47,XYY syndrome is the presence of two Y chromosomes and one X chromosome in a phenotypic male.
(See also Overview of Chromosomal Anomalies and see Overview of Sex Chromosome Anomalies.)
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.
