XYY Syndrome - Society for the Study of Behavioural Phenotypes

XYY Syndrome
First description and alternative names:
XYY syndrome (47, XYY); YY Syndrome; Jacob's syndrome. The first case of XYY syndrome was
reported as an incidental finding by Adam Sandberg and colleagues in 1961.
Genetics and molecular biology:
The majority of cases of XYY syndrome are due to a paternal non-disjunction during meiosis II,
following a normal meiosis I; a few cases resulting in an additional Y chromosome. In some cases it
arises during early embryogenesis in a post-zygotic mitotic error, in which case it can result in a
46,XY/47,XYY mosaic form (Robinson & Jacobs, 1999).
Incidence/prevalence:
The prevalence of 47,XXY is currently estimated at approximately 1/1000 males. As it is typically
not associated with marked phenotypic characteristics it is frequently undetected.
Physical features and natural history:
Physical phenotypic differences associated with XYY syndrome are usually mild. Boys have
increased growth velocity during childhood, and adult height is usually increased approximately 7cm
above what is expected. Puberty, testicular function and fertility are usually normal.
Behavioural and psychiatric characteristics:
Individuals with XYY syndrome are at increased risk for behavioural problems and psychiatric
disorders. There is a high rate of diagnosis of Attention Deficit Disorder, and increased risk of
problems with distractibility, impulsivity and difficulties with temper management. Problems with
social relatedness are also common. Individuals with XYY have been reported as having increased
scores on measures of autistic spectrum symptoms, although these were within clinically referred
populations and may not be indicative of individuals with XYY syndrome overall.
Neuropsychological characteristics:
XYY syndrome is usually associated with normal to slightly diminished cognitive function as
measured with IQ; verbal IQ may be more affected than performance IQ. Speech delay is common
and many boys require speech therapy and special education. Reading may be particularly affected.
Delayed motor development and impaired fine and gross motor function have been reported.
Educational performance may be more adversely affected than what would be expected based on IQ
measures alone. Difficulties with attention and impulse control are frequently reported.
Available guidelines for behavioural assessment/treatment/management:
Formal guidelines are not currently available. Current recommendations usually include
neuropsychological assessment and early intervention for learning disorders or behavioral
problems.
Useful websites/associations for more information
• KS & A (Knowledge, Support and Action), www.genetic.org
• www.rarechromo.org
SOCIETY FOR THE STUDY OF
BEHAVIOURAL PHENOTYPES
An International Organisation
The SSBP is a Registered Charity: Charity No:1013849

References
1. Aksglaede L., Skakkebaek N. , & Juul A. (2008) Abnormal sex chromosome constitution and longitudinal growth:
Serum levels of insulin-like growth factor (IGF)-1, IGF binding protein-3, luteinizing hormone, and testosterone in 109
males with 47,XXY, 47,XYY, or sex-determining region of the y chromosome (SRY)-positive 46,XX karyotypes. J Clin
Endocrin Metab 93,169-176.
2. Geerts M., Steyaert J., Fryns J. (2003) The XYY syndrome: a follow-up study on 38 boys. Genet Counsel 14, 267-
279.
3. Leggett V., Jacobs P., Nation K., et al. (2010) Neurocognitive outcomes of individuals with a sex chromosome
trisomy: XXX, XYY, or XXY: a systematic review. Dev Med Child Neurol 52, 119-129.
4. Robinson D.O., & Jacobs P.A. (1999) The origin of the extra Y chromosome in males with a 47, XYY karyotype. Hum
Mol Genet 8(12), 2205-9.
5. Ross J., Zeger M., Kushner H., et al. (2009) An extra X or Y chromosome: contrasting the cognitive and motor
phenotypes in childhood in boys with 47,XYY syndrome or 47,XXY Klinefelter Syndrome. Dev Disabil Res Rev 15,
309-317.
6. Visootsak J., Graham J. (2009) Social function in multiple X and Y chromosome disorders: XXY, XYY, XXYY,
XXXY. Dev Disabil Res Rev 15, 328-332.
Rhoshel K Lenroot, 2010