XYY Syndrome


XYY syndrome is a genetic condition in which males have 47 chromosomes instead of the usual 46 chromosomes. The karyotype is written as 47,XYY as these males have an extra Y chromosome. XYY occurs in approximately one in 1000 live male births and falls into the category of sex chromosome aneuploidy. Males with XYY often have tall stature but otherwise are not significantly different in physical appearance compared to other men. They are generally healthy; however, some XYY men can have learning disabilities or behaviour problems. It is possible that the information we know about XYY syndrome in the medical literature may be biased, as healthy, developmentally normal males do not often have a reason to have a karyotype performed. We may overestimate some of the problems associated with XYY such as learning disabilities and behaviour problems, as these are common reasons for children to have a karyotype.

Key Concepts:

  • Males with XYY syndrome have 47 chromosomes, which includes an extra Y chromosome.

  • Males with XYY syndrome appear physically normal, however often have tall stature.

  • Males with XYY syndrome generally have normal intelligence, however some may have learning disabilities or behaviour issues.

  • Males with XYY syndrome do not have criminal tendencies as suggested in the older literature.

Keywords: XYY; aneuploidy; sex chromosome; tall stature; learning disability; attention deficit hyperactivity disorder

Figure 1.

In XYY, the karyotype (chromosome count) is 47,XYY. This means that each of the somatic cells contains 47 chromosomes, 22 normal pairs of autosomes, and three sex chromosomes, one X chromosome and two Y chromosomes. Figure Courtesy of A. J. Dawson.



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Further Reading

Rimoin DL, Connor JM and Pyeritz RE (2006) Emery and Rimoin's Principles and Practice of Medical Genetics, 5th edn. New York: Churchill Livingstone.

Web Links

National Organization for Rare Disorders (NORD) http://www.rarediseases.org/

Unique – Rare Chromosome Disorder Support Group http://www.rarechromo.org http://www.rarechromo.org/files/XYYStudyDayReport.pdf

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How to Cite close
Goobie, Sharan, and Prasad, Chitra(Jul 2012) XYY Syndrome. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0005157.pub2]