Triple X syndrome, also termed 47,XXX syndrome occurs 1 in 1000 births, so that in the US five to ten triple X syndrome girls are born every day. The are growing a few centimeters taller than their female siblings, but usually weigh less. The extra X chromosome came from a random error in cell division in the formation of the reproductive cells (ovum or sperm), which is called “non disjunction”. Some individuals have a mix of cells with 46,XX (normal) and 47,XXX cells; they are said to be 46,XX/47,XXX mosaics. Advanced maternal age (age above 40) plays a role in causing a non disjunction in the mother and most cases are maternally derived.
Girls with triple X syndrome may be noticed first when they display a learning disability. They may have delayed speech and language skills. They have normal sexual development, but often have an early onset of menstruation. They tend to have more menstrual irregularities. Most triple X syndrome women can conceive children normally and they often do not get diagnosed during prenatal check-ups as genetic tests are not routinely done. However, a minority may present at infertility clinics for a work-up. If they have an amniocentesis done, they may be diagnosed by chance. Many professionals do not consider this to be an abnormality, just a variation of normal. The only reason it is of value to know about triple X syndrome as parents is that a learning disability can be detected earlier and thus get remedied early with better long-term results.
2. Goldman: Cecil Medicine, 23rd ed., copyright © 2007 Saunders, An Imprint of Elsevier: CHROMOSOMAL DISORDERS