Science Fair Project Encyclopedia
Triple X syndrome
Triple X syndrome is a chromosomal aneuploid abnormality characterized by the presence of an extra X chromosome in each cell of a human female. The syndrome is also known as XXX syndrome, trisomy X, triplo-X, 47xxx, or 47,XXX aneuploidy. Trisomy-x results during division of a parent's reproductive cells. Females with Trisomy-x are typically tall with slightly higher sensitivity levels, and are not at any increased risk for medical problems.
Most often, triple X syndrome causes no unusual physical features or medical problems. Females with the syndrome are usually taller than average, may have menstrual irregularities, and, although rarely mentally retarded, sometimes have an increased risk of learning disabilities and delayed speech and language skills. Researchers are not yet certain why an extra copy of the X chromosome is associated with tall stature and learning issues in some girls and women. These characteristics vary widely among affected individuals, however. Additionally, most females with triple X syndrome have normal sexual development and are able to conceive children.
Triple X syndrome is not inherited, but usually occurs as a random event during the formation of reproductive cells (ovum and sperm). An error in cell division called nondisjunction can result in reproductive cells with an abnormal number of 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 atypical reproductive cells contributes to the genetic makeup of a child, the child will have an extra X chromosome in each of his or her cells. In some cases, trisomy X occurs as an accident during cell division in early fetal 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.
Triple X syndrome occurs in about 1 in 1,000 newborn girls. Five to ten girls with triple X syndrome are born in the United States each day.
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