XYY syndrome
| XYY syndrome | |
|---|---|
 |
|
| Karyotype from a male with 47,XYY | |
| Classification and external resources | |
| Specialty | Medical genetics |
| ICD-10 | Q98.5 |
| ICD-9-CM | 758.8 |
| DiseasesDB | 33038 |
| MeSH | D014997 |
| Orphanet | 8 |
XYY syndrome is a genetic condition in which a human male has an extra male (Y) chromosome, giving a total of 47 chromosomes instead of the more usual 46. This produces a 47,XYY karyotype, which occurs every 1 in 1,000 male births.
Some medical geneticists question whether the term "syndrome" is appropriate for this condition because its clinical phenotype is normal and the vast majority of XYY males do not know their karyotype.
People with the 47,XYY karyotype have a increased growth velocity from early childhood, with an average final height approximately 7 cm (3") above expected final height. In Edinburgh, Scotland, eight 47,XYY boys born 1967–1972 and identified in a newborn screening programme had an average height of 188.1 cm (6'2") at age 18—their fathers' average height was 174.1 cm (5'8½"), their mothers' average height was 162.8 cm (5'4"). 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.
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) are normal in 47,XYY males. Most 47,XYY males have normal sexual development and have normal fertility.
In contrast to the other common sex chromosome aneuploidies—47,XXX, 45,X (Turner syndrome), and 47,XXY (Klinefelter syndrome)—the average IQ scores of 47,XYY boys identified by newborn screening programs were not reduced compared to the general population. In a summary of six prospective studies of 47,XYY boys identified by newborn screening programmes, twenty-eight 47,XYY boys had an average 100.76 verbal IQ, 108.79 performance IQ, and 105.00 full-scale IQ. In a systematic review including two prospective studies of 47,XYY boys identified by newborn screening programs and one retrospective study of 47,XYY men identified by screening men over 184 cm (6'½") in height, forty-two 47,XYY boys and men had an average 99.5 verbal IQ and 106.4 performance IQ.
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