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47,XYY Syndrome

By Nina N. Powell-Hamilton, MD, Clinical Assistant Professor of Pediatrics ;Medical Geneticist, Sidney Kimmel Medical College at Thomas Jefferson University;Nemours/Alfred I. duPont Hospital for Children

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47,XYY syndrome is two Y chromosomes and one X, resulting in a phenotypic male.

The 47,XYY syndrome occurs in about 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.