Triple X syndrome: What causes it?

XXX syndrome, also called triple X syndrome, is a rare chromosomal abnormality that affects only females. As the name implies, females with XXX syndrome have three X chromosomes instead of the usual two. The cause of this gene defect isn't known.

XXX syndrome is the most common X chromosome disorder in females. In many cases, XXX syndrome causes no signs or symptoms. When signs and symptoms do appear, they may include:

• Tall stature
• Small head (microcephaly)
• Vertical skinfolds that may cover the inner corners of the eyes (epicanthal folds)
• Delayed development of certain motor skills, speech and language
• Learning disabilities such as dyslexia
• Infertility

A doctor may make a diagnosis of XXX syndrome by a chromosome analysis of a blood sample. The disorder may be found during prenatal genetic testing, such as amniocentesis. Often, XXX syndrome is identified in older children as part of an evaluation of developmental delay.

A female with XXX syndrome may be referred to a pediatric geneticist for counseling. There's no cure for XXX syndrome. When possible, treatment is directed at managing the signs and symptoms of the disorder.