Traits

Traits linked to SLC6A8

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The Human Phenotype Ontology links 58 traits to SLC6A8, 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	Always
Intellectual disability	Always
Reduced brain creatine level by MRS	Always
Delayed speech and language development	Very often (80–99%)
Epilepsy	Very often (80–99%)
Ataxia	Often (30–79%)
Autism spectrum disorder	Often (30–79%)
Chorea	Often (30–79%)
Dystonia	Often (30–79%)
Involuntary writhing movements in fingers, hands, toes, and feet	Often (30–79%)
More active than typical	Often (30–79%)
Self-mutilation	Often (30–79%)
Speech apraxia	Often (30–79%)
Wide based walk	Often (30–79%)
Abnormal gait	Not recorded
Aggressive behavior	Not recorded
Attention deficit	Not recorded
Delayed myelination	Not recorded
Motor delay	Not recorded
Poor hand-eye coordination	Not recorded
Poor social interactions	Not recorded
Repetitive movements	Not recorded
Underdevelopment of part of brain called corpus callosum	Not recorded

Abnormality of head or neck

Trait	How often it is seen
Abnormally small head	Often (30–79%)
Open mouth	Often (30–79%)
Zygomatic flattening	Often (30–79%)
Expressionless face	Sometimes (5–29%)
Big lower jaw	Not recorded
Broad forehead	Not recorded
Long face	Not recorded
Midface retrusion	Not recorded
Myopathic facies	Not recorded
Narrow face	Not recorded

Abnormality of the musculoskeletal system

Trait	How often it is seen
Low muscle tone	Often (30–79%)
Low muscle tone in trunk	Often (30–79%)
Spasticity and rigidity of muscles	Often (30–79%)
Double-Jointed	Sometimes (5–29%)
Involuntary muscle stiffness, contraction, or spasm	Not recorded
Low muscle tone, in neonatal onset	Not recorded

Abnormality of the digestive system

Trait	How often it is seen
Constipation	Often (30–79%)
Enlarged colon lacking nerve cells	Often (30–79%)
Ileus	Often (30–79%)
Feeding difficulties in infancy	Not recorded
Vomiting	Not recorded

Growth abnormality

Trait	How often it is seen
Faltering weight	Often (30–79%)
Short stature	Often (30–79%)
Wasting syndrome	Often (30–79%)
Tall stature	Not recorded

Abnormality of the eye

Trait	How often it is seen
Drooping upper eyelid	Sometimes (5–29%)
Farsightedness	Not recorded
Outward facing eye ball	Not recorded

Laboratory abnormality

Trait	How often it is seen
Elevated circulating creatine concentration	Always
Abnormality of creatine metabolism	Very often (80–99%)
Elevated urinary creatine/creatinine ratio	Not recorded

Abnormality of limbs

Trait	How often it is seen
High-arched foot	Not recorded

Abnormality of the cardiovascular system

Trait	How often it is seen
Prolonged QT interval	Often (30–79%)

Abnormality of the ear

Trait	How often it is seen
Underfolded superior helices	Not recorded

Abnormality of the integument

Trait	How often it is seen
Loose redundant skin	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 SLC6A8 and how often each is seen. Find out more at hpo.jax.org.

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