SSBP Information Sheet
XYY syndrome

Incidence/prevalence
About 1 in 1,000 live male births.

Genetics
Primary non-disjunction of the Y chromosome. About 10% have mosaic 46,XY/47,XYY chromosome complement. Offspring rarely have two Y chromosomes.

Physical phenotype
Increase in body and leg length between years 4 and 9. Most are over 10cm taller than their fathers, as adults. Sexual development and fertility are unaffected. Balance and coordination may be minimally compromised.

Life expectancy
Normal.

Behavioural characteristics
Distractibility, hyperactivity and temper tantrums appear relatively common in childhood.

Cognitive characteristics
Speech and language problems are common. Overactivity and distractibility may lead to educational problems. IQ is usually lower than siblings’ IQ, but only just below population means.

www.rarechromo.org

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