XYY syndrome is a rare chromosomal disorder that affects males. It is caused by the presence of an extra Y chromosome. Males normally have one X and one Y chromosome. However, individuals with this syndrome have one X and two Y chromosomes. Affected individuals are usually very tall. Many experience severe acne during adolescence. Additional symptoms may include learning disabilities and behavioral problems such as impulsivity. Intelligence is usually in the normal range, although IQ is on average 10-15 points lower than siblings.
In the past, there were many misconceptions about this disease. It was sometimes called the super-male disease because men with this syndrome were thought to be overly-aggressive and lacking in empathy. Recent studies have shown that this is not the case. Although individuals with XYY syndrome have an increased risk for learning disabilities and behavioral problems, they are not overly aggressive, nor are they at an increased risk of any serious mental illness. Because these boys are at a higher risk for having learning disabilities, they may benefit from speech therapy, tutoring, and general awareness of the specific issues they struggle with. Although the first years of school may be more challenging for boys with XYY syndrome, they generally go on to lead full, healthy, and normal lives.
Characteristics of XYY syndrome are often subtle and do not necessarily suggest a serious chromosomal disorder. Thus, males with this condition are often undiagnosed or misdiagnosed. The most common physical difference is increased height, which usually becomes apparent after the age of five or six, and results in an average height of about 6 feet, 3 inches by adulthood. Some individuals with XYY also develop severe cystic acne during adolescence. Fertility and sexual development are normal. Besides the potential for increased height, most affected individuals typically have a normal physical appearance (phenotype).
Boys with XYY syndrome typically have normal intelligence, although, on average, IQ is 10 to 15 points lower than siblings. Affected boys may exhibit mild delays in reaching developmental milestones. Learning disabilities have been reported in up to 50 percent of cases, most commonly speech delays and language problems. Reading difficulties are common due to an increased incidence of dyslexia.
In some cases, affected individuals develop behavioral problems such as an explosive temper, hyperactivity, impulsivity, defiant actions, or, in some cases, antisocial behavior. There is a higher rate of attention deficit and hyperactivity disorder and a smaller increased risk for having an autism spectrum disorder.
XYY syndrome is a rare chromosomal disorder caused by the presence of an extra Y chromosome. Normally, males have 46 chromosomes including one X and one Y chromosome. Males with XYY syndrome have 47 chromosomes, two of which are Y chromosomes. Most cases of XYY syndrome are due to a cell division error in the sperm prior to conception. Rarely, the cell division error occurs after conception resulting in a mosiac of cells with 46 chromosomes and 47 chromosomes. The exact cause for why these errors in cell division occur is not understood.
XYY syndrome is a rare chromosomal disorder present at birth that affects only males. It is estimated to occur in approximately one in 1,000 live births.
A diagnosis of XYY syndrome is made based upon a thorough clinical evaluation, a detailed patient history, and specialized tests (i.e., chromosomal analysis) that detect the presence of an extra Y chromosome (47,XYY karyotype).
A diagnosis of XYY syndrome may be made before birth (prenatally) through amniocentesis or chorionic villus sampling (CVS). During amniocentesis, a sample of fluid that surrounds the developing fetus is removed and analyzed, while CVS involves the removal of tissue samples from a portion of the placenta. Chromosomal studies performed on such fluid or tissue samples may reveal the presence of an extra Y chromosome.
Clinical Testing and Work-Up
Speech and language assessment should occur during the first 24 months. Reading assessment should occur by school age to rule out dyslexia. Behavioral assessment should be considered for children who are having difficulty with symptoms such as impulsivity, poor attention, or social skills.
Treatment of XYY syndrome is symptomatic and supportive. Speech therapy, occupational therapy, or assistance for learning disabilities in the school setting may be of benefit. In most cases, affected individuals are very responsive to early intervention and treatment, and problems may resolve altogether within a few years. Treatment of acne may help an affected individual's self-image. Attention deficit and hyperactivity disorder, difficulties with social interactions, or other behavioral problems can be treated with therapy or medication the same as in individuals who do not have XYY.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.
For information about clinical trials being conducted at the National Institutes of Health (NIH) in Bethesda, MD, contact the NIH Patient Recruitment Office:
Tollfree: (800) 411-1222
TTY: (866) 411-1010
For information about clinical trials sponsored by private sources, contact:
Contact for additional information about XYY syndrome:
Professor Rhoshel K. Lenroot, M.D.
Chair of Infant, Child, and Adolescent Psychiatry
University of New South Wales
Director of Child and Adolescent Mental Health Services
South Eastern Sydney Local Health District
Neuroscience Research Australia
Corner of Barker and Easy Streets
Randwick, Sydney NSW 2031
+61 2 9399 1089 (phone)
+61 4 3416 1044 (mobile)
+61 2 9399 1082 (fax)
Leggett V, Jacobs P, Nation K, et al. Neurocognitive outcomes of individuals with a sex chromosome trisomy: XXX, XYY, or XXY: a systematic review. Dev Med Child Neurol. 2010;52:119-129.
Ross J, Zeger M, Kushner H, et al. 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. 2009;15:209-317.
Visootsak J, Graham J. Social function in multiple X and Y chromosome disorders: XXY, XYY, XXYY, XXXY. Dev Disabil Res Rev. 2009;15:328-332.
Aksglaede L, Skakkebaek N, Juul A. 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 a 47,XXY, 47,XYY, or sex-determining region of the y chromosome (SRY)-positive 46,XX karyotypes. J Clin Endocrin Metab. 2008;93 (1):169-176.
Shi Q, Martin RH. Multicolor fluorescence in situ hybridization analysis of meiotic chromosome segregation in a 47,XYY male and a review of the literature. Am J Med Genet. 2000;93:40-6. Erratum in: Am J Med Genet. 2001;99:76.
47, XYY Syndrome, Genetics Home References. http://ghr.nlm.nih.gov/condition/47xyy-syndrome. Updated January 2009. Accessed October 3, 2012.
Lenroot RK. XYY Syndrome. Society For The Study Of Behavioural Phenotypes. http://www.ssbp.org.uk/site/images/stories/ssbp/downloads/XYY.pdf. 2010. Accessed October 3, 2012.