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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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Your Question

What are some of the signs or symptoms associated with trisomy 18p? What are some of the behavioural characteristics of this syndrome if any? What are some treatment options for an adolescent with this syndrome, ASD (autism spectrum disorder), and no intellectual disability displaying challenging behaviours?

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

What is trisomy 18p?

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

What are signs and symptoms seen in trisomy 18p?

According to Rodríguez (2007) et al., all the cases of trisomy 18p show a noncharacteristic facial appearance and a mental development ranging from normal to moderate impairment.[2]

Examples of Cases:

  • Taylor et al. (1975) - female with no physical or mental abnormalities
  • Takeda et al. (1989) - female without mental retardation
  • Wolff et al. (1991) - mother and daughter were of normal intelligence and had a short pinky finger on both of their hands
  • Moog et al. (1994) - mother and son; mother had developmental delay and learning disabilities and son had moderate mental retardation and slight craniofacial anomalies
  • Li et al. (1998) - male with developmental delay, hypotonia (low muscle tone) and minor physical abnormalities

Some have suggested that several of the cases of trisomy 18p reported in the medical literature of people with signs and symptoms represent cases in which other chromosomal abnormalities not yet identified may explain the signs and symptoms present, suggesting that pure trisomy 18p results in little, if any, signs and symptoms.[1][3] As more advanced techniques for identifying chromosomal abnormalities become available, we will learn more about the signs and symptoms associated with trisomy 18p. It is possible that some cases of trisomy 18p are being missed because they do not have any signs and symptoms and are of normal intelligence.[1]  

Last updated: 7/16/2009

What behaviors might be observed in people with trisomy 18p?

Because of the limited data published on trisomy 18p, we were unable to locate information that discusses behaviors which might be observed in patients diagnosed with trisomy 18p. If you are interested in learning more about behaviors that might be seen in people with trisomy 18p, we recommend you contact the advocacy organizations located in the "Support Groups" section of the GARD resource Web page on trisomy 18, specifically the groups listed under "Disease-Specific Organizations", as these groups have families of people with trisomy 18p registered with them. The members of these advocacy groups might be able to share information regarding behaviors present in their family members; Click here to view these groups.
Last updated: 7/16/2009

What treatment is available for trisomy 18p?

Because the presence and severity of signs and symptoms vary from person to person, treatment will also vary. It is important to work with the person's health care provider to determine the appropriate medical management plan.
Last updated: 7/16/2009

What resources are available to people with autism spectrum disorders (ASD)?

To locate supportive resources for people with autism spectrum disorders, you can click on the Support Groups tab above or access this inforamtion by clicking here.
Last updated: 10/19/2011

  • 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;
  • 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;
  • Schinzel A. Catalogue of Unbalanced Chromosome Aberrations in Man. New York: Walter de Gruyter; 2001;