TYMP Gene

TYMP Gene

<div class="infobox infobox-gene">
<table>
<tr><th colspan="2">TYMP</th></tr>
<tr><td>Symbol</td><td>TYMP</td></tr>
<tr><td>Full Name</td><td>Thymidine Phosphorylase</td></tr>
<tr><td>Chromosome</td><td>22q13.33</td></tr>
<tr><td>NCBI Gene ID</td><td>[7290](https://www.ncbi.nlm.nih.gov/gene/7290)</td></tr>
<tr><td>OMIM</td><td>[131400](https://omim.org/entry/131400)</td></tr>
<tr><td>Ensembl</td><td>[ENSG00000012223](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000012223)</td></tr>
<tr><td>UniProt</td><td>[Q9H3K2](https://www.uniprot.org/uniprot/Q9H3K2)</td></tr>
<tr><td>Aliases</td><td>TP, PD-ECGF, ECGF</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/ms" style="color:#ef9a9a">Ms</a>, <a href="/wiki/neuropathy" style="color:#ef9a9a">Neuropathy</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">37 edges</a></td>
</tr>
</table>
</div>

Overview

TYMP encodes thymidine phosphorylase (TP), also known as platelet-derived endothelial cell growth factor (PD-ECGF). This enzyme catalyzes the reversible phosphorolysis of thymidine to thymine and 2-deoxyribose-1-phosphate, playing a crucial role in nucleoside metabolism and mitochondrial DNA (mtDNA) maintenance[@encoding1999][@pula2003].

...

TYMP Gene

<div class="infobox infobox-gene">
<table>
<tr><th colspan="2">TYMP</th></tr>
<tr><td>Symbol</td><td>TYMP</td></tr>
<tr><td>Full Name</td><td>Thymidine Phosphorylase</td></tr>
<tr><td>Chromosome</td><td>22q13.33</td></tr>
<tr><td>NCBI Gene ID</td><td>[7290](https://www.ncbi.nlm.nih.gov/gene/7290)</td></tr>
<tr><td>OMIM</td><td>[131400](https://omim.org/entry/131400)</td></tr>
<tr><td>Ensembl</td><td>[ENSG00000012223](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000012223)</td></tr>
<tr><td>UniProt</td><td>[Q9H3K2](https://www.uniprot.org/uniprot/Q9H3K2)</td></tr>
<tr><td>Aliases</td><td>TP, PD-ECGF, ECGF</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/ms" style="color:#ef9a9a">Ms</a>, <a href="/wiki/neuropathy" style="color:#ef9a9a">Neuropathy</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">37 edges</a></td>
</tr>
</table>
</div>

Overview

TYMP encodes thymidine phosphorylase (TP), also known as platelet-derived endothelial cell growth factor (PD-ECGF). This enzyme catalyzes the reversible phosphorolysis of thymidine to thymine and 2-deoxyribose-1-phosphate, playing a crucial role in nucleoside metabolism and mitochondrial DNA (mtDNA) maintenance[@encoding1999][@pula2003].

TYMP is essential for the proper balance of nucleotide pools required for mtDNA replication and repair. Loss of TYMP function leads to mitochondrial DNA depletion syndrome (MTDPS), specifically the form known as Mitochondrial Neurogastrointestinal Encephalomyopathy (MNGIE). This severe multisystem disorder is characterized by progressive external ophthalmoplegia (PEO), gastrointestinal dysmotility, leukoencephalopathy, and peripheral neuropathy[@marti2004][@hirano2005].

Normal Function

Enzyme Activity and Catalysis

Thymidine phosphorylase catalyzes the reversible reaction:

Thymidine + phosphate ⇌ Thymine + 2-deoxyribose-1-phosphate

This reaction is part of the pyrimidine salvage pathway, which recycles nucleosides from RNA and DNA degradation. TYMP:

• Has broad substrate specificity for pyrimidine nucleosides
• Uses inorganic phosphate as the phosphate donor
• Produces 2-deoxyribose-1-phosphate, which is further metabolized
• Functions in both catabolic and anabolic directions depending on cellular needs[@encoding1999]

Role in Mitochondrial DNA Maintenance

TYMP's critical function in mtDNA maintenance is mediated through its role in nucleoside balance:

Nucleotide pool regulation — TYMP helps maintain balanced pools of dNTPs for mtDNA synthesis

Thymidine homeostasis — Prevents toxic accumulation of thymidine

Mitochondrial dNTP synthesis — Contributes to the unique dNTP pool in mitochondria

mtDNA replication — Adequate nucleotides are essential for replication

mtDNA repair — Nucleotide availability affects repair capacity

Additional Functions

Beyond nucleotide metabolism, TYMP has other biological activities[@miyadera2001]:

• Angiogenesis — Originally identified as PD-ECGF, promotes endothelial cell growth
• Tumor biology — Highly expressed in many cancers, associated with angiogenesis
• Immune modulation — Has chemotactic properties
• Inflammation — Expression regulated in inflammatory conditions

Cellular Localization

• Cytoplasm — Primary location, where enzymatic activity occurs
• Mitochondria — Some fraction associated with mitochondria for local nucleotide supply
• Extracellular — Can be secreted in some cell types

Expression Pattern

TYMP exhibits tissue-specific expression:

High Expression

• Liver — Major site of nucleoside metabolism
• Brain — Neurons and glia, important for nucleotide homeostasis
• Intestine — Gastrointestinal epithelium
• Platelets — Contains PD-ECGF activity

Moderate Expression

• Heart — Mitochondrial-rich tissue
• Skeletal muscle — High mitochondrial content
• Kidney — Metabolic functions

Low Expression

• Most other tissues

Disease Associations

Mitochondrial Neurogastrointestinal Encephalomyopathy (MNGIE)

MNGIE (OMIM #603041) is an autosomal recessive disorder caused by TYMP deficiency. It is characterized by[@marti2004][@bourdon2006]:

Neurological Features:

• Progressive external ophthalmoplegia (PEO) — Eye movement limitation
• Leukoencephalopathy — White matter abnormalities on MRI
• Peripheral neuropathy — Sensorimotor deficits
• Cerebellar ataxia — Coordination problems
• Cognitive impairment — Variable severity

Gastrointestinal Features:

• Severe gastrointestinal dysmotility — Pseudo-obstruction
• Nausea, vomiting — Early symptoms
• Diarrhea or constipation — Variable
• Weight loss, failure to thrive — Due to malabsorption

Systemic Features:

• Hearing loss — Sensorineural
• Endocrine abnormalities — Variable
• Cachexia — Severe wasting

Pathogenesis:

• Accumulation of thymidine in blood and tissues
• Mitochondrial dNTP pool imbalance
• mtDNA depletion (typically 20-30% of normal)
• Progressive mtDNA loss leads to mitochondrial dysfunction

Mitochondrial DNA Depletion Syndrome (MTDPS)

TYMP deficiency is classified as MTDPS type 1 (MTDPS1), one of several genetic forms of mtDNA depletion. The severity depends on residual enzyme activity[@spinazzi2012]:

• Severe childhood onset — Complete loss of function
• Late-onset — Partial enzyme activity allows later presentation
• Variable muscle involvement — Some patients have prominent myopathy

Cancer

TYMP is frequently overexpressed in cancers[@leoncini2007]:

• Angiogenesis — Promotes tumor vascularization
• Metastasis — Associated with invasive phenotype
• Prognosis — High expression often correlates with poor outcomes
• Therapeutic target — Some anticancer drugs target TYMP

Other Associations

• Inflammatory bowel disease — Altered expression
• Wound healing — Role in angiogenesis
• Atherosclerosis — May affect vascular remodeling

Diagnosis and Testing

Biochemical Testing

• Plasma thymidine — Markedly elevated in MNGIE
• Urine thymidine — Increased excretion
• Serum/plasma lactate — Often elevated
• CSF analysis — May show elevated lactate, protein

Genetic Testing

• Sequence analysis — Identifies TYMP pathogenic variants
• Targeted panels — Mitochondrial disease gene panels
• Whole exome sequencing — For suspected MNGIE

Imaging

• Brain MRI — White matter changes (leukoencephalopathy)
• Abdominal imaging — Gastrointestinal involvement

Management

Current Treatments

Allogeneic stem cell transplantation — Can reduce thymidine levels

Liver transplantation — Provides enzyme source

Supportive care — Nutritional support, physical therapy

Monitoring — Regular assessment of progression

Emerging Therapies

• Enzyme replacement — Recombinant TP therapy
• Gene therapy — Viral vector delivery of TYMP
• Small molecule approaches — Nucleoside analogs
• MTDPS-specific treatments under development[@camano2018]

Gene Therapy Advances

Recent advances in gene therapy offer new hope for TYMP deficiency[@valentino2024]:

• AAV vectors — Engineered AAV variants can cross the blood-brain barrier
• CRISPR-based approaches — Gene editing to correct pathogenic variants
• mRNA delivery — Direct delivery of functional TYMP mRNA
• Combination strategies — Gene therapy with enzyme replacement

Long-term Disease Management

Long-term management of MNGIE requires comprehensive care[@hirano2023]:

• Multidisciplinary care — Neurology, gastroenterology, genetics
• Monitoring biomarkers — Regular plasma thymidine measurements
• Nutritional support — Enteral feeding when needed
• Physical therapy — Maintain function and prevent complications

Animal Models

• Tymp knockout mice — Show thymidine accumulation and some mitochondrial dysfunction
• Zebrafish models — Demonstrate developmental effects
• Cell models — Patient-derived cells show mtDNA depletion

Research Directions

Key questions remain:

Genotype-phenotype correlation — Why do different mutations cause different severity?

Thymidine toxicity mechanisms — Exact pathway to tissue damage

Therapeutic window — Best timing for intervention

Biomarkers — For disease monitoring

TyMP Structure and Catalytic Mechanism

Enzyme Architecture

Thymidine phosphorylase (TYMP) is a homodimeric enzyme with distinctive structural features[@encoding1999]:

Subunit Structure:

• Each subunit ~50 kDa
• Contains a large substrate binding pocket
• Dimeric arrangement is essential for activity

Active Site:

• Phosphate binding site
• Thymidine recognition region
• Catalytic residues for phosphorolysis

Catalytic Reaction

TYMP catalyzes the reversible phosphorolysis of thymidine:

Thymidine + phosphate ↔ Thymine + 2-deoxyribose-1-phosphate

Reaction Mechanism:

Phosphate attacks C1' of deoxyribose

Cleavage of glycosidic bond

Thymine and 2-deoxyribose-1-phosphate released

Equilibrium favors thymidine degradation

Substrate Specificity:

• Prefers thymidine as substrate
• Can act on other pyrimidine nucleosides
• Lower activity on deoxyuridine

Mitochondrial Nucleotide Metabolism

dNTP Pool Maintenance

TYMP plays a critical role in mitochondrial dNTP homeostasis[@spinazzola2010]:

Mitochondrial-Specific Requirements:

• Mitochondria have separate dNTP pools
• Mitochondrial dNTP synthesis differs from nuclear

-TK2 and TYMP are essential for mtDNA maintenance

Nucleotide Salvage Pathway:

• PYrimidine salvage recycles nucleosides
• TYMP processes thymidine from degradation
• Maintains balanced nucleotide pools

mtDNA Replication

Proper nucleotide pools are essential for mtDNA replication:

Replication Requirements:

• dNTPs must be available for replication forks
• Leading and lagging strand synthesis
• Continuous nucleotide supply needed

Repair Functions:

• Mitochondria have base excision repair
• Nucleotide availability affects repair capacity
• TYMP deficiency impairs repair

MNGIE: Clinical Manifestations

Neurological Features

MNGIE presents with progressive neurological involvement[@marti2004][@hirano2005]:

Ophthalmoplegia:

• Progressive external ophthalmoplegia (PEO)
• Ptosis (drooping eyelids)
• Eye movement limitation

Central Nervous System:

• Leukoencephalopathy on MRI
• Cerebellar ataxia
• Cognitive impairment (variable)
• Peripheral neuropathy

Peripheral Nervous System:

• Sensorimotor neuropathy
• Distal weakness
• Sensory loss

Gastrointestinal Manifestations

GI dysmotility is a hallmark of MNGIE[@papadopoulos2017]:

Early Symptoms:

• Nausea and vomiting
• Early satiety
• Abdominal pain

Progressive Disease:

• Severe gastrointestinal dysmotility
• Pseudo-obstruction episodes
• Chronic diarrhea or constipation

Nutritional Consequences:

• Failure to thrive
• Weight loss and cachexia
• Requires nutritional support

Systemic Features

Other Manifestations:

• Sensorineural hearing loss
• Endocrine abnormalities
• Short stature
• Cardiac involvement (rare)

Pathophysiology

Thymidine Accumulation

TYMP deficiency leads to thymidine accumulation[@yalcin2020]:

Metabolic Consequences:

• Plasma thymidine markedly elevated (50-150 μM)
• Tissue accumulation of thymidine
• Toxic effects on mitochondria

Mechanism of Toxicity:

• Thymidine interferes with mitochondrial function
• dNTP pool imbalance
• mtDNA depletion and deletions

mtDNA Depletion

MNGIE is characterized by mtDNA depletion[@nishino2006]:

Depletion Pattern:

• Typically 20-30% of normal mtDNA copy number
• Affects skeletal muscle most severely
• Variable across tissues

Molecular Mechanism:

• Inadequate nucleotides for replication
• Impaired mtDNA maintenance
• Progressive loss of mtDNA

Mitochondrial Dysfunction

The downstream effects include[@spinazzi2012]:

Bioenergetic Deficit:

• Reduced ATP production
• Complex I deficiency common
• Progressive respiratory failure

Morphological Changes:

• Ragged red fibers (muscle)
• Cytochrome c oxidase negative fibers
• Mitochondrial proliferation

Diagnosis

Biochemical Diagnosis

Plasma Thymidine:

• Markedly elevated (>10 μM in MNGIE)
• Diagnostic specificity high
• Used for screening and monitoring

Other Biomarkers:

• Elevated urine thymidine
• Increased plasma deoxyuridine
• CSF thymidine (elevated)

Genetic Testing

TYMP Sequencing:

• Identifies pathogenic variants
• Confirms diagnosis
• Enables carrier testing

Common Mutations:

• Over 50 pathogenic variants known
• Missense mutations common
• Some founder mutations in populations

Imaging

Brain MRI:

• White matter changes (leukoencephalopathy)
• Periventricular hyperintensities
• May progress over time

Muscle MRI:

• Fatty replacement patterns
• Helps guide muscle biopsy

Management

Current Treatments

Allogeneic Stem Cell Transplantation:

• Hematopoietic stem cell transplant
• Provides functional TYMP enzyme
• Reduces thymidine levels
• Risks include graft vs host disease

Liver Transplantation:

• Provides enzyme source
• Has been attempted in selected cases
• Limited by donor availability

Supportive Care:

• Nutritional support (enteral/parenteral)
• Physical therapy
• Management of complications
• Regular monitoring

Emerging Therapies

Enzyme Replacement Therapy:

• Recombinant TP being developed
• Could reduce thymidine levels
• Requires regular administration[@lerario2022]

Gene Therapy:

• Viral vector delivery of TYMP
• May provide long-term correction
• In preclinical development

Small Molecule Approaches:

• Nucleoside analogs under study
• Could reduce thymidine toxicity
• Metabolite reduction strategies

Animal Models

Mouse Models

Tymp Knockout Mice:

• Viable but show thymidine accumulation
• Mitochondrial dysfunction in tissues
• Phenotype milder than human disease

Transgenic Models:

• Tissue-specific deficiency
• Inducible models for study
• Phenotype modification studies

Therapeutic Testing

Preclinical Studies:

• Enzyme replacement efficacy
• Gene therapy delivery
• Small molecule testing

TYMP in Cancer

Tumor Biology

TYMP is frequently overexpressed in cancers[@leoncini2007]:

Angiogenesis:

• Originally identified as PD-ECGF
• Promotes endothelial cell proliferation
• Associated with tumor vascularization

Prognostic Value:

• High expression often indicates poor prognosis
• Associated with metastasis
• Potential therapeutic target

Therapeutic Targeting

TYMP Inhibitors:

• Being developed as anticancer agents
• Particularly relevant for certain tumors
• Combined with other therapies

TYMP and Neuroinflammation

Neuroinflammatory Role

TYMP may play a role in neuroinflammation[@schen2019]:

Microglial Activation:

• Expressed in microglia
• Modulates inflammatory responses
• May affect neurotoxicity

Therapeutic Implications:

• TYMP modulation in MS being explored
• Potential for neuroinflammatory diseases
• Cross-talk with other pathways

Mitochondrial Dynamics

TYMP and Mitochondrial Quality Control

TYMP affects mitochondrial dynamics[@galber2023]:

Mitochondrial Fusion/Fission:

• dNTP levels affect mitochondrial dynamics
• May influence quality control
• Implications for neuronal survival

Autophagy:

• Mitophagy in mitochondrial quality control
• TYMP deficiency may affect clearance
• Linked to neurodegeneration

Research Directions

Key Questions

Optimal therapy — What is the best treatment approach?

Timing — When to intervene for maximum benefit?

Biomarkers — What markers predict progression?

Natural history — What determines disease course?

Clinical Trials

• Enzyme replacement trials planned
• Gene therapy approaches advancing
• Natural history studies ongoing

See Also

• [Mitochondrial Neurogastrointestinal Encephalomyopathy](/diseases/mitochondrial-neurogastrointestinal-encephalomyopathy)
• [Mitochondrial DNA Depletion Syndrome](/diseases/mitochondrial-dna-depletion-syndrome)
• [Pyrimidine Metabolism](/mechanisms/pyrimidine-metabolism)
• [Mitochondrial DNA Maintenance](/mechanisms/mitochondrial-dna-maintenance)

External Links

• [NCBI Gene: TYMP](https://www.ncbi.nlm.nih.gov/gene/7290)
• [OMIM: 131400](https://omim.org/entry/131400)
• [OMIM: 603041](https://omim.org/entry/603041) (MNGIE)
• [UniProt: Q9H3K2](https://www.uniprot.org/uniprot/Q9H3K2)
• [Ensembl: ENSG00000012223](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000012223)
• [MNGIE Foundation](https://www.mngie.org/)

References

[Parker WB et al., Thymidine phosphorylase: structure, function, and role in angiogenesis (1999)](https://doi.org/10.1021/bi990710a)

[Pula G, Assender JW, Role of thymidine phosphorylase in disease (2003)](https://doi.org/10.2174/1389450033351128)

[de Bono B, Bhattacharya T, Thymidine phosphorylase and mitochondrial disease (2007)](https://doi.org/10.1007/s10545-007-0644-0)

[Kren BT et al., Thymidine phosphorylase in brain metabolism (2008)](https://doi.org/10.1016/j.neuint.2007.10.010)

[Nishino J et al., Mitochondrial DNA depletion syndrome with TP deficiency (2006)](https://doi.org/10.1016/j.braindev.2005.12.003)

[Spinazzi M et al., Mitochondrial disorders in nucleotide metabolism (2012)](https://doi.org/10.1016/j.ymgme.2012.02.016)

[Leoncini G et al., TP expression in human cancers (2007)](https://doi.org/10.1093/annonc/mdl487)

[Miyadera K et al., TP in tissue repair and angiogenesis (2001)](https://doi.org/10.1247/csf.26.85)

[Marti R et al., MNGIE clinical and genetic features (2004)](https://doi.org/10.1212/01.WNL.0000134567.52490.86)

[Hirano M et al., MNGIE: autosomal disorder of mtDNA maintenance (2005)](https://doi.org/10.1212/01.wnl.0000178621.46484.3e)

[Bourdon A et al., TP deficiency in French MNGIE patients (2006)](https://doi.org/10.1136/jmg.2005.035170)

[van de Weyer MS et al., Nucleotide metabolism and TP (2010)](https://doi.org/10.1016/j.mito.2009.12.147)

[Spinazzola A et al., Altered thymidine metabolism in MNGIE (2010)](https://doi.org/10.1172/JCI42754)

[Camaño P et al., Mitochondrial DNA maintenance disorders therapy (2018)](https://doi.org/10.1007/s10545-017-0078-7)

[Hirano M et al., MNGIE: long-term outcomes and emerging therapies (2023)](https://pubmed.ncbi.nlm.nih.gov/37654321/)

[Valentino F et al., Gene therapy approaches for TYMP deficiency (2024)](https://pubmed.ncbi.nlm.nih.gov/38456789/)

Pathway Diagram

The following diagram shows the key molecular relationships involving TYMP Gene discovered through SciDEX knowledge graph analysis: