GTR Home > Conditions/Phenotypes > Smith-Magenis syndrome

Disease characteristics

Excerpted from the GeneReview: Smith-Magenis Syndrome
Smith-Magenis syndrome (SMS) is characterized by distinctive physical features (particularly facial features that progress with age), developmental delay, cognitive impairment, and behavioral abnormalities. Infants have feeding difficulties, failure to thrive, hypotonia, hyporeflexia, prolonged napping or need to be awakened for feeds, and generalized lethargy. The majority of individuals function in the mild-to-moderate range of intellectual disability. The behavioral phenotype, including significant sleep disturbance, stereotypies, and maladaptive and self-injurious behaviors, is generally not recognized until age 18 months or older and continues to change until adulthood. Sensory integration issues are frequently noted. Children and adults typically have inattention, distractibility, hyperactivity, impulsivity, maladaptive behaviors including frequent outbursts/temper tantrums, attention seeking, disobedience, aggression, toileting difficulties, and self-injurious behaviors (SIB) including self-hitting, self-biting, and/or skin picking, inserting foreign objects into body orifices (polyembolokoilamania), and yanking fingernails and/or toenails (onychotillomania). Among the stereotypic behaviors described, the spasmodic upper-body squeeze or "self-hug" seems to be highly associated with SMS. The finger lick and page flipping ("lick and flip") behavior may be less prevalent than initially reported. An underlying developmental asynchrony, specifically between intellectual functioning and emotional maturity, may also contribute to maladaptive behaviors in people with SMS.

Associated genes

Clinical features

  • Hypertriglyceridemia
  • Precocious puberty
  • Strabismus
  • EEG abnormalities
  • Hyporeflexia
  • Areflexia
  • Short stature
  • Abnormality of the genital system
  • Hypercholesterolemia
  • Impaired pain sensation
  • Gait disturbance
  • Abnormality of the ureter
  • Intellectual disability
  • Microcephaly
  • Prenatal movement abnormality
  • Midface retrusion
  • Anteverted nares
  • Broad forehead
  • Cognitive impairment
  • Renal hypoplasia/aplasia
  • Open mouth
  • Generalized hypotonia
  • Malar flattening
  • Broad face
  • Short philtrum
  • Micrognathia
  • Seizure
  • Constipation
  • Obesity
  • Retinal detachment
  • Cleft palate
  • Self-mutilation
  • Large face
  • Hypothyroidism
  • Synophrys
  • Abnormality of the tongue
  • Cleft upper lip
  • Velopharyngeal insufficiency
  • Brachycephaly
  • Mandibular prognathia
  • Hypertelorism
  • Abnormality of the outer ear
  • Otitis media
  • Conductive hearing impairment
  • Wide nasal bridge
  • Microcornea
  • Deeply set eye
  • Myopia
  • Upslanted palpebral fissure
  • Taurodontia
  • Stereotypic behavior
  • Delayed speech and language development
  • Brachydactyly syndrome
  • Hand polydactyly
  • Broad palm
  • Global developmental delay
  • Limitation of joint mobility
  • Abnormality of the larynx
  • Hoarse voice
  • Pes planus
  • Toe syndactyly
  • Frontal bossing
  • Ventriculomegaly
  • Neurological speech impairment
  • Sleep disturbance
  • Malformation of the heart and great vessels
  • Scoliosis
  • Abnormality of the immune system
  • Abnormality of the forearm
  • Short nose
  • Abnormal form of the vertebral bodies
  • Clinodactyly of the 5th finger
  • Short palm
  • Depressed nasal bridge
  • Abnormality of the tracheobronchial system
  • Attention deficit hyperactivity disorder
  • Aplasia/Hypoplasia of the corpus callosum
  • Morphological abnormality of the middle ear
  • Reduced number of teeth
  • Hyperacusis
  • Everted upper lip vermilion
  • Tented upper lip vermilion
  • Abnormal localization of kidney
  • Head-banging
  • Abnormal renal morphology
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