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| Specialty | Medical genetics  |
Triple X syndrome (also known as triplo-X, trisomy X, XXX syndrome, super female, and 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. The condition occurs only in females. Females with triple X syndrome have three X chromosomes instead of two. The karyotype reads 47,XXX. 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. 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 women with triple X and the rest of the female population.
Cause
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Triple X syndrome is not inherited, but usually occurs as an event during the formation of reproductive cells (ovum and sperm). An error in cell division called nondisjunction can result in reproductive cells with additional chromosomes. For example, an oocyte or sperm cell may gain an extra copy of the X chromosome as a result of the non-disjunction. If one of these cells contributes to the genetic makeup of a child, the child will have an extra X chromosome in each of her cells. In some cases, trisomy X occurs during cell division in early embryonic development.
Some females with triple X syndrome have an extra X chromosome in only some of their cells. These cases are called 46,XX/47,XXX mosaics.
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 non-representative or biased.
Because of the lyonization, inactivation, and formation of a Barr body 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); delayed development of certain motor skills, speech and language; learning disabilities, such as dyslexia; or weak muscle tone. 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.
Girls 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 women seem to have normal fertility. Triple X females are more likely to struggle with personality and psychological problems, and low self-esteem, but these respond well to treatment. Triple X girls 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. However, much more research is needed to fully understand the effects of this condition.
Incidence
Triple X syndrome occurs in around 1 in 1,000 girls. On average, five to ten girls with triple X syndrome are born in the United States each day.
First case
The first published report of a woman with a 47,XXX karyotype was by Patricia A. Jacobs, et al. at Western General Hospital in Edinburgh, Scotland, in 1959. It was found in a 35‑year-old, 5 ft. 9 in. (176 cm) tall, 128 lb. (58.2 kg) woman who had premature ovarian failure at age 19; her mother was age 41 and her father was 40 at the time of her conception.
Diagnosis
The vast majority of Triple X women are never diagnosed, unless they undergo tests for other medical reasons later in life. Triple X can be diagnosed by a blood test which is able to look at a person’s chromosomes (karyotype).
Triple X syndrome can be diagnosed prenatally through amniocentesis or chorionic villus sampling. In Denmark, between 1970 and 1984, 76% of the prenatally diagnosed fetuses with triple-X were aborted. Between 1985-1987, this figure dropped to 56%. With improved information, the number of abortions diminished. In the Netherlands, between 1991 and 2000, 33% (18/54) of the couples that were confronted with a prenatal diagnosis of 47,XXX elected to abort. If balanced information is provided to prospective parents, pre-natally, the incidence of voluntary termination (abortion) is reduced.
See also
References
- Jacobs, Patricia A.; Baikie, Albert G.; Court Brown, W. Michael; MacGregor, Thomas N.; Harnden, David G. (September 26, 1959). "Evidence for the existence of the human "super female"". Lancet. 274 (7100): 423–5. doi:10.1016/S0140-6736(59)90415-5. PMID 14406377.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - 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
- http://www.mayoclinic.com/health/triple-x-syndrome/DS01090/DSECTION=symptoms
- http://www.nature.com/ejhg/journal/v18/n3/full/ejhg2009109a.html
- National Library of Medicine (2007). "Genetics Home Reference: Triple X syndrome". Retrieved 2007‑03‑22.
{{cite web}}: Check date values in:|accessdate=(help) - Jacobs PA, Baikie AG, Brown WM, MacGregor TN, Maclean N, Harnden DG (1959). "Evidence for the existence of the human "super female"". Lancet. 274 (7100): 423–5. doi:10.1016/S0140-6736(59)90415-5. PMID 14406377.
{{cite journal}}: Unknown parameter|month=ignored (help); no-break space character in|author=at position 7 (help)CS1 maint: multiple names: authors list (link) - written by Connie T.R.M. Schrander-Stumpel, MD, PhD, Professor of Clinical Genetics, Academic Hospital Maastricht, Netherlands. http://www.triple-x-syndroom.nl/document31/patient+care+article+triplexsyndrome+or+trisomy+x
External links
- NLM (2007). Triple X syndrome Genetics Home Reference
- Guy's Hospital Clinical Genetics Department (2001). Triple X information leaflet
- Nielsen, Johannes (1998). Triple-X Females. An Orientation. The Turner Center, Aarhus Psychiatric Hospital, Risskov, Denmark.
- Triple X information booklet by Dr. Nielsen, a psychiatrist and geneticist who led the longest running of 8 international newborn screening studies of sex chromosome abnormalities.