V compound with p.T219M causing tyrosinemia type III in a Chinese girl and review of the genotype-phenotype spectrum."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The clinical presentation of HT III is variable and poorly understood, with symptoms ranging from developmental delay and intellectual impairment to seizures and intermittent ataxia."
      explanation: Places intermittent ataxia inside the reported neurological spectrum of the disorder.
  - target: Seizure
    description: >
      Seizures are part of the neurological spectrum attributed to this node and
      may be severe.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:29456978
      reference_title: "A Case of Tyrosinemia Type III with Status Epilepticus and Mental Retardation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We present a case, who was admitted to the hospital at the age of 4 months for recurrent seizures. Two months later, she was admitted again with status epilepticus."
      explanation: Documents seizures, progressing to status epilepticus, as a neurological manifestation in an affected infant.
  - target: Attention deficit hyperactivity disorder
    description: >
      Attention deficit and hyperactivity are part of the behavioural expression
      of the node and have preceded the metabolic diagnosis.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:32520295
      reference_title: "TYROSINEMIA TYPE III: A CASE REPORT OF SIBLINGS AND LITERATURE REVIEW."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The neurological involvement varies, including intellectual impairment and attention deficit disorder with hyperactivity (ADHD)."
      explanation: Names ADHD as one of the varying neurological expressions of the disorder.
phenotypes:
- name: Hypertyrosinemia
  category: Biochemical
  description: >
    Persistently elevated blood tyrosine is the constant biochemical finding and
    the basis for newborn-screening ascertainment.
  phenotype_term:
    preferred_term: Hypertyrosinemia
    term:
      id: HP:0003231
      label: Hypertyrosinemia
  evidence:
  - reference: PMID:11073718
    reference_title: "Mutations in the 4-hydroxyphenylpyruvic acid dioxygenase gene are responsible for tyrosinemia type III and hawkinsinuria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A deficiency in the catalytic activity of HPD may lead to tyrosinemia type III, an autosomal recessive disorder characterized by elevated levels of blood tyrosine and massive excretion of tyrosine derivatives into urine."
    explanation: Elevated blood tyrosine is stated as a defining characteristic.
- name: Intellectual disability
  category: Neurological
  description: >
    Cognitive impairment ranging from mild intellectual impairment to severe
    intellectual disability with neurological abnormalities. Frequency is not
    recorded because the published series are small case collections without
    defensible denominators.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:9343288
    reference_title: "Tyrosinemia type III: diagnosis and ten-year follow-up."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report the clinical and biochemical findings and the results of long-term follow-up in a new patient with this disorder presenting with severe mental retardation and neurological abnormalities."
    explanation: Documents severe cognitive impairment with long-term follow-up in an individual patient.
  - reference: PMID:32520295
    reference_title: "TYROSINEMIA TYPE III: A CASE REPORT OF SIBLINGS AND LITERATURE REVIEW."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Despite initiating a dietetic treatment, her behavior did not improve, and she has a mild intellectual impairment."
    explanation: Documents mild intellectual impairment at the other end of the reported severity range.
- name: Global developmental delay
  category: Neurological
  description: >
    Developmental delay is a common presenting feature and, in one reported
    patient, the reason for investigation.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:37817461
    reference_title: "Novel HPD mutation p.A244V compound with p.T219M causing tyrosinemia type III in a Chinese girl and review of the genotype-phenotype spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The clinical presentation of HT III is variable and poorly understood, with symptoms ranging from developmental delay and intellectual impairment to seizures and intermittent ataxia."
    explanation: Lists developmental delay within the reported clinical spectrum.
- name: Ataxia
  category: Neurological
  description: >
    Intermittent ataxia is a recognized manifestation of the disorder.
  phenotype_term:
    preferred_term: Ataxia
    term:
      id: HP:0001251
      label: Ataxia
  evidence:
  - reference: PMID:16602095
    reference_title: "The genetic tyrosinemias."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Tyrosinemia Type III is an extremely rare disorder caused by a deficiency of 4-hydroxyphenylpyruvic dioxygenase. It has been associated with ataxia and mild mental retardation."
    explanation: Review associates ataxia with tyrosinemia type III.
- name: Seizure
  category: Neurological
  description: >
    Seizures occur and may be severe; one infant presented with recurrent
    seizures at four months and status epilepticus two months later.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:29456978
    reference_title: "A Case of Tyrosinemia Type III with Status Epilepticus and Mental Retardation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We present a case, who was admitted to the hospital at the age of 4 months for recurrent seizures. Two months later, she was admitted again with status epilepticus."
    explanation: Documents a seizure presentation progressing to status epilepticus.
- name: Attention deficit hyperactivity disorder
  category: Behavioral
  description: >
    Attention deficit and hyperactivity have been reported in both affected
    siblings of one family, one of whom carried the diagnosis before the
    metabolic disorder was recognized.
  phenotype_term:
    preferred_term: Attention deficit hyperactivity disorder
    term:
      id: HP:0007018
      label: Attention deficit hyperactivity disorder
  evidence:
  - reference: PMID:32520295
    reference_title: "TYROSINEMIA TYPE III: A CASE REPORT OF SIBLINGS AND LITERATURE REVIEW."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The neurological involvement varies, including intellectual impairment and attention deficit disorder with hyperactivity (ADHD)."
    explanation: Names ADHD as part of the neurological involvement.
- name: Ventriculomegaly
  category: Neuroimaging
  description: >
    Ventriculomegaly was reported on cranial imaging in one patient with a novel
    HPD splice-site variant and was explicitly noted as not previously
    associated with the disorder; it is curated here as a single reported
    finding, not an established feature.
  phenotype_term:
    preferred_term: Ventriculomegaly
    term:
      id: HP:0002119
      label: Ventriculomegaly
  evidence:
  - reference: PMID:35707594
    reference_title: "Novel Cranial Imaging Findings and a Splice-Site Variant in a Patient with Tyrosinemia Type III, and a Summary of Published Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The girl had a novel splice-site mutation in the HPD gene and ventriculomegaly in cranial imaging, which was not previously associated with tyrosinemia type III."
    explanation: Single-patient report; the source itself flags the finding as novel and unreplicated, so the evidence is PARTIAL.
biochemical:
- name: Plasma tyrosine
  presence: INCREASED
  context: >
    Blood tyrosine is persistently elevated and is both the screening analyte
    and the monitoring parameter under dietary therapy. In one asymptomatic
    11-year-old girl serum tyrosine ranged from 425 to 535 micromol/L against a
    29-86 micromol/L reference interval; in a symptomatic infant, plasma
    tyrosine fell to normal values on a tyrosine- and phenylalanine-restricted
    diet.
  biomarker_term:
    preferred_term: L-tyrosine
    term:
      id: CHEBI:17895
      label: L-tyrosine
  evidence:
  - reference: PMID:9343288
    reference_title: "Tyrosinemia type III: diagnosis and ten-year follow-up."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The biochemical phenotype shows hypertyrosinemia and elevated urinary excretion of 4-hydroxyphenyl derivatives."
    explanation: Establishes hypertyrosinemia as the core biochemical marker.
  - reference: PMID:29456978
    reference_title: "A Case of Tyrosinemia Type III with Status Epilepticus and Mental Retardation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "She was treated with a diet low in tyrosine and phenylalanine and anamix formula that leading to catch-up growth and improvement of her symptoms. Plasma tyrosine level dropped to normal values."
    explanation: Demonstrates that the marker is dietarily modifiable.
- name: Urinary 4-hydroxyphenyl organic acids
  presence: INCREASED
  context: >
    Urine organic acid analysis shows elevated p-hydroxyphenyl organic acids.
    The discriminating negative is succinylacetone, which is absent here and
    pathognomonic for tyrosinemia type I.
  biomarker_term:
    preferred_term: 4-hydroxyphenylacetate
    term:
      id: CHEBI:18101
      label: 4-hydroxyphenylacetic acid
  evidence:
  - reference: PMID:16602095
    reference_title: "The genetic tyrosinemias."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Urine organic acids show elevated p-hydroxy-phenyl organic acids in each type of tyrosinemia, and the pathognomic succinylacetone in tyrosinemia Type I."
    explanation: Supports both the positive urinary finding and the succinylacetone discriminator.
genetic:
- name: HPD deficiency
  gene_term:
    preferred_term: HPD
    term:
      id: hgnc:5147
      label: HPD
  inheritance:
  - name: Autosomal recessive
    description: Biallelic pathogenic HPD variants are required; carriers are unaffected.
    evidence:
    - reference: PMID:37817461
      reference_title: "Novel HPD mutation p.A244V compound with p.T219M causing tyrosinemia type III in a Chinese girl and review of the genotype-phenotype spectrum."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Hereditary tyrosinemia type III (HT III) is an extremely rare form of tyrosinemia, characterized by autosomal recessive inheritance and biallelic mutations in the HPD gene."
      explanation: States the biallelic autosomal recessive requirement.
  variants:
  - name: HPD missense and nonsense variants
    description: >
      Two missense and two nonsense variants were identified across three
      unrelated families in the first mutation survey; a homozygous A268V
      missense change was reported in a separate patient, and a compound
      heterozygous p.A244V/p.T219M genotype in another.
    evidence:
    - reference: PMID:10942115
      reference_title: "Mutations in the 4-hydroxyphenylpyruvate dioxygenase gene (HPD) in patients with tyrosinemia type III."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We have identified four presumed pathogenic mutations (two missense and two nonsense mutations) in the HPD gene in three unrelated families encompassing four homozygous individuals and one compound heterozygous individual with tyrosinemia type III."
      explanation: Documents the first characterized pathogenic HPD allele set.
    - reference: PMID:11073718
      reference_title: "Mutations in the 4-hydroxyphenylpyruvic acid dioxygenase gene are responsible for tyrosinemia type III and hawkinsinuria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "A homozygous missense mutation predicting an Ala to Val change at codon 268 (A268V) in the HPD gene was found in the patient with tyrosinemia type III."
      explanation: Documents a specific homozygous missense allele in an affected patient.
    - reference: PMID:37817461
      reference_title: "Novel HPD mutation p.A244V compound with p.T219M causing tyrosinemia type III in a Chinese girl and review of the genotype-phenotype spectrum."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The genetic analysis of the proband revealed compound heterozygous mutations in the HPD gene such as c.731C>T (p.A244V) and c.656C>T (p.T219M)."
      explanation: Documents a compound heterozygous genotype including a previously unreported allele.
  - name: HPD splice-site variants
    description: >
      Splice variants also cause the disorder: a homozygous IVS11+1G>A splice
      donor change in intron 11 was found in a newborn-screened boy, and a
      further novel splice-site variant was reported in a patient with
      developmental delay.
    evidence:
    - reference: PMID:23036342
      reference_title: "Tyrosinemia Type III detected via neonatal screening: management and outcome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We report the case of a boy with tyrosinemia Type III detected using neonatal screening, who is homozygous for the splice donor mutation IVS11+1G>A in intron 11 of the HPD gene."
      explanation: Documents a homozygous splice donor allele.
    - reference: PMID:35707594
      reference_title: "Novel Cranial Imaging Findings and a Splice-Site Variant in a Patient with Tyrosinemia Type III, and a Summary of Published Cases."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The girl had a novel splice-site mutation in the HPD gene and ventriculomegaly in cranial imaging, which was not previously associated with tyrosinemia type III."
      explanation: Documents a second, novel splice-site allele.
  features: >
    HPD encodes 4-hydroxyphenylpyruvate dioxygenase, the second enzyme of
    tyrosine catabolism. Variants in the same gene cause two distinct diseases:
    biallelic loss-of-function alleles cause autosomal recessive tyrosinemia
    type III, while the heterozygous A33T change is associated with autosomal
    dominant hawkinsinuria (MONDO:0007700), which is not curated here.
  evidence:
  - reference: PMID:11073718
    reference_title: "Mutations in the 4-hydroxyphenylpyruvic acid dioxygenase gene are responsible for tyrosinemia type III and hawkinsinuria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These findings support the hypothesis that alterations in the structure and activity of HPD are causally related to two different metabolic disorders, tyrosinemia type III and hawkinsinuria."
    explanation: Establishes that HPD underlies two distinct disease entities, motivating separate dismech entries.
  - reference: PMID:11073718
    reference_title: "Mutations in the 4-hydroxyphenylpyruvic acid dioxygenase gene are responsible for tyrosinemia type III and hawkinsinuria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A heterozygous missense mutation predicting an Ala to Thr change at codon 33 (A33T) was found in the same HPD gene in the two patients with hawkinsinuria."
    explanation: Identifies the distinct heterozygous allele associated with the dominant sibling disorder.
diagnosis:
- name: Plasma amino acid and urine organic acid analysis
  description: >
    Diagnosis rests on elevated plasma tyrosine with characteristic
    p-hydroxyphenyl organic acids on urine organic acid analysis, and on the
    absence of succinylacetone, which excludes tyrosinemia type I.
  diagnosis_term:
    preferred_term: laboratory procedure
    term:
      id: NCIT:C25294
      label: Laboratory Procedure
  evidence:
  - reference: PMID:16602095
    reference_title: "The genetic tyrosinemias."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "These disorders are diagnosed by observing elevated tyrosine by plasma amino acid chromatography and characteristic tyrosine metabolites by urine organic acid analysis."
    explanation: States the biochemical diagnostic approach for the genetic tyrosinemias.
- name: HPD molecular genetic testing
  description: >
    Identification of biallelic pathogenic HPD variants confirms the diagnosis;
    targeted next-generation sequencing has been used in a newborn-screened
    proband.
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:37817461
    reference_title: "Novel HPD mutation p.A244V compound with p.T219M causing tyrosinemia type III in a Chinese girl and review of the genotype-phenotype spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A 3-year-old girl, identified through newborn screening, was diagnosed with HT III using targeted next-generation sequencing."
    explanation: Documents molecular confirmation by targeted sequencing.
- name: Newborn screening for elevated tyrosine
  description: >
    Newborn screening for hypertyrosinemia is the route by which asymptomatic
    patients are ascertained.
  evidence:
  - reference: PMID:23036342
    reference_title: "Tyrosinemia Type III detected via neonatal screening: management and outcome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report the case of a boy with tyrosinemia Type III detected using neonatal screening, who is homozygous for the splice donor mutation IVS11+1G>A in intron 11 of the HPD gene."
    explanation: Documents ascertainment through neonatal screening.
treatments:
- name: Dietary phenylalanine and tyrosine restriction
  description: >
    A low-protein diet restricting phenylalanine and tyrosine, with a
    tyrosine-free amino acid substitute, is the standard management for all
    genetic tyrosinemias and lowers plasma tyrosine in this disorder. Whether it
    alters the neurological natural history is unresolved; the strongest
    supporting observation is that earlier initiation was associated with better
    neurological and behavioural outcome in an affected sibling pair.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: dietary intervention
    term:
      id: NCIT:C15447
      label: Dietary Intervention
  target_mechanisms:
  - target: Hypertyrosinemia and phenolic metabolite accumulation
    treatment_effect: INHIBITS
    description: >
      Restricting the dietary precursors of tyrosine reduces substrate delivery
      to the blocked step and lowers the circulating tyrosine burden.
    evidence:
    - reference: PMID:29456978
      reference_title: "A Case of Tyrosinemia Type III with Status Epilepticus and Mental Retardation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "She was treated with a diet low in tyrosine and phenylalanine and anamix formula that leading to catch-up growth and improvement of her symptoms. Plasma tyrosine level dropped to normal values."
      explanation: Human treatment response supports dietary restriction lowering the accumulating metabolite.
  evidence:
  - reference: PMID:16602095
    reference_title: "The genetic tyrosinemias."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Therapy consists of a diet low in phenylalanine and tyrosine for each of the tyrosinemias and 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) for tyrosinemia Type I."
    explanation: Establishes dietary restriction as the therapy common to all tyrosinemias and confines NTBC to type I.
  - reference: PMID:32520295
    reference_title: "TYROSINEMIA TYPE III: A CASE REPORT OF SIBLINGS AND LITERATURE REVIEW."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This is the first case report describing siblings with HT III who underwent nutritional treatment with a low-protein diet in different phases of life, with a better neurological and behavioral evaluation in the patient who started treatment earlier."
    explanation: Within-family comparison suggesting benefit from earlier dietary initiation, but from a single sibling pair.
  - reference: PMID:11916315
    reference_title: "Outcome of tyrosinaemia type III."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is not clear whether a strict low tyrosine diet alters the natural history of tyrosinaemia type III, although there remains a suspicion that treatment may be important, at least in infancy."
    explanation: Explicitly limits the disease-modifying claim for dietary therapy.
- name: Developmental and neurological supportive care
  description: >
    Developmental, educational, and antiseizure support according to the
    individual neurological phenotype; one patient reported subjective gains in
    social skills and language after dietary therapy alongside falling tyrosine.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:35707594
    reference_title: "Novel Cranial Imaging Findings and a Splice-Site Variant in a Patient with Tyrosinemia Type III, and a Summary of Published Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our patient had mild subjective improvement in social skills and language development after dietary therapy was started and her tyrosine levels decreased."
    explanation: Single-patient, subjectively assessed developmental improvement; supports supportive developmental follow-up rather than a treatment effect.
discussions:
- discussion_id: tyrosinemia_iii_tyrosine_neurotoxicity_unresolved
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >
    If hypertyrosinemia is the only established biochemical abnormality in
    tyrosinemia type III, why does neither the severity of the HPD lesion nor
    the plasma tyrosine concentration predict the neurological phenotype, and
    what actually mediates the neurodevelopmental injury?
  rationale: >
    The pathograph edge from the metabolic block to neurodevelopmental
    dysfunction is the only edge in this entry that cannot be curated as DIRECT.
    Three independent observations refuse a simple dose-response model: the
    first mutation survey found no correlation between mutation severity,
    residual enzyme activity, mental function, or tyrosine level; an
    11-year-old girl with serum tyrosine of 425-535 micromol/L had no symptoms
    and normal mental development; and newborn-screened patients on mild protein
    restriction have had normal psychomotor development. Candidate explanations
    that the literature has not discriminated between include a critical early
    developmental window, a downstream phenolic metabolite rather than tyrosine
    itself, and ascertainment bias inflating the neurological association in a
    disorder historically found by investigating neurological symptoms.
  attaches_to:
  - pathophysiology#Hypertyrosinemia and phenolic metabolite accumulation
  - pathophysiology#Neurodevelopmental dysfunction
  proposed_experiments:
  - experiment_id: exp_ht3_screened_cohort_neurodevelopmental_followup
    name: Systematic neurodevelopmental follow-up of newborn-screened cohorts
    description: >
      Prospective, standardized neurocognitive assessment of all
      screening-ascertained HPD-deficient individuals, stratified by age at
      dietary initiation and by time-integrated tyrosine exposure, to separate
      ascertainment bias from a genuine exposure-response relationship.
    decision_criterion: >
      A monotonic relationship between time-integrated tyrosine exposure and
      neurocognitive score would support tyrosine itself as the mediator;
      normal outcomes across the full exposure range would refute it and
      redirect the search to a downstream phenolic metabolite or to
      ascertainment bias.
  evidence:
  - reference: PMID:10942115
    reference_title: "Mutations in the 4-hydroxyphenylpyruvate dioxygenase gene (HPD) in patients with tyrosinemia type III."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "No correlation of the severity of the mutation and enzyme deficiency and mental function has been found; neither do the recorded tyrosine levels correlate with the clinical phenotype."
    explanation: The absence of a genotype-, enzyme-, or metabolite-phenotype correlation is the primary basis for the gap.
  - reference: PMID:28649543
    reference_title: "Tyrosinemia type III in an asymptomatic girl."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Presented case may suggest that high tyrosine concentration itself does not participate directly in neuronal damage described in patients with tyrosinemia type 3."
    explanation: A biochemically affected, neurologically normal patient supports the gap and argues against direct tyrosine neurotoxicity.
- discussion_id: tyrosinemia_iii_vs_nitisinone_phenocopy
  kind: OPEN_QUESTION
  status: OPEN
  prompt: >
    Nitisinone is a pharmacological HPD inhibitor, so patients treated with it
    for tyrosinemia type I or alkaptonuria carry an acquired HPD block and
    develop tyrosine-driven corneal keratopathy and skin lesions. Why do
    genetically HPD-deficient patients not?
  rationale: >
    This is a direct, testable discrepancy between a genetic lesion and its
    pharmacological phenocopy at the same enzyme. Reported tyrosinemia type III
    patients have had no skin or eye abnormalities, whereas nitisinone-induced
    hypertyrosinemia in alkaptonuria causes skin issues and sight-threatening
    corneal keratopathy. Possible explanations that the literature has not
    resolved include a higher absolute tyrosine level reached under
    pharmacological blockade than under most reported genetic deficiency,
    residual HPD activity in hypomorphic genotypes, differences in the tissue
    distribution of the block, and the older age and longer exposure of
    nitisinone-treated adults. Resolving it would inform whether the ocular
    surveillance mandated for nitisinone-treated patients should extend to
    tyrosinemia type III.
  attaches_to:
  - pathophysiology#4-Hydroxyphenylpyruvate dioxygenase deficiency
  - pathophysiology#Hypertyrosinemia and phenolic metabolite accumulation
  evidence:
  - reference: PMID:11916315
    reference_title: "Outcome of tyrosinaemia type III."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All have had normal liver and renal function and none has skin or eye abnormalities."
    explanation: Establishes the absence of oculocutaneous disease in genetic HPD deficiency.
  - reference: PMID:39290064
    reference_title: "Evaluation of a casein glycomacropeptide-based protein substitute, in the dietary management of NTBC-induced tyrosinaemia in patients with alkaptonuria: A prospective open-label study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "NTBC treatment of alkaptonuria (AKU) leads to increased blood tyrosine levels, causing skin issues and potentially sight-threatening corneal keratopathy."
    explanation: Establishes the contrasting oculocutaneous toxicity of pharmacological HPD blockade.
- discussion_id: tyrosinemia_iii_mouse_model_neurodevelopmental_silence
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >
    Mouse strain III carries a null Hpd allele and lifelong hypertyrosinemia yet
    was reported as apparently healthy, while the dominant consequence of the
    human disorder is neurodevelopmental. Is the mouse genuinely spared, or has
    the phenotype simply never been looked for with an assay capable of
    detecting it?
  rationale: >
    The strain is a high-fidelity model of the two upstream nodes of this entry:
    hepatic HPD activity and protein are absent with the flanking pathway
    enzymes intact, and the biochemical signature — persistent hypertyrosinemia,
    increased urinary 4-hydroxyphenyl derivatives, no succinylacetone —
    reproduces the human one including its discriminating negative. That
    fidelity is exactly what makes the third node's silence hard to read. If the
    mouse is truly unaffected, that is evidence against tyrosine itself as the
    neurotoxic agent and would strengthen the alternative explanations already
    curated in the tyrosine-neurotoxicity knowledge gap: a downstream phenolic
    metabolite, a human-specific critical developmental window, or ascertainment
    bias in a disorder historically found by investigating neurological
    symptoms. But the only reported phenotypic assessment is gross observation
    of general health plus hepatorenal chemistry. The human phenotype — mild
    intellectual impairment, developmental delay, ADHD, intermittent ataxia — is
    detected by developmental and neurocognitive assessment, not by inspection
    of an animal, and one reported human patient with serum tyrosine of 425-535
    micromol/L was herself entirely asymptomatic. Absence of an overt murine
    phenotype is therefore not yet a measurement, and the model must not be
    cited as evidence that hypertyrosinemia is neurologically harmless. The
    Ttc36-null mouse is the direct contrast that settles the reading: a mouse
    whose hepatic HPD is lowered post-translationally, and which was given
    actual learning and memory testing, shows hippocampal neuronal damage and
    cognitive deficits. Reduced HPD with tyrosinemia is therefore not inherently
    silent in mouse, and the difference between the two strains is most
    parsimoniously a difference in what was measured rather than in what
    happened — though the two models also differ in genetic architecture,
    completeness of the block, and the confound of TTC36's other substrates, so
    the comparison motivates the experiment below rather than substituting for
    it.
  attaches_to:
  - pathophysiology#Neurodevelopmental dysfunction
  proposed_experiments:
  - experiment_id: exp_ht3_mouse_strain_iii_neurobehavioural_phenotyping
    name: Standardized neurobehavioural phenotyping of the Hpd-null mouse strain
    description: >
      Battery-based neurobehavioural and neurodevelopmental assessment of
      homozygous strain III mice against littermate controls — learning and
      memory, motor coordination, activity and attention-analogous measures —
      paired with brain histology and myelination assessment, and with
      time-integrated plasma tyrosine measured so murine exposure can be placed
      on the human scale.
    decision_criterion: >
      A measurable deficit that tracks tyrosine exposure would support tyrosine
      or a proximal metabolite as the mediator and make the strain usable for
      intervention studies. A negative battery in animals whose exposure
      overlaps the human range would be genuine evidence of a human-specific
      mechanism and would redirect the search away from tyrosine itself. A
      negative battery at sub-human exposure would resolve nothing, which is the
      current state.
  evidence:
  - reference: PMID:2014797
    reference_title: "A murine model for type III tyrosinemia: lack of immunologically detectable 4-hydroxyphenylpyruvic acid dioxygenase enzyme protein in a novel mouse strain with hypertyrosinemia."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "All the animals were apparently healthy, and there was no evidence of hepatorenal dysfunction."
    explanation: The sole reported phenotypic assessment of the strain, and the observation the mismatch turns on.
  - reference: PMID:2014797
    reference_title: "A murine model for type III tyrosinemia: lack of immunologically detectable 4-hydroxyphenylpyruvic acid dioxygenase enzyme protein in a novel mouse strain with hypertyrosinemia."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "These features are similar to type III tyrosinemia in humans."
    explanation: Establishes the biochemical fidelity that makes the absent neurological phenotype worth flagging rather than dismissing.
  - reference: PMID:35707594
    reference_title: "Novel Cranial Imaging Findings and a Splice-Site Variant in a Patient with Tyrosinemia Type III, and a Summary of Published Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Although the clinical spectrum of the disease is not fully known, most patients present with neurodevelopmental symptoms."
    explanation: States the human phenotype that the model does not display, which is the other half of the mismatch.
  - reference: PMID:31537781
    reference_title: "HPD degradation regulated by the TTC36-STK33-PELI1 signaling axis induces tyrosinemia and neurological damage."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "and exhibit tyrosinemia, damage to hippocampal neurons, and deficits of learning and memory."
    explanation: >-
      A second mouse, with reduced hepatic HPD and tyrosinemia, does show
      neurological damage when learning and memory are actually tested — the
      contrast that makes strain III's silence a question about assay
      sensitivity. PARTIAL because these mice are Ttc36-null rather than
      Hpd-mutant.
notes: >
  Position in the pathway. Tyrosine catabolism runs TAT then HPD then HGD then
  GSTZ1 then FAH. Dismech already curates the enzymatic block at three of these
  steps: Tyrosinemia Type II (TAT), Alkaptonuria (HGD), and Tyrosinemia Type I
  (FAH). This entry fills the HPD step. The clinical logic of the series is that
  severity tracks the toxicity of what accumulates behind the block, not the
  height of the tyrosine level: a block at FAH generates fumarylacetoacetate and
  succinylacetone and causes liver failure and hepatocellular carcinoma, a block
  at TAT deposits tyrosine crystals in cornea and skin, and a block at HPD
  accumulates only tyrosine and unreactive phenolic acids and produces neither.

  Nitisinone. HPD is the molecular target of nitisinone, the drug used to treat
  tyrosinemia type I and trialled in alkaptonuria. Nitisinone therefore has no
  role here: it would reproduce the lesion rather than correct it, which is
  consistent with the cited review confining NTBC to type I. The mirror-image
  relationship is curated as an OPEN_QUESTION discussion because the
  pharmacological block causes oculocutaneous disease that the genetic block
  does not.

  Hawkinsinuria. The same gene causes a second, autosomal dominant disorder
  (hawkinsinuria, MONDO:0007700) through the heterozygous A33T allele. That is a
  distinct disease entity with a distinct mechanism and inheritance and is
  deliberately not modelled as a subtype here; it remains an open IEMbase
  WP-002 row (1.4.04.01).

  Frequencies. No phenotype carries a frequency band. The published literature
  is a small number of individual case reports and a 19-patient summary without
  a defensible denominator, and per the repository's frequency-evidence SOP an
  omitted band is preferred to a fabricated one.
experimental_models: []
animal_models:
- name: Mouse strain III (spontaneous Hpd-null mouse)
  species: Mouse
  genotype: Hpd exon 7 nonsense mutation, homozygous (spontaneous)
  publication: PMID:2014797
  description: >
    A spontaneously arising inbred mouse strain with autosomal recessive
    hypertyrosinemia, characterised in 1991 as the murine counterpart of human
    tyrosinemia type III. Hepatic 4-hydroxyphenylpyruvate dioxygenase activity
    is virtually absent and the enzyme subunit is undetectable on immunoblot,
    while fumarylacetoacetase and both tyrosine aminotransferase isoforms are
    normal — so the lesion is confined to the same single step of tyrosine
    catabolism as the human disease. Blood tyrosine is persistently high with
    increased urinary 4-hydroxyphenylpyruvic acid derivatives and no
    succinylacetone, reproducing the biochemical discriminant that separates
    type III from type I. The causal allele was resolved in 1995 as a nonsense
    substitution in exon 7 of Hpd that additionally causes skipping of that
    constitutive exon in most transcripts.
  evidence:
  - reference: PMID:2014797
    reference_title: "A murine model for type III tyrosinemia: lack of immunologically detectable 4-hydroxyphenylpyruvic acid dioxygenase enzyme protein in a novel mouse strain with hypertyrosinemia."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "These features are similar to type III tyrosinemia in humans."
    explanation: The characterising study concludes the strain's biochemical phenotype matches human tyrosinemia type III.
  - reference: PMID:7774914
    reference_title: "A nonsense mutation in the 4-hydroxyphenylpyruvic acid dioxygenase gene (Hpd) causes skipping of the constitutive exon and hypertyrosinemia in mouse strain III."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Mouse strain III is a model for human tyrosinemia type 3 (McKusick 276710), and this strain together with recently established models for tyrosinemia type 1 will facilitate studies of hereditary tyrosinemias."
    explanation: Identifies the causal Hpd allele and states the strain's status as the model for this disorder.
  modeled_mechanisms:
  - target: 4-Hydroxyphenylpyruvate dioxygenase deficiency
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Enzymatically and immunologically null for hepatic 4-hydroxyphenylpyruvate
      dioxygenase, with the neighbouring enzymes of the pathway intact, so the
      block sits at the same step as the human lesion.
    limitations: >-
      The causal allele is a spontaneous murine exon-7 nonsense substitution
      acting partly through exon skipping, not one of the human patient alleles,
      so it models complete loss of function and cannot speak to the hypomorphic
      missense genotypes that make up much of the human series. Enzyme activity
      and protein were assayed in liver only; the human enzyme is also expressed
      in kidney, and this model says nothing about residual extrahepatic
      activity.
    readouts:
    - name: Hepatic 4-hydroxyphenylpyruvate dioxygenase activity
      target: 4-Hydroxyphenylpyruvate dioxygenase deficiency
      description: >-
        Enzyme assay of hepatic tyrosine-pathway enzymes in mutant versus
        control mice, with fumarylacetoacetase and both tyrosine
        aminotransferase isoforms measured as internal specificity controls.
      direction: DECREASED
      interpretation: >-
        Loss of activity restricted to HPD, with the flanking pathway enzymes
        normal, is what makes this a model of the HPD step rather than of
        hypertyrosinemia generally.
      evidence:
      - reference: PMID:2014797
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "4-hydroxyphenylpyruvic acid dioxygenase activity was virtually absent, while fumarylacetoacetase and tyrosine aminotransferases (cytosolic and mitochondrial forms) were normal in these mutant mice"
        explanation: Reports the enzyme measurement and its specificity controls.
    - name: Hepatic HPD subunit protein on immunoblot
      target: 4-Hydroxyphenylpyruvate dioxygenase deficiency
      description: >-
        Immunoblot for the 4-hydroxyphenylpyruvate dioxygenase subunit in liver
        from mutant mice.
      direction: ABOLISHED
      interpretation: >-
        Absence of the protein, not merely of activity, establishes the lesion
        as loss of the enzyme rather than inhibition of it.
      evidence:
      - reference: PMID:2014797
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Immunoblot analysis of 4-hydroxyphenylpyruvic acid dioxygenase protein in the liver indicated that the subunit protein of the enzyme was absent."
        explanation: Reports the protein-level measurement underlying this readout.
    evidence:
    - reference: PMID:7774914
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "We report a nucleotide substitution that generates a termination codon in exon 7 of the 4-hydroxyphenylpyruvic acid dioxygenase gene in III mice."
      explanation: >-
        Establishes that the strain's defect is a lesion in Hpd itself, which is
        what licenses treating it as informative for this node.
  - target: Hypertyrosinemia and phenolic metabolite accumulation
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Reproduces the full biochemical signature of the human disorder,
      including the discriminating negative: persistent hypertyrosinemia with
      increased urinary 4-hydroxyphenyl derivatives and no succinylacetone.
    limitations: >-
      Absolute tyrosine concentrations in the mutant strain are not directly
      comparable with human plasma values, and the reported metabolite panel is
      qualitative; the model therefore supports the pattern of accumulation but
      not the exposure levels the human neurotoxicity question turns on.
    readouts:
    - name: Blood tyrosine and urinary 4-hydroxyphenylpyruvic acid derivatives
      target: Hypertyrosinemia and phenolic metabolite accumulation
      description: >-
        Blood amino acid and urinary organic acid analysis in the mutant strain.
      direction: INCREASED
      interpretation: >-
        The two-component biochemical phenotype curated on this node -
        hypertyrosinemia plus urinary 4-hydroxyphenyl derivative excretion - is
        reproduced in the mouse.
      evidence:
      - reference: PMID:2014797
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "The blood tyrosine level was persistently high, and increased amounts of 4-hydroxyphenylpyruvic acid and its derivatives were excreted into the urine."
        explanation: Reports both measurements behind this readout.
    - name: Urinary succinylacetone
      target: Hypertyrosinemia and phenolic metabolite accumulation
      description: >-
        Urinary succinylacetone assay in the mutant strain, the discriminant
        against a block at fumarylacetoacetase (tyrosinemia type I).
      direction: UNCHANGED
      interpretation: >-
        A deliberate negative result. Absence of succinylacetone confirms the
        block lies upstream of fumarylacetoacetate, matching the human type III
        biochemistry and the absence of hepatorenal disease that follows from
        it.
      evidence:
      - reference: PMID:2014797
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Succinylacetone was not detected in urine samples from these mice."
        explanation: Reports the negative succinylacetone measurement.
    evidence:
    - reference: PMID:2014797
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "We have characterized a new mutant strain of mouse that has hypertyrosinemia."
      explanation: >-
        Establishes hypertyrosinemia as the defining phenotype of the strain,
        which is the node this link attaches to.
  - target: Neurodevelopmental dysfunction
    relationship: FAILS_TO_RECAPITULATE
    fidelity: LOW
    description: >-
      Despite lifelong hypertyrosinemia from a null HPD allele, the mutant
      animals were reported as apparently healthy with no evidence of
      hepatorenal dysfunction. No overt disease counterpart of the human
      neurodevelopmental phenotype was described.
    limitations: >-
      This is a negative on gross observation, not a measured absence. The
      characterising report describes no standardized neurobehavioural or
      neurodevelopmental testing, no neuropathology, and no cognitive or motor
      endpoints, so "apparently healthy" cannot exclude a phenotype that in
      humans is detected by developmental assessment rather than by inspection.
      Absolute tyrosine exposure in the strain is also not calibrated against
      the human range. The model therefore cannot currently adjudicate the
      tyrosine-neurotoxicity knowledge gap in either direction - see the
      tyrosinemia_iii_mouse_model_neurodevelopmental_silence discussion.
    readouts:
    - name: Overt disease on gross observation
      target: Neurodevelopmental dysfunction
      description: >-
        General health assessment of the mutant animals, reported alongside
        hepatic and renal function testing.
      direction: UNCHANGED
      interpretation: >-
        No gross phenotype accompanied the biochemical abnormality; the human
        disorder's dominant clinical consequence has no reported counterpart in
        this strain.
      evidence:
      - reference: PMID:2014797
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "All the animals were apparently healthy, and there was no evidence of hepatorenal dysfunction."
        explanation: The only reported phenotypic assessment of the strain, and the basis for the negative claim.
    evidence:
    - reference: PMID:2014797
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "All the animals were apparently healthy, and there was no evidence of hepatorenal dysfunction."
      explanation: >-
        Substantiates the negative claim that the model does not display an
        overt counterpart of the human neurodevelopmental consequence.
  notes: >
    The strain predates targeted mutagenesis and arose spontaneously; the 1991
    paper characterises the biochemistry and the 1995 paper resolves the allele.
    No later study appears to have subjected it to neurobehavioural phenotyping,
    which is why its bearing on the tyrosine-neurotoxicity question is recorded
    as a HUMAN_MODEL_MISMATCH rather than as evidence against neurotoxicity. The
    Ttc36-null mouse below is the informative contrast: reduced hepatic HPD
    assessed with learning and memory testing rather than by inspection.
- name: Ttc36-null mouse (post-translational HPD depletion)
  species: Mouse
  genotype: Ttc36 knockout, homozygous
  publication: PMID:31537781
  description: >
    A knockout of the liver-enriched chaperone TTC36, which normally shields HPD
    from STK33-mediated T382 phosphorylation and subsequent PELI1-mediated
    polyubiquitylation and proteasomal degradation. Losing TTC36 therefore
    lowers hepatic HPD protein post-translationally, with no lesion in Hpd
    itself, and the animals develop tyrosinemia together with hippocampal
    neuronal damage and deficits of learning and memory. This is not a model of
    tyrosinemia type III — the genetic architecture is different and the route
    to low HPD is regulatory rather than allelic — but it is the only reported
    rodent in which reduced HPD and hypertyrosinemia have been paired with
    actual neurobehavioural testing, which is what makes it the necessary
    counterweight to the silence of the Hpd-null strain III.
  evidence:
  - reference: PMID:31537781
    reference_title: "HPD degradation regulated by the TTC36-STK33-PELI1 signaling axis induces tyrosinemia and neurological damage."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "and exhibit tyrosinemia, damage to hippocampal neurons, and deficits of learning and memory."
    explanation: >-
      Establishes the model's tyrosinemia-plus-neurological phenotype. Marked
      PARTIAL because the mice are Ttc36-null rather than Hpd-mutant, so the
      model is informative for the consequences of low HPD but is not a genetic
      model of this disease.
  modeled_mechanisms:
  - target: 4-Hydroxyphenylpyruvate dioxygenase deficiency
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: >-
      Reaches the same end state as the human lesion — reduced hepatic HPD
      protein — by an entirely different route: loss of a chaperone that
      normally blocks STK33/PELI1-driven degradation of the enzyme.
    limitations: >-
      There is no variant in Hpd. The reduction is post-translational and
      partial rather than a biallelic loss-of-function null, so residual enzyme
      remains and the degree of block is not comparable to the human genotypes.
      TTC36 loss also has HPD-independent consequences that this entry does not
      curate, so any phenotype in these animals may be only partly attributable
      to the HPD reduction.
    readouts:
    - name: Hepatic HPD protein abundance
      target: 4-Hydroxyphenylpyruvate dioxygenase deficiency
      description: >-
        Immunoblot of HPD in liver and in primary hepatocytes from Ttc36-null
        versus wild-type mice, with ubiquitylation and cycloheximide-chase
        assays establishing the degradative mechanism.
      direction: DECREASED
      interpretation: >-
        Confirms the model arrives at reduced HPD protein, the same node state
        as the human enzyme deficiency, without an Hpd allele.
      evidence:
      - reference: PMID:31537781
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "deficiency or depletion of TTC36 results in enhanced STK33-mediated HPD T382 phosphorylation and binding of PELI1 to HPD and subsequent PELI1-mediated HPD downregulation"
        explanation: States the measured mechanism and direction of the HPD reduction.
    evidence:
    - reference: PMID:31537781
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Ttc36-/- mice have reduced HPD expression in the"
      explanation: >-
        Supports treating the model as informative for reduced HPD, while the
        absence of an Hpd lesion is why the link is PARTIALLY_RECAPITULATES at
        LOW fidelity.
  - target: Neurodevelopmental dysfunction
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: >-
      The one rodent result pairing reduced HPD and tyrosinemia with a measured
      neurological outcome: hippocampal neuronal damage with learning and memory
      deficits.
    limitations: >-
      The route to low HPD is regulatory, not allelic, so the phenotype cannot
      be attributed to HPD reduction alone — TTC36 has other substrates and the
      knockout is whole-body. The readout is adult rodent hippocampal
      learning and memory, which is not the human phenotype of childhood
      developmental delay, intellectual impairment, ataxia and ADHD, and the
      animals' tyrosine exposure is not calibrated against the human range.
      This model therefore does not establish that hypertyrosinemia causes the
      human neurodevelopmental phenotype; it establishes only that reduced HPD
      with tyrosinemia is not inherently neurologically silent in mouse.
    readouts:
    - name: Hippocampal neuronal integrity and learning and memory performance
      target: Neurodevelopmental dysfunction
      description: >-
        Hippocampal neuropathology together with behavioural learning and memory
        testing in Ttc36-null versus wild-type mice.
      direction: DECREASED
      interpretation: >-
        A positive neurological result in a low-HPD, tyrosinemic mouse, obtained
        with assays the Hpd-null strain III was never given. It is the direct
        contrast that makes strain III's "apparently healthy" reading a question
        about assay sensitivity rather than a finding of safety.
      evidence:
      - reference: PMID:31537781
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "and exhibit tyrosinemia, damage to hippocampal neurons, and deficits of learning and memory."
        explanation: Reports both the neuropathological and the behavioural measurement behind this readout.
    evidence:
    - reference: PMID:31537781
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "highlight the physiological significance of TTC36-STK33-PELI1-regulated HPD expression in tyrosinemia and tyrosinemia-associated neurological disorders"
      explanation: >-
        The authors frame the result as bearing on tyrosinemia-associated
        neurological disease, which is the node this link attaches to; PARTIAL
        because the genetic architecture is not that of tyrosinemia type III.
  notes: >
    Surfaced by the independent Falcon deep-research pass rather than by the
    original curation, and verified against the cached abstract before use. It
    is deliberately curated as a model of the low-HPD state and not as a model
    of this disease.
computational_models: []
datasets: []
review_notes: >
  Curated from twelve cached PubMed references anchored to MONDO:0010162 and HPD
  (hgnc:5147). Identity was confirmed before curation against the MONDO record:
  RO:0004003 HGNC:5147 (HPD), OMIM:276710, Orphanet:69723 — matching IEMbase
  WP-002 row 1.4.03.01 exactly, with no named-entity confusion against
  tyrosinemia types I and II or hawkinsinuria, which are separate MONDO
  entities. Every evidence snippet is an exact substring of the cached abstract
  for its PMID. One animal model is curated: the spontaneous Hpd-null mouse
  strain III, which is a high-fidelity model of the enzyme block and of the
  biochemical phenotype but shows no overt counterpart of the human
  neurodevelopmental consequence, recorded as FAILS_TO_RECAPITULATE with a
  HUMAN_MODEL_MISMATCH discussion because the only reported assessment was gross
  observation rather than neurobehavioural testing. A second, non-allelic model
  is curated as the deliberate contrast: the Ttc36-null mouse, in which hepatic
  HPD is lowered post-translationally by STK33/PELI1-mediated degradation and
  which does show hippocampal damage and learning and memory deficits when those
  are actually tested. It is curated as a model of the low-HPD state, not of
  this disease, and its links are PARTIALLY_RECAPITULATES at LOW fidelity
  throughout. No non-animal experimental
  or computational model, and no public dataset with an evidence-supported
  mechanism link, was identified, so those sections are explicitly empty rather
  than speculatively populated. The single
  edge from the metabolic block to neurodevelopmental dysfunction is curated as
  INDIRECT_UNKNOWN_INTERMEDIATES with a PARTIAL counter-citation, because the
  literature explicitly reports no correlation between tyrosine level and
  phenotype and at least one biochemically affected but neurologically normal
  patient; a KNOWLEDGE_GAP discussion carries that reasoning. Phenotype
  frequencies were omitted throughout for want of defensible denominators.
references:
- reference: PMID:10942115
  title: "Mutations in the 4-hydroxyphenylpyruvate dioxygenase gene (HPD) in patients with tyrosinemia type III."
- reference: PMID:11073718
  title: "Mutations in the 4-hydroxyphenylpyruvic acid dioxygenase gene are responsible for tyrosinemia type III and hawkinsinuria."
- reference: PMID:11916315
  title: "Outcome of tyrosinaemia type III."
- reference: PMID:23036342
  title: "Tyrosinemia Type III detected via neonatal screening: management and outcome."
- reference: PMID:9343288
  title: "Tyrosinemia type III: diagnosis and ten-year follow-up."
- reference: PMID:16602095
  title: "The genetic tyrosinemias."
- reference: PMID:35707594
  title: "Novel Cranial Imaging Findings and a Splice-Site Variant in a Patient with Tyrosinemia Type III, and a Summary of Published Cases."
- reference: PMID:28649543
  title: "Tyrosinemia type III in an asymptomatic girl."
- reference: PMID:37817461
  title: "Novel HPD mutation p.A244V compound with p.T219M causing tyrosinemia type III in a Chinese girl and review of the genotype-phenotype spectrum."
- reference: PMID:32520295
  title: "TYROSINEMIA TYPE III: A CASE REPORT OF SIBLINGS AND LITERATURE REVIEW."
- reference: PMID:29456978
  title: "A Case of Tyrosinemia Type III with Status Epilepticus and Mental Retardation."
- reference: PMID:39290064
  title: "Evaluation of a casein glycomacropeptide-based protein substitute, in the dietary management of NTBC-induced tyrosinaemia in patients with alkaptonuria: A prospective open-label study."
- reference: PMID:2014797
  title: "A murine model for type III tyrosinemia: lack of immunologically detectable 4-hydroxyphenylpyruvic acid dioxygenase enzyme protein in a novel mouse strain with hypertyrosinemia."
- reference: PMID:7774914
  title: "A nonsense mutation in the 4-hydroxyphenylpyruvic acid dioxygenase gene (Hpd) causes skipping of the constitutive exon and hypertyrosinemia in mouse strain III."
- reference: PMID:31537781
  title: "HPD degradation regulated by the TTC36-STK33-PELI1 signaling axis induces tyrosinemia and neurological damage."
📚

References & Deep Research

References

15
PMID:10942115
Mutations in the 4-hydroxyphenylpyruvate dioxygenase gene (HPD) in patients with tyrosinemia type III.
No top-level findings curated for this source.
PMID:11073718
Mutations in the 4-hydroxyphenylpyruvic acid dioxygenase gene are responsible for tyrosinemia type III and hawkinsinuria.
No top-level findings curated for this source.
PMID:11916315
Outcome of tyrosinaemia type III.
No top-level findings curated for this source.
PMID:23036342
Tyrosinemia Type III detected via neonatal screening: management and outcome.
No top-level findings curated for this source.
PMID:9343288
Tyrosinemia type III: diagnosis and ten-year follow-up.
No top-level findings curated for this source.
PMID:16602095
The genetic tyrosinemias.
No top-level findings curated for this source.
PMID:35707594
Novel Cranial Imaging Findings and a Splice-Site Variant in a Patient with Tyrosinemia Type III, and a Summary of Published Cases.
No top-level findings curated for this source.
PMID:28649543
Tyrosinemia type III in an asymptomatic girl.
No top-level findings curated for this source.
PMID:37817461
Novel HPD mutation p.A244V compound with p.T219M causing tyrosinemia type III in a Chinese girl and review of the genotype-phenotype spectrum.
No top-level findings curated for this source.
PMID:32520295
TYROSINEMIA TYPE III: A CASE REPORT OF SIBLINGS AND LITERATURE REVIEW.
No top-level findings curated for this source.
PMID:29456978
A Case of Tyrosinemia Type III with Status Epilepticus and Mental Retardation.
No top-level findings curated for this source.
PMID:39290064
Evaluation of a casein glycomacropeptide-based protein substitute, in the dietary management of NTBC-induced tyrosinaemia in patients with alkaptonuria: A prospective open-label study.
No top-level findings curated for this source.
PMID:2014797
A murine model for type III tyrosinemia: lack of immunologically detectable 4-hydroxyphenylpyruvic acid dioxygenase enzyme protein in a novel mouse strain with hypertyrosinemia.
No top-level findings curated for this source.
PMID:7774914
A nonsense mutation in the 4-hydroxyphenylpyruvic acid dioxygenase gene (Hpd) causes skipping of the constitutive exon and hypertyrosinemia in mouse strain III.
No top-level findings curated for this source.
PMID:31537781
HPD degradation regulated by the TTC36-STK33-PELI1 signaling axis induces tyrosinemia and neurological damage.
No top-level findings curated for this source.

Deep Research

2
Claude Code ▸
1. Disease Information
claude-haiku-4-5-20251001, claude-opus-4-8[1m] 12 citations 2026-08-23T00:55:16.465293

1. Disease Information

Overview. Tyrosinemia type III is the rarest of the three genetic tyrosinemias — an autosomal recessive inborn error caused by biallelic loss-of-function variants in HPD, encoding 4-hydroxyphenylpyruvate dioxygenase (HPD/HPPD), the second enzyme of the tyrosine catabolic pathway. Loss of HPD activity blocks conversion of 4-hydroxyphenylpyruvate to homogentisate, producing hypertyrosinemia and massive urinary excretion of 4-hydroxyphenyl organic acids. Critically, because the block sits upstream of the maleylacetoacetate/fumarylacetoacetate steps, no succinylacetone or other hepatotoxic intermediate is generated — reported patients have normal liver and renal function and no eye or skin disease. This is the mechanistic feature that separates HT III from tyrosinemia type I (FAH; liver failure, hepatocellular carcinoma) and type II (TAT; oculocutaneous disease). The clinical picture is dominated by variable neurodevelopmental manifestations, but the causal route from tyrosine elevation to neurological injury is unresolved (PMID:16602095; PMID:11916315; PMID:10942115).

Key identifiers: - MONDO:0010162 (tyrosinemia type III) - OMIM #276710 (TYRSN3, disease); OMIM 609695 (HPD, gene) - Orphanet ORPHA:69723 - ICD-10: E70.2 (Disorders of tyrosine metabolism); ICD-11: 5C50.0 (Disorders of tyrosine metabolism) - MeSH: Tyrosinemias (D020176) - Enzyme: EC 1.13.11.27; UniProt P32754* (human HPD)

Synonyms / alternative names: Hereditary tyrosinemia type III; HT III; 4-hydroxyphenylpyruvate dioxygenase deficiency; HPD deficiency; tyrosinemia due to 4-hydroxyphenylpyruvate dioxygenase deficiency; TYRSN3.

Data provenance: Aggregated disease-level resources (OMIM, Orphanet, HPO, MONDO) plus individual patient case reports. No EHR-cohort data exist owing to rarity.

Sources: OMIM #276710, Wikipedia: Tyrosinemia type III, StatPearls: Hypertyrosinemia.

2. Etiology

Primary cause (genetic). Biallelic (homozygous or compound heterozygous) pathogenic variants in HPD (12q24.31) causing deficient 4-hydroxyphenylpyruvate dioxygenase activity. This is a monogenic Mendelian defect; there are no established environmental, infectious, or mechanistic non-genetic causes.

"Tyrosinemia type III (OMIM 276710) is an autosomal recessive disorder caused by the deficiency of 4-hydroxyphenylpyruvate dioxygenase (HPD), the second enzyme in the tyrosine catabolic pathway." — PMID:10942115

Genetic risk factors. The only established risk factor is inheritance of two pathogenic HPD alleles. Consanguinity raises the risk of homozygosity (several reported families are consanguineous). No susceptibility loci or modifier genes have been mapped (the case count is far too small for association studies).

Environmental risk factors. None causal. Dietary protein/tyrosine intake modulates the biochemical burden (higher intake → higher plasma tyrosine) but does not cause the disease. Note the important differential: transient tyrosinemia of the newborn (the most common cause of neonatal hypertyrosinemia, ~1 in 10 newborns) is non-genetic, attributed to hepatic immaturity/prematurity and relative ascorbate (vitamin C) deficiency, and must be distinguished from HT III.

Protective factors. No genetic protective variants documented. Early dietary tyrosine/phenylalanine restriction is the candidate protective/modifying intervention, though its disease-modifying effect on neurological outcome is unproven (see §12).

Gene–environment interaction. The principal G×E axis is genotype (HPD residual activity) × dietary tyrosine load determining circulating tyrosine — but strikingly, neither genotype severity nor tyrosine level predicts neurological phenotype (PMID:10942115), so any G×E model for the clinical outcome remains speculative.

Sources: PMID:10942115, PMID:11916315; Wadsworth NBS: Tyrosinemia type III; MedlinePlus Genetics: Tyrosinemia.

3. Phenotypes

The phenotype is bimodal by ascertainment: screening-detected individuals may be asymptomatic with normal development, while clinically-ascertained individuals present with neurological disease after the neonatal period. Because published denominators are unreliable, frequency bands are deliberately omitted (per curation SOP — omit rather than fabricate).

Phenotype Category HPO term Onset Severity/course Evidence
Hypertyrosinemia Laboratory/biochemical HP:0003231 Hypertyrosinemia Congenital (constant) Persistent; diet-modifiable PMID:11073718, PMID:9343288
Intellectual disability Neurological HP:0001249 Intellectual disability Childhood Mild → severe; variable PMID:9343288, PMID:32520295
Global developmental delay Neurological HP:0001263 Global developmental delay Infancy/childhood Variable; presenting feature PMID:37817461, PMID:35707594
Ataxia (intermittent) Neurological HP:0001251 Ataxia Childhood Episodic/intermittent PMID:16602095
Seizure Neurological HP:0001250 Seizure Infancy May progress to status epilepticus PMID:29456978
ADHD / attention deficit with hyperactivity Behavioral HP:0007018 Attention deficit hyperactivity disorder Childhood May precede metabolic diagnosis PMID:32520295
Ventriculomegaly (single report) Neuroimaging HP:0002119 Ventriculomegaly — Novel/unreplicated finding PMID:35707594

Key characteristics. Onset of neurological features is typically post-neonatal (infancy–childhood). Severity is highly variable and does not correlate with plasma tyrosine level or genotype — a defining and unusual feature of this disorder:

"No correlation of the severity of the mutation and enzyme deficiency and mental function has been found; neither do the recorded tyrosine levels correlate with the clinical phenotype." — PMID:10942115

"Presented case may suggest that high tyrosine concentration itself does not participate directly in neuronal damage described in patients with tyrosinemia type 3." — PMID:28649543 (asymptomatic girl, serum tyrosine 425–535 µmol/L; ref interval 29–86)

Notable absences (discriminating negatives). No hepatic disease, no renal tubular dysfunction, no corneal keratopathy/photophobia, no palmoplantar keratoderma — the features that define types I and II respectively:

"All have had normal liver and renal function and none has skin or eye abnormalities." — PMID:11916315

Quality-of-life impact. Not formally measured (no EQ-5D/SF-36/PROMIS data). Burden, where present, is confined to the neurodevelopmental/educational domain; screened-and-treated individuals may have normal function.

4. Genetic / Molecular Information

Causal gene: HPD (HGNC:5147; NCBI Gene 3242; Ensembl ENSG00000158104), chromosome 12q24.31, 14 exons, encoding 4-hydroxyphenylpyruvate dioxygenase (UniProt P32754; 393 aa; functions as a homodimer in humans).

Pathogenic variants (from the small reported allele set): - First mutation survey (PMID:10942115): 4 presumed pathogenic variants — 2 missense + 2 nonsense — across 3 unrelated families (4 homozygotes, 1 compound heterozygote). - Homozygous missense p.Ala268Val (A268V) in an HT III patient (PMID:11073718). - Compound heterozygous c.731C>T (p.Ala244Val / A244V) + c.656C>T (p.Thr219Met / T219M) in a Chinese girl (PMID:37817461). - Homozygous splice-donor IVS11+1G>A (intron 11) in a newborn-screened boy (PMID:23036342). - Novel splice-site variant in a patient with developmental delay + ventriculomegaly (PMID:35707594). - ClinVar records include NM_002150.3(HPD):c.774T>G (p.Tyr258Ter) associated with HT III.

Variant classes represented: missense, nonsense, and splice-site. All are loss-of-function in effect. Population allele frequencies (gnomAD) are consistent with individually ultra-rare alleles; no common founder allele is established. All variants are germline; somatic origin is not relevant.

"We have identified four presumed pathogenic mutations (two missense and two nonsense mutations) in the HPD gene in three unrelated families encompassing four homozygous individuals and one compound heterozygous individual with tyrosinemia type III." — PMID:10942115

One gene, two diseases (allelic disorders). HPD variants cause two distinct entities: biallelic LOF → autosomal recessive tyrosinemia type III; the heterozygous p.Ala33Thr (A33T) change → autosomal dominant hawkinsinuria (MONDO:0007700, OMIM 140350):

"These findings support the hypothesis that alterations in the structure and activity of HPD are causally related to two different metabolic disorders, tyrosinemia type III and hawkinsinuria." — PMID:11073718

Modifier genes / epigenetics / chromosomal abnormalities. None established (cohort too small). No epigenetic mechanism or structural/cytogenetic abnormality is implicated.

Sources: PMID:10942115, PMID:11073718, PMID:37817461, PMID:23036342, PMID:35707594; OMIM *609695; ClinVar RCV000001640; GTR HPD.

5. Environmental Information

  • Environmental / occupational toxins: None causal. Of mechanistic interest, HPPD-inhibitor herbicides (triketones, e.g. sulcotrione/mesotrione; the drug nitisinone/NTBC is the pharmaceutical analog) chemically phenocopy the enzyme block — relevant to the pharmacology discussion in §12, not to disease etiology.
  • Lifestyle / dietary factors: Dietary protein (tyrosine + phenylalanine) intake governs the magnitude of hypertyrosinemia and is the target of therapy; it is a modulator, not a cause.
  • Infectious agents: Not applicable.

6. Mechanism / Pathophysiology

Pathway context. Tyrosine catabolism proceeds: TAT → HPD → HGD → GSTZ1 → FAH. The reactions are: tyrosine →(TAT)→ 4-hydroxyphenylpyruvate →(HPD)→ homogentisate →(HGD)→ maleylacetoacetate → fumarylacetoacetate →(FAH)→ fumarate + acetoacetate. HT III is the block at the HPD (second) step (KEGG map00350, tyrosine metabolism; Reactome R-HSA-8963684 tyrosine catabolism).

Causal chain (upstream → downstream):

  1. [Trigger, MOLECULAR] 4-Hydroxyphenylpyruvate dioxygenase deficiency. Biallelic LOF HPD variants abolish/reduce HPD activity, blocking 4-hydroxyphenylpyruvate → homogentisate. Expression is principally hepatic, with lesser renal expression.

  2. Gene: HPD (hgnc:5147). Molecular function: GO:0003868 4-hydroxyphenylpyruvate dioxygenase activity (DECREASED). Process: GO:0006572 L-tyrosine catabolic process (DECREASED). Product homogentisate (CHEBI:16169) DECREASED. Locations: UBERON:0002107 liver, UBERON:0002113 kidney.

    "The enzyme 4-hydroxyphenylpyruvic acid dioxygenase (HPD) catalyzes the reaction of 4-hydroxyphenylpyruvic acid to homogentisic acid in the tyrosine catabolism pathway." — PMID:11073718

  3. [Central effector, ORGANISM] Hypertyrosinemia + phenolic-metabolite accumulation. Substrate proximal to the block accumulates: L-tyrosine (CHEBI:17895) INCREASED, 4-hydroxyphenylpyruvate (CHEBI:15999) INCREASED. Because the block is upstream of maleyl-/fumaryl-acetoacetate, succinylacetone is NOT produced → no hepatorenal toxicity (the discriminant vs type I).

    "...an autosomal recessive disorder characterized by elevated levels of blood tyrosine and massive excretion of tyrosine derivatives into urine." — PMID:11073718

  4. [Biomarker, ORGANISM] Urinary 4-hydroxyphenyl organic acids — 4-hydroxyphenylpyruvate, 4-hydroxyphenyllactate, 4-hydroxyphenylacetate (CHEBI:18101) INCREASED; diagnostic organic-acid signature.

  5. [Consequence, ORGANISM] Neurodevelopmental dysfunction (intellectual disability, developmental delay, ataxia, seizures, ADHD). This edge is curated INDIRECT / UNKNOWN INTERMEDIATES: the mediator is unresolved because tyrosine level, residual enzyme activity, and genotype all fail to predict the phenotype (PMID:10942115, PMID:28649543).

Enzyme biochemistry / protein dysfunction. HPD is a non-heme Fe(II)-dependent α-keto acid dioxygenase (EC 1.13.11.27). It performs an unusual single-cycle reaction — oxidative decarboxylation + side-chain 1,2-migration + aromatic hydroxylation — converting 3-(4-hydroxyphenyl)pyruvate + O₂ → homogentisate + CO₂. The catalytic non-heme iron is coordinated by a 2-His-1-carboxylate facial triad (His/His/Glu). Pathogenic missense variants are predicted to impair catalysis/stability; nonsense and splice variants cause loss of enzyme protein (in the mouse model, exon skipping and undetectable subunit; see §15).

Cellular processes / tissue-damage mechanism. The proximate defect is a hepatic/renal metabolic block; there is no fibrosis, apoptosis cascade, or inflammatory tissue destruction (unlike type I). The neurological injury mechanism is unknown — candidate hypotheses (none discriminated by evidence) include: a downstream phenolic metabolite rather than tyrosine itself; a human-specific critical developmental window; and ascertainment bias inflating the neurological association in a disorder historically found by investigating neurological symptoms.

Metabolomics / omics. The disease signature is a targeted metabolomic one (plasma amino acids: ↑tyrosine; urine organic acids: ↑4-hydroxyphenyl-lactate/-pyruvate/-acetate, absent succinylacetone). No transcriptomic, proteomic, single-cell, or functional-genomics screen data specific to HT III exist.

Suggested GO/CL/UBERON/CHEBI terms: GO:0003868, GO:0006572, GO:0006559 (L-phenylalanine catabolic process, adjacent); CHEBI:17895, CHEBI:15999, CHEBI:16169, CHEBI:18101; UBERON:0002107 (liver), UBERON:0002113 (kidney), UBERON:0000955 (brain, affected downstream); cell types not well-defined (hepatocyte CL:0000182; renal proximal tubule CL:1000838).

Sources: PMID:11073718, PMID:10942115, PMID:16602095, PMID:28649543; BRENDA EC 1.13.11.27; Wikipedia: 4-Hydroxyphenylpyruvate dioxygenase; P. fluorescens HPD crystal structure.

7. Anatomical Structures Affected

  • Organ level (primary, metabolic): Liver (UBERON:0002107) and kidney (UBERON:0002113) — sites of HPD expression and of the metabolic block. Notably, these organs are biochemically affected but not structurally damaged.
  • Organ level (clinically affected, downstream): Brain / central nervous system (UBERON:0000955; nervous system UBERON:0001016) — the site of the dominant clinical manifestations. Cranial imaging is usually normal; ventriculomegaly reported once (PMID:35707594).
  • Body systems: Metabolic (amino-acid metabolism) primary; nervous system clinically dominant.
  • Tissue/cell level: hepatocytes (CL:0000182) and renal proximal tubular epithelium (CL:1000838) carry the enzymatic defect; no specific neuronal population is implicated mechanistically.
  • Subcellular level: HPD is cytosolic (GO:0005829 cytosol / GO:0005737 cytoplasm).
  • Lateralization: Not applicable (systemic metabolic disease; neurological features bilateral/diffuse).

8. Temporal Development

  • Onset: Biochemical abnormality is congenital (present from birth; detectable on newborn screening). Clinical/neurological onset is typically post-neonatal (infancy–childhood); pattern insidious to subacute (seizures can be acute).
  • Progression: No defined staging. Course is variable — from stable/asymptomatic (screened, early-treated) to progressive neurodevelopmental impairment or acute seizure crises. It is a chronic, lifelong metabolic condition.

    "The majority of the nine previously reported patients have presented with neurological symptoms after the neonatal period, while others detected by neonatal screening have been asymptomatic." — PMID:11916315

  • Patterns / critical periods: A putative early-infancy window where treatment may matter most is suspected but unproven:

    "It is not clear whether a strict low tyrosine diet alters the natural history of tyrosinaemia type III, although there remains a suspicion that treatment may be important, at least in infancy." — PMID:11916315

  • Screened example of a benign early course: normal growth and psychomotor development at 30 months on mild protein restriction (PMID:23036342).
  • Severe example: recurrent seizures at 4 months → status epilepticus at 6 months (PMID:29456978).

9. Inheritance and Population

Inheritance: Autosomal recessive (HP:0000007). Requires biallelic pathogenic HPD variants; heterozygous carriers are unaffected.

"Hereditary tyrosinemia type III (HT III) is an extremely rare form of tyrosinemia, characterized by autosomal recessive inheritance and biallelic mutations in the HPD gene." — PMID:37817461

  • Penetrance: For the biochemical phenotype (hypertyrosinemia), effectively complete. For the neurological phenotype, incomplete and unpredictable (asymptomatic biallelic patients exist — PMID:28649543).
  • Expressivity: Highly variable (mild ADHD/intellectual impairment → severe ID + status epilepticus), uncorrelated with genotype or tyrosine level (PMID:10942115).
  • Genetic anticipation: Not applicable (not a repeat-expansion disorder).
  • Founder effects / carrier frequency: No established founder allele; carrier frequency undetermined (too rare). Consanguinity contributes in reported families.

Epidemiology: - Prevalence/incidence: No robust population rate. Estimated incidence < 1 in 1,000,000; the rarest genetic tyrosinemia. ~19 patients reported worldwide as of 2022 (PMID:35707594); ~23 by 2025 counts. Curated prevalence class: BELOW_1_IN_1000000 (ultra-rare).

"Tyrosinemia type III is an extremely rare autosomal recessive disease, with only 19 patients yet reported." — PMID:35707594 - Geographic/ethnic distribution: No documented predisposition; cases reported across Europe, the Middle East, and East Asia. Ascertainment depends on whether a region's newborn-screening panel measures tyrosine. - Sex ratio: No established skew (cases in both sexes). - Age distribution: Neonatal (screened) or infancy–childhood (symptomatic).

Sources: PMID:35707594, PMID:32520295, PMID:11916315, PMID:37817461, PMID:23036342; Wadsworth NBS.

10. Diagnostics

Biochemical (first-line): - Plasma amino acids — elevated tyrosine (screening + monitoring analyte). LOINC candidates: Tyrosine [Moles/volume] in plasma. - Urine organic acids — elevated 4-hydroxyphenyl derivatives (4-OH-phenyllactate, -pyruvate, -acetate); succinylacetone ABSENT (excludes type I — the key discriminator).

"These disorders are diagnosed by observing elevated tyrosine by plasma amino acid chromatography and characteristic tyrosine metabolites by urine organic acid analysis." — PMID:16602095 "Urine organic acids show elevated p-hydroxy-phenyl organic acids in each type of tyrosinemia, and the pathognomic succinylacetone in tyrosinemia Type I." — PMID:16602095

Newborn screening: Detection of elevated tyrosine by tandem mass spectrometry (MS/MS) on dried blood spot. Note that MS/MS tyrosine is a poor primary marker for type I (succinylacetone is preferred there), but it does flag HT III/II and transient tyrosinemia. Confirmation requires repeat quantitation + urine organic acids + genetics (PMID:23036342).

Genetic testing: HPD single-gene / targeted NGS sequencing to identify biallelic pathogenic variants confirms diagnosis; HPD is offered on inborn-errors and tyrosinemia gene panels (also covers hawkinsinuria).

"A 3-year-old girl, identified through newborn screening, was diagnosed with HT III using targeted next-generation sequencing." — PMID:37817461

Enzyme assay: Direct hepatic HPD activity assay is possible but rarely needed given molecular testing.

Imaging / electrophysiology: Cranial MRI usually normal (ventriculomegaly reported once, PMID:35707594); EEG as indicated for seizures. Neither is diagnostic of HT III per se.

NCIT diagnostic terms: Laboratory Procedure (NCIT:C25294); Genetic Testing (NCIT:C15709).

Differential diagnosis: Transient tyrosinemia of the newborn (most common; resolves, non-genetic); tyrosinemia type I (FAH — succinylacetone+, liver/renal disease); tyrosinemia type II (TAT — oculocutaneous, no organic aciduria of this pattern); hawkinsinuria (HPD, dominant); liver disease causing secondary hypertyrosinemia; scurvy/ascorbate deficiency.

Sources: PMID:16602095, PMID:23036342, PMID:37817461; Oklahoma tyrosine screening fact sheet.

11. Outcome / Prognosis

  • Survival/mortality: Not life-limiting through the metabolic lesion itself — no hepatic, renal, or oncologic risk (contrast type I). No disease-specific mortality data; life expectancy presumed normal.
  • Morbidity/disability: Confined to the neurodevelopmental/behavioral domain. Long-term disability ranges from none (screened, treated) to significant intellectual disability with neurological abnormality (PMID:9343288).
  • Complications: Seizures/status epilepticus (PMID:29456978); learning/behavioral difficulties.
  • Recovery potential: Some patients report subjective gains after diet + falling tyrosine (PMID:35707594), but disease-modifying benefit is unproven.
  • Prognostic factors: None validated. Age at dietary initiation is the leading candidate modifier (within-family sib comparison favored earlier treatment — PMID:32520295), but plasma tyrosine and genotype are not prognostic (PMID:10942115).

"All have had normal liver and renal function and none has skin or eye abnormalities." — PMID:11916315 (bounds the burden to the neurological domain)

12. Treatment

1. Dietary phenylalanine + tyrosine restriction (mainstay). Low-protein diet with a tyrosine-/phenylalanine-free amino-acid substitute ("anamix"-type formula). Reliably lowers plasma tyrosine; disease-modifying effect on neurology unresolved. - Modality: BEHAVIORAL/dietary. NCIT: Dietary Intervention (NCIT:C15447). - Target mechanism: reduces substrate delivery to the blocked step (INHIBITS "Hypertyrosinemia and phenolic metabolite accumulation").

"She was treated with a diet low in tyrosine and phenylalanine and anamix formula that leading to catch-up growth and improvement of her symptoms. Plasma tyrosine level dropped to normal values." — PMID:29456978 "Therapy consists of a diet low in phenylalanine and tyrosine for each of the tyrosinemias and 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) for tyrosinemia Type I." — PMID:16602095 "...a better neurological and behavioral evaluation in the patient who started treatment earlier." — PMID:32520295 (single sib pair; suggestive only)

2. Developmental/neurological supportive care. Antiseizure therapy, developmental/educational support, neurodevelopmental follow-up per phenotype. NCIT: Supportive Care (NCIT:C15747) (PMID:35707594).

Nitisinone (NTBC) — contraindicated in concept, not therapeutic here. Nitisinone is a pharmacological HPD inhibitor; it reproduces the HT III lesion rather than correcting it, and is confined to type I (and trialed in alkaptonuria). This is a key teaching point: the drug that treats type I would recreate the exact enzymatic block of type III.

Pharmacogenomics / advanced therapeutics / surgery / experimental trials: None applicable/reported. No gene, cell, RNA, or targeted therapy; no HT III–specific clinical trials (rarity).

Treatment outcomes: Biochemical response (falling tyrosine) is reliable; clinical/neurological response is variable and unproven as disease-modifying.

Sources: PMID:16602095, PMID:29456978, PMID:32520295, PMID:11916315, PMID:35707594, PMID:39290064 (NTBC-induced tyrosinemia toxicity in alkaptonuria).

13. Prevention

  • Primary prevention: None (Mendelian). Genetic/reproductive counseling for at-risk families; carrier testing, prenatal diagnosis, and PGT-M are technically feasible where the familial variants are known. Consanguinity counseling relevant.
  • Secondary prevention (early detection): Newborn screening for elevated tyrosine (MS/MS) enables presymptomatic diagnosis and early dietary intervention — the practical prevention lever, though its effect on neurological outcome is unproven.
  • Tertiary prevention: Dietary control of tyrosine + neurodevelopmental monitoring to mitigate complications.
  • Immunization / public-health / environmental interventions: Not applicable.

Sources: PMID:23036342; Wadsworth NBS.

14. Other Species / Natural Disease

  • Taxonomy: Best-characterized non-human counterpart is mouse (Mus musculus, NCBITaxon:10090) — spontaneous "mouse strain III" with hereditary hypertyrosinemia.
  • Ortholog: Mouse Hpd (NCBI Gene 15445); human HPD (NCBI Gene 3242). HPD is deeply conserved across mammals, plants, and bacteria (the enzyme is the target of HPPD-inhibitor herbicides).
  • Natural disease / comparative biology: The mouse strain reproduces the human biochemical phenotype faithfully — absent hepatic HPD activity/protein, persistent hypertyrosinemia, urinary 4-hydroxyphenyl derivatives, no succinylacetone — while being "apparently healthy" (no overt neurological/hepatorenal disease). This species divergence (biochemical fidelity without the human neurodevelopmental phenotype) is itself informative for the neurotoxicity question. No prominent naturally occurring companion-animal/wildlife HT III is catalogued in OMIA.
  • Transmission / zoonosis: Not applicable.

"These features are similar to type III tyrosinemia in humans." — PMID:2014797

15. Model Organisms

Mouse strain III (spontaneous Hpd-null mouse) — the principal and essentially only established model.

  • Type: mammalian, spontaneous (pre-targeted-mutagenesis) inbred strain; autosomal recessive.
  • Genotype/lesion: Hpd exon-7 nonsense substitution, homozygous, additionally causing skipping of the constitutive exon 7 in most transcripts → undetectable HPD subunit and virtually absent hepatic activity, with flanking enzymes (fumarylacetoacetase, both TAT isoforms) intact.

    "...4-hydroxyphenylpyruvic acid dioxygenase activity was virtually absent, while fumarylacetoacetase and tyrosine aminotransferases (cytosolic and mitochondrial forms) were normal..." — PMID:2014797 "We report a nucleotide substitution that generates a termination codon in exon 7 of the 4-hydroxyphenylpyruvic acid dioxygenase gene in III mice. This mutation is associated with partial exon skipping..." — PMID:7774914

  • Phenotype recapitulation:
  • HIGH fidelity for the enzyme block (RECAPITULATES): hepatic HPD activity and protein both null, pathway-specific.
  • HIGH fidelity for the biochemical phenotype (RECAPITULATES): persistent hypertyrosinemia + ↑urinary 4-hydroxyphenylpyruvate derivatives + succinylacetone absent (the discriminating negative reproduced).
  • FAILS TO RECAPITULATE the neurodevelopmental consequence: animals "apparently healthy," no hepatorenal dysfunction. Caveat: this is a negative on gross observation only — no standardized neurobehavioral/neurocognitive testing, neuropathology, or tyrosine-exposure calibration against the human range was performed. It therefore cannot be cited as evidence that hypertyrosinemia is neurologically harmless.

    "All the animals were apparently healthy, and there was no evidence of hepatorenal dysfunction." — PMID:2014797

  • Model limitations: Murine allele (exon-7 nonsense/skipping), not a human patient allele — models complete LOF, not the hypomorphic missense genotypes common in patients; enzyme measured in liver only (renal HPD not assessed); metabolite panel qualitative, absolute tyrosine not human-calibrated.
  • Applications: Studying the metabolic block and biochemistry of tyrosine catabolism; complements type I mouse models; available for (not-yet-done) neurobehavioral phenotyping to test the tyrosine-neurotoxicity hypothesis.
  • Other systems: No non-animal experimental model (organoid/iPSC), no computational model, and no public omics dataset with a mechanism link specific to HT III were identified.

Sources: PMID:2014797, PMID:7774914.

Cross-cutting open questions (knowledge gaps)

  1. Tyrosine neurotoxicity is unexplained. Neither HPD-lesion severity, residual enzyme activity, nor plasma tyrosine predicts the neurological phenotype, and biochemically affected patients with normal development exist. Candidate mediators (a downstream phenolic metabolite; a human-specific early developmental window; ascertainment bias) are undiscriminated. Proposed: prospective standardized neurocognitive follow-up of screened cohorts stratified by time-integrated tyrosine exposure (PMID:10942115, PMID:28649543).
  2. Genetic vs pharmacological HPD block discrepancy. Nitisinone-induced (acquired) HPD blockade in type-I/alkaptonuria patients causes tyrosine corneal keratopathy and skin lesions; genetic HT III patients do not develop oculocutaneous disease. Possible explanations (higher absolute tyrosine under pharmacological block, residual activity in hypomorphs, tissue-distribution differences, older/longer-exposed nitisinone-treated adults) are unresolved and bear on whether HT III patients need ocular surveillance (PMID:11916315, PMID:39290064).
  3. Mouse-model silence. The high-biochemical-fidelity Hpd-null mouse shows no overt neuro phenotype — but only gross observation was ever done; this is a HUMAN_MODEL_MISMATCH, not evidence of safety (PMID:2014797 vs PMID:35707594).

Consolidated Evidence Citations (PMIDs)

PMID Role in report
10942115 HPD mutations in HT III; no genotype/tyrosine–phenotype correlation
11073718 HPD underlies both HT III and hawkinsinuria; A268V; A33T
11916315 Outcome review; no liver/renal/skin/eye disease; diet-uncertain
9343288 Diagnosis + 10-yr follow-up; severe ID case; biochemical phenotype
16602095 "The genetic tyrosinemias" review; diagnosis, therapy, succinylacetone discriminator
23036342 NBS-detected boy; IVS11+1G>A; benign early course
35707594 Novel splice-site variant + ventriculomegaly; 19-patient summary
28649543 Asymptomatic girl (tyrosine 425–535 µmol/L); argues against direct neurotoxicity
37817461 Compound het p.A244V/p.T219M; genotype–phenotype review; NGS diagnosis
32520295 Sibling case report/review; ADHD; earlier-treatment advantage
29456978 Status epilepticus + ID; diet lowers tyrosine
39290064 NTBC-induced tyrosinemia toxicity (alkaptonuria) — pharmacological phenocopy
2014797 Mouse strain III characterization (biochemistry, healthy animals)
7774914 Mouse Hpd exon-7 nonsense/exon-skipping allele

Web/database sources: OMIM #276710 · OMIM *609695 (HPD) · MedlinePlus: Tyrosinemia · Wikipedia: Tyrosinemia type III · StatPearls: Hypertyrosinemia · Wadsworth NBS: Tyrosinemia type III · ClinVar RCV000001640 · GTR: HPD gene 3242 · BRENDA EC 1.13.11.27 (human) · Wikipedia: 4-Hydroxyphenylpyruvate dioxygenase.

Note for KB curation: This report corresponds closely to the already-curated kb/disorders/Tyrosinemia_Type_III.yaml entry on this branch, which independently verifies each snippet against cached abstracts. The report adds contextualizing detail not carried in the YAML (gene locus 12q24.31 / 14 exons, UniProt P32754, EC/enzyme mechanism, ICD/OMIM-gene identifiers, transient-tyrosinemia differential, mouse Hpd Gene ID) that could enrich the entry; note that any such additions to the YAML would require their own verified PMID snippets (the enzyme-mechanism and locus facts above are sourced to BRENDA/OMIM/Wikipedia, not to the cached PMIDs, and should not be added as PMID-attributed evidence without fetching a citable primary source).

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Tyrosinemia Type III: Disease-Characteristics Research Report
Edison Scientific Literature 39 citations 2026-08-23T01:04:35.522519

Tyrosinemia Type III: Disease-Characteristics Research Report

Evidence cutoff: searches prioritized literature through 2024. Because tyrosinemia type III (HT3) is exceptionally rare, most human evidence consists of case reports, small series, and retrospective literature reviews rather than cohorts or trials. Statements about treatment, penetrance, and prognosis should therefore be interpreted cautiously.

Executive summary

Tyrosinemia type III is an autosomal-recessive amino-acid disorder caused by biallelic loss-of-function variants in HPD, encoding 4-hydroxyphenylpyruvate dioxygenase. HPD normally converts 4-hydroxyphenylpyruvate to homogentisate in hepatic tyrosine catabolism. Deficiency causes persistent hypertyrosinemia and urinary excretion of 4-hydroxyphenylpyruvate, 4-hydroxyphenyllactate, and 4-hydroxyphenylacetate. Unlike tyrosinemia type I, HT3 ordinarily does not cause progressive hepatorenal failure or succinylacetone accumulation. Neurologic expression is heterogeneous: developmental delay, intellectual disability, seizures, ataxia, and autistic features have been reported, but a substantial fraction of molecularly confirmed patients are asymptomatic. Five of 16 patients summarized in a 2022 review were asymptomatic despite biochemical abnormalities. No reliable genotype–phenotype relationship, population prevalence, standardized treatment guideline, disease-specific clinical trial, or validated prognostic biomarker exists. (szymanska2015tyrosinemiatypeiii pages 3-3, beyzaei2022themutationspectrum pages 3-5, alsharhan2020disordersofphenylalanine pages 31-33)

The principal ontology-ready facts are summarized below.

domain established finding suggested ontology identifiers/terms evidence strength/limitations
Disease identity Tyrosinemia type III is an ultra-rare inborn error of tyrosine metabolism caused by deficiency of 4-hydroxyphenylpyruvate dioxygenase; recognized disease identifiers include MONDO:0010162, OMIM:276710, Orphanet:69723 (OpenTargets Search: Tyrosinemia type III-HPD, beyzaei2022themutationspectrum pages 1-2) MONDO:0010162; OMIM:276710; Orphanet:69723; suggested label synonym: “4-hydroxyphenylpyruvate dioxygenase deficiency” Strong for identifiers/disease concept from curated resources and review; rarity means phenotype boundaries remain incompletely defined (OpenTargets Search: Tyrosinemia type III-HPD, beyzaei2022themutationspectrum pages 1-2)
Synonyms Reported names include tyrosinemia type III, tyrosinemia type 3, hereditary hypertyrosinemia type III, and 4-hydroxyphenylpyruvate dioxygenase deficiency (szymanska2015tyrosinemiatypeiii pages 1-3, endo2003animalmodelsreveal pages 4-5) Suggested synonyms only; exact ontology synonym set should be verified in MONDO/Orphanet Moderate; terminology varies across case reports and older literature (szymanska2015tyrosinemiatypeiii pages 1-3, endo2003animalmodelsreveal pages 4-5)
Etiology/gene Causal gene is HPD, encoding 4-hydroxyphenylpyruvate dioxygenase, in the tyrosine catabolic pathway (OpenTargets Search: Tyrosinemia type III-HPD, endo2003animalmodelsreveal pages 1-2, xie2019hpddegradationregulated pages 1-2) HPD (HGNC symbol); suggested functional term: loss of function/absent or deficient HPD activity; suggested pathway: tyrosine catabolic process Strong for gene-disease link, including ClinGen-definitive curation noted in Open Targets-linked evidence; variant-level functional data are sparse for many alleles (OpenTargets Search: Tyrosinemia type III-HPD)
Inheritance Autosomal recessive inheritance with biallelic HPD variants (szymanska2015tyrosinemiatypeiii pages 1-3, sarkargar2023acompoundheterozygous pages 1-3, OpenTargets Search: Tyrosinemia type III-HPD, beyzaei2022themutationspectrum pages 1-2) Suggested inheritance term: autosomal recessive inheritance [HPO term suggested, exact ID not confirmed here] Strong for inheritance; penetrance/expressivity remain uncertain because some patients are asymptomatic (beyzaei2022themutationspectrum pages 3-5)
Molecular defect HPD normally converts 4-hydroxyphenylpyruvate to homogentisate; deficiency blocks this step and causes accumulation of upstream tyrosine-related metabolites without the toxic downstream metabolites typical of type I disease (szymanska2015tyrosinemiatypeiii pages 3-3, endo2003animalmodelsreveal pages 1-2, xie2019hpddegradationregulated pages 1-2) Suggested GO term: tyrosine catabolic process; suggested CHEBI terms: L-tyrosine, 4-hydroxyphenylpyruvate, homogentisate Strong for pathway position; downstream neurotoxicity mechanism in humans remains unresolved (szymanska2015tyrosinemiatypeiii pages 3-3, xie2019hpddegradationregulated pages 1-2)
Pathogenic variants Review of published patients found 11 HPPD/HPD variants in 16 patients by 2022: 7 missense, 2 nonsense, 1 splice-site, 1 frameshift; recurrent p.Tyr160Cys reported in 2 families; later 2023 case added compound heterozygous p.W25Ter and p.T138M (beyzaei2022themutationspectrum pages 3-5, sarkargar2023acompoundheterozygous pages 1-3) Suggested sequence consequence terms: missense variant, nonsense variant, splice donor/acceptor variant, frameshift variant Moderate-strong for published spectrum; many are private variants and genotype-phenotype correlation is not established (beyzaei2022themutationspectrum pages 3-5)
Core biochemical phenotype Elevated blood/serum tyrosine with increased urinary excretion of 4-hydroxyphenylpyruvate, 4-hydroxyphenyllactate, and 4-hydroxyphenylacetate/related p-hydroxyphenyl derivatives is characteristic (szymanska2015tyrosinemiatypeiii pages 1-3, alsharhan2020disordersofphenylalanine pages 31-33, endo2003animalmodelsreveal pages 2-2) Suggested HPO: Hypertyrosinemia [exact ID not confirmed]; suggested lab terms: increased urinary 4-hydroxyphenylpyruvate, increased urinary 4-hydroxyphenyllactate, increased urinary 4-hydroxyphenylacetate Strong for biochemical signature; exact analyte nomenclature varies by report (szymanska2015tyrosinemiatypeiii pages 1-3, alsharhan2020disordersofphenylalanine pages 31-33)
Typical tyrosine levels Reported blood tyrosine values are often ~350–650 μmol/L; examples include 425–535 μmol/L in an asymptomatic girl and 709 μmol/L neonatally in a 2023 Iranian case (szymanska2015tyrosinemiatypeiii pages 1-3, alsharhan2020disordersofphenylalanine pages 31-33, sarkargar2023acompoundheterozygous pages 1-3) Suggested quantitative lab annotation rather than ontology term Moderate; based on small case series/case reports with assay/reference-range variation (szymanska2015tyrosinemiatypeiii pages 1-3, sarkargar2023acompoundheterozygous pages 1-3)
Neurologic phenotypes Neurologic manifestations reported across cases include developmental delay/psychomotor retardation, intellectual disability/mental retardation, seizures/convulsions, ataxia, and autism; however, some genetically confirmed individuals are asymptomatic (szymanska2015tyrosinemiatypeiii pages 1-3, alsharhan2020disordersofphenylalanine pages 31-33, endo2003animalmodelsreveal pages 2-2, beyzaei2022themutationspectrum pages 3-5) Suggested HPO terms: Developmental delay; Psychomotor retardation; Intellectual disability; Seizure; Ataxia; Autistic behavior [exact IDs not confirmed here] Moderate; recurrently reported but case numbers are tiny and causality of neurologic findings versus ascertainment bias remains debated (szymanska2015tyrosinemiatypeiii pages 1-3, alsharhan2020disordersofphenylalanine pages 31-33)
Asymptomatic presentation A substantial minority of published patients were asymptomatic despite persistent biochemical abnormalities; 5 of 16 patients in the 2022 review were asymptomatic (szymanska2015tyrosinemiatypeiii pages 1-3, szymanska2015tyrosinemiatypeiii pages 3-3, beyzaei2022themutationspectrum pages 3-5) Suggested phenotype annotation: asymptomatic hypertyrosinemia [suggestion only] Strong for existence of asymptomatic cases; weak for predicting who will remain asymptomatic long term (beyzaei2022themutationspectrum pages 3-5)
Renal phenotype Classical liver and kidney dysfunction are generally absent, but recurrent proteinuria has been reported in at least one asymptomatic patient and increased propensity for proteinuria has been noted (szymanska2015tyrosinemiatypeiii pages 3-3, sarkargar2023acompoundheterozygous pages 1-3) Suggested HPO: Proteinuria [exact ID not confirmed] Weak-moderate; renal involvement is not a consistent core feature and is based on limited case-level evidence (szymanska2015tyrosinemiatypeiii pages 3-3, sarkargar2023acompoundheterozygous pages 1-3)
Hepatic phenotype Unlike tyrosinemia type I, hepatocellular injury is typically absent; reports emphasize no liver damage as a distinguishing feature, though isolated neonatal hepatitis has been described in a 2023 case report (alsharhan2020disordersofphenylalanine pages 31-33, sarkargar2023acompoundheterozygous pages 1-3, endo2003animalmodelsreveal pages 2-2) Suggested differential annotation rather than core phenotype; UBERON suggestion: liver Moderate; absence of hepatic disease is a useful differentiator, but occasional hepatic presentations may reflect ascertainment complexity or comorbidity (sarkargar2023acompoundheterozygous pages 1-3)
Anatomy/organs Main tissues relevant to disease biology are liver and kidney, where HPD is mainly expressed; nervous system/brain involvement is implicated clinically by neurologic symptoms (endo2003animalmodelsreveal pages 1-2, beyzaei2022themutationspectrum pages 1-2) Suggested UBERON: liver, kidney, brain; suggested body systems: metabolic, nervous Strong for organ expression/pathway anatomy; direct tissue pathology data in humans are sparse (endo2003animalmodelsreveal pages 1-2, beyzaei2022themutationspectrum pages 1-2)
Cell types Human mechanistic literature suggests hepatocytes as primary metabolic cell type; neurons are implicated by neurologic phenotype; one paper also discusses neutrophils/neurons in relation to nitric oxide release, but this is limited evidence (sarkargar2023acompoundheterozygous pages 3-5) Suggested CL terms: hepatocyte, neuron; suggested CL term: neutrophil (exploratory) Moderate for hepatocyte/neuron; weak for neutrophil relevance to disease mechanism (sarkargar2023acompoundheterozygous pages 3-5)
Subcellular compartments Disease mechanism involves enzyme deficiency in metabolic pathways; a mouse/mechanistic study identified regulation of HPD protein stability through phosphorylation, ubiquitination, and proteasomal degradation (TTC36-STK33-PELI1 axis) (xie2019hpddegradationregulated pages 1-2, xie2019hpddegradationregulated pages 6-7) Suggested GO cellular component terms: cytosol/cytoplasm, proteasome complex; suggested process terms: protein ubiquitination, proteasomal protein catabolic process Moderate for HPD regulation biology, but this evidence is mainly experimental/model-based and not specific to human inherited alleles (xie2019hpddegradationregulated pages 1-2, xie2019hpddegradationregulated pages 6-7)
Diagnosis Diagnostic approach relies on metabolic screening showing elevated tyrosine plus urinary p-hydroxyphenyl metabolites, followed by molecular confirmation of biallelic HPD variants by targeted sequencing, gene panel, WES, or Sanger confirmation (szymanska2015tyrosinemiatypeiii pages 1-3, alsharhan2020disordersofphenylalanine pages 31-33, sarkargar2023acompoundheterozygous pages 1-3) Suggested diagnostic categories: plasma amino acids, urine organic acids, molecular genetic testing Strong for core diagnostic workflow; no universally standardized diagnostic criteria specific to type III were identified (alsharhan2020disordersofphenylalanine pages 31-33)
Differential diagnosis Important differentials include tyrosinemia type I, tyrosinemia type II, transient neonatal tyrosinemia, and hawkinsinuria; type III differs from type I by lack of succinylacetone accumulation/hepatorenal disease and from type II by generally lower tyrosine levels and absence of corneal/skin disease (szymanska2015tyrosinemiatypeiii pages 3-3, endo2003animalmodelsreveal pages 4-5, alsharhan2020disordersofphenylalanine pages 31-33) Suggested related disease mappings: tyrosinemia type I, tyrosinemia type II, hawkinsinuria, transient neonatal tyrosinemia [exact ontology IDs not confirmed] Moderate; differential framework is well supported in reviews, but formal criteria are not standardized for this ultra-rare disorder (alsharhan2020disordersofphenylalanine pages 31-33)
Newborn screening Type III can be detected after elevated tyrosine on newborn screening, but routine screening specificity is limited because tyrosine elevation is nonspecific; published cases include neonatal-screen-detected patients, while some regions report no dedicated HT3 screening program (szymanska2015tyrosinemiatypeiii pages 3-3, beyzaei2022themutationspectrum pages 5-6, sarkargar2023acompoundheterozygous pages 3-5) Suggested screening annotation: elevated tyrosine on tandem MS/MS newborn screening Moderate; real-world implementation exists indirectly through tyrosine elevation, but population screening performance metrics for HT3 are not established here (beyzaei2022themutationspectrum pages 5-6, sarkargar2023acompoundheterozygous pages 3-5)
Treatment Main reported treatment is dietary restriction of tyrosine and phenylalanine; one review cites ascorbic acid supplementation (50 mg/day) with normalization of tyrosine and improvement of seizures in a case; some asymptomatic patients were not treated and remained well (szymanska2015tyrosinemiatypeiii pages 1-3, alsharhan2020disordersofphenylalanine pages 31-33, sarkargar2023acompoundheterozygous pages 3-5) Suggested NCIT intervention terms: Dietary modification; Low phenylalanine diet; Low tyrosine diet; Ascorbic acid supplementation Moderate; evidence is based on case reports/experience only, and benefit for long-term neuroprotection is uncertain (alsharhan2020disordersofphenylalanine pages 31-33)
Monitoring/outcomes Follow-up generally centers on plasma tyrosine, urinary metabolites, neurologic/developmental assessment, and growth; outcomes are variable, with some patients improving on diet and others remaining asymptomatic without clear progression (szymanska2015tyrosinemiatypeiii pages 1-3, sarkargar2023acompoundheterozygous pages 3-5, alsharhan2020disordersofphenylalanine pages 31-33) Suggested monitoring concepts: plasma tyrosine, urine organic acids, developmental assessment Weak-moderate; no formal longitudinal natural-history dataset or validated outcome measures were identified (sarkargar2023acompoundheterozygous pages 3-5, alsharhan2020disordersofphenylalanine pages 31-33)
Epidemiology Ultra-rare disorder: only 13 cases were noted by 2015, 16 patients by the 2022 variant review, and about 18 cases cited in a 2023 case report; no robust prevalence or incidence estimates were identified (szymanska2015tyrosinemiatypeiii pages 1-3, beyzaei2022themutationspectrum pages 3-5, sarkargar2023acompoundheterozygous pages 3-5) Suggested epidemiology annotation: ultra-rare Mendelian disease Moderate for approximate published case counts; weak for true prevalence/incidence because underdiagnosis is likely (szymanska2015tyrosinemiatypeiii pages 3-3, beyzaei2022themutationspectrum pages 3-5)
Population distribution Reported patients/variants have come from Europe and parts of Asia, including Portugal, Turkey, Sweden, Poland, Japan, Iran, and China; no data were noted from North/Central America, Africa, Australia, or Oceania in the 2022 review (beyzaei2022themutationspectrum pages 3-5) Suggested demographic annotation only; no founder effect established for type III Moderate for published geographic distribution; reflects publication bias rather than true population risk (beyzaei2022themutationspectrum pages 3-5)
Modifier/protective factors No validated genetic protective variants, modifier genes, or environmental protective factors specific to human HT3 were identified; genotype-phenotype correlation remains unclear (beyzaei2022themutationspectrum pages 3-5) None established; leave ontology mapping blank/NA Weak due to lack of evidence (beyzaei2022themutationspectrum pages 3-5)
Prevention/genetic counseling Primary prevention is not established; secondary prevention may occur through newborn screening flagging elevated tyrosine; tertiary prevention is dietary/metabolic management. Carrier testing, family screening, and prenatal testing are plausible for known familial HPD variants, but disease-specific protocols were not well detailed in retrieved evidence (sarkargar2023acompoundheterozygous pages 1-3, beyzaei2022themutationspectrum pages 5-6) Suggested counseling concepts: carrier testing, cascade testing, prenatal diagnosis [suggestions only] Weak-moderate; inferred from Mendelian genetics and review conclusions rather than disease-specific prospective studies (beyzaei2022themutationspectrum pages 5-6)
Human evidence quality Evidence base is dominated by case reports, small series, and reviews; 2022 review explicitly states genotype-phenotype correlation cannot be clearly concluded due to small numbers and private mutations (beyzaei2022themutationspectrum pages 3-5) Evidence tag suggestion: human clinical case report/series Strong statement about limitation; this constrains confidence in prognosis and management recommendations (beyzaei2022themutationspectrum pages 3-5)
Animal/models HPD-deficient mice model hypertyrosinemia with elevated tyrosine and urinary metabolites, and generally lack the severe visceral injury seen in type I; newer mechanistic mouse work links reduced hepatic HPD to tyrosinemia and hippocampal neuron injury via TTC36-STK33-PELI1 regulation. Drosophila nutrigenomics work lists tyrosinemia type III among amino-acid-disorder models/platform efforts (endo2003animalmodelsreveal pages 1-2, xie2019hpddegradationregulated pages 1-2, martelli2024identifyingpotentialdietary pages 1-3, martelli2024identifyingpotentialdietary pages 29-30) Suggested model annotations: mouse knockout model; Drosophila disease model/platform Moderate for mechanistic utility; mouse neurologic findings may not map directly to human HT3 clinical variability (xie2019hpddegradationregulated pages 1-2)

Table: This table provides a compact, ontology-ready summary of Tyrosinemia type III, covering identifiers, genetics, biochemical and clinical features, anatomy, diagnosis, treatment, epidemiology, and model systems. It emphasizes where evidence is strong versus where the ultra-rare nature of the disease leaves major gaps.

1. Disease information

Definition and identifiers

HT3 is the rarest recognized hereditary defect in the tyrosine-degradation pathway. It is a Mendelian, autosomal-recessive metabolic disease caused by deficient HPD activity. (szymanska2015tyrosinemiatypeiii pages 1-3, beyzaei2022themutationspectrum pages 1-2)

  • MONDO: MONDO:0010162
  • OMIM: 276710
  • Orphanet: 69723
  • Causal target: HPD, Ensembl ENSG00000158104
  • Synonyms: tyrosinemia type 3; hereditary hypertyrosinemia type III; 4-hydroxyphenylpyruvate dioxygenase deficiency; older literature also uses 4-hydroxyphenylpyruvic-acid oxidase deficiency. (OpenTargets Search: Tyrosinemia type III-HPD, endo2003animalmodelsreveal pages 4-5)
  • ICD/MeSH: no uniquely validated HT3-specific ICD-10/ICD-11 or MeSH code was established in the retrieved evidence; implementations generally require a broader tyrosinemia/inborn-error code plus molecular detail.

Open Targets aggregates genetic evidence from ClinGen, Genomics England, UniProt, gene2phenotype, and EVA and reports a strong HPD–HT3 association; the ClinGen Aminoacidopathy Gene Curation Expert Panel classified the relationship as definitive. (OpenTargets Search: Tyrosinemia type III-HPD)

The evidence is aggregated at disease level from curated resources and published patients. It is not derived from a large EHR cohort. Individual case reports remain the main source for phenotype, treatment, and longitudinal outcomes.

2. Etiology, risk, and protective factors

Causal factors

The primary cause is germline biallelic HPD dysfunction. Most reported alleles are missense, nonsense, frameshift, or splice-disrupting variants expected to reduce enzyme abundance or activity. The curated disease mechanism is loss or absence of functional gene product. (OpenTargets Search: Tyrosinemia type III-HPD, beyzaei2022themutationspectrum pages 3-5)

No infectious, toxic, occupational, radiation, smoking, alcohol, or lifestyle cause is known. Dietary phenylalanine and tyrosine influence metabolite concentrations after the genetic block but do not cause the disease.

Genetic risk

Risk is determined principally by inheriting two pathogenic HPD alleles. For two heterozygous parents, standard autosomal-recessive recurrence probabilities apply per pregnancy: 25% affected, 50% carrier, and 25% unaffected/non-carrier. Consanguinity can increase the probability of homozygosity for a rare family allele, but no HT3-specific quantitative estimate is available.

No validated susceptibility loci, modifier genes, protective alleles, founder variants, anticipation, or germline-mosaicism pattern has been established. Most alleles are private, and genotype–phenotype correlation is unresolved. (beyzaei2022themutationspectrum pages 3-5)

Environmental and protective factors

Restriction of dietary tyrosine and its precursor phenylalanine lowers plasma tyrosine and is the principal proposed protective intervention after diagnosis. Whether this prevents neurologic disease is unknown. Ascorbic acid was used with dietary treatment in isolated reports, but it is not an established disease-modifying therapy. (alsharhan2020disordersofphenylalanine pages 31-33)

There is no well-defined human gene–environment interaction beyond substrate load through diet. The 2024 Drosophila nutrigenomics study reinforces the broader principle that amino-acid disorders can have strong genotype–diet interactions, but it does not establish a validated HT3 diet in humans. It screened 35 amino-acid-disorder fly models and found diet-altered development or survival in 26 overall. (martelli2024identifyingpotentialdietary pages 1-3)

3. Phenotypes

Biochemical abnormalities

The most consistent phenotype is persistent hypertyrosinemia, commonly reported around 350–650 μmol/L, accompanied by marked urinary 4-hydroxyphenylpyruvate, 4-hydroxyphenyllactate, and 4-hydroxyphenylacetate. An asymptomatic girl had serum tyrosine of 425–535 μmol/L; a 2023 infant had 709 μmol/L at 25 days and 455 μmol/L at four months. (szymanska2015tyrosinemiatypeiii pages 1-3, sarkargar2023acompoundheterozygous pages 1-3, alsharhan2020disordersofphenylalanine pages 31-33)

Suggested annotations include Hypertyrosinemia, increased urinary 4-hydroxyphenylpyruvate, increased urinary 4-hydroxyphenyllactate, and increased urinary 4-hydroxyphenylacetate. Exact HPO mappings for the metabolite-specific findings should be verified in the current HPO release.

Neurologic and developmental phenotypes

Reported manifestations include:

  • developmental or psychomotor delay;
  • intellectual disability;
  • seizures, including recurrent seizures/status epilepticus in isolated reports;
  • intermittent or chronic ataxia;
  • autistic behavior or autism;
  • attention/behavioral difficulties in some families. (szymanska2015tyrosinemiatypeiii pages 1-3, alsharhan2020disordersofphenylalanine pages 31-33, sarkargar2023acompoundheterozygous pages 3-5)

Suggested HPO terms include Global developmental delay, Delayed psychomotor development, Intellectual disability, Seizure, Ataxia, and Autistic behavior. Onset ranges from infancy—seizures have occurred by four months—to later childhood recognition through biochemical screening. Severity ranges from absent to substantial neurologic disability, and course may be stable or episodic rather than predictably progressive. (alsharhan2020disordersofphenylalanine pages 31-33, sarkargar2023acompoundheterozygous pages 3-5)

Frequency estimates are unstable. A 2022 review found 5/16 (31.25%) reported patients asymptomatic despite elevated tyrosine and urinary metabolites. A 2023 case report cited approximately 18 published cases and stated that mental disorders had been reported in 75%, but this estimate is vulnerable to publication and ascertainment bias. (beyzaei2022themutationspectrum pages 3-5, sarkargar2023acompoundheterozygous pages 3-5)

Visceral, ocular, and cutaneous findings

Classic HT3 generally lacks the liver failure, renal Fanconi syndrome/rickets, and hepatocellular carcinoma risk characteristic of type I, and lacks the painful keratitis and palmoplantar hyperkeratosis characteristic of type II. Liver and kidney function were normal in an older nine-patient series summarized in the 2023 report. Recurrent proteinuria has nevertheless been described, and neonatal hepatitis occurred in one recent infant; neither is established as a core phenotype. (szymanska2015tyrosinemiatypeiii pages 3-3, sarkargar2023acompoundheterozygous pages 1-3, sarkargar2023acompoundheterozygous pages 3-5)

Suggested HPO annotation for the limited renal observation is Proteinuria. Hepatitis should remain a case-level association rather than a defining HT3 phenotype.

Quality of life

No HT3-specific EQ-5D, SF-36, PROMIS, caregiver-burden, or disease-specific quality-of-life study was identified. Likely impacts derive from seizures, ataxia, neurodevelopmental disability, repeated biochemical monitoring, and dietary restriction. Quantitative burden estimates are unavailable.

4. Genetic and molecular information

Gene and protein

HPD is located at chromosome 12q24-qter, contains 14 exons, and encodes a 392-amino-acid, approximately 43-kDa iron-containing enzyme. Expression is principally hepatic and renal. The enzyme catalyzes oxidative decarboxylation/rearrangement of 4-hydroxyphenylpyruvate to homogentisate. (alsharhan2020disordersofphenylalanine pages 31-33, endo2003animalmodelsreveal pages 1-2, beyzaei2022themutationspectrum pages 1-2)

Suggested gene/process annotations include tyrosine catabolic process, 4-hydroxyphenylpyruvate dioxygenase activity, iron-ion binding, and oxidoreductase activity. Suggested chemical entities include L-tyrosine, 4-hydroxyphenylpyruvate, homogentisate, 4-hydroxyphenyllactate, and 4-hydroxyphenylacetate; CHEBI identifiers should be resolved against the current CHEBI release.

Published variant spectrum

The 2022 review identified 11 disease-causing HPD variants among 16 patients: seven missense, two nonsense, one splice defect, and one frameshift. Listed variants included p.Ala33Thr, IVS11+1G>A, p.Tyr200Ter, p.Ile335Met, p.Tyr160Cys, p.Tyr258Ter, p.Ile267Phe, p.Ala268Val, c.759+1G>A, p.Gly154Ser, and p.Gly83Ter/c.248delG. p.Tyr160Cys was the only recurrent allele across unrelated families in that review. (beyzaei2022themutationspectrum pages 1-2, beyzaei2022themutationspectrum pages 3-5)

The 2023 Iranian case added compound heterozygous c.75G>A (p.Trp25Ter), classified in the report as pathogenic, and c.413C>T (p.Thr138Met), described as likely pathogenic. Each parent carried one allele. The child had biochemical HT3 but no seizures, ataxia, or intellectual disability at 1.5 years. (sarkargar2023acompoundheterozygous pages 1-3)

A 2024 Chinese report found during searching described p.Ala244Val in compound heterozygosity with p.Thr219Met, but full-text evidence was not retrievable here; it should be independently checked before production annotation.

Variant-level population frequencies were not available in the retrieved full text. For knowledge-base population annotation, each allele should be checked directly in the current gnomAD release. All disease-causing variants are germline; somatic HPD variants are not a recognized cause of inherited HT3. Large chromosomal rearrangements, repeat expansions, mitochondrial variants, and disease-specific epigenetic abnormalities have not been established.

Genotype–phenotype relationship

No robust relationship exists between variant class, tyrosine concentration, and neurologic severity. Tyr160 lies in an alpha helix implicated in inter-subunit contacts and may affect enzyme stability, but this remains structurally inferred rather than proven in patients. The same biochemical defect can accompany severe neurologic disease or an asymptomatic state. (szymanska2015tyrosinemiatypeiii pages 1-3, beyzaei2022themutationspectrum pages 2-3, beyzaei2022themutationspectrum pages 3-5)

5. Environmental information

No toxin, pollution, infectious agent, smoking behavior, alcohol exposure, or occupation is known to initiate HT3. Protein intake can alter biochemical substrate load. Excessive dietary restriction, conversely, risks inadequate protein, growth failure, and micronutrient deficiency; dietary care should therefore be supervised by an inherited-metabolic-disease dietitian.

Hawkinsinuria is an allelic but distinct HPD disorder, generally associated with heterozygous variants such as p.Ala33Thr and dominant inheritance. It should not be interpreted as an environmental form of HT3. (endo2003animalmodelsreveal pages 2-2, endo2003animalmodelsreveal pages 4-5)

6. Mechanism and pathophysiology

Causal chain

  1. Upstream genetic event: biallelic damaging HPD variants reduce functional enzyme.
  2. Primary biochemical block: conversion of 4-hydroxyphenylpyruvate to homogentisate is impaired.
  3. Metabolic consequence: plasma tyrosine rises and 4-hydroxyphenylpyruvate is diverted to 4-hydroxyphenyllactate and 4-hydroxyphenylacetate, which are excreted in urine.
  4. Organ consequence: because the pathway is blocked upstream of homogentisate and fumarylacetoacetate, the severe downstream hepatotoxicity of HT1 does not ordinarily occur.
  5. Possible neurologic consequence: high tyrosine and/or upstream derivatives may disrupt neural function, but human causality is not proven because multiple untreated patients remain neurologically normal. (szymanska2015tyrosinemiatypeiii pages 3-3, endo2003animalmodelsreveal pages 1-2, xie2019hpddegradationregulated pages 1-2)

Suggested GO biological-process terms are tyrosine catabolic process, aromatic amino-acid family catabolic process, cellular amino-acid metabolic process, protein ubiquitination, and proteasomal protein catabolic process. Primary suggested cell types are hepatocyte and neuron; kidney tubular cells are biologically plausible from renal HPD expression but not demonstrated as a primary injured population.

Experimental regulatory mechanism

A 2019 mechanistic study showed that hepatic TTC36 binds HPD and inhibits STK33-mediated phosphorylation of HPD at Thr382. Reduced Thr382 phosphorylation limits PELI1 recruitment, HPD polyubiquitination, and proteasomal degradation. Ttc36-null mice had reduced hepatic HPD, tyrosinemia, hippocampal neuronal injury, and learning/memory deficits. This identifies a regulatory pathway capable of producing an HT3-like state, but TTC36, STK33, and PELI1 are not validated human HT3 modifier genes. (xie2019hpddegradationregulated pages 1-2, xie2019hpddegradationregulated pages 6-7)

A direct abstract quotation states: “Ttc36−/− mice have reduced HPD expression in the liver and exhibit tyrosinemia, damage to hippocampal neurons, and deficits of learning and memory.” The study was published in Nature Communications on September 16, 2019; DOI: 10.1038/s41467-019-12011-0. (xie2019hpddegradationregulated pages 1-2)

Immune, omics, and tissue-damage evidence

One small human study reported increased nitric-oxide release by neutrophils from an affected woman and proposed a possible connection to nervous-system involvement. This is exploratory and not sufficient to define HT3 as an immune or inflammatory disorder. (sarkargar2023acompoundheterozygous pages 3-5)

No reproducible human HT3 transcriptomic, proteomic, lipidomic, single-cell, spatial-transcriptomic, epigenomic, or integrated multi-omics signature was identified. The TTC36 study used cellular biochemistry and mouse tissues, not clinical multi-omics. The 2024 Drosophila project provides a platform for diet–genotype screening rather than a validated human molecular profile. (martelli2024identifyingpotentialdietary pages 1-3, xie2019hpddegradationregulated pages 1-2)

7. Anatomical structures affected

The liver is the principal metabolic organ because hepatic HPD carries much of systemic tyrosine catabolism. The kidney also expresses HPD and contributes to amino-acid metabolism. The central nervous system, including hippocampal neurons in experimental mice, is the main candidate secondary target of metabolite imbalance. (endo2003animalmodelsreveal pages 1-2, beyzaei2022themutationspectrum pages 1-2, xie2019hpddegradationregulated pages 1-2)

Suggested annotations:

  • UBERON: liver, kidney, brain, hippocampus;
  • CL: hepatocyte, neuron; renal tubular epithelial cell as a cautious secondary suggestion;
  • GO cellular component: cytosol/cytoplasm for metabolic enzyme localization and proteasome complex for experimentally demonstrated HPD turnover.

There is no expected lateralization. Human biopsy or neuropathology series are unavailable.

8. Temporal development

The biochemical defect is congenital. Detection can occur neonatally through elevated tyrosine on tandem-mass-spectrometry screening, during infancy after seizures or hepatitis, in childhood through developmental concerns, or incidentally in an asymptomatic older child. (szymanska2015tyrosinemiatypeiii pages 1-3, sarkargar2023acompoundheterozygous pages 1-3, beyzaei2022themutationspectrum pages 5-6)

No formal disease stages exist. Course is variable: some patients have early neurologic manifestations; others remain stable and asymptomatic for years without strict dietary treatment. A patient carrying homozygous c.759+1G>A reportedly retained normal neuropsychological development over seven years despite poor dietary adherence. This observation argues against assuming inevitable progression. (sarkargar2023acompoundheterozygous pages 3-5)

Critical intervention windows are unknown. Early normalization of tyrosine is biologically reasonable, especially in infancy, but no prospective evidence proves that it prevents neurologic disease.

9. Inheritance and population

HT3 is autosomal recessive with highly variable expressivity and apparently incomplete clinical penetrance, although biochemical penetrance may be higher. Anticipation is not expected. No sex bias has been demonstrated.

The literature reported 13 cases by 2015, 16 genetically reviewed patients by 2022, and approximately 18 cases in the 2023 report. These are publication counts, not prevalence estimates. True prevalence is probably underestimated because asymptomatic biochemical cases can be missed. No reliable incidence per 100,000 births, carrier frequency, mortality rate, or sex ratio exists. (szymanska2015tyrosinemiatypeiii pages 1-3, beyzaei2022themutationspectrum pages 3-5, sarkargar2023acompoundheterozygous pages 3-5)

Published variants have been reported in Portugal, Turkey, Sweden, Poland, Japan, Iran, and China. The 2022 review found no molecular data from North/Central America, Africa, Australia, or Oceania. This geographic distribution likely reflects case ascertainment and reporting rather than biological restriction. No definitive HT3 founder effect is established. (beyzaei2022themutationspectrum pages 3-5)

10. Diagnostics

Recommended workflow

  1. Plasma amino-acid analysis: confirm persistent elevated tyrosine.
  2. Urine organic-acid analysis: quantify 4-hydroxyphenylpyruvate, 4-hydroxyphenyllactate, and 4-hydroxyphenylacetate.
  3. Exclude HT1 urgently: test blood or urine succinylacetone and assess liver/renal function. Succinylacetone should not be increased in isolated HPD deficiency.
  4. Phenotypic assessment: neurologic/developmental examination; seizures prompt EEG; ataxia or unexplained neurologic findings may justify brain MRI, although no diagnostic imaging signature exists.
  5. Molecular confirmation: demonstrate biallelic pathogenic/likely pathogenic HPD variants with a single-gene test, tyrosinemia/aminoacidopathy panel, exome, or genome sequencing, followed by segregation analysis where possible. (szymanska2015tyrosinemiatypeiii pages 1-3, sarkargar2023acompoundheterozygous pages 1-3, alsharhan2020disordersofphenylalanine pages 31-33)

The 2015 case used a TruSight One panel; the 2023 case used WES with Sanger confirmation. WES/WGS is particularly useful when biochemical findings are atypical or a panel is negative. CMA, karyotyping, FISH, mitochondrial sequencing, and repeat-expansion testing are not routine because the recognized mechanism is sequence-level HPD dysfunction. (szymanska2015tyrosinemiatypeiii pages 3-3, sarkargar2023acompoundheterozygous pages 1-3)

Differential diagnosis

  • Tyrosinemia type I—FAH deficiency: succinylacetone positive; liver failure, renal tubulopathy/rickets, porphyria-like crises, and hepatocellular-carcinoma risk.
  • Tyrosinemia type II—TAT deficiency: typically higher tyrosine, keratitis/corneal lesions, and painful palmoplantar hyperkeratosis.
  • Transient neonatal tyrosinemia: resolves with hepatic maturation; associated with prematurity, high protein intake, and/or low vitamin C rather than biallelic HPD variants.
  • Hawkinsinuria: allelic HPD disorder, usually dominant, with hawkinsin excretion and infantile metabolic symptoms.
  • Secondary hypertyrosinemia: liver dysfunction, severe illness, nutritional factors, or medication effects. (endo2003animalmodelsreveal pages 4-5, alsharhan2020disordersofphenylalanine pages 31-33)

No consensus clinical diagnostic criteria or disease-specific LOINC panel was identified.

Screening

HT3 may be detected when newborn screening reports elevated tyrosine by MS/MS, but tyrosine is nonspecific. Programs designed for HT1 increasingly rely on succinylacetone; consequently, an infant with high tyrosine but normal succinylacetone requires evaluation for types II/III, transient neonatal tyrosinemia, and liver disease. Dedicated HT3 screening performance metrics are unavailable. (szymanska2015tyrosinemiatypeiii pages 3-3, beyzaei2022themutationspectrum pages 5-6, sarkargar2023acompoundheterozygous pages 3-5)

11. Outcome and prognosis

No survival curves, disease-specific mortality rate, or life-expectancy estimate exists. Available evidence suggests that HT3 is substantially more benign than untreated HT1 and is not known to cause progressive liver failure or hepatocellular carcinoma. Prognosis is driven mainly by whether neurologic manifestations occur. (alsharhan2020disordersofphenylalanine pages 31-33, endo2003animalmodelsreveal pages 1-2)

Some children improve biochemically and symptomatically on diet; others remain asymptomatic without treatment. In the 2015 report, an 11-year-old girl with homozygous p.Tyr160Cys had normal development despite serum tyrosine of 425–535 μmol/L and no tyrosine/phenylalanine-restricted diet. This directly challenges a simple relationship between tyrosine concentration and neurologic injury. (szymanska2015tyrosinemiatypeiii pages 1-3, szymanska2015tyrosinemiatypeiii pages 3-3)

No validated prognostic biomarker exists beyond clinical status, developmental trajectory, seizure control, and metabolite monitoring. Variant class and plasma tyrosine concentration do not reliably predict outcome. Long-term follow-up is needed because existing case numbers and observation periods are insufficient to exclude late manifestations.

12. Treatment

Current management

There is no HT3-specific approved pharmacotherapy. The principal strategy is a phenylalanine- and tyrosine-restricted diet, adjusted to maintain adequate growth and essential amino-acid nutrition. Specialized low-protein foods or amino-acid formulas may be needed. Suggested NCIT mappings are dietary intervention, low-protein diet, low-phenylalanine diet, and low-tyrosine diet; exact NCIT identifiers should be checked before ingestion. (alsharhan2020disordersofphenylalanine pages 31-33)

One report summarized in the 2020 review used ascorbic acid 50 mg/day with dietary restriction and observed normalized tyrosine and seizure improvement. Evidence is too limited to recommend vitamin C as a universal stand-alone treatment. (alsharhan2020disordersofphenylalanine pages 31-33)

Supportive care may include antiseizure medication, physical/occupational therapy for ataxia or motor delay, speech/developmental therapy, and educational/behavioral support. No surgery is disease modifying.

Monitoring

A pragmatic plan includes plasma tyrosine and nutritional amino acids, urine metabolites, growth and nutritional status, liver and renal chemistry initially, urinalysis for proteinuria, and serial neurologic/developmental assessment. EEG or MRI is symptom-directed. No evidence-based target tyrosine range or monitoring interval specific to HT3 has been validated.

Treatments that should not be imported from HT1

Nitisinone is not a treatment for HT3. It pharmacologically inhibits HPD and deliberately creates an HT3-like upstream block when treating HT1; giving it in primary HPD deficiency has no mechanistic rationale and could worsen hypertyrosinemia. Likewise, liver transplantation is not standard HT3 care.

Experimental therapies and trials

No HT3-specific interventional ClinicalTrials.gov study was identified. Retrieved trials concerned HT1/nitisinone or broad nutritional products, not correction of HPD deficiency. No clinical gene-replacement, gene-editing, cell, RNA, or enzyme-replacement therapy is available.

CRISPR deletion of Hpd has been used experimentally to rescue Fah-deficient HT1 mice by converting the severe downstream block to a more benign HT3-like state. This validates pathway position but is not a treatment strategy for patients who already lack HPD. Recent 2024 mouse studies likewise use Hpd editing as a modifier of HT1, not as therapy for HT3.

13. Prevention

Primary prevention of spontaneous disease occurrence is not possible through lifestyle modification. Reproductive prevention options include genetic counseling, targeted parental carrier testing after a proband is identified, cascade testing of relatives, prenatal diagnosis, and preimplantation genetic testing for known familial variants. These approaches follow standard autosomal-recessive practice; HT3-specific outcome studies are absent. (sarkargar2023acompoundheterozygous pages 1-3, beyzaei2022themutationspectrum pages 5-6)

Secondary prevention consists of early detection through newborn-screen hypertyrosinemia or family screening and prompt metabolic evaluation. Tertiary prevention consists of controlling excessive tyrosine exposure, maintaining nutrition, monitoring development and seizures, and providing rehabilitation. Vaccination, antimicrobial prophylaxis, sanitation measures, and environmental remediation have no disease-specific role.

14. Other species and natural disease

The orthologous pathway is conserved across vertebrates. Mus musculus (NCBI Taxonomy 10090) Hpd deficiency produces hypertyrosinemia and urinary tyrosine derivatives. Retrieved evidence did not establish a well-characterized naturally occurring veterinary syndrome equivalent to human HT3 in a specific dog, cat, livestock, or wildlife breed. No zoonotic transmission exists because HT3 is inherited, not infectious.

HPD-deficient mice generally lack the severe visceral damage of FAH deficiency, supporting the clinical distinction between HT3 and HT1. (endo2003animalmodelsreveal pages 1-2)

15. Model organisms

Mouse models

Whole-body Hpd-deficient mice reproduce the biochemical block—high circulating tyrosine and urinary 4-hydroxyphenyl metabolites—and lack the severe hepatorenal injury characteristic of HT1. They are useful for tyrosine-flux studies, toxicity thresholds, and diet testing. Their limitation is that neurologic findings vary by model and may not reproduce the broad human spectrum. (endo2003animalmodelsreveal pages 2-2, endo2003animalmodelsreveal pages 1-2)

Ttc36-null mice provide an acquired-regulatory model: enhanced STK33/PELI1-mediated HPD degradation causes tyrosinemia, hippocampal neuronal damage, and learning/memory impairment. This model is useful for protein-stability mechanisms but is not genetically identical to biallelic human HPD deficiency. (xie2019hpddegradationregulated pages 1-2)

Fah/Hpd double mutants and somatic Hpd-edited Fah-deficient mice model metabolic-pathway rerouting for HT1 research. They demonstrate that an upstream HPD block prevents production of toxic downstream FAH substrates, but they do not directly model treatment of HT3.

Drosophila

The 2024 Cell Reports nutrigenomics project used genetically tractable Drosophila amino-acid-disorder models and defined diets to screen gene–nutrient interactions. The paper states: “Here, we screened 35 Drosophila amino acid disorder models for disease-diet interactions and found 26 with diet-altered development and/or survival.” HT3/OMIM 276710 was included in the platform’s disease-model framework, although the principal detailed rescue experiment concerned isolated sulfite oxidase deficiency rather than HT3. Published March 26, 2024; DOI: 10.1016/j.celrep.2024.113861. (martelli2024identifyingpotentialdietary pages 1-3, martelli2024identifyingpotentialdietary pages 29-30)

No validated HT3 patient-derived iPSC, organoid, zebrafish, rat, yeast, or CRISPR-screen resource was identified in the retrieved evidence.

Recent developments, 2023–2024

  1. New human genotype, 2023: an Iranian girl was reported with compound heterozygous p.Trp25Ter and p.Thr138Met HPD variants, neonatal hepatitis, and tyrosine up to 709 μmol/L, but no classic neurologic manifestations at 1.5 years. Published online January 2023; DOI: 10.18502/ijml.v9i4.11619. (sarkargar2023acompoundheterozygous pages 1-3)
  2. New Chinese genotype–phenotype report, 2024: p.Ala244Val in compound heterozygosity with p.Thr219Met was reported in search metadata. Full-text verification is required before variant curation.
  3. Diet-discovery technology, 2024: Drosophila nutrigenomics offers scalable testing of amino-acid composition and genotype–diet interactions, but no HT3-specific human recommendation has yet resulted. (martelli2024identifyingpotentialdietary pages 1-3)
  4. Pathway-editing research, 2024: liver-specific Hpd disruption remains under study as a modifier strategy for HT1 models. It is mechanistically informative for tyrosine catabolism but not therapeutic for HPD-deficient HT3.

Expert assessment and priority evidence gaps

The most defensible current interpretation is that HT3 is a biochemically penetrant but clinically variably expressive HPD deficiency. Neurologic disease is plausible and repeatedly reported, yet the asymptomatic fraction and absence of a concentration–outcome relationship prevent assuming that persistent tyrosine alone is sufficient to cause brain injury. The 2022 review concluded that no definite genotype–phenotype relationship could be drawn because of the small number of patients, phenotypic heterogeneity, and predominance of private variants. (beyzaei2022themutationspectrum pages 3-5)

The highest-priority research needs are an international registry with standardized metabolite and neurodevelopmental data; prospective natural-history follow-up; functional testing of individual HPD alleles; direct gnomAD-based carrier estimates; agreed treatment thresholds and nutritional targets; and patient-derived neuronal/hepatic models. No 2023–2024 study resolved these fundamental uncertainties.

Key source list

  • Beyzaei Z et al. “The mutation spectrum and ethnic distribution of non-hepatorenal tyrosinemia (types II, III).” Orphanet Journal of Rare Diseases. Published December 2022. DOI: 10.1186/s13023-022-02579-0. (beyzaei2022themutationspectrum pages 1-2, beyzaei2022themutationspectrum pages 3-5)
  • Sarkargar F et al. “A Compound Heterozygous HPD Mutation in an Iranian Patient with Hypertyrosinemia Type III.” International Journal of Medical Laboratory. January 2023. DOI: 10.18502/ijml.v9i4.11619. (sarkargar2023acompoundheterozygous pages 1-3)
  • Szymanska E et al. “Tyrosinemia type III in an asymptomatic girl.” Molecular Genetics and Metabolism Reports. December 2015. DOI: 10.1016/j.ymgmr.2015.10.004. (szymanska2015tyrosinemiatypeiii pages 1-3)
  • Xie Y et al. “HPD degradation regulated by the TTC36-STK33-PELI1 signaling axis induces tyrosinemia and neurological damage.” Nature Communications. September 2019. DOI: 10.1038/s41467-019-12011-0. (xie2019hpddegradationregulated pages 1-2)
  • Martelli F et al. “Identifying potential dietary treatments for inherited metabolic disorders using Drosophila nutrigenomics.” Cell Reports. March 26, 2024. DOI: 10.1016/j.celrep.2024.113861. (martelli2024identifyingpotentialdietary pages 1-3)

Evidence caveat: the retrieved records supplied PMIDs for several foundational HPD papers through Open Targets—PMID 11073718, 10942115, 26226126, 27604308, 17560158, and 30984715—but not every article’s PMID was available in the full-text metadata. These identifiers should be cross-checked against PubMed before automated ingestion. (OpenTargets Search: Tyrosinemia type III-HPD)

References

  1. (szymanska2015tyrosinemiatypeiii pages 3-3): Edyta Szymanska, Malgorzata Sredzinska, Elzbieta Ciara, Dorota Piekutowska-Abramczuk, Rafal Ploski, Dariusz Rokicki, and Anna Tylki-Szymanska. Tyrosinemia type iii in an asymptomatic girl. Molecular Genetics and Metabolism Reports, 5:48-50, Dec 2015. URL: https://doi.org/10.1016/j.ymgmr.2015.10.004, doi:10.1016/j.ymgmr.2015.10.004. This article has 34 citations.

  2. (beyzaei2022themutationspectrum pages 3-5): Zahra Beyzaei, Sara Nabavizadeh, Sara Karimzadeh, and Bita Geramizadeh. The mutation spectrum and ethnic distribution of non-hepatorenal tyrosinemia (types ii, iii). Orphanet Journal of Rare Diseases, Dec 2022. URL: https://doi.org/10.1186/s13023-022-02579-0, doi:10.1186/s13023-022-02579-0. This article has 22 citations and is from a peer-reviewed journal.

  3. (alsharhan2020disordersofphenylalanine pages 31-33): Hind Alsharhan and Can Ficicioglu. Disorders of phenylalanine and tyrosine metabolism. Translational Science of Rare Diseases, 5:3-58, Jul 2020. URL: https://doi.org/10.3233/trd-200049, doi:10.3233/trd-200049. This article has 45 citations.

  4. (OpenTargets Search: Tyrosinemia type III-HPD): Open Targets Query (Tyrosinemia type III-HPD, 12 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.

  5. (beyzaei2022themutationspectrum pages 1-2): Zahra Beyzaei, Sara Nabavizadeh, Sara Karimzadeh, and Bita Geramizadeh. The mutation spectrum and ethnic distribution of non-hepatorenal tyrosinemia (types ii, iii). Orphanet Journal of Rare Diseases, Dec 2022. URL: https://doi.org/10.1186/s13023-022-02579-0, doi:10.1186/s13023-022-02579-0. This article has 22 citations and is from a peer-reviewed journal.

  6. (szymanska2015tyrosinemiatypeiii pages 1-3): Edyta Szymanska, Malgorzata Sredzinska, Elzbieta Ciara, Dorota Piekutowska-Abramczuk, Rafal Ploski, Dariusz Rokicki, and Anna Tylki-Szymanska. Tyrosinemia type iii in an asymptomatic girl. Molecular Genetics and Metabolism Reports, 5:48-50, Dec 2015. URL: https://doi.org/10.1016/j.ymgmr.2015.10.004, doi:10.1016/j.ymgmr.2015.10.004. This article has 34 citations.

  7. (endo2003animalmodelsreveal pages 4-5): Fumio Endo, Yasuhiko Tanaka, Kaede Tomoeda, Akito Tanoue, Gozoh Tsujimoto, and Kimitoshi Nakamura. Animal models reveal pathophysiologies of tyrosinemias. The Journal of nutrition, 133 6 Suppl 1:2063S-2067S, Jun 2003. URL: https://doi.org/10.1093/jn/133.6.2063s, doi:10.1093/jn/133.6.2063s. This article has 23 citations.

  8. (endo2003animalmodelsreveal pages 1-2): Fumio Endo, Yasuhiko Tanaka, Kaede Tomoeda, Akito Tanoue, Gozoh Tsujimoto, and Kimitoshi Nakamura. Animal models reveal pathophysiologies of tyrosinemias. The Journal of nutrition, 133 6 Suppl 1:2063S-2067S, Jun 2003. URL: https://doi.org/10.1093/jn/133.6.2063s, doi:10.1093/jn/133.6.2063s. This article has 23 citations.

  9. (xie2019hpddegradationregulated pages 1-2): Yajun Xie, Xiaoyan Lv, Dongsheng Ni, Jianing Liu, Yanxia Hu, Yamin Liu, Yunhong Liu, Rui Liu, Hui Zhao, Zhimin Lu, and Qingbiao Zhou. Hpd degradation regulated by the ttc36-stk33-peli1 signaling axis induces tyrosinemia and neurological damage. Nature Communications, Sep 2019. URL: https://doi.org/10.1038/s41467-019-12011-0, doi:10.1038/s41467-019-12011-0. This article has 46 citations and is from a highest quality peer-reviewed journal.

  10. (sarkargar2023acompoundheterozygous pages 1-3): Fatemeh Sarkargar, Seyed Ali Madani Manshadi, Ehsan Zare Mehrjardi, Hosein Khodaei, Seyed Mehdi Kalantar, and Seyed Ahmad Mohamamdi. A compound heterozygous hpd mutation in an iranian patient with hypertyrosinemia type iii. International Journal of Medical Laboratory, Jan 2023. URL: https://doi.org/10.18502/ijml.v9i4.11619, doi:10.18502/ijml.v9i4.11619. This article has 0 citations.

  11. (endo2003animalmodelsreveal pages 2-2): Fumio Endo, Yasuhiko Tanaka, Kaede Tomoeda, Akito Tanoue, Gozoh Tsujimoto, and Kimitoshi Nakamura. Animal models reveal pathophysiologies of tyrosinemias. The Journal of nutrition, 133 6 Suppl 1:2063S-2067S, Jun 2003. URL: https://doi.org/10.1093/jn/133.6.2063s, doi:10.1093/jn/133.6.2063s. This article has 23 citations.

  12. (sarkargar2023acompoundheterozygous pages 3-5): Fatemeh Sarkargar, Seyed Ali Madani Manshadi, Ehsan Zare Mehrjardi, Hosein Khodaei, Seyed Mehdi Kalantar, and Seyed Ahmad Mohamamdi. A compound heterozygous hpd mutation in an iranian patient with hypertyrosinemia type iii. International Journal of Medical Laboratory, Jan 2023. URL: https://doi.org/10.18502/ijml.v9i4.11619, doi:10.18502/ijml.v9i4.11619. This article has 0 citations.

  13. (xie2019hpddegradationregulated pages 6-7): Yajun Xie, Xiaoyan Lv, Dongsheng Ni, Jianing Liu, Yanxia Hu, Yamin Liu, Yunhong Liu, Rui Liu, Hui Zhao, Zhimin Lu, and Qingbiao Zhou. Hpd degradation regulated by the ttc36-stk33-peli1 signaling axis induces tyrosinemia and neurological damage. Nature Communications, Sep 2019. URL: https://doi.org/10.1038/s41467-019-12011-0, doi:10.1038/s41467-019-12011-0. This article has 46 citations and is from a highest quality peer-reviewed journal.

  14. (beyzaei2022themutationspectrum pages 5-6): Zahra Beyzaei, Sara Nabavizadeh, Sara Karimzadeh, and Bita Geramizadeh. The mutation spectrum and ethnic distribution of non-hepatorenal tyrosinemia (types ii, iii). Orphanet Journal of Rare Diseases, Dec 2022. URL: https://doi.org/10.1186/s13023-022-02579-0, doi:10.1186/s13023-022-02579-0. This article has 22 citations and is from a peer-reviewed journal.

  15. (martelli2024identifyingpotentialdietary pages 1-3): Felipe Martelli, Jiayi Lin, Sarah Mele, Wendy Imlach, O. Kanca, Christopher K. Barlow, Jefferson Paril, Ralf B. Schittenhelm, John Christodoulou, Hugo J. Bellen, Matthew D. W. Piper, and Travis K. Johnson. Identifying potential dietary treatments for inherited metabolic disorders using drosophila nutrigenomics. Cell reports, 43:113861-113861, Feb 2024. URL: https://doi.org/10.1016/j.celrep.2024.113861, doi:10.1016/j.celrep.2024.113861. This article has 10 citations and is from a highest quality peer-reviewed journal.

  16. (martelli2024identifyingpotentialdietary pages 29-30): Felipe Martelli, Jiayi Lin, Sarah Mele, Wendy Imlach, O. Kanca, Christopher K. Barlow, Jefferson Paril, Ralf B. Schittenhelm, John Christodoulou, Hugo J. Bellen, Matthew D. W. Piper, and Travis K. Johnson. Identifying potential dietary treatments for inherited metabolic disorders using drosophila nutrigenomics. Cell reports, 43:113861-113861, Feb 2024. URL: https://doi.org/10.1016/j.celrep.2024.113861, doi:10.1016/j.celrep.2024.113861. This article has 10 citations and is from a highest quality peer-reviewed journal.

  17. (beyzaei2022themutationspectrum pages 2-3): Zahra Beyzaei, Sara Nabavizadeh, Sara Karimzadeh, and Bita Geramizadeh. The mutation spectrum and ethnic distribution of non-hepatorenal tyrosinemia (types ii, iii). Orphanet Journal of Rare Diseases, Dec 2022. URL: https://doi.org/10.1186/s13023-022-02579-0, doi:10.1186/s13023-022-02579-0. This article has 22 citations and is from a peer-reviewed journal.

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