GENE REFERENCE / HGNC:8582

PAH

phenylalanine hydroxylase

protein-coding gene12q23.2Gene information

What does this gene do?

The PAH gene provides instructions for making an enzyme called phenylalanine hydroxylase. This enzyme helps process phenylalanine, which is a building block of proteins (amino acid). Phenylalanine is obtained through the diet; it is found in certain foods (such as meat, eggs, nuts, and milk) and in some artificial sweeteners.

Phenylalanine hydroxylase is responsible for the conversion of phenylalanine to another amino acid, tyrosine. The enzyme works with a molecule called tetrahydrobiopterin (BH4) to carry out this chemical reaction. Tyrosine is used to make several types of hormones and a pigment called melanin, which gives hair and skin their color. It is also used to make neurotransmitters, which are chemicals that transmit signals in the brain. Tyrosine can also be broken down into smaller molecules that are used to produce energy.

Source: MedlinePlus, National Library of Medicine. Source publication: 2025-04-03. Source review: 2023-04.

ClinGen reviews

ClinGen reviews the evidence linking a particular gene to a condition. Each rating below describes the strength of that link. It does not classify a variant in your DNA file.

Condition	Inheritance	Evidence
phenylketonuriaMONDO:0009861 · Evaluated 2020-04-24	Autosomal recessive	DefinitiveAminoacidopathy Gene Curation Expert Panel

ClinVar records

These numbers show what has been submitted to ClinVar. They cannot tell you how likely you are to have a condition.

Submitted alleles: 1,778
Submissions for variants in or overlapping this gene: 5,470
Submissions explicitly reporting this gene: 5,367
Alleles reported pathogenic / likely pathogenic: 932
VariationIDs with uncertain significance: 359
VariationIDs with conflicting classifications: 15

The rows count different things: alleles, submissions or VariationIDs. Their categories can overlap, so do not add them together. Pathogenic/likely pathogenic counts exclude structural variants that merely overlap a gene. A dash in the source means “not reported,” not zero.

NCBI produces the gene-summary file each week using counts recorded at the start of the month. The numbers may differ from those on the live ClinVar website. Read the field definitions ↗

View this gene in ClinVar ↗

YOUR DNA FILE

Can your DNA file tell you about PAH?

From a DNA test kit (such as 23andMe, AncestryDNA or MyHeritage). These kits check a fixed list of about 600,000 to 700,000 positions across your whole genome. ClinVar lists 932 alleles in PAH reported as pathogenic or likely pathogenic. A kit checks only some of these positions, and often none of them.

From whole genome sequencing (a VCF file). Sequencing reads most of your genome. Your file lists the places where your DNA differs from the reference genome. Some regions are hard to sequence, including parts of some genes that have near-identical copies elsewhere, and a VCF file does not record which positions were read well.

If a variant is not in your file, that does not mean you don’t have it.

What BioDecode checks

BioDecode compares every variant in your file with ClinVar, on your own computer. For each match, it shows the ClinVar classification, the review status and the condition it was reported for. Your file is not uploaded.

A ClinVar classification applies to one particular variant and the condition it was reported for. It does not tell you about other variants in PAH.

BioDecode cannot fill gaps in your test, diagnose a condition or replace clinical testing.

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