Kariotip seorang laki-laki dengan 47,XYY
|Klasifikasi dan rujukan luar|
Sindrom XYY adalah suatu kondisi genetik ketika seorang laki-laki memiliki kromosom Y tambahan, sehingga secara keseluruhan memiliki 47 kromosom. Kondisi ini mengakibatkan kariotip 47,XYY dan dapat ditemui dalam 1 dari 1.000 kelahiran anak laki-laki.
Beberapa genetikawan medis mempertanyakan penggunaan istilah "sindrom" karena fenotip klinis penyandang tetap normal dan sebagian besar laki-laki dengan kromosom XYY tidak mengetahui kariotip mereka.
Ciri-ciri fisik[sunting | sunting sumber]
Orang yang memiliki kariotip 47,XYY tumbuh lebih cepat dan rata-rata tingginya lebih tinggi 7 cm (3") dari rata-rata tinggi pada umumnya. Di Edinburgh, Skotlandia, delapan anak laki-laki dengan kariotip 47,XYY yang lahir pada tahun 1967–1972 memiliki rata-rata tinggi sebesar 188.1 cm (6'2") pada umur 18 tahun, sementara rata-rata tinggi ayah mereka hanya 174.1 cm (5'8½") dan ibunya 162.8 cm (5'4"). Tingkat testosteron (sebelum kelahiran) laki-laki 47,XYY juga normal, dan begitu pula perkembangan seksual dan tingkat kesuburannya.
Catatan kaki[sunting | sunting sumber]
- ^ a b c d Gravholt, Claus Højbjerg (2013). "Sex chromosome abnormalities". Dalam Pyeritz, Reed E.; Rimoin, David L.; Korf, Bruce R. Emery and Rimoin's principles and practice of medical genetics (edisi ke-6th). San Diego: Elsevier Academic Press. hlm. 1180–1211. ISBN 978-0-12-383834-6.
This sex chromosome aneuploidy is not characterized by distinct physical features and, because there does not appear to be recognizable pattern of neurodevelopment or behavioral characteristics, the use of the term syndrome may be inappropriate. Males with an extra Y chromosome are phenotypically normal and most never come to medical attention.
Pubertal development, testicular histology, and spermatogenesis are most often normal.
…it appears that XY pairing and recombination occur normally in 47,XYY, the extra Y chromosome being lost during spermatogenesis, so that many XYY men have fathered chromosomally normal children. It has generally been observed that reproductive risks for males with 47,XYY are no higher than for euploid males, despite the fact that in situ hybridization studies demonstrated a lower frequency of single Y-bearing sperm than expected and a variably higher rate of disomic XX, XY and YY spermatozoa in males with 47,XYY.
Population-based studies have demonstrated that intellectual abilities tend to be slightly lower than those of siblings and matched controls and that boys with an extra Y chromosome are more likely to require educational help. However, intelligence is usually well within the normal range.
During school age, learning disabilities requiring educational intervention are present in approximately 50% and are as responsive to therapy as they are in children with normal chromosomes. Expressive and receptive language delays and reading disorders are common.
- ^ a b Milunsky, Jeff M. (2010). "Prenatal diagnosis of sex chromosome abnormalities". Dalam Milunsky, Aubrey; Milunsky, Jeff M. (eds.). Genetic disorders and the fetus: diagnosis, prevention and treatment (edisi ke-6th). Oxford: Wiley-Blackwell. hlm. 273–312. ISBN 1-4051-9087-6.
The addition of a Y chromosome to a normal male chromosome constitution does not produce a discernible phenotype. Males with 47,XYY cannot be characterized by discriminating physical or behavioral features. The first diagnosis of this condition, therefore, was a karyotypic and not a phenotypic discovery.
Pubertal development is normal and these men are usually fertile.
- ^ Jacobs, Patricia A. (March 3–5, 2006). The discovery and history of Trisomy X and XYY syndrome. National Conference on Trisomy X and XYY, UC Davis M.I.N.D. Institute,. DVD 02. Sacramento: KS&A.
Oxford Data Base — XYY total ascertainment: ~ 3% — 934 XYYs (801 XYYs + 133 XYY mosaics) in Britain (population 60 million)
- ^ Nielsen, Johannes (1998). "How is height growth?". XYY males. An orientation. The Turner Center, Aarhus Psychiatric Hospital, Risskov, Denmark. Diarsipkan dari versi asli tanggal 2010-03-07.
- ^ Ratcliffe, Shirley G.; Pan, Huiqi; McKie, Mark (November–December 1992). "Growth during puberty in the XYY boy". Annals of Human Biology. 19 (6): 579–587. doi:10.1080/03014469200002392. PMID 1476413.
- ^ Ratcliffe, Shirley G.; Read, Graham; Pan, Huiqi; Fear, Claudine; Lindenbaum, Richard; Crossley, Jennifer (September 1994). "Prenatal testosterone levels in XXY and XYY males". Horm Res. 42 (3): 106–109. doi:10.1159/000184157. PMID 7995613.
- ^ Gardner, R.J. McKinlay; Sutherland, Grant R. (2004). Chromosome abnormalities and genetic counseling (edisi ke-3rd). Oxford: Oxford University Press. hlm. 29–30, 42, 199, 207, 257, 263, 393, 424–430. ISBN 0-19-514960-2.
From early meiotic studies, it was concluded that the extra Y was eliminated before the spermatocyte formed, with an X-Y bivalent usually seen at diakinesis, and more recent studies support this concept. However, FISH analyses of sperm, enabling hundreds of cells to be analyzed, have shown a very small increased faction of 24,YY spermatozoa in the ejaculate of XYY men (Table 12-1). Thus it appears the vast majority of spermatocytes lose the extra Y before entering meiosis, a very few XYY primary spermatocytes are able to slip through and produce YY (and XY) spermatozoa. These cytogenetic findings parallel the observation that XYY men have no discernible increase in risk to have children with a sex chromosome abnormality. A true increased risk of a fraction of a per cent could be distinguished only with the greatest of difficulty when the background population risk is of a similar order of magnitude. As for the autosomes, no convincing case exists for any increased risk for aneuploidy in the children of men with 47,XYY.
To our knowledge, there is no report of a discernibly increased risk for the XYY male to have chromosomally abnormal children. A slight increase in gonosomal imbalances in sperm (Table 12-1) might nevertheless lead some to choose prenatal diagnosis.
- ^ Gardner, R.J. McKinlay; Sutherland, Grant R.; Shaffer, Lisa G. (2012). Chromosome abnormalities and genetic counseling (edisi ke-4th). Oxford: Oxford University Press. hlm. 9–10, 12, 36, 52, 221, 224, 230, 285–286, 293, 440–441, 477–480, 484. ISBN 978-0-19-537533-6.
The two other conditions, XXX and XYY, apparently have little effect on fertility; furthermore, they are not discernibly associated with any increased risk for chromosomally abnormal offspring.
While the IQ is in the normal range, it is usually lower than those of sibs or controls, and about half of XYY boys have a mild learning difficulty, and may display poor attention and impulsivity in the classroom.
Pranala luar[sunting | sunting sumber]
- Nielsen, Johannes (1998). XYY males. An orientation. The Turner Center, Aarhus Psychiatric Hospital, Risskov, Denmark.
- XYY information booklet by Dr. Nielsen, a psychiatrist and geneticist who led the longest running of 7 international newborn screening studies of sex chromosome abnormalities.
- XYY syndrome page on the Contact a Family Directory website
- has background and medical information and details of UK support groups