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Question answered:05/10/06 Warning! this question is over two years old.
Several sources of information suggest that triple X is not usually passed from mothers to their female offspring.
The NLH Clinical Genetics Specialist Library states:
“47,XXX occurs sporadically. As with other chromosomal abnormalities there is an increased incidence with increasing maternal age. Although there is some evidence to suggest that those with 47,XXX have an increased risk of having offspring with chromosomal abnormalities, mothers with 47,XXX do not usually have children with the same chromosome complement.”
It also offers a general overview of the condition:
“Triple X syndrome affects approximately 1 in 1000 females, and is due to the presence of an extra X chromosome. There is no physical phenotype but girls tend to be taller than average. It is often diagnosed incidentally due to investigations for other causes. It is under diagnosed due to many females being asymptomatic. Those who do have symptoms are affected by cognitive and motor delay as well as psychological problems. The IQ may be ten to fifteen points lower than their siblings. Adult adaptation tends to be normal with independent living.
It has been shown that those diagnosed antenatally tend to have a better prognosis, and that a supportive and loving environment is beneficial.” [1]
A second source, the National Library of Medicine also considers whether triple X syndrome can be inherited:
“Trisomy X usually is not inherited, but occurs as a random event during the formation of reproductive cells (eggs and sperm). An error in cell division called nondisjunction can result in reproductive cells with an abnormal number of chromosomes. For example, an egg or sperm cell may gain an extra copy of the X chromosome as a result of nondisjunction. If one of these atypical reproductive cells contributes to the genetic makeup of a female child, the child will have an extra X chromosome in each of the body's cells.
In some cases, trisomy X results from nondisjunction during cell division in early embryonic development. These cases are usually 46,XX/47,XXX mosaics.” [2]
The Contact A Family organisation also contains information about Triple-X syndrome on its website which notes:
“Triple-X occurs sporadically and is not usually passed on from a triple-X mother to her daughters. However, there is an increased risk in the children of older mothers.”
“The effect of having an extra X chromosome can be very varied. Some females with triple-X syndrome show no, or very few, symptoms and are entirely 'normal', whilst others have learning difficulties, developmental delay and/or behavioural problems. Individuals may show some or all features and furthermore may be differently affected by the severity of their symptoms. It is not possible to offer a precise prediction of the symptoms either before or even immediately after the birth of each triple-X girl.”
Concerning prenatal diagnosis, it simply states that, “Chorionic villus sampling at ten to twelve weeks or amniocentesis at about sixteen weeks is available to all mothers with Triple X syndrome, and routinely to older mothers, to confirm or exclude Triple X syndrome.” [3]
References
1. NLH Clinical Genetics Specialist Library. Triple X Syndrome. July 2005. (http://www.library.nhs.uk/genepool/ViewResource.aspx?resID=93920&tabID=290&catID=9779).
2. NLM Genetics Home Reference. Triple X syndrome. September 2006. (http://ghr.nlm.nih.gov/condition=triplexsyndrome).
3. Contact A Family. Triple-X Syndrome. 2002. (http://www.cafamily.org.uk/Direct/t40.html).
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