Smith-Magenis syndrome

Last revised by Daniel J Bell on 14 Jan 2019

Smith-Magenis Syndrome (SMS) is a rare genetic syndrome which results from an interstitial deletion in chromosome 17p11.2.

The condition is known by several other names which are all similar variants related to its underlying karyotype: 17p deletion syndrome17p11.2 monosomychromosome 17p deletion syndrome and partial monosomy 17p.

Smith-Magenis syndrome is an uncommon and rarely diagnosed condition with limited data available to accurately quantify incidence. The limited available data suggests an incidence in the region of 1:25,000 individuals 1. Globally over 100 cases of the condition have been described in the medical literature 1

Reported clinical manifestations of the syndrome include 1-3

  • intellectual disability
  • delayed speech
  • delayed language skills
  • sleep disturbance (reverse circadian rhythm)
  • behavioral problems
  • short stature
  • brachydactyly and more rarely polydactyly 
  • scoliosis
  • hoarse voice
  • facial features
    • square-shaped face 
    • deep-set eyes
    • mandibular prominence
    • buccal prominence
    • midface flattening  
    • dental abnormalities
  • cardiac defects (rare)
  • renal defects (rare) 

Fluorescence in situ hybridization (FISH) or a comparative genomic hybridization array can be used to confirm a clinically suspected diagnosis in approximately 95% of affected individuals. The remaining 5% may warrant sequencing analysis of the RAI1 gene 1

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