One of the goals of AXYS is to encourage families to become aware of the developmental, medical and psychosocial issues that may accompany 47,XYY. The condition affects about 1 in 1,000 males. One in 34 require testosterone treatment, which affects their fertility. Adding to its relative rarity, it is diagnosed in only about 10 percent of cases, often during prenatal testing.

Many boys and men with 47,XYY have no symptoms at all. Others can demonstrate significant developmental and behavioral issues. Approximately 30 percent of affected boys have mild autism, but nearly all develop functional language skills.

47,XYY is sometimes referred to as “Jacob’s syndrome.”

XYY Symptoms

47,XYY may produce a wide array of symptoms, although most people with the extra Y chromosome it entails will exhibit only some, but not all, of the following:

  • Tall stature
  • Low muscle tone
  • Speech delay/expressive language disorder
  • Subtle developmental delays
  • Autism
  • Learning disability
  • Attention deficits
  • Depression/anxiety

The Case for Testing

When children show a history of symptoms such as speech delay, learning disability, or autism, parents should strongly consider genetic testing to determine if the cause is a sex chromosome aneuploidy (SCA). Testing for 47,XYY involves a specialized blood test, either a “karyotyping” or a “microarray.” Health care professionals, including physicians, are often unfamiliar with the developmental and cognitive deficits associated with SCAs. They often associate genetic syndromes with dysmorphia (characteristic facial or body features) or with intellectual disability, and fail to suggest genetic testing.

Dispelling Myths

Similar myths to those associated with XXY/Klinefelter syndrome also circulate about those with XYY, including the identical myth that it is linked to increased criminality. This is the result of scientifically disproven studies completed in the early 1960s within prison populations, which were biased and unrepresentative of XYY adults. Other myths claim XYY results in a “super male” withtoo much testosterone, making him aggressive and violent. There is no truth to these claims, although some affected boys and men may be impulsive due to attention deficits.

Frequently Asked Questions about 47,XYY (Scroll to section partway down the page)

Downloadable Brochure- About 47,XYY
Trifold brochure printing instructions: Be sure you are printing in two-sided (duplex) mode, and to select the “Flip on Short Edge” or “Short-Edge Binding” option, if available in the Print dialog box or any associated dialog boxes.

Living with Klinefelter Syndrome (47,XXY) Trisomy X (47, XXX) and 47, XYY: A Guide for Families and Individuals Affected by Extra X and Y Chromosome Variations

Thanks to the generosity of the book’s author, Virginia Isaac’s Cover, MSW, AXYS is pleased to make this book available to the X and Y variation community, in its entirety, at no cost. Please feel free to download and/or print it for your personal use. (Those wishing to purchase a soft-bound copy can do so at Amazon or Kindle. All proceeds from the sale of this book benefit AXYS.)

Spanish: “A Guide for Families and Individuals Affected by X and Y Chromosome Variations”

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