XYY syndrome

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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. This condition is usually asymptomatic and affects 1 in 1000 male births.

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.[1][2]

Contents

Physical traits

Most often, the extra Y chromosome causes no unusual physical features or medical problems. Since XYY is not characterized by distinct physical features, the condition is usually detected only during genetic analysis for another reason.

47,XYY boys have an increased growth velocity during earliest childhood, with an average final height approximately 7 cm (3 in) above expected final height.[3] The increased gene dosage of three X/Y chromosome pseudoautosomal region (PAR1) SHOX genes has been postulated as a cause of the increased stature seen in all three sex chromosome trisomies: 47,XXX, 47,XXY, and 47,XYY.[4]

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.[5]

Testosterone levels (prenatally and postnatally) are normal in 47,XYY males.[6] Most 47,XYY males have normal sexual development and usually have normal fertility.

Behavioral characteristics

47,XYY boys have an increased risk of learning difficulties (in up to 50%) and delayed speech and language skills.[1][7][8][9][10][11][12][13][14] In comparison, a national survey of US children conducted in 2004 for the CDC found that 10% of all boys had a learning disability.[15]

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