Traits

Traits linked to SMS

spermine synthase

The Human Phenotype Ontology links 91 traits to SMS, by body system: features seen in people with one of the gene's rare conditions.

Abnormality of head or neck

Trait	How often it is seen
Broad head shape	Always
Bulbous nose	Always
Dental crowding	Always
Facial asymmetry	Always
Full lower lip	Always
High, narrow palate	Always
Increased thickness of skull cap	Always
Monobrow	Always
Nasal tip, upturned	Always
Prominent nasal bridge	Always
Smooth philtrum	Always
Sparse eyebrow	Always
Webbed neck	Always
Cleft palate	Often (30–79%)
Long face	Often (30–79%)
Narrow face	Often (30–79%)
Short neck	Often (30–79%)
Abnormal facial shape	Sometimes (5–29%)
High palate	Sometimes (5–29%)
Narrow mouth	Sometimes (5–29%)
Upward slanting of the opening between the eyelids	Sometimes (5–29%)
Big lower jaw	Rarely (1–4%)
Drooping lower lip	Rarely (1–4%)
Short philtrum	Rarely (1–4%)
Bifid uvula	Not recorded

Abnormality of the nervous system

Trait	How often it is seen
Global developmental delay	Always
Intellectual disability	Always
Unsteady walk	Often (30–79%)
Absent speech development	Sometimes (5–29%)
Delayed speech and language development	Sometimes (5–29%)
EEG abnormality	Sometimes (5–29%)
Focal motor seizure	Sometimes (5–29%)
Generalized myoclonic seizure	Sometimes (5–29%)
Inability to walk	Sometimes (5–29%)
Intellectual disability, mild	Sometimes (5–29%)
Involuntary movements	Sometimes (5–29%)
Jerking	Sometimes (5–29%)
Enlarged brain	Rarely (1–4%)
IQ less than 20	Rarely (1–4%)
Difficulty articulating speech	Not recorded
Epilepsy	Not recorded
Wide based walk	Not recorded

Abnormality of the musculoskeletal system

Trait	How often it is seen
Funnel chest	Always
Scoliosis	Always
Thin bony cortex	Always
Kyphoscoliosis	Very often (80–99%)
Compression fracture of a vertebral body	Often (30–79%)
Decreased muscle mass	Often (30–79%)
Decreased muscle tone in infant	Often (30–79%)
Hunched back	Often (30–79%)
Osteoporosis	Often (30–79%)
Recurrent fractures	Often (30–79%)
Difficulty in standing	Sometimes (5–29%)
Permanent flexion of the finger or toe	Rarely (1–4%)
Pigeon chest	Rarely (1–4%)
Generalized decreased muscle tone	Not recorded
Low muscle tone	Not recorded

Abnormality of limbs

Trait	How often it is seen
Long big toe	Always
Long slender fingers	Often (30–79%)
Long toe	Often (30–79%)
Single transverse palmar crease	Often (30–79%)
Slender toe	Often (30–79%)
Club feet	Not recorded
Finger joint hyperextensibility	Not recorded
Long fingers	Not recorded
Long palm	Not recorded
Narrow palm	Not recorded

Abnormality of the ear

Trait	How often it is seen
Asymmetric ears	Sometimes (5–29%)
Low-set ears	Sometimes (5–29%)
Cupped ear	Rarely (1–4%)
Small earlobe	Rarely (1–4%)
Thickened helices	Rarely (1–4%)
Abnormally shaped ears	Not recorded

Abnormality of the eye

Trait	How often it is seen
Drooping upper eyelid	Always
Dropping of one upper eyelid	Sometimes (5–29%)
Wide-set eyes	Sometimes (5–29%)
Bulging eye	Rarely (1–4%)
Severe near sightedness	Rarely (1–4%)

Abnormality of the genitourinary system

Trait	How often it is seen
Hypospadias	Sometimes (5–29%)
Testicular degeneration	Sometimes (5–29%)
Undescended testes	Sometimes (5–29%)
Abnormal kidney location	Rarely (1–4%)
Abnormality of the Leydig cells	Rarely (1–4%)

Growth abnormality

Trait	How often it is seen
Disproportionate tall stature	Often (30–79%)
Short stature	Rarely (1–4%)
Tall stature	Not recorded

Abnormality of the voice

Trait	How often it is seen
Hoarse voice	Always
Nasal speech	Often (30–79%)

Abnormality of the breast

Trait	How often it is seen
Wide-spaced nipples	Always

Abnormality of the integument

Trait	How often it is seen
Patchy hypo- and hyperpigmentation	Sometimes (5–29%)

Laboratory abnormality

Trait	How often it is seen
Brain swelling	Rarely (1–4%)

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

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