XXX syndrome is a disorder in which affected females have three X chromosomes. It may also be referred to as Chromosome X, Triplo-X, and Chromosome 47, XXX karyotype. XXX syndrome was first described by P. A. Jacobs in the Lancet in 1959. It is the most frequent X chromosomal anomaly in females. The incidence of XXX syndrome is 0.3-1 per 1000 newborn females.