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Genetic and Rare Diseases Information Center (GARD)

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Chromosome 18p duplication

Other Names for this Disease
  • 18p duplication
  • 18p trisomy
  • Duplication 18p
  • Partial trisomy 18p
  • Trisomy 18p
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Trisomy 18p is a rare chromosomal abnormality in which there are three copies of the p arm of chromosome 18 in each cell, rather than the usual two copies. As a quick review, chromosomes are structures that hold our DNA. Our DNA contains the instructions, called genes, which tell our bodies how to develop and function. Each chromosome has a constriction, called the "centromere", at one point along its length dividing it into a shorter arm which is called the p (petite) arm and a longer arm, called the q arm. We have two copies of each chromosome, one copy inherited from our mother and the other copy from our father. Therefore, people typically have two copies of chromosome 18, one from mom and one from dad, and thus two copies of the p arm of chromosome 18. (Click here to read more about chromosomes.) 

Trisomy 18p has rarely been reported. According to Mabboux et al. (2007) only 21 cases have been documented in the medical literature.[1] The signs and symptoms vary greatly from person to person and is characterized by mental retardation, foot or hand anomalies and craniofacial anomalies. Treatment is based on the specific findings present.[1]

Last updated: 7/16/2009


  1. Mabboux P, Brisset S, Aboura A, Pineau D, Kourbi V, Joannidis S et al. Pure and Complete Trisomy 18p Due to a Supernumerary Marker Chromosome Associated with Moderate Mental Retardation. American Journal of Medical Genetics Part A. 2007;
  2. Rodríguez L, Liehr T, Mrasek K, Mansilla E, Martínez-Fernández ML, Garcia A, Martínez-Frías ML. Small Supernumerary Chromosome Marker Generating Complete and Pure Trisomy 18p, Characterized by Molecular Cytogenetic Techniques and Review. American Journal of Medical Genetics Part A. 2007;
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Basic Information

  • The National Human Genome Research Institute, part of the National Institutes of Health (NIH), has developed a fact sheet on chromosome abnormalities, which may be helpful to you. To read this information, visit the link.

    MedlinePlus, the National Library of Medicine Web site designed to direct you to information and resources that help you research your health questions, provides further information about chromosomes. Click on the link.
  • Genetics Home Reference (GHR) contains information on Chromosome 18p duplication. This website is maintained by the National Library of Medicine.

In Depth Information

  • Orphanet is a European reference portal for information on rare diseases and orphan drugs.  Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Chromosome 18p duplication. Click on the link to view a sample search on this topic.