Triple X syndrome
|Triple X syndrome|
Triple X syndrome is a form of chromosomal variation characterized by the presence of an extra X chromosome in each cell of a human female. The condition is also known as triplo-X, trisomy X, XXX syndrome, and 47,XXX aneuploidy. Triple X results during division of a parent's reproductive cells, which occurs about once in every 1,000 births. People with trisomy X do not exhibit any symptoms and cannot be distinguished from normal XX females unless karyotyping is performed.
Triple X syndrome is not inherited, but usually occurs as a quite random 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 nondisjunction. 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.
Due to inactivation and formation of a Barr body in all female cells, only one X chromosome is active at any time in a female cell. Thus, triple X syndrome most often causes no unusual physical features of medical problems. Females with the condition are usually taller than average, and their weight may be low in comparison to their height. They may have menstrual irregularities,and, although rarely exhibiting severe mental impariments, have an increased risk of learning disabilities, delayed speech, and language skills.
A similar range of body types and characteristics are present in both triple X and Klinefelter's syndrome. These include a lanky/youthful appearance, non-affectedness, or varying degrees of androgyny. The additional X chromosome can come from either the maternal or paternal side. Although body types and characteristics are distinguishable in triple X, the condition is verified only by karyotype testing.
Most woman with triple X have normal sexual development and are able to conceive children. A few may experience an early onset of menstruation. Triple X woman are rarely diagnosed, apart from pre-natal testing methods, such as amniocentesis. Most medical professionals do not regard the condition a disability. However, such status can be sought by parents for early intervention treatment if mild delays are present.
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.
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.
- National Library of Medicine (2007). "Genetics Home Reference: Triple X syndrome". Retrieved 2007-03-22.
- 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. PMID 14406377. Unknown parameter
|quotes=ignored (help); Unknown parameter