Trisomy X

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Trisomy X or Triple X syndrome refers to a condition where a female's cells contain one extra X chromosome.  Some women with this condition only have the trisomy in some of their cells, which is called 46 XX/47 XXX mosaicism.  Trisomy X affects approximately 1 in 1000 newborn girls, but normally has very few, if any, adverse effects on the child's life.  The only physical manifestation of this condition is tall stature, with no related risk of reproductive issues, however there is some risk of mild learning and speech difficulties.  Throughout the girl's life its progress would be monitored to ensure that development is continuing as expected, with regular check ups from infancy to childhood, followed by less regular, normally annual, assessments once adulthood is reached[1].  Some more serious abnormalities can occur such as kidney issues and seizures, but these only occur in approximately 10% of affected women with this condition, as well as some behavioural and motor skill issues occurring in some cases.  Most commonly, this is a non-inherited condition, and occurs due to non-disjunction during cell division.  It is also known as XXX syndrome  [2].


  1. Linden, M. G., Bender, B. G. and Robinson, A. (2002), Genetic counseling for sex chromosome abnormalities. Am. J. Med. Genet., 110: 3–10. doi: 10.1002/ajmg.10391fckLRfckLRResearch article detailing findings on research into sex chromosome abnormalities
  2. National Library of Medicine (US). Genetics Home Reference [Internet]. Bethesda (MD): The Library; 2013 Nov 11. Triple X syndrome; [reviewed 2009 Jan; cited 2013 Nov 11]; [about 2 screens]. Available from:

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