Jacobs syndrome in Wikipedia
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It uses material from the Wikipedia article "XYY syndrome".
(Source - Retrieved 2006-09-07 14:08:51 from https://en.wikipedia.org/wiki/XYY_syndrome)
XYY syndrome is an aneuploidy (specifically a trisomy) of the sex chromosomes in which a human male receives an extra Y chromosome, producing 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.$$
Most often, this chromosomal change causes no unusual physical features or medical problems. 47,XYY boys and men are usually taller than average and several centimeters taller than their parents and siblings. Severe acne was noted in a very few early case reports, but dermatologists specializing in acne now doubt the existence of a relationship with 47,XYY.$$
Testosterone levels (prenatally and postnatally) are normal in 47,XYY males.$$ Most 47,XYY males have normal sexual development and usually have normal fertility. Since there are no distinct physical characteristics, the condition usually is only detected during genetic analysis for another reason.
47,XYY boys have an increased risk of learning difficulties (in up to 50%) and delayed speech and language skills.$$$$$$$$$$$$$$$$ For context, surveys report 10% of all boys had a learning disability.$$
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.$$
Developmental delays and behavioral problems are also possible, but these characteristics vary widely among affected boys and men, are not unique to 47,XYY and are managed no differently than in 46,XY males.$$$$ Aggression is not seen more frequently in 47,XYY males.$$$$$$$$$$
47,XYY is not inherited, but usually occurs as a random event during the formation of sperm cells. An error in cell division during meiosis II called nondisjunction can result in sperm cells with an extra copy of the Y chromosome. If one of these atypical sperm cells contributes to the genetic makeup of a child, the child will have an extra Y chromosome in each of the body's cells.$$$$
In some cases, the addition of an extra Y chromosome results from nondisjunction during cell division during a post-zygotic mitosis in early embryonic development. This can produce 46,XY/47,XYY mosaics.$$$$
About 1 in 1,000 boys are born with a 47,XYY karyotype. The incidence of 47,XYY is not affected by advanced paternal (or maternal) age.$$$$$$
The first published report of a man with a 47,XYY karyotype was by Dr. Avery A. Sandberg and colleagues at Roswell Park Memorial Institute in Buffalo, New York in 1961. It was an incidental finding in a normal 44-year-old, 6 ft. [183 cm] tall man of average intelligence who was karyotyped because he had a Down syndrome daughter.$$
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