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Triple x syndrome

The meaning of «triple x syndrome»

Triple X syndrome, also known as trisomy X and 47,XXX, is characterized by the presence of an extra X chromosome in each cell of a female.[1] Those affected are often taller than average.[1] Usually there are no other physical differences and normal fertility.[1] Occasionally there are learning difficulties, decreased muscle tone, seizures, or kidney problems.[1]

Triple X is due to a random event.[1] Triple X can result either during the division of the mother's reproductive cells or during division of cells during early development.[2] It is not typically inherited from one generation to the next.[1] A form where only a percentage of the body cells contain XXX can also occur.[1] Diagnosis is by chromosomal analysis.[3]

Treatment may include speech therapy, physical therapy, and counseling.[3] It occurs in about one in every 1,000 female births.[2] It is estimated that 90% of those affected are not diagnosed as they either have no or only few symptoms.[2] It was first identified in 1959.[4]

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. Because of the lyonization, inactivation, and formation of Barr bodies in all female cells, only one X chromosome is active at any time. A person with triple X syndrome will have two Barr bodies in each cell, leading to most persons having only mild effects or no effects. The symptoms vary from person to person, with some people being more affected than others.

Symptoms may include tall stature, vertical skin folds that may cover the inner corners of the eyes (epicanthal folds), poor muscle tone, and a curve in the 5th finger towards the 4th.[2] There may also be a small head (microcephaly).[5] There are seldom any observable physical anomalies in triple X females, other than being taller than average.

Poor coordination may be present.[6] Those affected appear to have higher rates of scoliosis.[6]

Epicanthal folds and increased distance between the eyes in a 2-year-old female with trisomy X[2]

The type of finger curvature frequently seen in triple X syndrome

Females with triple X syndrome often have delayed language development.[6] On average those affected have IQs that are 20 points lower.[6] Poor self-esteem, anxiety, and depression are also common.[2][6]

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.

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