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.

Last full review/revision February 2003