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XXY Syndrome

Klinefelter's syndrome, 47, XXY, or XXY syndrome is a condition in which a human has an extra X chromosome. While females have an XX chromosomal makeup, and males an XY, affected individuals have at least two X chromosomes and at least one Y chromosome. Because of the extra chromosome, individuals with the condition are usually referred to as "XXY Males", or "47, XXY Males". This chromosome constitution (karyotype) exists in roughly between 1:500 to 1:1000 live male births but many of these people may not show symptoms. The physical traits of the syndrome become more apparent after the onset of puberty, if at all. In humans, 47,XXY is the most common sex chromosome aneuploidy in males and the second most common condition caused by the presence of extra chromosomes. Other mammals also have the XXY syndrome, including mice. Principal effects include hypogonadism and reduced fertility. A variety of other physical and behavioural differences and problems are common, though severity varies and many XXY boys have few detectable symptoms. Not all XXY boys and men develop the symptoms of Klinefelter syndrome. There are many variances within the XXY population, just as within the 46,XY population. While it is possible to characterise XXY males with certain body types and physical characteristics, that in itself should not be the method of identification as to whether or not someone has XXY. The only reliable method of identification is karyotype testing. The degree to which XXY males are affected, both physically and developmentally, differs widely from person to person