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Major physical traits and behaviors
  • Characteristic facial appearance (may be subtle)
  • Low muscle tone (hypotonia)
  • Oral-sensory motor dysfunction
    • Poor suck/swallow
    • Decreased tongue strength and movement
    • Open mouth posture
    • Frequent drooling
    • Possible aversion to certain textures
  • Below normal or absent reflexes
  • Peripheral neuropathy (weakness, numbness, and pain typically in hands and feet)
  • Distinct, broad-based gait (walking pattern)
  • Decreased sensitivity to pain
  • Short stature
  • Small hands and feet
    • Markedly flat or highly arched feet
  • Abnormalities of the larynx
    • Polyps
    • Nodules
    • Edema
    • Partial vocal cord paralysis
    • Horse deep voice
    • Hypernasal speech
    • Velopharyngeal insufficiency (impoper closing in the soft palate) and/or structural vocal fold abnormalities
  • Middle ear abnormalities
    • Hearing loss
      • Ear infections can lead to conductive hearing loss 
      •  Hyperacusis (oversensitivity to certain frequencies and sounds) is common
  • Missing teeth
  • Major developmental and behavioral features (>75% of affected individuals)
Children with SMS may have some or many of the following:
  • Positive behavior
    • Endearing/appealing personalities
    • Excellent long term memory for names, places, events
    • Great sense of humor
  • Developmental delay and variable intellectual disability (usually mild to moderate)
  • Tendancy to mouth objects or hands. This may persist beyond early childhood.
  • Speech delay and articulation problems
  • Autism or autistic-like features
  • Sensory integration issues
  • Tendancy to grind teeth
  • Delayed toileting skills
  • Challenging behaviors
    • Hyperactivity
    • Impulsivity
    • Attention seeking (especially from adults)
    • Easy excitability or distractibility
    • Sudden mood shifts
    • Explosive outbursts
    • Prolonged tantrums
    • Aggressive or destructive behavior
  • Chronic sleep disturbances 
    • Frequent nighttime awakenings
    • Increased daytime sleepiness/naps
    • Early morning waking times (5:30 a.m. - 6:30 a.m.)
  • Other stereotypic or repetitive behaviors include:
    • Arm hugging/hand squeezing when excited
    • “Lick and flip” behavior (compulsively lick their fingers and flip through pages)
  • Self-injurious behaviors
    • Head banging
    • Hand biting
    • Picking at skin, sores, and nails
    • Pulling off fingernails and toenails
    • Inserting foreign object into ears, nose, or other body orifices.
Less common (present in 25-50% of those with SMS) traits
  • Congenital heart defects
  • Scoliosis (curvature of the spine)
  • Eye problem
    • Strabismus
    • Nearsightedness
    • Small cornea
    • Iris anomalies
  • Constipation
  • High cholesterol and high triglycerides
  • Abnormal EEG without seizures
  • Thyroid function abnormalities
  • Immune function abnormalities
Occasional traits
  • Kidney differences
  • Cleft lip/palate
  • Forearm differences
  • Retinal detachment