PAH Gene
Introduction
<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">PAH Gene</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>PAH</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>PAH</td>
</tr>
<tr>
<td class="label">Type</td>
<td>Gene</td>
</tr>
<tr>
<td class="label">NCBI</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/?term=PAH" target="_blank">Search NCBI</a></td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/aging" style="color:#ef9a9a">Aging</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">Alzheimer</a>, <a href="/wiki/amyotrophic-lateral-sclerosis" style="color:#ef9a9a">Amyotrophic Lateral Sclerosis</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">151 edges</a></td>
</tr>
</table>
PAH (Phenylalanine Hydroxylase) encodes the enzyme that catalyzes the hydroxylation of phenylalanine to tyrosine, the rate-limiting step in phenylalanine catabolism. This enzyme is essential for normal phenylalanine metabolism and for the synthesis of tyrosine, which is a precursor for dopamine, norepinephrine, and melanin.
Overview
...PAH Gene
Introduction
<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">PAH Gene</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>PAH</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>PAH</td>
</tr>
<tr>
<td class="label">Type</td>
<td>Gene</td>
</tr>
<tr>
<td class="label">NCBI</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/?term=PAH" target="_blank">Search NCBI</a></td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/aging" style="color:#ef9a9a">Aging</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">Alzheimer</a>, <a href="/wiki/amyotrophic-lateral-sclerosis" style="color:#ef9a9a">Amyotrophic Lateral Sclerosis</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">151 edges</a></td>
</tr>
</table>
PAH (Phenylalanine Hydroxylase) encodes the enzyme that catalyzes the hydroxylation of phenylalanine to tyrosine, the rate-limiting step in phenylalanine catabolism. This enzyme is essential for normal phenylalanine metabolism and for the synthesis of tyrosine, which is a precursor for dopamine, norepinephrine, and melanin.
Overview
Mermaid diagram (expand to render)
PAH is located on chromosome 12q23.2 and encodes a tetrahydrobiopterin (BH4)-dependent monooxygenase. The enzyme is primarily expressed in the liver but is also expressed in the kidney and brain. Mutations in PAH cause phenylketonuria (PKU), an autosomal recessive metabolic disorder that leads to elevated phenylalanine levels and severe neurotoxicity if untreated. [@fitzpatrick1999]
Key Points: [@scriver2001]
- Gene: PAH (chromosome 12q23.2)
- Protein Class: BH4-dependent aromatic amino acid monooxygenase
- Protein Size: 527 amino acids
- Primary Localization: Cytoplasm (primarily liver)
- Cofactor Requirement: Tetrahydrobiopterin (BH4), iron
- Disease Associations: Phenylketonuria (PKU), hyperphenylalaninemia, variant forms
- Therapeutic Relevance: Target for PKU treatment, enzyme replacement, gene therapy
Molecular Structure
The PAH protein has several key structural features: [@blau2010]
- N-terminal regulatory domain: Contains the phenylalanine binding site and controls enzyme activity
- Catalytic domain: Contains the BH4 binding site and iron
- Tetramerization domain: The functional enzyme forms tetramers
The enzyme exists as a tetramer of identical subunits, with each subunit containing one BH4 binding site and one phenylalanine binding site. [@muntau2019]
Function
PAH catalyzes the hydroxylation of phenylalanine to tyrosine: [@van2021]
Phenylalanine → (PAH + BH4 + O2) → Tyrosine + H2O + Dihydrobiopterin (BH2) [@lk2018]
Biological Significance
PAH is crucial for: [@hoshide2016]
- Phenylalanine catabolism: Prevents toxic accumulation of phenylalanine
- Tyrosine synthesis: Tyrosine is a precursor for:
- Dopamine (via L-DOPA)
- Norepinephrine
- Epinephrine
- Melanin
- Thyroid hormones (T3, T4)
- Protein synthesis: Normal tyrosine availability for protein synthesis
Cofactor Requirements
PAH requires:
- Tetrahydrobiopterin (BH4): Essential cofactor, also known as tetrahydropterin
- Molecular oxygen: Source of oxygen atom in tyrosine
- Iron: Catalytic center (Fe2+)
Disease Associations
Phenylketonuria (PKU)
Mutations in PAH cause PKU, characterized by:
- Elevated phenylalanine in blood and brain
- Intellectual disability if untreated
- Seizures
- Eczema
- Musty odor
- Hypopigmentation
Classification of PAH Variants
- Classical PKU: <10% residual activity
- Variant PKU: 10-50% residual activity
- Non-PKU hyperphenylalaninemia: >50% residual activity
Neurodegenerative Disease Links
Alzheimer's Disease
- Altered phenylalanine metabolism in AD
- Elevated phenylalanine may be neurotoxic
- BH4 deficiency in AD brains
- Tyrosine metabolism linked to catecholamine dysfunction
Parkinson's Disease
- L-DOPA (derived from tyrosine) is the primary treatment
- PAH activity may be affected in PD
- BH4 deficiency in PD
Expression Pattern
PAH is expressed in:
- Liver (primary site)
- Kidney
- Brain (lower levels)
- Pancreas
In the brain, PAH is expressed in:
- [Astrocytes](/entities/astrocytes)
- Certain [neurons](/entities/neurons)
Therapeutic Relevance
PAH is a target for several therapeutic approaches:
Dietary phenylalanine restriction: Classic PKU treatment
BH4 supplementation: Sapropterin dihydrochloride (Kuvan)
Pegvaliase (Palynziq): Enzyme substitution therapy
Gene therapy: Experimental approaches for PKU
Dietary tyrosine supplementation: For patients with limited tyrosine synthesisResearch Directions
Current research focuses on:
- Understanding PAH mutations and genotype-phenotype relationships
- Developing new enzyme replacement therapies
- Gene therapy approaches for PKU
- Investigating phenylalanine metabolism in neurodegeneration
- BH4 supplementation for neurodegenerative diseases
See Also
- [Phenylketonuria](/diseases/phenylketonuria)
- [Tyrosine](/entities/tyrosine)
- [Tetrahydrobiopterin](/entities/tetrahydrobiopterin)
- [BH4 Pathway](/mechanisms/bh4-pathway)
- [L-DOPA](/therapeutics/levodopa)
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Parkinson's Disease](/diseases/parkinsons-disease)
Background
The study of Pah Gene has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
External Links
- [PAH Gene - NCBI](https://www.ncbi.nlm.nih.gov/gene/5080)
- [PAH - UniProt](https://www.uniprot.org/uniprot/P00439)
- [PKU - NPKUA](https://www.pkunews.org/)
- [BH4 - Explorer](https://www.bh4.org/)
References
[Woolf LI, (1973) (1973)](https://doi.org/10.1111/j.1471-4159.2004.02388.x)
[Fitzpatrick PF, (1999) (1999)](https://doi.org/10.1146/annurev.biochem.68.1.355)
Scriver CR, Kaufman S, (2001) (2001)
[Blau N, et al, (2010) (2010)](https://doi.org/10.1016/j.ymgme.2010.03.015)
[Muntau AC, et al, (2019) (2019)](https://doi.org/10.1056/NEJMoa1803757)
[van Spronsen FJ, et al, (2021) (2021)](https://doi.org/10.1038/s41572-021-00267-0)
[L我想找K, et al, (2018) (2018)](https://doi.org/10.1111/jnc.14237)
[Hoshide R, et al, (2016) (2016)](https://doi.org/10.3233/JAD-160261)Pathway Diagram
The following diagram shows the key molecular relationships involving PAH Gene discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)