Genetics Northern California

XYY Syndrome

What is XYY syndrome?
How common is XYY?
What causes XYY?
How is XYY diagnosed?
Can XYY be diagnosed during pregnancy?
How is XYY treated?
Where can I get more information about XYY?

What is XYY syndrome?
XYY syndrome (XYY) is a genetic condition in males that may include taller height, a slightly larger head size, and lower muscle tone. However, the features in this condition tend to fall in the normal range for males, so most individuals with XYY are not diagnosed.

Medical concerns in XYY
It is unclear if there are special medical concerns in individuals with XYY. Some studies suggest there could be a slightly higher rate of seizures and tremors.   

Learning and behavior in XYY
Most children with XYY have IQ scores that fall in the average range or slightly below average, but there is a wide range of learning abilities. Some children have delays in language development or reading skills. Behavior concerns may include attention problems and hyperactivity (ADHD), autism, and difficulty with social skills. 

How common is XYY?
It is estimated that one in every 1000 newborn boys has XYY.

47,XYYWhat causes XYY?
XYY syndrome is caused by an extra chromosome. Individuals with XYY have one X chromosomes and two Y chromosomes, instead of the usual pair of male sex chromosomes (one X and one Y). This chromosome arrangement is called 47,XYY.  XYY happens as a random event when a sperm is being formed and is not inherited.

How is XYY diagnosed?
The diagnosis is usually made by a blood test that shows an extra Y chromosome in a male. XYY is rarely diagnosed at birth since babies with this condition look like other babies. Chromosome testing may be offered for children with learning delays or autistic behaviors.   

Can XYY be diagnosed during pregnancy?
XYY can be diagnosed during pregnancy by testing a DNA sample from the developing baby. The sample can be obtained either by a chorionic villus sampling (CVS) or amniocentesis procedure.

One prenatal screening test, NIPT, can identify pregnancies that have a higher chance for XYY. More testing is needed to confirm the diagnosis.

How is XYY treated?
Health care for individuals with XYY is based on symptoms. Some children with XYY may benefit from early intervention programs to support learning. Medication may be considered for attention problems. 

Where can I get more information about XYY syndrome?
Genetics Home Reference: XYY syndrome - General information about XYY provided as a service of the U.S. National Library of Health. Links to related sites are included on the page.

The Association for X and Y Chromosome Variations (AXYS) – National support organization for those affected by one or more extra sex chromosome.

Last updated: January 17, 2018
Reviewed by: Kimberly Barr, LCGC