XYY syndrome

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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 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 centimeters 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. There have been suggestions of elevated frequency of XYY genotype in inmates and delinquents. A common myth is that the Y Chromosome (male sex chromosome) adds to the aggression and antisocial behavior of people who have this syndrome. No clear evidence exists of it leading to aggression, however scientists have noticed that some prison inmates have the XYY chromosome.

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.