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The Merck Manual--Second Home Edition logo
 
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Chapter 266. Chromosomal and Genetic Abnormalities
Topics: Introduction | Down Syndrome | Fragile X Syndrome | Turner Syndrome | Noonan Syndrome | Triple X Syndrome | Klinefelter Syndrome | XYY Syndrome | Long QT Syndrome
 
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Triple X Syndrome

Triple X (trisomy X) syndrome is a rare disorder in which female infants are born with three X chromosomes.

Girls with triple X syndrome tend to have slightly lower intelligence and particular problems with verbal skills. Sometimes the syndrome causes infertility, although some women with triple X syndrome have given birth to physically normal children who had normal chromosomes.

Extremely rare cases of infants with four or even five X chromosomes have been identified. The more X chromosomes the girl has, the greater the chance of mental retardation and physical abnormalities.

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