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Triple X syndrome
Triple X syndrome (also known as triplo-X, trisomy X, XXX syndrome, 47,XXX aneuploidy) is a form of chromosomal variation characterized by the presence of an extra X chromosome in each cell of a human female. A mosaic form also occurs where only a percentage of the body cells contain XXX while the remainder carry XX. The extent to which an individual is affected by the condition will depend upon the proportion of XXX to XX throughout.〔Medical text written August 2002 by Contact a Family. Last reviewed February 2008 by Dr R Stanhope, Consultant Paediatric Endocrinologist, Institute of Child Health, London, UK. http://www.cafamily.org.uk/medicalinformation/conditions/azlistings/t40_1.html〕 Triple X results during division of a parent's reproductive cells and occurs about once in every 1,000 female births. Unlike most other chromosomal conditions (such as Down syndrome), there is usually no distinguishable difference to the naked eye between those with triple X and the rest of the female population.
==Signs and symptoms==
Because the vast majority of Triple X females are never diagnosed, it may be very difficult to make generalizations about the effects of this syndrome. The samples that were studied were small and may be nonrepresentative or biased.
Because of the lyonization, inactivation, and formation of Barr bodies in all female cells, only one X chromosome is active at any time. Thus, Triple X syndrome most often has only mild effects, or has no unusual effects at all. Symptoms may include tall stature; small head (microcephaly); vertical skinfolds that may cover the inner corners of the eyes (epicanthal folds); speech and language learning disabilities, such as dyslexia; or weak muscle tone.〔http://www.mayoclinic.com/health/triple-x-syndrome/DS01090/DSECTION=symptoms〕 The symptoms vary from person to person, with some women being more affected than others. There are seldom any observable physical anomalies in Triple X females, other than being taller than average.
Females with Triple X syndrome are at increased risk of delayed language development, EEG abnormalities, motor coordination problems and auditory processing disorders, and scoliosis. They tend to show accelerated growth until puberty. Premature ovarian failure seems to be more prevalent in these women, but most Triple X females seem to have normal fertility. They are more likely to struggle with personality and psychological problems, and low self-esteem, but these respond well to treatment. Triple X females are at increased risk of poor academic results at school, and some may need special education. Sometimes, they may suffer from anxiety and be very shy, and this may affect their relations with school peers. They seem to feel much better after leaving school. They benefit very much from a stable home environment.〔http://www.nature.com/ejhg/journal/v18/n3/full/ejhg2009109a.html〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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