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XYY syndrome is a aneuploidy of the sex chromosomes in which a human male receives an extra Y chromosome in each cell, hence having a karyotype of 47,XYY. XYY syndrome is also called Jacob’s Syndrome, XYY-trisomy, 47,XYY aneuploidy, or Supermale syndrome.

First case

The first published 4% incidence, report of a man with a 47,XYY chromosome constitution was by Dr. Avery A. Sandberg, et al. in 1961. It was an incidental finding in a normal 44-year-old, 6 ft. [183 cm] tall man of average intelligence.


Physical traits

XYY syndrome typically causes no unusual physical features or medical problems. Males with this syndrome may be slightly taller than average and are typically a few centimetres taller than their father and siblings.

Skeletal malformations may also accompany XYY syndrome at a higher rate than in the general population. Severe facial acne has occasionally been reported, but dermatologists specializing in acne (Plewig & Kligman, 2000) now doubt the existence of a relationship with XYY. Several other physical characteristics, including large hands and feet, have been associated (although not definitively) with XYY syndrome. Any physical characteristics, however, are usually so slight that they are insufficient evidence to suggest a diagnosis.

Most males with XYY syndrome have normal sexual development and are able to conceive children.

Since there are no distinct physical characteristics, the condition usually is only detected during genetic analysis for other reasons.

Behavioral characteristics

XYY boys have an increased risk of minor speech and motor skill delays and learning disabilities with roughly half requiring some special education intervention. Behavior problems are common, but are not unique to XYY boys and are managed no differently than in XY boys.

Cause and prevalence

XYY syndrome is not inherited, but usually occurs as a random event during the formation of sperm cells. An error in cell division called nondisjunction can result in sperm cells with an extra copy of the Y chromosome. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have an extra Y chromosome in each of the body’s cells. In some cases, the addition of an extra Y chromosome occurs as an accident during cell division in early fetal development.

The incidence of this condition is approximately one in 850 males.

See also


  • Public domain text from NLM Genetics Home Reference: 47,XYY syndrome.
  • Sandberg, A. A.; Koepf, G. F.; Ishihara, T.; Hauschka, T. S. (August 26, 1961) “An XYY human male“. Lancet 2, 488-9.
  • Milunsky, Jeff M. (2004). Prenatal Diagnosis of Sex Chromosome Abnormalities. In Milunsky, Aubrey (Ed.), Genetic Disorders and the Fetus : Diagnosis, Prevention, and Treatment (5th ed.), pp. 297-340. Baltimore: The Johns Hopkins University Press. ISBN 0801879280.
  • Allanson, Judith E.; Graham, Gail E. (2002). Sex chromosome abnormalities. In Rimoin, David L.; Connor, J. Michael.; Pyeritz, Reed E.; Korf, Bruce R. (Eds.), Emery and Rimoin’s
  • Principles and Practice of Medical Genetics (4th ed.), pp. 1184-1201. London: Churchill-Livingstone. ISBN 0443064342.
  • Plewig, Gerd; Kligman, Albert M. (2000). Acne and Rosacea (3rd ed.). Berlin: Springer-Verlag. ISBN 3540667512.

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