PAH Gene and Phenylketonuria: Mutations and Clinical Trials
The PAH gene sits on chromosome 12q23.2, and its full name is phenylalanine hydroxylase. Orphanet links PAH to 3 rare conditions and lists variants in the gene as a cause of all of them. Trial Friend's Phenylketonuria page lists PAH among the genes behind the condition. As of September 29, 2026, 3 recruiting or soon-opening trials on ClinicalTrials.gov name PAH as a gene.
Other symbols for PAH in gene databases: PH.
What the PAH gene does
PAH makes phenylalanine hydroxylase, the enzyme that turns phenylalanine, an amino acid found in protein foods and some artificial sweeteners, into tyrosine. It works with a helper molecule called BH4.
Summarized from the PAH page on MedlinePlus Genetics, U.S. National Library of Medicine, checked September 29, 2026.
PAH and Phenylketonuria
These condition pages list PAH among the genes behind the condition, checked against genetics references when each page was written.
The condition usually appears only when both copies of the gene carry a disease-causing variant. One variant alone usually means a person is a carrier.
Nearly all cases are biallelic PAH variants; residual enzyme activity determines whether it is classic PKU or milder hyperphenylalaninemia.
PAH mutation clinical trials
These recruiting or soon-opening trials mention PAH as a gene in their title, summary, eligibility rules or keywords. Some want people with a variant in it, and others study it more broadly, which is why each trial's own words are shown. In cancer trials the gene change is usually one found in the tumor rather than one a person inherited.
3 trials, checked September 29, 2026. The list refreshes from ClinicalTrials.gov every few hours.
All conditions linked to PAH gene mutations
Orphanet records how each gene relates to each condition. Orphanet links PAH to 3 rare conditions and lists variants in the gene as a cause of all of them.
- Causes it. Disease-causing variants in this gene are a direct cause of the condition.
PAH genetic test results and what a variant can mean
Labs sort each variant they find into 5 groups, from pathogenic and likely pathogenic through uncertain significance to likely benign and benign. Only the first 2 are usually treated as the cause of a condition. A variant of uncertain significance, or VUS, is one without enough evidence either way yet, and labs can reclassify it as research builds.
A genetic counselor or your doctor can explain what a specific result means for you and your family. Our genetic testing guide covers the terms, and MedlinePlus Genetics from the National Library of Medicine has a plain-language page on PAH.
PAH gene questions
What does the PAH gene do?
PAH makes phenylalanine hydroxylase, the enzyme that turns phenylalanine, an amino acid found in protein foods and some artificial sweeteners, into tyrosine. It works with a helper molecule called BH4. This summary follows MedlinePlus Genetics from the U.S. National Library of Medicine.
Are there clinical trials for people with PAH gene variants?
As of September 29, 2026, 3 recruiting or soon-opening trials on ClinicalTrials.gov name PAH as a gene. Each one is listed on this page with the words from the trial that mention the gene. ClinicalTrials.gov also lists 35 open trials for Phenylketonuria, and Match Me on Trial Friend can check those against age, sex, location and treatment history.
What conditions are linked to the PAH gene?
Orphanet links PAH to 3 rare conditions and lists variants in the gene as a cause of all of them. They include Maternal phenylketonuria syndrome, Tetrahydrobiopterin-responsive phenylketonuria and Tetrahydrobiopterin-unresponsive phenylketonuria. Orphanet is the European rare disease database run by INSERM in Paris.
How is Phenylketonuria inherited?
The inheritance pattern is autosomal recessive. The condition usually appears only when both copies of the gene carry a disease-causing variant. One variant alone usually means a person is a carrier. Nearly all cases are biallelic PAH variants; residual enzyme activity determines whether it is classic PKU or milder hyperphenylalaninemia.
What does a PAH variant of uncertain significance mean?
A variant of uncertain significance, or VUS, is a change in the gene that labs don't yet have enough evidence to call disease-causing or harmless. It is not used on its own to diagnose a condition, and labs can reclassify it as research builds. A genetic counselor can explain what a specific result means for you and your family.
Sources
- Gene and condition links from Orphadata (Orphanet, INSERM US14), used under CC BY 4.0, read September 29, 2026.
- Trials from ClinicalTrials.gov, read September 29, 2026.
- PAH gene, MedlinePlus Genetics, U.S. National Library of Medicine.
- Inheritance and gene notes from the Trial Friend condition pages above, each checked against genetics references.
Other gene pages
The gene search covers every gene Orphanet links to a rare disease.