Traits

Traits linked to GAMT

guanidinoacetate N-methyltransferase

The Human Phenotype Ontology links 43 traits to GAMT, 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
Delayed speech and language development	Always
Elevated brain guanidinoacetate level by MRS	Always
Intellectual disability, severe	Always
Severe global developmental delay	Always
Epilepsy	Very often (80–99%)
Abnormality of extrapyramidal motor function	Often (30–79%)
Abnormality of movement	Often (30–79%)
Absent speech development	Often (30–79%)
Aggressive behavior	Often (30–79%)
Ataxia	Often (30–79%)
Behavioral abnormality	Often (30–79%)
Poor speech	Often (30–79%)
Progressive extrapyramidal movement disorder	Often (30–79%)
Sudden loss of muscle tone	Often (30–79%)
Abnormal head movements	Sometimes (5–29%)
Autism	Sometimes (5–29%)
Chorea	Sometimes (5–29%)
Dystonia	Sometimes (5–29%)
Febrile seizure (within the age range of 3 months to 6 years)	Sometimes (5–29%)
Focal impaired awareness seizure	Sometimes (5–29%)
Generalized myoclonic seizure	Sometimes (5–29%)
Grand mal seizures	Sometimes (5–29%)
Involuntary writhing movements in fingers, hands, toes, and feet	Sometimes (5–29%)
Loss of developmental milestones	Sometimes (5–29%)
More active than typical	Sometimes (5–29%)
Partial paralysis of legs	Sometimes (5–29%)
Self-injurious behavior	Sometimes (5–29%)
Tremor	Sometimes (5–29%)
Global developmental delay	Not recorded
Increased reflexes	Not recorded
Intellectual disability	Not recorded
Jerking	Not recorded
Reduced brain creatine level by MRS	Not recorded

Abnormality of the musculoskeletal system

Trait	How often it is seen
Low muscle tone	Always
Rigidity	Often (30–79%)
Spasticity and rigidity of muscles	Often (30–79%)
Lower limb spasticity	Sometimes (5–29%)
Decreased muscle tone in infant	Not recorded

Laboratory abnormality

Trait	How often it is seen
Decreased serum creatinine	Always
Elevated circulating guanidinoacetic acid concentration	Always
Reduced tissue guanidinoacetate methyltransferase activity	Always
Decreased urinary creatine level	Not recorded

Abnormality of the digestive system

Trait	How often it is seen
Episodic vomiting	Sometimes (5–29%)

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 GAMT and how often each is seen. Find out more at hpo.jax.org.

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