Definition
XYY syndrome is an abnormal number of the sex chromosomes in which a human male receives an extra Y chromosome, giving a total of 47 chromosomes instead of the more usual 46.
Topics of Interest
XYY syndrome is an aneuploidy (abnormal number) of the sex chromosomes in which a human male receives an extra Y chromosome, giving a total of 47 chromosomes instead of the more usual 46. This produces a 47,XYY karyotype.
Some medical geneticists question whether the term "syndrome" is appropriate for this condition because its phenotype is normal and the vast majority (an estimated 97% in the UK) of 47,XYY males do not know their karyotype.
Most often, the extra Y chromosome causes no unusual physical features or medical problems. 47,XYY boys have an increased growth velocity during earliest childhood, with an average final height approximately 7 cm above expected final height. Severe acne was noted in a very few early case reports, but dermatologists specializing in acne now doubt the existence of a relationship with 47,XYY.
Testosterone levels (prenatally and postnatally) are normal in 47,XYY males. Most 47,XYY males have normal sexual development and usually have normal fertility. Since XYY is not characterized by distinct physical features, the condition is usually detected only during genetic analysis for another reason.
Behavioral characteristics: 47,XYY boys have an increased risk of learning difficulties (in up to 50%) and delayed speech and language skills. In contrast, a national survey of US children conducted in 2004 for the CDC found that 10% of all boys had a learning disability.
As with 47,XXY boys and 47,XXX girls, IQ scores of 47,XYY boys average 10–15 points below their siblings. It is important to realize that this amount of variation—an average difference of 12 IQ points—occurs naturally between children in the same family. In 14 prenatally diagnosed 47,XYY boys from high socioeconomic status families, IQ scores available for 6 boys ranged from 100–147 with a mean of 120. For 11 boys with siblings, in 9 instances their siblings were stronger academically, but in one case they were performing equal to and in another case superior to their brothers and sisters.
Developmental delays and behavioral problems are also possible, but these characteristics vary widely among affected boys and men, are not unique to 47,XYY and are managed no differently than in 46,XY males. Aggression is not seen more frequently in 47,XYY males.
Cause: 47,XYY is not inherited, but usually occurs as a random event during the formation of sperm cells. An error in chromosome separation during anaphase II (of meiosis II) called nondisjunction can result in sperm cells with an extra copy of the Y chromosome. If one of these atypical sperm cells contributes to the genetic makeup of a child, the child will have an extra Y chromosome in each of the body's cells. In some cases, the addition of an extra Y chromosome results from nondisjunction during cell division during a post-zygotic mitosis in early embryonic development. This can produce 46,XY/47,XYY mosaics.
Incidence: About 1 in 1,000 boys are born with a 47,XYY karyotype. The incidence of 47,XYY is not affected by advanced paternal or maternal age.
First case: The first published report of a man with a 47,XYY karyotype was by Avery A. Sandberg and colleagues at Roswell Park Memorial Institute in Buffalo, New York in 1961. It was an incidental finding in a normal 44-year-old, 6 ft. [183 cm] tall man of average intelligence who was karyotyped because he had a daughter with Down syndrome.
47,XYY was the last of the common sex chromosome aneuploidies to be discovered, two years after the discoveries of 47,XXY, 45,X, and 47,XXX in 1959. Even the much less common 48,XXYY had been discovered in 1960, a year before 47,XYY. Screening for these X chromosome aneuploidies was possible by noting the presence or absence of "female" sex chromatin bodies (Barr bodies) in the nuclei of interphase cells in buccal smears, a technique developed a decade before the first reported sex chromosome aneuploidy.
An analogous technique to screen for Y chromosome aneuploidies by noting supernumerary "male" sex chromatin bodies was not developed until 1970, a decade after the first reported sex chromosome aneuploidy. In December 1969, Lore Zech at the Karolinska Institute in Stockholm first reported intense fluorescence of the AT-rich distal half of the long arm of the Y chromosome in the nuclei of metaphase cells treated with quinacrine mustard. Four months later, in April 1970, Peter L. Pearson and Martin Bobrow at the MRC Population Genetics Unit in Oxford and Canino G. Vosa at the University of Oxford reported fluorescent "male" sex chromatin bodies in the nuclei of interphase cells in buccal smears treated with quinacrine dihdyrochloride.
Klinefelter's syndrome, 47, XXY, or XXY syndrome is a condition in which males have an extra X sex 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. Klinefelter's syndrome is the most common sex chromosome disorder and the second most common condition caused by the presence of extra chromosomes. The condition exists in roughly 1 out of every 1,000 males. One in every 500 males have an extra X chromosome but do not have the syndrome.
Triple X syndrome is a form of chromosomal variation characterized by the presence of an extra X chromosome in each cell of a human female. The condition is also known as triplo-X, trisomy X, XXX syndrome, and 47,XXX aneuploidy. Triple X results during division of a parent's reproductive cells and occurs about once in every 1,000 births. Unlike most other chromosomal conditions (such as fragile X), there is usually no distinguishable difference to the naked eye between women with triple X and the rest of the female population.
Turner syndrome or Ullrich-Turner syndrome (also known as "Gonadal dysgenesis") encompasses several conditions, of which monosomy X (absence of an entire sex chromosome) is most common. It is a chromosomal disorder in which all or part of one of the sex chromosomes is absent (unaffected humans have 46 chromosomes, of which 2 are sex chromosomes). Typical females have 2 X chromosomes, but in Turner syndrome, one of those sex chromosomes is missing or has other abnormalities. In some cases, the chromosome is missing in some cells but not others, a condition referred to as mosaicism or 'Turner mosaicism'.
48,XXYY syndrome is a sex chromosome anomaly. It was previously considered to be a variation of Klinefelter's syndrome It is still considered a part of the syndrome by some definitions. The zygote contains two sex chromosomes, one from the mother and one from the father. Usually, females have two X chromosomes (XX) and males have one X and one Y chromosome (XY). The appearance of at least one Y chromosome makes a male. Therefore, XXYY only affects males. Males affected with XXYY Syndrome have 48 chromosomes instead of the typical 46. This is why XXYY Syndrome is sometimes written as 48, XXYY Syndrome. Typically, males do not have barr bodies, but males affected by XXYY syndrome have one, like females. Normal males only have one X chromosome, so barr body inactivation typically does not occur.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)
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