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What is 18q: A Sixty-Second Summary

(Aliases: 18q deletion syndrome, partial monosomy 18q, de Grouchy Syndrome, chromosome 18 long-arm deletion syndrome)
ICD-10 = Q99.9 or Q93.89

Key points on genotype

  • Every patient has a unique deletion; thus 18q- is not a single “syndrome.” (For guidance developing an individualized  gene-based interpretation see subsequent pages.)
  • Some genotype-phenotype correlations have been established and are explored more in the following pages.
  • ~19% are interstitial deletions
  • ~8% with terminal deletions have  duplications just proximal to the breakpoint of up to 15 Mb in size
  • 94% are de novo events as opposed to inherited from a parent with a translocation.
  • Occurs in 1 out of  55,000 live births

Key Points on phenotype

  • Multiple congenital anomalies are possible. Specific phenotypes are dependent on the specific genes deleted  – see the section of this report on molecular implications.
  • Developmental milestones are  always delayed  but with considerable variability
  • Intellectual disability is common but not inevitable
  • Failure to thrive and growth hormone deficiency are common
  • The risk for autism spectrum is higher than average
  • Life expectancy is believed to be near normal except for individuals whose deletion includes TCF4.
  • Deletions that include the TCF4 gene (at band q21.2; or at 52.9 Mb) result in a much more severe phenotype, making it important to  determine if someone’s deletion includes this gene.


  • Affected individuals  are not at increased risk for adverse reactions to drugs or standard medical treatments
  • Treatment is primarily symptomatic
  • Recommendations for specific evaluations  and treatments are in the following sections


  • The Chromosome 18 Clinical Research Center is enrolling anyone with any chromosome 18 abnormality in our longitudinal study of all aspects of the conditions.
  • Parents need to contact Annice Hill at or call (210) 567-5321
  • We need the diagnostic genetics report and any other informative medical records
  • Then we will schedule a blood draw and shipment


  • Daniel Hale, MD, Medical Director of the Chromosome 18 Clinical Research Center can be reached through Annice Hill at or call (210) 567-5321.

Updated 2020