Triple X syndrome, also known as 47,XXX syndrome or trisomy X, is characterized by a trisomy of the X chromosome. Patients do not usually show significant physical symptoms apart from above average height. As the clinical impact is highly variable, many women with triple X are never diagnosed with this chromosomal aberration. About 70% of women are fertile, but some present with menstrual irregularities and premature menopause. Intelligence may be 10-15 points below the family average. Speech development may be delayed. Offspring of triple X women are not found to be at a higher risk for gonosomal aneuploidy.
The prevalence of triple X syndrome is reported to be approximately 1:1,000 in female newborns. In 98% of patients, trisomy X is found in all cells, while 2% show mosaicism.
References
Ogata et al. 2001, J Med Genet 38:1 / Müller-Henbach et al. 1977, Am J Obstet Gynecol 127:211