Traits

Traits linked to PAH

phenylalanine hydroxylase

The Human Phenotype Ontology links 55 traits to PAH, by body system: features seen in people with one of the gene's rare conditions.

Abnormality of the nervous system

Trait	How often it is seen
Global developmental delay	Often (30–79%)
Intellectual disability	Often (30–79%)
Epilepsy	Sometimes (5–29%)
More active than typical	Sometimes (5–29%)
Underdevelopment of part of brain called corpus callosum	Sometimes (5–29%)
Aggressive behavior	Not recorded
Anxiety	Not recorded
Attention deficit	Not recorded
Depression	Not recorded
Increased reflexes	Not recorded
Irritability	Not recorded
Obsessive compulsive behavior	Not recorded
Psychosis	Not recorded
Self-mutilation	Not recorded

Abnormality of head or neck

Trait	How often it is seen
Abnormal facial shape	Often (30–79%)
Abnormally small head	Often (30–79%)
High palate	Sometimes (5–29%)
Little lower jaw	Sometimes (5–29%)
Long philtrum	Sometimes (5–29%)
Nasal tip, upturned	Sometimes (5–29%)
Wide nasal bridge	Sometimes (5–29%)
Deviated nasal septum	Rarely (1–4%)
Eye folds	Rarely (1–4%)
Sloping forehead	Rarely (1–4%)

Abnormality of the cardiovascular system

Trait	How often it is seen
Abnormality of the heart	Very often (80–99%)
Narrowing of aorta	Often (30–79%)
Underdeveloped left heart	Often (30–79%)
Double outlet right ventricle	Sometimes (5–29%)
Hole in heart wall separating two lower heart chambers	Sometimes (5–29%)
Tetralogy of Fallot	Sometimes (5–29%)

Laboratory abnormality

Trait	How often it is seen
Elevated urinary gamma-glutamylphenylalanine level	Always
Increased level of hippuric acid in urine	Always
Elevated urinary phenylpyruvic acid level	Not recorded
Hyperphenylalaninemia	Not recorded
Phenylpyruvic acidemia	Not recorded
Reduced phenylalanine hydroxylase level	Not recorded

Abnormality of the eye

Trait	How often it is seen
Abnormally close eyes	Rarely (1–4%)
Cross-eyed	Rarely (1–4%)
Drooping of both upper eyelids	Rarely (1–4%)
Blue eyes	Not recorded
Clouding of the lens of the eye	Not recorded

Abnormality of the integument

Trait	How often it is seen
Dry skin	Not recorded
Fair hair	Not recorded
Fair skin	Not recorded
Scleroderma	Not recorded

Abnormality of limbs

Trait	How often it is seen
Curvature of digit	Rarely (1–4%)
Notched outermost bone of the thumb	Rarely (1–4%)
Short fingers or toes	Rarely (1–4%)

Abnormality of the digestive system

Trait	How often it is seen
Birth defect in which part of esophagus did not develop	Rarely (1–4%)
Bladder exstrophy	Rarely (1–4%)

Abnormality of the ear

Trait	How often it is seen
Hypoplastic helices	Rarely (1–4%)

Abnormality of the genitourinary system

Trait	How often it is seen
Abnormally shaped kidney	Rarely (1–4%)

Abnormality of the immune system

Trait	How often it is seen
Eczema	Not recorded

Abnormality of the musculoskeletal system

Trait	How often it is seen
Abnormal deposits of calcium in the brain	Not recorded

Growth abnormality

Trait	How often it is seen
Prenatal growth deficiency	Often (30–79%)

How often is among people with one of the gene's conditions, the most often across them, as the Human Phenotype Ontology records it. These pages describe traits and the research behind them; they are not a diagnosis, and a doctor or genetic counsellor is the person to ask about symptoms.

Where this comes from

The Human Phenotype Ontology, release 2026-09-01: the traits linked to PAH and how often each is seen. Find out more at hpo.jax.org.

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