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.

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.

Artifacts

• Edison artifact artifact-00

Reference Validation

Checked with linkml-reference-validator 0.2.1.

All extracted references resolved successfully.