47,XYY Syndrome

ByNina N. Powell-Hamilton, MD, Sidney Kimmel Medical College at Thomas Jefferson University
Reviewed/Revised Oct 2023
View Patient Education

    47,XYY syndrome is the presence of two Y chromosomes and one X chromosome in a phenotypic male.

    (See also Overview of Chromosomal Abnormalities and see Overview of Sex Chromosome Abnormalities.)

    The 47,XYY syndrome occurs in approximately 1/1000 live male births.

    Affected boys tend to be taller than average and have a 10- to 15-point IQ reduction compared with family members. There are few physical problems. Minor behavior disorders, hyperactivity, attention-deficit disorder, and learning disorders are more common.

    XYY syndrome was once thought to cause aggressive or violent criminal behavior, but this theory has been disproved.

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